On the 6pm News tonight
John Leister
powered by a laser beam that was shot up it's rear into a combustion
chamber and it took off with little smoke and only a slight whining
sound. Anyone care to comment about how effecient this machine may or
may not be?
--
Love the controversy,
To play Devil's advocate,
To see the truths in life,
The inner meanings to everything.
John D Leister
Jogging through my homepage at:
http://www.geocities.com/southbeach/shores/6340
Mirrored at: For faster loading
http://www.senet.com.au/~johndk/index.htm
Running up to my mailbox at:
joh...@academy.net.au
skribe
John Leister <joh...@senet.com.au> writes:
> On the 6pm news tonight we saw this experimental rocket that was
> powered by a laser beam that was shot up it's rear into a combustion
> chamber and it took off with little smoke and only a slight whining
> sound. Anyone care to comment about how effecient this machine may or
> may not be?
Quite efficient if they can get them to actually carry a payload. There have
been articles in New Scientist and on one of the tv science shows (ie Quantum,
Beyond 2000) about it. Now they're just trying to convince the US govt to give
them enough money to by a big enough laser to run some serious tests.
Robert Whyte
wrote:
> On the 6pm news tonight we saw this experimental rocket that was
> powered by a laser beam that was shot up it's rear into a combustion
> chamber and it took off with little smoke and only a slight whining
> sound. Anyone care to comment about how effecient this machine may or
> may not be?
It's VERY efficient, considering that it doesn't have to carry it's
fuel. 90% of the Space Shuttle's fuel is required to go the first 20%
of the distance to orbit and this ship, even allowing for diffusion of
the laser beam through the atmosphere, will be substantially more
efficient than that.
The one disadvantage that I can see is that it will lose efficiency as
it gets higher due to the lack of air to expand with the laser.
Robert Whyte
Andrei Florescu
>
> On the 6pm news tonight we saw this experimental rocket that was
> powered by a laser beam that was shot up it's rear into a combustion
> chamber and it took off with little smoke and only a slight whining
> sound. Anyone care to comment about how effecient this machine may or
> may not be?
This sounds interesting, i missed it, but if anyone would please
elaborate i would really appreciate.
[snip]
----------------------------------------------------------------
Andrei Florescu
aaf...@student.monash.edu.au
----------------------------------------------------------------
David Milne
> On the 6pm news tonight we saw this experimental rocket that was
> powered by a laser beam that was shot up it's rear into a combustion
> chamber and it took off with little smoke and only a slight whining
> sound. Anyone care to comment about how effecient this machine may or
> may not be?
Larry Niven and Jerry Pournelle re-voiced this idea in a book about20
years ago. Can't think of the title though. They also had a number
of other good ideas.
> --
> Love the controversy,
> To play Devil's advocate,
> To see the truths in life,
> The inner meanings to everything.
>
> John D Leister
> Jogging through my homepage at:
> http://www.geocities.com/southbeach/shores/6340
> Mirrored at: For faster loading
> http://www.senet.com.au/~johndk/index.htm
> Running up to my mailbox at:
> joh...@academy.net.au
--
Regards
David Milne
Reply to
dmi...@camtech.com.au or
dmi...@watt.mecheng.adelaide.edu.au Remove NOSPAM in e-mail address
Are you a Klingon or is that a turtle on your head?
William Ferguson
>years ago. Can't think of the title though. They also had a number
>of other good ideas.
Larry Niven has all the good ideas. (IMHO) BIG fan ;-)
I can't recall the book you're referring to unless you're confusing the
concept of the light sail used in 'Mote in God's eye' (and one or two
shorts).
Chris Drew
covered this. I cant remember the name (it was something like "The Origin
of the Death Ray"), but it covered this system. The basis for the "rocket"
was a ground-based pulsed laser, pointed vertically to impact the underside
of a very small object, which resembled a lightweight metallic and highly
polished frisby, about 1 ft in diameter. On launch their was a ripping
sound, and the disc shot into the air, reaching an altitude of over 90 ft.
On descent, the ground crew tried to catch the thing in devices which
resembled butterfly nets (Honest!). The major problem with the process was
that the disc would be windblown out of the beam powering the thing.
The entire documentary concerned the development and use of military lasers,
and included some rare footage of experimental anti-missile lasers, both
ground and air based.
The Channel 4 UK website may have more info
--
Chris Drew
To reply by email, remove SPAMT from address.
Andrei Florescu wrote in message
<35D6983D...@student.monash.edu.au>...
>John Leister wrote:
>>
>> On the 6pm news tonight we saw this experimental rocket that was
>> powered by a laser beam that was shot up it's rear into a combustion
>> chamber and it took off with little smoke and only a slight whining
>> sound. Anyone care to comment about how effecient this machine may or
>> may not be?
>
John Whear
>John Leister wrote:
>
>> On the 6pm news tonight we saw this experimental rocket that was
>> powered by a laser beam that was shot up it's rear into a combustion
>> chamber and it took off with little smoke and only a slight whining
>> sound. Anyone care to comment about how effecient this machine may or
>> may not be?
>
>years ago. Can't think of the title though. They also had a number
>of other good ideas.
Are you thinking of Footfall? Use of nuclear devices detonating behind a
concave plate to provide propulsion.
BTW, this reminded me of "Deep Impact". The Russian drive (name escapes
me) looked like it dropped something from the stern, which detonated behind
the space craft, the rear of the craft appeared to be a substantial concave
plate. My recollection of Footfall is a little fuzzy & my recollection of
Deep Impact even fuzzier.
See You Out There!
<*>
J.W.
jwh...@comcen.com.au
Michael Fuller
[Re. experimental rocket powered by laser beam shot into a combustion chamber]
>Larry Niven and Jerry Pournelle re-voiced this idea in a book about20
>years ago. Can't think of the title though.
One of several thematically related stories collected as "High Justice";
IIRC the above concept was described in the title story.
Michael
John Leister
Andrei Florescu wrote:
> John Leister wrote:
> >
> > On the 6pm news tonight we saw this experimental rocket that was
> > powered by a laser beam that was shot up it's rear into a combustion
> > chamber and it took off with little smoke and only a slight whining
> > sound. Anyone care to comment about how effecient this machine may or
> > may not be?
>
> This sounds interesting, i missed it, but if anyone would please
> elaborate i would really appreciate.
>
> [snip]
>
> ----------------------------------------------------------------
> Andrei Florescu
> aaf...@student.monash.edu.au
> ----------------------------------------------------------------
Andrei apparently the test model which is only a couple of feet across in
size is very effecient but as others have pointed out the higher the model
flies the less coherent is the laser beam that they are targeting at the
ship's combustion chamber. It's less poluting too as in the news footage
showed there was very little in the way of smoke and other things that you
would associate with a rocket taking off.
Apparently the people who are testing this want to build a full size ship
able to carry a payload and possibly a crew but can you imagine the power
that they might need from the targeting laser on the ground?
It will be interesting though and good luck to them in their endeavour.
--
The Earth goes around the sun
The Earth spins to make a day
Why aren't I dizzy?
Robert Whyte
<aaf...@student.monash.edu.au> wrote:
> John Leister wrote:
>> On the 6pm news tonight we saw this experimental rocket that was
>> powered by a laser beam that was shot up it's rear into a combustion
>> chamber and it took off with little smoke and only a slight whining
>> sound. Anyone care to comment about how effecient this machine may or
>> may not be?
> This sounds interesting, i missed it, but if anyone would please
> elaborate i would really appreciate.
Th ship is shaped like a smaller cone placed upside-down within a
larger one. It is spun up to a high rotational speed and then a
high-power laser is fired at it's base in a circular pattern. The
shape of the bottom of the ship focuses the laser and causes explosive
heating of the air surrounding the smaller cone which is used to
propel the ship upwards.
I have seen several laboratory demonstrations of the prototype ship,
but last week's experiment was the first real-world test of the
design.
Robert Whyte
Justin Downey
The idea was used by the Motie probe in "The Mote in God's Eye", as well
as the invader's shuttles in "Footfall". The Moties had the jump-drive
system but couldn't use it as they kept popping up in the middle of a
star. They were forced to use the laser drive method of interstellar
travel, hence the noticeable brightening of their star 200-odd years
before the probe arrived at the human colony.
JD
Justin Downey
"The Millenial Project" by Marshall Savage describes the use of a block
of ice attached to the base of the spacecraft which is vapourised by the
laser, providing propulsion. He also desribed using multiple lasers at
different frequencies to attempt to overcome atmospheric attenuation.
All speculative, of course.
Paul Wilson
>
> > John Leister wrote:
> > >
> > > On the 6pm news tonight we saw this experimental rocket that was
> > > powered by a laser beam that was shot up it's rear into a combustion
> > > chamber and it took off with little smoke and only a slight whining
> > > sound. Anyone care to comment about how effecient this machine may or
> > > may not be?
> >
> > This sounds interesting, i missed it, but if anyone would please
> > elaborate i would really appreciate.
I've got links to information in the US about this, try :
<a href="http://www.iinet.net.au/~hooker/l.html#laser-propulsion">
www.iinet.net.au/~hooker/l.html#laser-propulsion</a>
as a starting point.
Paul
Michael Fuller
[Re. experimental rocket powered by laser beam shot into a combustion chamber]
Justin Downey <re...@chatnet.net.au> writes:
>The idea was used by the Motie probe in "The Mote in God's Eye", as well
>as the invader's shuttles in "Footfall". The Moties had the jump-drive
>system but couldn't use it as they kept popping up in the middle of a
>star. They were forced to use the laser drive method of interstellar
>travel, hence the noticeable brightening of their star 200-odd years
>before the probe arrived at the human colony.
Not the same thing.
IIRC, that was a laser-supplemented light-sail; the Motie ship would have
been "blown" along by light pressure on the sail. The experimental rocket
described in the original posting is powered by using a pulsed laser to heat
air in a "combustion" chamber at the base of the rocket; the rocket is driven
by the expulsion of rapidly expanding gases.
(Feel free to correct if I'm wrong---it's been a while since I read either
book, and I'm working second-hand from the reports of the news footage.)
Michael
Owen Godfrey
> Andrei apparently the test model which is only a couple of feet across in
> size is very effecient but as others have pointed out the higher the model
> flies the less coherent is the laser beam that they are targeting at the
> ship's combustion chamber. It's less poluting too as in the news footage
> showed there was very little in the way of smoke and other things that you
> would associate with a rocket taking off.
>
> Apparently the people who are testing this want to build a full size ship
> able to carry a payload and possibly a crew but can you imagine the power
> that they might need from the targeting laser on the ground?
Hmmmm ... one misfire could really spoil the day for somone in orbit.
--
Owen Godfrey - (08) 9333 8808 - <mailto:god...@ccis.adisys.com.au>
"...there is sometimes little to choose between
the reality of illusion and the illusion of reality."
Patrick White, The Aunt's Story , 1948
David Milne
> >Larry Niven and Jerry Pournelle re-voiced this idea in a book about20
> >years ago. Can't think of the title though. They also had a number
> >of other good ideas.
>
> Larry Niven has all the good ideas. (IMHO) BIG fan ;-)
>
> I can't recall the book you're referring to unless you're confusing the
> concept of the light sail used in 'Mote in God's eye' (and one or two
> shorts).
No, it wasn't a fiction book. Just a book that discussed ideas that
possibly had merit.
I think it was called "A Step Further Out".
Justin Downey
Aaaah yes, you are right. In the motie ship the laser itself would
provide the equal and opposite reaction. The ship would effectively be
pushing against the planet holding the laser. In the experimental rocket
and the Marshall Savage version, the rocket would be pushing against the
reaction mass attached to the rocket (assuming it carries its own air
supply to ag as reaction mass.)
>
> Michael
Owen Godfrey
> Michael Fuller wrote:
> >
> ><snip>
> >
> > IIRC, that was a laser-supplemented light-sail; the Motie ship would have
> > been "blown" along by light pressure on the sail. The experimental rocket
> > described in the original posting is powered by using a pulsed laser to heat
> > air in a "combustion" chamber at the base of the rocket; the rocket is driven
> > by the expulsion of rapidly expanding gases.
> >
> > (Feel free to correct if I'm wrong---it's been a while since I read either
> > book, and I'm working second-hand from the reports of the news footage.)
>
> Aaaah yes, you are right. In the motie ship the laser itself would
> provide the equal and opposite reaction. The ship would effectively be
> pushing against the planet holding the laser. In the experimental rocket
> and the Marshall Savage version, the rocket would be pushing against the
> reaction mass attached to the rocket (assuming it carries its own air
> supply to ag as reaction mass.)
Ummmm ... the logic isn't too bad, but no cigar.
Looking at the Propulsion Directorate page at Edwards Air Force Base, you'll see
that the emphasis of the design is atmoshperic hyper-sonic travel. If you can say
that the Motie ship is pushing against the planet in the first case, then you can
certainly say the same in the second. However, I think it would be more correct to
say that the Motie ship was pushing against the solar winds and had laser
assistance.
Your "action and reaction" is actually in the first case the capturing of the energy
of the solar wind and laser, and in the second it is against the atmosphere.
I think people have missed one tiny feature of the design ... this engine appears to
have air inlets. In the documentation, it says "This airbreathing pulsed detonation
engine concept owes its origins to the German V1 "Buzz Bomb" of WW II that ran on
aviation fuel." My understanding is that this not a pure plasma engine; like a jet
engine, it pulls air in and accelerates it using the pulse detonation. This would
mean, I think, that outside the atmosphere, it would lose a lot of efficiency.
In any case, there are some problems with operating this system outside of an
atmosphere;
1. The efficiency is low. The longer you need to accelerate, the heavier you need
to be. Include attenuation for distance in the equation, and I think chemical
rockets win.
2. Keeping a laser of that power focussed so tightly over those kinds of distances
outside of the atmosphere is tricky, and while spin can correct for some
mis-alignments, long term you can end up in trouble.
3. A laser of that intensity operating over long periods is to say the heast
hazardous.
4. With this initial design, the laser has to be directly behind the vehicle. I
can imagine a design which has the laser ahead of the vehicle, but I don't want
to even try to imagine a spinning design that tries to harness laser energy
coming from even slightly to the side. That makes this kind of propulsion very
uni-directional.
I think that it would be better to have a vehicle that uses the laser pulse
detonation drive to get out of the atmoshpere, then difuse the laser and deploy
solar sails. I think solar sails are more versatile, and can operate even without a
ground laser system.
I just have one question; we can use this system to get a vehicle into orbit, but
how do we get it back down again? Since it is an air-breathing engine, you can't
just reverse it back down the beam. By the time the atmosphere is thick enough, it
would already be burning, and besides, I don't think it would travel backwards well.
I suppose you could focus the laser ahead to create a shockwave ahead, but while
that would stop it burning, would not slow it down. Also the design is not one that
particularly likes heat tiles.
So how do you do it?
Justin Downey
>
> Justin Downey wrote:
>
> > Michael Fuller wrote:
> > >
> > ><snip>
> > >
> > > IIRC, that was a laser-supplemented light-sail; the Motie ship would have
> > > been "blown" along by light pressure on the sail. The experimental rocket
> > > described in the original posting is powered by using a pulsed laser to heat
> > > air in a "combustion" chamber at the base of the rocket; the rocket is driven
> > > by the expulsion of rapidly expanding gases.
> > >
> > > (Feel free to correct if I'm wrong---it's been a while since I read either
> > > book, and I'm working second-hand from the reports of the news footage.)
> >
> > Aaaah yes, you are right. In the motie ship the laser itself would
> > provide the equal and opposite reaction. The ship would effectively be
> > pushing against the planet holding the laser. In the experimental rocket
> > and the Marshall Savage version, the rocket would be pushing against the
> > reaction mass attached to the rocket (assuming it carries its own air
> > supply to ag as reaction mass.)
>
> Ummmm ... the logic isn't too bad, but no cigar.
>
> Looking at the Propulsion Directorate page at Edwards Air Force Base, you'll see
> that the emphasis of the design is atmoshperic hyper-sonic travel. If you can say
> that the Motie ship is pushing against the planet in the first case, then you can
> certainly say the same in the second. However, I think it would be more correct to
> say that the Motie ship was pushing against the solar winds and had laser
> assistance.
Nope. The Motie ship would certainly have been assisted by the solar
wind at the early stage of the journey, but recall that it was an
interstellar craft. The solar wind from the originating star would not
have any significant effect for the major part of the journey. Also, the
solar wind from the target star would be acting against the forward
motion of the craft in the later parts of the journey. Assuming that the
stars were roughly the same order of magnitude, solar wind would have no
net effect on the voyage.
I can't remember what mechanism the moties used to slow down the ship at
the end of their journey...
> Your "action and reaction" is actually in the first case the capturing of the energy
> of the solar wind and laser,
Yep. The laser is pushing against the ship (assuming it is a using a
solar sail and the laser is not being used to heat reaction mass. In the
latter case, the ship would be pushing against the reaction mass, not
the laser.) The solar wind is pushing against the ship and equally hard
against the sun.
> and in the second it is against the atmosphere.
No. This is the same mistake made by ummm....can't remember his name,
when he heard about Goddard's (Tsiokovski's?) rocket. He said rocket
travel outside the atmosphere is impossible because there is nothing for
the rocket to push against. Of course, the rocket does not need to push
against the atmosphere at all. The rocket moves forward because it is
pushing against the reaction mass being expelled out the back of the
rocket.
>
> I think people have missed one tiny feature of the design ... this engine appears to
> have air inlets. In the documentation, it says "This airbreathing pulsed detonation
> engine concept owes its origins to the German V1 "Buzz Bomb" of WW II that ran on
> aviation fuel." My understanding is that this not a pure plasma engine; like a jet
> engine, it pulls air in and accelerates it using the pulse detonation. This would
> mean, I think, that outside the atmosphere, it would lose a lot of efficiency.
>
I haven't seen the original document. I don't think using a ground based
laser to heat reaction mass would be practical for long voyages. The
ship would need to carry large amounts of fuel. Why bother lighting the
fuel using a huge ground based laser when you could just light it at the
source like current rockets? However, I think the concept has value for
orbital launches, where the amount of reaction mass would be reasonable
small. If you could use a block of ice for fuel, you would not need the
complex (read: heavy) storage and pumping systems needed for chemical
rockets.
> In any case, there are some problems with operating this system outside of an
> atmosphere;
>
> 1. The efficiency is low. The longer you need to accelerate, the heavier you need
> to be. Include attenuation for distance in the equation, and I think chemical
> rockets win.
> 2. Keeping a laser of that power focussed so tightly over those kinds of distances
> outside of the atmosphere is tricky, and while spin can correct for some
> mis-alignments, long term you can end up in trouble.
I'm not sure focus would be excessively tricky. Look at adaptive-optic
telescopes. I think generating the power for the laser would be the real
trick.
> 3. A laser of that intensity operating over long periods is to say the heast
> hazardous.
Heheheh. I wouldn't build my house next to it, that's for sure. But
isn't sitting on what is effectively a controlled explosion equally
risky?
> 4. With this initial design, the laser has to be directly behind the vehicle. I
> can imagine a design which has the laser ahead of the vehicle, but I don't want
> to even try to imagine a spinning design that tries to harness laser energy
> coming from even slightly to the side. That makes this kind of propulsion very
> uni-directional.
Yep.
>
> I think that it would be better to have a vehicle that uses the laser pulse
> detonation drive to get out of the atmoshpere, then difuse the laser and deploy
> solar sails. I think solar sails are more versatile, and can operate even without a
> ground laser system.
I agree. Solar sails are well suited to IP travel. THe GBL would be
overkill and probably clunky in comparison. Remember though that the
Moties were a clunky civilisation :)
>
> I just have one question; we can use this system to get a vehicle into orbit, but
> how do we get it back down again? Since it is an air-breathing engine, you can't
> just reverse it back down the beam. By the time the atmosphere is thick enough, it
> would already be burning, and besides, I don't think it would travel backwards well.
> I suppose you could focus the laser ahead to create a shockwave ahead, but while
> that would stop it burning, would not slow it down. Also the design is not one that
> particularly likes heat tiles.
>
> So how do you do it?
I haven't looked at the material, but I like Marshall Savage's approach:
a ship with a heat shield and manoevering rockets, a large, cheap
reaction mass stuck on the base. Use the laser to heat the reaction mass
to boost into orbit. When you need to come down, use your small chemical
rockets to deorbit and heat shields to protect you during re-entry. He
also described a maglev for the initial part of the launch, only when
the ship was about 10 km agl would the lasers be used
Revenant
> John Leister wrote:
> > Apparently the people who are testing this want to build a full size
ship
> > able to carry a payload and possibly a crew but can you imagine the
power
> > that they might need from the targeting laser on the ground?
> Hmmmm ... one misfire could really spoil the day for somone in orbit.
And this is different from rockets exactly how?
Shane
wrote:
I think he probably means someone else in orbit - the laser misses its
target and fries someone else.
--
- Shane
Sig? I don't need no steenkin' sig.
Revenant
<35daaab6...@news.accsoft.com.au>...
> On 19 Aug 98 07:23:24 GMT, "Revenant" <k...@rosella.apana.org.au>
> wrote:
> >Owen Godfrey <god...@ccis.adisys.zebra.com.au> wrote
> > And this is different from rockets exactly how?
> I think he probably means someone else in orbit - the laser misses its
> target and fries someone else.
I know. Don't you run the exact same risk from a rocket? If it misfires
it could smack into all sorts of things up there...
John Leister
John Leister wrote:
<snipped myself Ouch!>
As I read all your replies my memories came alive of something I read
years and years ago. I can't pinpoint where the idea came from but
I have read something else like this and as a teenager I can
remember doing drawings of the ship I am about to describe. Solar
sail ships with huge billowing sails. Yeah! It's kind of romantic.
Just thinking but how about this for an idea? Build a ship big enough
for a a crew and the systems necessary to keep them alive. Make it
conical in shape and at the rear end of the ship place a ring of high
intensity spotlights, well we'll use lasers in our test model since
that's what the real ship on the news uses. Aim each laser at an
angle pointing away from the ship. Now before the lasers are
activated we extend a massive solar sail from the very rear of
the ship and once it's fully erected the circle of beams
radiating from the ship's base pushes on the sail thus moving
it in space.
We could power the lasers by a nuclear or solar generator as
deep space probes use or a combination of the two. As the laser
beams hit the sail there is an action and an opposite reaction
ala Newton and the ship moves. We could tilt the sail and the
beams and thus turn and we could mount sensors on the ship to sense
the real solar wind and thus tack into it much like a yacht.
I think this idea has been thought of somewhere else but I thought it
sounded really nice.
David Ralphs
: John writes:
: John Leister wrote:
: <snipped myself Ouch!>
Ill snip you as well...
: Just thinking but how about this for an idea? Build a ship big enough
: for a a crew and the systems necessary to keep them alive. Make it
: conical in shape and at the rear end of the ship place a ring of high
: intensity spotlights, well we'll use lasers in our test model since
: that's what the real ship on the news uses. Aim each laser at an
: angle pointing away from the ship. Now before the lasers are
: activated we extend a massive solar sail from the very rear of
: the ship and once it's fully erected the circle of beams
: radiating from the ship's base pushes on the sail thus moving
: it in space.
: We could power the lasers by a nuclear or solar generator as
: deep space probes use or a combination of the two. As the laser
: beams hit the sail there is an action and an opposite reaction
: ala Newton and the ship moves. We could tilt the sail and the
: beams and thus turn and we could mount sensors on the ship to sense
: the real solar wind and thus tack into it much like a yacht.
Hmm - have I read this wrong.
Lights on the ship, aimed at a sail attatched to the ship?
Was this suppose to be sarcastic?
: I think this idea has been thought of somewhere else but I thought it
: sounded really nice.
Yeah - its called the perpetual motion machine.
Your action/reaction are both on the same object. So it wont move.
The whole idea of using lasers on board a ship to move is silly,
its not an efficient way of moving.
The neat idea of a laser for lift a ship from the planet is that
the laser is the main power source, but is not on the ship.
Hence the ship is "thrown" rather than "lifts itself".
: --
: The Earth goes around the sun
: The Earth spins to make a day
: Why aren't I dizzy?
I dont know, but Im dizzy after reading your post...
DN
--
A snake you were when we met
I loved you anyway
Pulling out your poisoned fangs
The venom never goes away
D. Mustaine - "Poison Was The Cure"
John Leister
David Ralphs wrote:
<big snip>
No I was not being sarcastic at all after all I was impressed by the ship in
the news story I wrote about. I was very impressed in fact.
Just out of asking wouldn't the ship move if it started from a stationary
position in space. If the ship was standing still and the lasers were aimed
at the sail there would be an action/reaction wouldn't there?
Just wondering as that's how I saw the ship when I wrote the posting.
--
The Earth goes around the sun
The Earth spins to make a day
Why aren't I dizzy?
John D Leister
David Ralphs
: John writes:
: David Ralphs wrote:
: <big snip>
: No I was not being sarcastic at all after all I was impressed by the ship in
: the news story I wrote about. I was very impressed in fact.
: Just out of asking wouldn't the ship move if it started from a stationary
: position in space. If the ship was standing still and the lasers were aimed
: at the sail there would be an action/reaction wouldn't there?
: Just wondering as that's how I saw the ship when I wrote the posting.
If the lasers are on the ship, aiming at its own sails,
then it wont move.
In terms of action/recation, yes the sails and lasers get pushed
opposite directions, but since they are connected the forces
would then cancel and all you are doing is pushing the ship apart.
Imagine sitting in your car and pushing on the dash...
does the car move forward??
You need to push against an external object.
DN
--
Everlasting life for me
in a perfect world
but I gotta die first...
please god send me on my way.
D. Mustaine - "In My Darkest Hour"
Chris Severn
> John Leister (joh...@senet.com.au) wrote:
> : John writes:
> : David Ralphs wrote:
> : No I was not being sarcastic at all after all I was impressed by the ship in
> : the news story I wrote about. I was very impressed in fact.
> : Just out of asking wouldn't the ship move if it started from a stationary
> : position in space. If the ship was standing still and the lasers were aimed
> : at the sail there would be an action/reaction wouldn't there?
> : Just wondering as that's how I saw the ship when I wrote the posting.
> If the lasers are on the ship, aiming at its own sails,
> then it wont move.
> In terms of action/recation, yes the sails and lasers get pushed
> opposite directions, but since they are connected the forces
> would then cancel and all you are doing is pushing the ship apart.
Well, actually it depends on whether the sail absorbs or reflects the
light. If it reflects the light (and it doesn't hit any part of the ship
after that), then shining the light at the sail will push the ship along.
It will push it along at the same rate as if the laser was just reversed,
without the light hitting the ship after leaving the laser.
> Imagine sitting in your car and pushing on the dash...
> does the car move forward??
> You need to push against an external object.
True, but with light, if it is reflected off the sail, the light will
eventually end up hitting something else. That's the external object.
So, if the laser is pointing away from Earth, and being reflected back
towards earth by the sail, then effectively the ship is pushing itself
off earth. Sort of. Maybe not.
Chris Severn.
--
Delete the 'x's to remove the spamblock.
John Leister
fact to be actual particles it would seem only fair that particles hitting the sail
would cause a reaction in that the ship would move. And yes I had pictured that the
sail would reflect the lasers away from the main part of the ship they would be
immense in size and the beams are set at an angle remember so the light should not
go back to the ship but propel it.
John Leister
Revenant
> <35d7d...@nexus.comcen.com.au>...
[SNIP]
> BTW, this reminded me of "Deep Impact". The Russian drive
> (name escapes me) looked like it dropped something from the
> stern, which detonated behind the space craft, the rear of
> the craft appeared to be a substantial concave plate. My
> recollection of Footfall is a little fuzzy & my recollection
> of Deep Impact even fuzzier.
The drive was called an "Orion" drive. The Orion drive is
one of those inventions of sci-fi novels that has become
essentially mainstream - like Dyson Spheres. I forget who
originally invented it though. Niven?
terry russell
>
> Well since light is compsed of photons and photos have been proven in scientific
> fact to be actual particles it would seem only fair that particles hitting the sail
> sail would reflect the lasers away from the main part of the ship they would be
> immense in size and the beams are set at an angle remember so the light should not
> go back to the ship but propel it.
then you don't need a sail at all
for photons to provide decent propulsion you need a lot of light, and a
big black
absorber, its probably easier to just use a bigger simpler sail and tack
using the the solar wind
an external laser would be best used to carry energy to the ship, the
reverse of your sail
idea, but as a an enrgy concentrator only, the sail to bounce propulsion
just means
you need tethers twice as strong as the laser generator mountings
incoming light reflected by a large surface onto a heater or other
device where reaction mass
is vaporised or ,better, ionised and expelled in the usual rocket way,
reflector means
the beam need not be too intense, solar reflectors would probably be
better but a beam
more easily controlled for straight line flight
besides, it gives the star wars development a cover for laser weapons
development
with an external power source the reaction mass can be dense and inert,
safer smaller ships
with reaction mass drivers you can still power deceleration from the
single laser source
and all ship mass can be used as reaction mass, crews in transit would
be encouraged to
take as many showers as possible to keep the effluent tanks full for
deceleration ;-)
Chris Fiddyment
> Imagine sitting in your car and pushing on the dash...
> does the car move forward??
Not if the handbrake is on :-)
Actually if I sit in the back seat, leap forward and hit the dash, the car
should move then.
--
.-_|\ Chris Fiddyment.
/ \ <Chris.F...@dsto.defence.gov.au>
\.--._/ Salisbury, Adelaide.
v
Owen Godfrey
> <snip>
> Just thinking but how about this for an idea? Build a ship big enough
> for a a crew and the systems necessary to keep them alive. Make it
> conical in shape and at the rear end of the ship place a ring of high
> intensity spotlights, well we'll use lasers in our test model since
> that's what the real ship on the news uses. Aim each laser at an
> angle pointing away from the ship. Now before the lasers are
> activated we extend a massive solar sail from the very rear of
> the ship and once it's fully erected the circle of beams
> radiating from the ship's base pushes on the sail thus moving
> it in space.
>
> We could power the lasers by a nuclear or solar generator as
> deep space probes use or a combination of the two. As the laser
> beams hit the sail there is an action and an opposite reaction
> ala Newton and the ship moves. We could tilt the sail and the
> beams and thus turn and we could mount sensors on the ship to sense
> the real solar wind and thus tack into it much like a yacht.
>
> I think this idea has been thought of somewhere else but I thought it
> sounded really nice.
It does sound nice :) Sorry though, it won't work like that :(
* The motion of the large sail away from the vessel is independent of
the motion of the vessel; you would get the same effect without the
sail. Effectively, the large sail is just catching a lift on the wind
you create.
* However, if you reflect the light back again, you can use the light
again. This is the concept the Moties used for braking as the larger
outer sail broke away, and because of its shape, reflected light back
to the smaller inner sail, which slowed the ship down as it
approached the new star. However, the laser that drove the system was
still back at the Motie home world, and I think is was turned off by
then.
* The energy needed to power the laser is going to far exceed the
energy needed to expel a reaction mass for the same benefit. There
are more efficient ways of using a nuclear reactor as a drive. The
advantage with having a ground based laser is that you don't have to
carry your own energy supply; your power is delivered to you at the
speed of light at no cost.
The idea is cool, but it is on par with Wile E. Cyotee putting a sail on a
skate-board and carrying an electric fan to try and catch the Road Runner.
Keep the ideas coming though, cause I still like the idea. :)
Owen Godfrey
<snipped>
I think the main objection, regardless of the physics or photon action and
reaction, is whether it is viable as a drive. The amount of energy that
has to be output to move the vessel is going to be tremendous, and that
means carrying powerful generators to power the lazers. Add it up, and I
think chemical drives win. The only thing that makes a lazer propultion
system feasible is the fact that the power source for the drive does not
have to be mounted on the vessel, and a coherent lazer beam can deliver
the energy to the vessel at a very low cost for distance, both in terms of
efficiency and gross vessel mass. However, I have feeling that if you
actually add up the cost in terms of thrust generated for power expended,
you'd find it shockingly ineficient. The ONLY thing that makes it
efficient is the fact that the vessel is not carrying its own power
source.
(Mind you, I am not a physics major, so this is partly logic and partly
guess work)
Christian McNeill
<01bdcfe8$48346ec0$b3bf...@fmtacg0d.deetya.gov.au>...
Yeah Larry Niven.... well... atleast it was in his book where it talked
about the Dyson Sphere... but he could have got the idea from somewhere
else... Just like Star Trek got the idea from him...probably...
--------------------------------------
Christian McNeill
e-mail: red...@ozemail.com.au
--------------------------------------
Gregory Bond
> Yeah Larry Niven.... well... atleast it was in his book where it talked
> about the Dyson Sphere... but he could have got the idea from somewhere
> else... Just like Star Trek got the idea from him...probably...
Dyson (as in spheres) is Freeman Dyson, a well-known "futurist" who
thunked up a whole bunch of good ideas. (I think beanstalks might have
been one of his as well). Dyson is (was?) also active in the US space
& sf communities and is well known to Niven, Pournelle & others.
--
Gregory Bond ITG Australia Ltd, Melbourne, Australia
<mailto:g...@itga.com.au> <http://www.bby.com.au/~gnb>
From: br...@itga.com.au (Do not use this address. It catches junk email.)
From: br...@bby.com.au, br...@melba.bby.com.au (So do these ones)
David Ralphs
: Well since light is compsed of photons and photos have been proven in scientific
: fact to be actual particles it would seem only fair that particles hitting the sail
: would cause a reaction in that the ship would move. And yes I had pictured that the
: sail would reflect the lasers away from the main part of the ship they would be
: immense in size and the beams are set at an angle remember so the light should not
: go back to the ship but propel it.
So why do you need the sail?
Yes you could just aim the laser out the back of the ship.
But it wouldnt be a very effective way of moving..
You would do better pissing out the back of the ship!
DN
--
all these years I thought I was wrong
now I know it was you.
Brian Raynor
>John Leister (joh...@senet.com.au) wrote:
>: Well since light is compsed of photons and photos have been proven in scientific
>: fact to be actual particles it would seem only fair that particles hitting the sail
>: would cause a reaction in that the ship would move. And yes I had pictured that the
>: sail would reflect the lasers away from the main part of the ship they would be
>: immense in size and the beams are set at an angle remember so the light should not
>: go back to the ship but propel it.
>
>So why do you need the sail?
>
>Yes you could just aim the laser out the back of the ship.
>But it wouldnt be a very effective way of moving..
>You would do better pissing out the back of the ship!
I only have a vague memory of "The Mote in God's Eye", but as I recall the
sail was primarily to catch the Solar Wind, and it was HUGE. It's surface
area was enormous, something like the surface area of the moon (or
something, again memory is vague)
To work at all, the sail had to be HUGE but also incredibly light.
I forget the reason for the ground-based laser (extra boost when starting
the journey maybe ?) but I believe the sail relied primarily on the Solar
Wind.
It would ride the Solar Wind away from the Star it was leaving,
accelerating as it did so. As it travelled further from the Star the Solar
Wind would diminish to a point where it no longer assisted the craft. It
would then work in reverse and rely on the sail to decelerate the craft as
it approached the destination Star.
Using light as a propulsion system can ONLY be practical if you have a
huge supply of it that you dont need to drag along with you. A Star
provides such a supply.
Regards,
Brian Raynor
Advanced Project Solutions
br...@advproj.com.au
Brian Raynor
>da...@atn.atn7.oz.au (David Ralphs) writes:
>
>> Imagine sitting in your car and pushing on the dash...
>> does the car move forward??
>
>Not if the handbrake is on :-)
>
>Actually if I sit in the back seat, leap forward and hit the dash, the car
>should move then.
The car would move backward as you leap forward, and then move forward
when you hit the dash. Effectively going nowhere.
David Johnston
>da...@atn.atn7.oz.au (David Ralphs) writes:
>
>> Imagine sitting in your car and pushing on the dash...
>> does the car move forward??
>
>Not if the handbrake is on :-)
>
>Actually if I sit in the back seat, leap forward and hit the dash, the car
>should move then.
>
Yes, backwards a short distance :-) - assumming, of course, that the bearing
of the wheels are perfect, or the car is sitting on a perfectly frictionless,
perfectly flat plane...
david
--
David Johnston
da...@canopus.apana.org.au
David Johnston
>Chris Fiddyment <c...@itd.dsto.gov.au> wrote:
>
>>da...@atn.atn7.oz.au (David Ralphs) writes:
>>
>>> Imagine sitting in your car and pushing on the dash...
>>> does the car move forward??
>>
>>Not if the handbrake is on :-)
>>
>>Actually if I sit in the back seat, leap forward and hit the dash, the car
>>should move then.
>
>when you hit the dash. Effectively going nowhere.
>
Nah. The car will stop when you hit the dashboard - the net result will be
that the car moves back a (very) short distance.
Remember that by moving from the back seat to the front seat, you have
moved the center of gravity of the system composed of you and the car
slightly forward. Since there is no external force acting on the system,
the center of gravity must not change (Newtons first law). Thus the car
must move backwards slightly to compensate.
John Leister
Owen Godfrey wrote:
> John Leister wrote:
> <snipped>
>
> I think the main objection, regardless of the physics or photon action and
> reaction, is whether it is viable as a drive. The amount of energy that
> has to be output to move the vessel is going to be tremendous, and that
> means carrying powerful generators to power the lazers. Add it up, and I
> think chemical drives win. The only thing that makes a lazer propultion
> system feasible is the fact that the power source for the drive does not
> have to be mounted on the vessel, and a coherent lazer beam can deliver
> the energy to the vessel at a very low cost for distance, both in terms of
> efficiency and gross vessel mass. However, I have feeling that if you
> actually add up the cost in terms of thrust generated for power expended,
> you'd find it shockingly ineficient. The ONLY thing that makes it
> efficient is the fact that the vessel is not carrying its own power
> source.
Well I beg to differ on this but imagine that the ship has started off, over
time with a constant source of light it would build momentum wouldn't it.
Assuming we could find a stable power source and effecient enough lasers our
speed would build up gradually. And anyway who needs speed and time this would
be the perfect way to travel for a a vessel that was used for say a generation
ship. Or for a vessel carrying it's crew for an indeterminate period in
suspended animation.
--
The Earth goes around the sun
The Earth spins to make a day
Why aren't I dizzy?
John D Leister
Jogging through my homepage at:
http://www.geocities.com/southbeach/shores/6340
Mirrored at: For faster loading
http://www.senet.com.au/~johndk/index.htm
Running up to my mailbox at:
mgib...@quondong.aus.fruit.and.vege
: Dyson (as in spheres) is Freeman Dyson, a well-known "futurist" who
: thunked up a whole bunch of good ideas. (I think beanstalks might have
: been one of his as well). Dyson is (was?) also active in the US space
: & sf communities and is well known to Niven, Pournelle & others.
Dyson wasn't just a futurist. He's also a physicist and contemporary
of Richard Feynman. AFAIR the Star Trek representation of a Dyson sphere being
a solid object is incorrect. It is supposed to be an interlinked array of
satelites that generates a field effect. Consider that obtaining the materials
to surround the outer atmosphere of a planet with a solid sphere would be
horrendous in both time and materials.
The best person to give an explanation would be a physicist....
Is there a physicist in the house :-)
________
Matthew Gibbins
email : mgib...@mindless.com
Joel Kelso
> John Whear <jwh...@comcen.com.au> wrote in article
> > <35d7d...@nexus.comcen.com.au>...
> [SNIP]
> > BTW, this reminded me of "Deep Impact". The Russian drive
> > (name escapes me) looked like it dropped something from the
> > stern, which detonated behind the space craft, the rear of
> > the craft appeared to be a substantial concave plate. My
> > recollection of Footfall is a little fuzzy & my recollection
> > of Deep Impact even fuzzier.
>
> The drive was called an "Orion" drive. The Orion drive is
> one of those inventions of sci-fi novels that has become
> essentially mainstream - like Dyson Spheres. I forget who
> originally invented it though. Niven?
I'm not sure if it originated in SF, but the US made some fairlydetailed
plans for a spaceship ("Orion") that moved by lobbing nuclear
bombs behind it every three seconds or so. I belive they actually flew
a scaled-down model, powered by ordinary chemical bombs.
In "Footfall" by Niven and Pournell, humans attack an orbiting alien
mother ship by building an Orion.
Actually, in the same novel, I think that the aliens launch rockets from
the surface of the earth which were powered by lasers sited on the
ground ... which is how this thread started, isn't it ?
Joel Kelso
-- jo...@ee.uwa.edu.au --------------------------------------
"... great Scott, he's turned into _more than one person_ !"
"Well, there was always enough of him."
- the Goon Show
-- http://ciips.ee.uwa.edu.au/~joel ------------------------
Joel Kelso
> I only have a vague memory of "The Mote in God's Eye", but as I recall the
> sail was primarily to catch the Solar Wind, and it was HUGE. It's surface
> area was enormous, something like the surface area of the moon (or
> something, again memory is vague)
>
> To work at all, the sail had to be HUGE but also incredibly light.
>
> I forget the reason for the ground-based laser (extra boost when starting
> the journey maybe ?) but I believe the sail relied primarily on the Solar
> Wind.
>
> It would ride the Solar Wind away from the Star it was leaving,
> accelerating as it did so. As it travelled further from the Star the Solar
> Wind would diminish to a point where it no longer assisted the craft. It
> would then work in reverse and rely on the sail to decelerate the craft as
> it approached the destination Star.
I think that the radiation pressure drops off way too rapidly to use starlightfor actual
interstellar propulsion. In "The Mote In God's Eye", the ship was
launched by banks of lasers back in the Mote system (the novel talks about
a speck of light that appeared for a decade (century) or so, which was the
light from the lauching lasers). I think that part of the sail was supposed to
be detached and used to reflect light back on a much smaller part of the ship
with its own small sail (facing the other way) to decelerate the ship near the
target star, but the Motie society being unstable as is was, the lasers back
home went out and the ship was left falling into the target star with only the
sunlight to slow it down.
> Using light as a propulsion system can ONLY be practical if you have a
> huge supply of it that you dont need to drag along with you. A Star
> provides such a supply.
I believe that Robert Forward and friends have done designs for laser propelled(and
microwave propelled) interstellar missions. There must be web sites on this ...
David Ralphs
: "Christian McNeill" <red...@ozemail.com.au> writes:
: > Yeah Larry Niven.... well... atleast it was in his book where it talked
: > about the Dyson Sphere... but he could have got the idea from somewhere
: > else... Just like Star Trek got the idea from him...probably...
: Dyson (as in spheres) is Freeman Dyson, a well-known "futurist" who
: thunked up a whole bunch of good ideas. (I think beanstalks might have
: been one of his as well). Dyson is (was?) also active in the US space
: & sf communities and is well known to Niven, Pournelle & others.
Dyson is more than just a well known futurist
he is actually a well known physicist!!
But the Dyson spheres have been shown not to work,
like the ringworld, they suffer from being an unstable system.
They are a huge sphere that surrounds a star.
So instead of living on a puny little planet like earth,
we can have a whole sphere at about this distance from the sun.
Most of the suns output would be able to be used (mega solar power!)
However, if the sphere got off-centre from the sun, it would
keep moving and one side would fall in towards the sun.
DN
--
----------------------------------------------------------
| David N Ralphs |
| ATN - Channel 7 Phone: (02) 9877 7707 |
| Mobbs Lane Fax: (02) 9877 7894 |
| Epping, NSW Email: d...@atn.atn7.eggs.oz.au |
| (remove 'eggs' to unspam me!) |
----------------------------------------------------------
These views are mine.. no one else would agree with them!
Everlasting life for me
in a perfect world
but I gotta die first...
please god send me on my way.
D. Mustaine - "In My Darkest Hour"
David Ralphs
: > Imagine sitting in your car and pushing on the dash...
: > does the car move forward??
: Not if the handbrake is on :-)
Damn - Id better redo the experiment!
: Actually if I sit in the back seat, leap forward and hit the dash, the car
: should move then.
No...
Leap forward - car goes backward
Hit dash - car stops, you go splat.
DN
--
I like the things that you try and fake
And your face when I see you break
And that you say you will pray for me
You realise you are prey for me
D. Mustaine - "Reckoning Day"
David Ralphs
: In article <35e5ca8c....@news.omen.net.au> br...@advproj.com.au writes:
: >Chris Fiddyment <c...@itd.dsto.gov.au> wrote:
: >
: >>da...@atn.atn7.oz.au (David Ralphs) writes:
: >>
: >>> Imagine sitting in your car and pushing on the dash...
: >>> does the car move forward??
: >>
: >>Not if the handbrake is on :-)
: >>Actually if I sit in the back seat, leap forward and hit the dash, the car
: >>should move then.
: >The car would move backward as you leap forward, and then move forward
: >when you hit the dash. Effectively going nowhere.
: >
: Nah. The car will stop when you hit the dashboard - the net result will be
: that the car moves back a (very) short distance.
: Remember that by moving from the back seat to the front seat, you have
: moved the center of gravity of the system composed of you and the car
: slightly forward. Since there is no external force acting on the system,
: the center of gravity must not change (Newtons first law). Thus the car
: must move backwards slightly to compensate.
Yup...
but then as you climb into the backseat the car would move forward.
So its not so much a method of propulsion, but a redistribution
of the mass of the object.
A spaceman who sticks his arm out, moves his body a small amount
the other direction - doesnt mean he is swimming!
DN
--
all these years I thought I was wrong
now I know it was you.
D. Mustaine - "In My Darkest Hour"
David Ralphs
: Well I beg to differ on this but imagine that the ship has started off, over
: time with a constant source of light it would build momentum wouldn't it.
: Assuming we could find a stable power source and effecient enough lasers our
: speed would build up gradually. And anyway who needs speed and time this would
: be the perfect way to travel for a a vessel that was used for say a generation
: ship. Or for a vessel carrying it's crew for an indeterminate period in
: suspended animation.
In terms of propulsion - lasers are not as good as other light sources.
The neat property of the laser is that the light is coherent.
But that doesnt make it any better to push you.
In fact losses in the laser compared to other light sources
would mean that it is probably less efficient.
It is still damn hard to beat throwing something off the ship
as a method of propulsion.
The momentum of a photon is purely from energy,
then momentum of an object is its mass and speed.
Due to e=mc^2 its pretty easy to see that a little bit
of mass is worth a lot of energy.
(conversly - a bit of light energy is worth not very much mass)
So throwing a pebble out the back of the ship
is worth a hell of a lot of light!
I still say that pissing out the back of the ship
would work better....
John Leister
But only after a full keg of beer in one sitting.
And then you could witness the fun as your dick decompresses being outside the ship
and all:)
Thorfinn
David Ralphs <da...@atn.atn7.oz.au> wrote:
>But the Dyson spheres have been shown not to work,
>like the ringworld, they suffer from being an unstable system.
That just means that they need stabilisers of some kind.
>They are a huge sphere that surrounds a star.
>So instead of living on a puny little planet like earth,
>we can have a whole sphere at about this distance from the sun.
>Most of the suns output would be able to be used (mega solar power!)
>However, if the sphere got off-centre from the sun, it would
>keep moving and one side would fall in towards the sun.
Hmm... maybe, with sufficiently funky materials tech, you could make
immense portions of the floor selectively transparent...
So, when you need to thrust in a direction, you make the half of the
sphere in the opposite direction transparent...
Instant light drive, using sunpower. :)
Whee! :)
Later,
Thorf
--
<a href="http://www.tertius.net.au/~thorfinn/">thor...@tertius.net.au</a>
Those who do not understand Unix are condemned to reinvent it, poorly.
-- Henry Spencer
Russell Dovey
(Shane) wrote:
>On 19 Aug 98 07:23:24 GMT, "Revenant" <k...@rosella.apana.org.au>
>wrote:
>
>>Owen Godfrey <god...@ccis.adisys.zebra.com.au> wrote
>>> John Leister wrote:
>>> > Apparently the people who are testing this want to build a full size
>>ship
>>> > able to carry a payload and possibly a crew but can you imagine the
>>power
>>> > that they might need from the targeting laser on the ground?
>>> Hmmmm ... one misfire could really spoil the day for somone in orbit.
>>
>> And this is different from rockets exactly how?
>
>I think he probably means someone else in orbit - the laser misses its
>target and fries someone else.
To quote Truman from Armageddon "Begging your pardon, sir, but it's a
big-ass sky." A random laser shot into space would be overwhelmingly
likely to hit nothing.
>
>--
>- Shane
>
>Sig? I don't need no steenkin' sig.
--------------------------------------------------------
Fight for what you believe in!
"The most beautiful experience we can have is the
mysterious." - Albert Einstein.
"Pinky, are you pondering what I'm pondering?"
"Uh, I think so, Brain, but how are we going to get all
those computers to fail all at the same time?"
Russell "Not Just For Lepers Any More" Dovey, Australia.
--------------------------------------------------------
Russell Dovey
<dmi...@camtech.net.au> wrote:
>John Leister wrote:
>
>> On the 6pm news tonight we saw this experimental rocket that was
>> powered by a laser beam that was shot up it's rear into a combustion
>> chamber and it took off with little smoke and only a slight whining
>> sound. Anyone care to comment about how effecient this machine may or
>> may not be?
>
>Larry Niven and Jerry Pournelle re-voiced this idea in a book about20
>years ago. Can't think of the title though. They also had a number
>of other good ideas.
Footfall, baby elephants invading the Earth. Great book. (Hell, all of
Larry Niven's books are great!)
His design was slightly different, though. In his, the exhaust was
partially vaporised rocket motor, partially superheated air. The one
being developed in the US is just plasmafied (superheated to a plasma)
air. For this reason, it doesn't work in a vacuum.
>
>> --
>> Love the controversy,
>> To play Devil's advocate,
>> To see the truths in life,
>> The inner meanings to everything.
>>
>> John D Leister
>> Jogging through my homepage at:
>> http://www.geocities.com/southbeach/shores/6340
>> Mirrored at: For faster loading
>> http://www.senet.com.au/~johndk/index.htm
>> Running up to my mailbox at:
>> joh...@academy.net.au
>
>--
>Regards
>
>David Milne
>
>Reply to
>
>dmi...@camtech.com.au or
>dmi...@watt.mecheng.adelaide.edu.au Remove NOSPAM in e-mail address
>
>Are you a Klingon or is that a turtle on your head?
Russell Dovey
<jwh...@comcen.com.au> wrote:
>David Milne wrote in message <35D703CB...@camtech.net.au>...
>>John Leister wrote:
>>
>>> On the 6pm news tonight we saw this experimental rocket that was
>>> powered by a laser beam that was shot up it's rear into a combustion
>>> chamber and it took off with little smoke and only a slight whining
>>> sound. Anyone care to comment about how effecient this machine may or
>>> may not be?
>>
>>Larry Niven and Jerry Pournelle re-voiced this idea in a book about20
>>years ago. Can't think of the title though. They also had a number
>>of other good ideas.
>
> Are you thinking of Footfall? Use of nuclear devices detonating behind a
>concave plate to provide propulsion.
No, no, that's Orion. FUN ship. :) :) But the book is right. Remember
the missile guys in South Africa who tried to blow up a laser facility
while the ship was launching?
> BTW, this reminded me of "Deep Impact". The Russian drive (name escapes
>me) looked like it dropped something from the stern, which detonated behind
>the space craft, the rear of the craft appeared to be a substantial concave
>plate. My recollection of Footfall is a little fuzzy & my recollection of
>Deep Impact even fuzzier.
Deep Impact's version was innacurate crap. The ship is supposed to
move in pulses, or WHAM's, not at a steady pace like it did.
>
> See You Out There!
> <*>
> J.W.
>jwh...@comcen.com.au
Russell Dovey
<red...@ozemail.com.au> wrote:
>Revenant wrote in message
><01bdcfe8$48346ec0$b3bf...@fmtacg0d.deetya.gov.au>...
>|John Whear <jwh...@comcen.com.au> wrote in article
>|> <35d7d...@nexus.comcen.com.au>...
>|[SNIP]
>|> BTW, this reminded me of "Deep Impact". The Russian drive
>|> (name escapes me) looked like it dropped something from the
>|> stern, which detonated behind the space craft, the rear of
>|> the craft appeared to be a substantial concave plate. My
>|> recollection of Footfall is a little fuzzy & my recollection
>|> of Deep Impact even fuzzier.
>|
>| The drive was called an "Orion" drive. The Orion drive is
>|one of those inventions of sci-fi novels that has become
>|essentially mainstream - like Dyson Spheres. I forget who
>|originally invented it though. Niven?
>
>
>Yeah Larry Niven.... well... atleast it was in his book where it talked
>about the Dyson Sphere... but he could have got the idea from somewhere
>else... Just like Star Trek got the idea from him...probably...
I'm sure Larry'd like to think that, but the Orion drive was cooked up
by some nuke scientist called Wheeler, AFAIK. The Dyson sphere was
conceptualised by Freeman Dyson, as the logical progression of an
industrial civilisation.
>
>
>--------------------------------------
>Christian McNeill
>e-mail: red...@ozemail.com.au
>--------------------------------------
>
>
--------------------------------------------------------
Russell Dovey
mgib...@quondong.aus.fruit.and.vege () wrote:
>Gregory Bond (g...@itga.com.au) wrote:
>
>: Dyson (as in spheres) is Freeman Dyson, a well-known "futurist" who
>: thunked up a whole bunch of good ideas. (I think beanstalks might have
>: been one of his as well). Dyson is (was?) also active in the US space
>: & sf communities and is well known to Niven, Pournelle & others.
>
> Dyson wasn't just a futurist. He's also a physicist and contemporary
> of Richard Feynman. AFAIR the Star Trek representation of a Dyson sphere being
> a solid object is incorrect. It is supposed to be an interlinked array of
> satelites that generates a field effect. Consider that obtaining the materials
>to surround the outer atmosphere of a planet with a solid sphere would be
> horrendous in both time and materials.
> The best person to give an explanation would be a physicist....
> Is there a physicist in the house :-)
Close enough....
The Dyson Sphere could quite easily be a solid shell, because you'd
want to capture every last smidgen of energy, and the materials would
be a small problem. You'd need to be able to transmute gas to solid
metal, or to some kind of flexible polymer, and use Jupiter for the
construction material. If you don't have to live on the shell, then a
kind of opaque balloon would be ok.
>________
> Matthew Gibbins
> email : mgib...@mindless.com
>
--------------------------------------------------------
Russell Dovey
wrote:
>Gregory Bond (g...@itga.com.au) wrote:
>: "Christian McNeill" <red...@ozemail.com.au> writes:
>
>: > Yeah Larry Niven.... well... atleast it was in his book where it talked
>: > about the Dyson Sphere... but he could have got the idea from somewhere
>: > else... Just like Star Trek got the idea from him...probably...
>
>: Dyson (as in spheres) is Freeman Dyson, a well-known "futurist" who
>: thunked up a whole bunch of good ideas. (I think beanstalks might have
>: been one of his as well). Dyson is (was?) also active in the US space
>: & sf communities and is well known to Niven, Pournelle & others.
>
>Dyson is more than just a well known futurist
>he is actually a well known physicist!!
>
>
>
>But the Dyson spheres have been shown not to work,
>like the ringworld, they suffer from being an unstable system.
>
>They are a huge sphere that surrounds a star.
>So instead of living on a puny little planet like earth,
>we can have a whole sphere at about this distance from the sun.
>
>Most of the suns output would be able to be used (mega solar power!)
>
>
>However, if the sphere got off-centre from the sun, it would
>keep moving and one side would fall in towards the sun.
Which is why you'd need attitude jets, like in Ringworld Engineers.
You wouldn't exactly have any problem with fuel, seeing as your sphere
would fill up with solar wind over the centuries unless you let it
out.
>
>
>
>
>DN
>--
>
>----------------------------------------------------------
>| David N Ralphs |
>| ATN - Channel 7 Phone: (02) 9877 7707 |
>| Mobbs Lane Fax: (02) 9877 7894 |
>| Epping, NSW Email: d...@atn.atn7.eggs.oz.au |
>| (remove 'eggs' to unspam me!) |
>----------------------------------------------------------
>These views are mine.. no one else would agree with them!
>
>Everlasting life for me
>in a perfect world
>but I gotta die first...
>please god send me on my way.
>
> D. Mustaine - "In My Darkest Hour"
--------------------------------------------------------
Russell Dovey
<re...@chatnet.net.au> wrote:
>Owen Godfrey wrote:
>>
>> Justin Downey wrote:
>>
>> > Michael Fuller wrote:
>> > >
>> > ><snip>
>> > >
>> > > IIRC, that was a laser-supplemented light-sail; the Motie ship would have
>> > > been "blown" along by light pressure on the sail. The experimental rocket
>> > > described in the original posting is powered by using a pulsed laser to heat
>> > > air in a "combustion" chamber at the base of the rocket; the rocket is driven
>> > > by the expulsion of rapidly expanding gases.
>> > >
>> > > (Feel free to correct if I'm wrong---it's been a while since I read either
>> > > book, and I'm working second-hand from the reports of the news footage.)
>> >
>> > Aaaah yes, you are right. In the motie ship the laser itself would
>> > provide the equal and opposite reaction. The ship would effectively be
>> > pushing against the planet holding the laser. In the experimental rocket
>> > and the Marshall Savage version, the rocket would be pushing against the
>> > reaction mass attached to the rocket (assuming it carries its own air
>> > supply to ag as reaction mass.)
>>
>> Ummmm ... the logic isn't too bad, but no cigar.
>>
>> Looking at the Propulsion Directorate page at Edwards Air Force Base, you'll see
>> that the emphasis of the design is atmoshperic hyper-sonic travel. If you can say
>> that the Motie ship is pushing against the planet in the first case, then you can
>> certainly say the same in the second. However, I think it would be more correct to
>> say that the Motie ship was pushing against the solar winds and had laser
>> assistance.
>
>Nope. The Motie ship would certainly have been assisted by the solar
>wind at the early stage of the journey, but recall that it was an
>interstellar craft. The solar wind from the originating star would not
>have any significant effect for the major part of the journey. Also, the
>solar wind from the target star would be acting against the forward
>motion of the craft in the later parts of the journey. Assuming that the
>stars were roughly the same order of magnitude, solar wind would have no
>net effect on the voyage.
>
>I can't remember what mechanism the moties used to slow down the ship at
>the end of their journey...
They turned around and dove into a star. :) That's the dramatic
version. The more realistic version is that they needed to use the
solar wind of the star to slow down, as well as the light pressure. To
do this they needed to go very close to the star. Apparently they were
heavily shielded, so were ok.
>
>> Your "action and reaction" is actually in the first case the capturing of the energy
>> of the solar wind and laser,
>
>Yep. The laser is pushing against the ship (assuming it is a using a
>solar sail and the laser is not being used to heat reaction mass. In the
>latter case, the ship would be pushing against the reaction mass, not
>the laser.) The solar wind is pushing against the ship and equally hard
>against the sun.
>
>> and in the second it is against the atmosphere.
>
>No. This is the same mistake made by ummm....can't remember his name,
>when he heard about Goddard's (Tsiokovski's?) rocket. He said rocket
>travel outside the atmosphere is impossible because there is nothing for
>the rocket to push against. Of course, the rocket does not need to push
>against the atmosphere at all. The rocket moves forward because it is
>pushing against the reaction mass being expelled out the back of the
>rocket.
>
>>
>> I think people have missed one tiny feature of the design ... this engine appears to
>> have air inlets. In the documentation, it says "This airbreathing pulsed detonation
>> engine concept owes its origins to the German V1 "Buzz Bomb" of WW II that ran on
>> aviation fuel." My understanding is that this not a pure plasma engine; like a jet
>> engine, it pulls air in and accelerates it using the pulse detonation. This would
>> mean, I think, that outside the atmosphere, it would lose a lot of efficiency.
>>
>
>I haven't seen the original document. I don't think using a ground based
>laser to heat reaction mass would be practical for long voyages. The
>ship would need to carry large amounts of fuel. Why bother lighting the
>fuel using a huge ground based laser when you could just light it at the
>source like current rockets? However, I think the concept has value for
>orbital launches, where the amount of reaction mass would be reasonable
>small. If you could use a block of ice for fuel, you would not need the
>complex (read: heavy) storage and pumping systems needed for chemical
>rockets.
>
>> In any case, there are some problems with operating this system outside of an
>> atmosphere;
>>
>> 1. The efficiency is low. The longer you need to accelerate, the heavier you need
>> to be. Include attenuation for distance in the equation, and I think chemical
>> rockets win.
>> 2. Keeping a laser of that power focussed so tightly over those kinds of distances
>> outside of the atmosphere is tricky, and while spin can correct for some
>> mis-alignments, long term you can end up in trouble.
>
>I'm not sure focus would be excessively tricky. Look at adaptive-optic
>telescopes. I think generating the power for the laser would be the real
>trick.
>
>> 3. A laser of that intensity operating over long periods is to say the heast
>> hazardous.
>
>Heheheh. I wouldn't build my house next to it, that's for sure. But
>isn't sitting on what is effectively a controlled explosion equally
>risky?
>
>> 4. With this initial design, the laser has to be directly behind the vehicle. I
>> can imagine a design which has the laser ahead of the vehicle, but I don't want
>> to even try to imagine a spinning design that tries to harness laser energy
>> coming from even slightly to the side. That makes this kind of propulsion very
>> uni-directional.
>
>Yep.
>
>>
>> I think that it would be better to have a vehicle that uses the laser pulse
>> detonation drive to get out of the atmoshpere, then difuse the laser and deploy
>> solar sails. I think solar sails are more versatile, and can operate even without a
>> ground laser system.
>
>I agree. Solar sails are well suited to IP travel. THe GBL would be
>overkill and probably clunky in comparison. Remember though that the
>Moties were a clunky civilisation :)
>
>>
>> I just have one question; we can use this system to get a vehicle into orbit, but
>> how do we get it back down again? Since it is an air-breathing engine, you can't
>> just reverse it back down the beam. By the time the atmosphere is thick enough, it
>> would already be burning, and besides, I don't think it would travel backwards well.
>> I suppose you could focus the laser ahead to create a shockwave ahead, but while
>> that would stop it burning, would not slow it down. Also the design is not one that
>> particularly likes heat tiles.
>>
>> So how do you do it?
>
>I haven't looked at the material, but I like Marshall Savage's approach:
>a ship with a heat shield and manoevering rockets, a large, cheap
>reaction mass stuck on the base. Use the laser to heat the reaction mass
>to boost into orbit. When you need to come down, use your small chemical
>rockets to deorbit and heat shields to protect you during re-entry. He
>also described a maglev for the initial part of the launch, only when
>the ship was about 10 km agl would the lasers be used
>
>>
>> --
>> Owen Godfrey - (08) 9333 8808 - <mailto:god...@ccis.adisys.com.au>
>> "...there is sometimes little to choose between
>> the reality of illusion and the illusion of reality."
>> Patrick White, The Aunt's Story , 1948
--------------------------------------------------------
Christian McNeill
<35e8d2eb...@newshost.dynamite.com.au>...
|On Thu, 27 Aug 1998 09:54:06 +1000,
|
|>Gregory Bond (g...@itga.com.au) wrote:
|>
|>: Dyson (as in spheres) is Freeman Dyson, a well-known "futurist" who
|>: thunked up a whole bunch of good ideas. (I think beanstalks might have
|>: been one of his as well). Dyson is (was?) also active in the US space
|>: & sf communities and is well known to Niven, Pournelle & others.
|>
|> of Richard Feynman. AFAIR the Star Trek representation of a Dyson sphere
being
|> a solid object is incorrect. It is supposed to be an interlinked array of
|> satelites that generates a field effect. Consider that obtaining the
materials
|>to surround the outer atmosphere of a planet with a solid sphere would be
|> horrendous in both time and materials.
|> The best person to give an explanation would be a physicist....
|> Is there a physicist in the house :-)
|
|Close enough....
|
|The Dyson Sphere could quite easily be a solid shell, because you'd
|want to capture every last smidgen of energy, and the materials would
|be a small problem. You'd need to be able to transmute gas to solid
|metal, or to some kind of flexible polymer, and use Jupiter for the
|construction material. If you don't have to live on the shell, then a
|kind of opaque balloon would be ok.
Star Trek had an episode about a Dyson Sphere.... it was the one that
brought back scotty still the same age he was 70 years before....
Russell Dovey
wrote:
>John writes:
>
>
>John Leister wrote:
>
><snipped myself Ouch!>
>
>As I read all your replies my memories came alive of something I read
>years and years ago. I can't pinpoint where the idea came from but
>I have read something else like this and as a teenager I can
>remember doing drawings of the ship I am about to describe. Solar
>sail ships with huge billowing sails. Yeah! It's kind of romantic.
>
>Just thinking but how about this for an idea? Build a ship big enough
>for a a crew and the systems necessary to keep them alive. Make it
>conical in shape and at the rear end of the ship place a ring of high
>intensity spotlights, well we'll use lasers in our test model since
>that's what the real ship on the news uses. Aim each laser at an
>angle pointing away from the ship. Now before the lasers are
>activated we extend a massive solar sail from the very rear of
>the ship and once it's fully erected the circle of beams
>radiating from the ship's base pushes on the sail thus moving
>it in space.
>
>We could power the lasers by a nuclear or solar generator as
>deep space probes use or a combination of the two. As the laser
>beams hit the sail there is an action and an opposite reaction
>ala Newton and the ship moves. We could tilt the sail and the
>beams and thus turn and we could mount sensors on the ship to sense
>the real solar wind and thus tack into it much like a yacht.
>
>I think this idea has been thought of somewhere else but I thought it
>sounded really nice.
This would be like putting a big fan on your yacht, pointed at the
sails, to push yourself along. It wouldn't work, I'm afraid, because
the lasers would push you backwards just as much as the sails would
pull you forwards.
>
>--
>The Earth goes around the sun
>The Earth spins to make a day
>Why aren't I dizzy?
>
>John D Leister
>Jogging through my homepage at:
>http://www.geocities.com/southbeach/shores/6340
>Mirrored at: For faster loading
>http://www.senet.com.au/~johndk/index.htm
>Running up to my mailbox at:
>joh...@academy.net.au
>
--------------------------------------------------------
Russell Dovey
wrote:
>John writes:
>
>David Ralphs wrote:
>
><big snip>
>
>No I was not being sarcastic at all after all I was impressed by the ship in
>the news story I wrote about. I was very impressed in fact.
>
>Just out of asking wouldn't the ship move if it started from a stationary
>position in space. If the ship was standing still and the lasers were aimed
>at the sail there would be an action/reaction wouldn't there?
No. Try standing on rollerskates, then pull on the front of the
rollerskates to get yourself going. That's a similar situation.
>
>Just wondering as that's how I saw the ship when I wrote the posting.
Russell Dovey
<sev...@iinetx.netx.aux> wrote:
>David Ralphs wrote:
>> John Leister (joh...@senet.com.au) wrote:
>> : John writes:
>> : David Ralphs wrote:
>
>> : No I was not being sarcastic at all after all I was impressed by the ship in
>> : the news story I wrote about. I was very impressed in fact.
>
>> : Just out of asking wouldn't the ship move if it started from a stationary
>> : position in space. If the ship was standing still and the lasers were aimed
>> : at the sail there would be an action/reaction wouldn't there?
>
>> : Just wondering as that's how I saw the ship when I wrote the posting.
>
>> If the lasers are on the ship, aiming at its own sails,
>> then it wont move.
>
>> In terms of action/recation, yes the sails and lasers get pushed
>> opposite directions, but since they are connected the forces
>> would then cancel and all you are doing is pushing the ship apart.
>
>Well, actually it depends on whether the sail absorbs or reflects the
>light. If it reflects the light (and it doesn't hit any part of the ship
>after that), then shining the light at the sail will push the ship along.
>It will push it along at the same rate as if the laser was just reversed,
>without the light hitting the ship after leaving the laser.
Yes, but this way there is no point in having the sail. You might as
well just point a laser out the back.
>
>> Imagine sitting in your car and pushing on the dash...
>> does the car move forward??
>> You need to push against an external object.
>
>True, but with light, if it is reflected off the sail, the light will
>eventually end up hitting something else. That's the external object.
>So, if the laser is pointing away from Earth, and being reflected back
>towards earth by the sail, then effectively the ship is pushing itself
>off earth. Sort of. Maybe not.
>
>Chris Severn.
>--
>Delete the 'x's to remove the spamblock.
Russell Dovey
wrote:
>Well since light is compsed of photons and photos have been proven in scientific
>fact to be actual particles it would seem only fair that particles hitting the sail
>would cause a reaction in that the ship would move. And yes I had pictured that the
>sail would reflect the lasers away from the main part of the ship they would be
>immense in size and the beams are set at an angle remember so the light should not
>go back to the ship but propel it.
Think of it this way. The lasers would experience a little push
backwards for each photon that they threw out. Then the photon would
hit the sail, and the sail would feel a little push forward. These
forward and backward pushes would exactly cancel.
Russell Dovey
<sev...@iinetx.netx.aux> wrote:
>David Ralphs wrote:
>> John Leister (joh...@senet.com.au) wrote:
>> : John writes:
>> : David Ralphs wrote:
>
>> : No I was not being sarcastic at all after all I was impressed by the ship in
>> : the news story I wrote about. I was very impressed in fact.
>
>> : Just out of asking wouldn't the ship move if it started from a stationary
>> : position in space. If the ship was standing still and the lasers were aimed
>> : at the sail there would be an action/reaction wouldn't there?
>
>> : Just wondering as that's how I saw the ship when I wrote the posting.
>
>> If the lasers are on the ship, aiming at its own sails,
>> then it wont move.
>
>> In terms of action/recation, yes the sails and lasers get pushed
>> opposite directions, but since they are connected the forces
>> would then cancel and all you are doing is pushing the ship apart.
>
>Well, actually it depends on whether the sail absorbs or reflects the
>light. If it reflects the light (and it doesn't hit any part of the ship
>after that), then shining the light at the sail will push the ship along.
>It will push it along at the same rate as if the laser was just reversed,
>without the light hitting the ship after leaving the laser.
Please disregard my other answer. No, sorry, this would not work. The
photons are not connected to the ship. All the ship cares about is the
laser pushing it backwards, and the sail pulling it forwards. The two
forces would cancel each other, and the ship would stay still.
>
>> Imagine sitting in your car and pushing on the dash...
>> does the car move forward??
>> You need to push against an external object.
>
>True, but with light, if it is reflected off the sail, the light will
>eventually end up hitting something else. That's the external object.
>So, if the laser is pointing away from Earth, and being reflected back
>towards earth by the sail, then effectively the ship is pushing itself
>off earth. Sort of. Maybe not.
>
>Chris Severn.
>--
>Delete the 'x's to remove the spamblock.
--------------------------------------------------------
Russell Dovey
<mor...@wantree.com.au> wrote:
>John Leister wrote:
>>
>> Well since light is compsed of photons and photos have been proven in scientific
>> fact to be actual particles it would seem only fair that particles hitting the sail
>> would cause a reaction in that the ship would move. And yes I had pictured that the
>> sail would reflect the lasers away from the main part of the ship they would be
>> immense in size and the beams are set at an angle remember so the light should not
>> go back to the ship but propel it.
>
>then you don't need a sail at all
>
>for photons to provide decent propulsion you need a lot of light, and a
>big black
>absorber, its probably easier to just use a bigger simpler sail and tack
>using the the solar wind
Actually, you can't tack using the solar wind. The solar wind is
composed of protons, not photons. The photons merely stick to whatever
they hit, and the resulting force can never be anything but directly
away from the sun. You have to use the light from the sun to tack.
>
>an external laser would be best used to carry energy to the ship, the
>reverse of your sail
>idea, but as a an enrgy concentrator only, the sail to bounce propulsion
>just means
>you need tethers twice as strong as the laser generator mountings
>
>incoming light reflected by a large surface onto a heater or other
>device where reaction mass
>is vaporised or ,better, ionised and expelled in the usual rocket way,
>reflector means
>the beam need not be too intense, solar reflectors would probably be
>better but a beam
>more easily controlled for straight line flight
>
> besides, it gives the star wars development a cover for laser weapons
>development
>
>with an external power source the reaction mass can be dense and inert,
>safer smaller ships
>
>with reaction mass drivers you can still power deceleration from the
>single laser source
>and all ship mass can be used as reaction mass, crews in transit would
>be encouraged to
>take as many showers as possible to keep the effluent tanks full for
>deceleration ;-)
Russell Dovey
wrote:
>John Leister (joh...@senet.com.au) wrote:
>: Well I beg to differ on this but imagine that the ship has started off, over
>: time with a constant source of light it would build momentum wouldn't it.
>: Assuming we could find a stable power source and effecient enough lasers our
>: speed would build up gradually. And anyway who needs speed and time this would
>: be the perfect way to travel for a a vessel that was used for say a generation
>: ship. Or for a vessel carrying it's crew for an indeterminate period in
>: suspended animation.
>
>In terms of propulsion - lasers are not as good as other light sources.
>The neat property of the laser is that the light is coherent.
>
>But that doesnt make it any better to push you.
>In fact losses in the laser compared to other light sources
>would mean that it is probably less efficient.
>
>
>It is still damn hard to beat throwing something off the ship
>as a method of propulsion.
>The momentum of a photon is purely from energy,
>then momentum of an object is its mass and speed.
>
>Due to e=mc^2 its pretty easy to see that a little bit
>of mass is worth a lot of energy.
>(conversly - a bit of light energy is worth not very much mass)
>
>So throwing a pebble out the back of the ship
>is worth a hell of a lot of light!
>
>
>I still say that pissing out the back of the ship
>would work better....
Ah, but if you could somehow develop a perfect mirror, and a way to
totally convert mass to energy, you could use light as a propulsion
method. In fact, this is by definition the most efficient way of
travel yet known that uses recation. (Unfortunately, there is the
problem of launching. Burning a hole through the planet that you are
launching from has disadvantages, one being that many people will die,
another that the vaporised, plasmafied rock would rapidly condense on
the ship, and make it a big ball of slag.)
>
>
>
>DN
>--
>
>I like the things that you try and fake
>And your face when I see you break
>And that you say you will pray for me
>You realise you are prey for me
>
> D. Mustaine - "Reckoning Day"
--------------------------------------------------------
Owen Godfrey
> On Wed, 26 Aug 1998 03:41:40 +0930, terry russell
> <mor...@wantree.com.au> wrote:
>
> >John Leister wrote:
> >>
> >> Well since light is compsed of photons and photos have been proven in scientific
> >> fact to be actual particles it would seem only fair that particles hitting the sail
> >> would cause a reaction in that the ship would move. And yes I had pictured that the
> >> sail would reflect the lasers away from the main part of the ship they would be
> >> immense in size and the beams are set at an angle remember so the light should not
> >> go back to the ship but propel it.
> >
> >then you don't need a sail at all
> >
> >for photons to provide decent propulsion you need a lot of light, and a big black
> >absorber, its probably easier to just use a bigger simpler sail and tack
> >using the the solar wind
>
> Actually, you can't tack using the solar wind. The solar wind is
> composed of protons, not photons. The photons merely stick to whatever
> they hit, and the resulting force can never be anything but directly
> away from the sun. You have to use the light from the sun to tack.
This is the best paper I could find on the subject. It goes directly against what you are
saying, and frankly, I believe it. Every paper I have read on the subject talks about
tacking. The paper is at <http://caliban.physics.utoronto.ca/neufeld/sailing.txt>.
Christopher Neufeld is a physics Ph.D. student at the University of Toronto and a team
member on the Canadian Solar Sail Project, which is an initiative of the Canadian Space
Society. Sadly, the project that he was working on is now defunct, but this material
suggests that the vessels we are talking about have already been designed and budgeted.
Hmmm ... I wonder ... if a 500kg GLB launcher could be built with a feasible recovery
system, then could Australia cooperate with Canada to piecemeal build a cheap solar sail
vessel designed for a trip to Mars and back? Wouldn't it be funny if Australia and Canada
got there first and left America behind?
> <snip>
Owen Godfrey
Russell Dovey wrote:
> On Thu, 27 Aug 1998 09:54:06 +1000,
> mgib...@quondong.aus.fruit.and.vege () wrote:
>
> >Gregory Bond (g...@itga.com.au) wrote:
> ><snip>
> > Dyson wasn't just a futurist. He's also a physicist and contemporary
> > of Richard Feynman. AFAIR the Star Trek representation of a Dyson sphere being
> > a solid object is incorrect. It is supposed to be an interlinked array of
> > satelites that generates a field effect. Consider that obtaining the materials
> >to surround the outer atmosphere of a planet with a solid sphere would be
> > horrendous in both time and materials.
> > The best person to give an explanation would be a physicist....
> > Is there a physicist in the house :-)
>
> Close enough....
>
> The Dyson Sphere could quite easily be a solid shell, because you'd
> want to capture every last smidgen of energy, and the materials would
> be a small problem. You'd need to be able to transmute gas to solid
> metal, or to some kind of flexible polymer, and use Jupiter for the
> construction material. If you don't have to live on the shell, then a
> kind of opaque balloon would be ok.
It could not work.
1. How do the "satelites" at the far northern and southern poles stay in place?
Since the sphere is spinning, the poles must be stationary in respect, and so
they should fall into the sun.
2. If they don't fall, then they are applying pressure on the surounding
"satelites". Add up the pressure at the equator for atht kind of diameter;
nothing made of matter could support that.
3. There isn't enough material in Jupiter to form any kind of shell at that
distance, and the energy needed to shift that mass to another orbit would be
prohibitive.
4. There is the problem of keeping ity stable. Things shift in orbit. Orbital
forces would eventually rip the structure apart.
tee...@spamtrap.com
: Well since light is compsed of photons and photos have been proven in scientific
: fact to be actual particles it would seem only fair that particles hitting the
: sail would cause a reaction in that the ship would move.
Huh?
Actually, photons have been proven to act like particles in certain
situations, but entirely unlike particles in others.
tee...@spamtrap.com
: Actually, you can't tack using the solar wind. The solar wind is
: composed of protons, not photons. The photons merely stick to whatever
: they hit, and the resulting force can never be anything but directly
: away from the sun. You have to use the light from the sun to tack.
Huh?
Light is photons. The very photons you just told us simply stick.
In case you meant protons, once the sail got a strong enough charge,
protons would stop simply sticking to it, and it would indeed become able
to tack. Protons do, after all, repel each other.
Adam Burke
>
> Hmmm ... I wonder ... if a 500kg GLB launcher could be built with a feasible recovery
> system, then could Australia cooperate with Canada to piecemeal build a cheap solar sail
> vessel designed for a trip to Mars and back? Wouldn't it be funny if Australia and Canada
> got there first and left America behind?
Yes, we could claim it in the name of the Queen.
(I know the Space Treaty prohibits it. Pish tosh.)
--
Adam Burke
http://student.uq.edu.au/~s335783
"... common sense - i.e. acceptance of the obvious and contempt for
quibbles and abstractions ..."
- George Orwell
Ian Davis
> This is the best paper I could find on the subject. It goes directly against what you are
> saying, and frankly, I believe it. Every paper I have read on the subject talks about
> tacking. The paper is at <http://caliban.physics.utoronto.ca/neufeld/sailing.txt>.
This link doesn't seem to be working, and I'm most interested in
following it up. I have never quite understood how you tack in a medium
where you are unable to resist or apply lateral force. In sailing, the
keel allows a force vector to be split into forces at right angles to
each other: you get movement at an angle to the incident wind, at a
lower velocity than the incident wind and in the direction the boat is
facing, while the remaining vector is applied perpendicular to the
keel. The resistance of the water to sideways movemnt of the keel means
that the end result is movement at an angle to the incident wind force.
Movement upwind is possible by the same mechanism and by remembering
that when tacking upwind sails aren't being pushed by the wind, but
pulled due to their shape (think of an aeroplane wing). In vacuum, the
only way to move in a direction other than the direction of the incident
solar wind would seem to be by applying lateral thrust from onboard
thrusters, which sort of defeats the purpose.
Do I have this completely wrong? Is it ever possible to tack in vacuum,
or will we always be running outsystem?
Ian Davis.
news
Russell Dovey wrote in message
>On Tue, 25 Aug 1998 23:34:59 +0930, John Leister <joh...@senet.com.au>
>wrote:
>
>>Well since light is compsed of photons and photos have been proven in
scientific
>>fact to be actual particles it would seem only fair that particles hitting
the sail
that the
>>sail would reflect the lasers away from the main part of the ship they
would be
>>immense in size and the beams are set at an angle remember so the light
should not
>>go back to the ship but propel it.
>
>backwards for each photon that they threw out. Then the photon would
>hit the sail, and the sail would feel a little push forward. These
>forward and backward pushes would exactly cancel.
then why not just use the lasers as a propulsion device??
they emit photons thus creating thrust, aim this down the center of the mass
to be moved, voila!! no need to push against sails and negating the effect,
(one of newtons laws, I dont remember which, its been a long day :-) the one
that talks about opposite and equal re-action) fire this laser long enough
and you will overcome enertia and then get to where you want to go!
correct answers go into the draw for a free pass to the Australia Cinema,
which can be redemed at the Australia Cinema in Orange NSW
----------------------------------------------------------------------------
------------
the only thing wrong with doing nothing is you cant stop to rest!!
----------------------------------------------------------------------------
------------
tee...@spamtrap.com
: I think the main objection, regardless of the physics or photon action and
: reaction, is whether it is viable as a drive. The amount of energy that
: has to be output to move the vessel is going to be tremendous, and that
: means carrying powerful generators to power the lazers. Add it up, and I
: think chemical drives win. The only thing that makes a lazer propultion
Actually, I think ion drives kinda win. They're a reaction drive that uses
solar power to accelerate their reaction mass to relativistic speeds.
Or if you wanna get there before the next millennium, you can use some
form of nuclear reactor drive, or fusion drive, or matter-antimatter
drive.
David Ralphs
: In aus.sf.babylon5, on Thu, 27 Aug 1998 00:07:20 GMT
: David Ralphs <da...@atn.atn7.oz.au> wrote:
: >But the Dyson spheres have been shown not to work,
: >like the ringworld, they suffer from being an unstable system.
: That just means that they need stabilisers of some kind.
Yes.
But its not a great design, one that is naturally unstable.
A planet in orbit is generally stable.
: >They are a huge sphere that surrounds a star.
: >So instead of living on a puny little planet like earth,
: >we can have a whole sphere at about this distance from the sun.
: >Most of the suns output would be able to be used (mega solar power!)
: >However, if the sphere got off-centre from the sun, it would
: >keep moving and one side would fall in towards the sun.
: Hmm... maybe, with sufficiently funky materials tech, you could make
: immense portions of the floor selectively transparent...
: So, when you need to thrust in a direction, you make the half of the
: sphere in the opposite direction transparent...
Yeah...
Just to add a real world comment here.
Part of the SETI (search for Extra Terrestrial Intelligence)
involved looking in the infra red spectrum for Dyson Spheres.
The idea is that the sphere will heat up and will radiate.
Its black body radiation would probably be in the infrared range.
The other thing is that such a civilization may not use radio
or other comes externally so they may not be very visible on
other parts of the spectrum (probably would use point to point
systems such as lasers instead of typical radio broadcasts
which spread out).
So although they can try and hide, there is not much they can do
to really stop some tell tale signs.
Ian Davis
>
> Owen Godfrey wrote:
> > This is the best paper I could find on the subject. It goes directly against what you are
> > saying, and frankly, I believe it. Every paper I have read on the subject talks about
> > tacking. The paper is at <http://caliban.physics.utoronto.ca/neufeld/sailing.txt>.
>
> This link doesn't seem to be working, and I'm most interested in
> following it up.
Must have been me, because it's working now. Very interesting, but I
must be thick because I still don't understand how thrust can be exerted
in any vector other than that in the direction of the solar wind. Can
someone clue me in?
Ian.
Joel Kelso
This use to puzzle me too when I first heard about "solar sailing". I don't claimto fully
understand it but ... It works because you ship is orbit around the sun.
To fly "outwards" from the sun, you angle your sail so that it pushes you _forward_
along the direction of your orbit. Your orbital velocity increases, so you start moving
too fast for your current orbit, and move "outwards" ie in a larger orbit. To travel
"inwards" you do the opposite. Angle your sail so that it pushes you backwards
against your orbit direction. Now you're not travelling fast enough for your current
orbit, and fall towards the sun (actually you spiral inwards slowly). This means of
course that it takes you years to get anywhere, but you do get your energy and
thrust for free. Is this right ? And, while we're on the subject of orbital mechanics,
can anyone explain why the "trojan" Legrange points (the ones 60 degrees in front
of an behind the satellite) in a two-body system are stable ?
-- jo...@ee.uwa.edu.au --------------------------------------
"... great Scott, he's turned into _more than one person_ !"
"Well, there was always enough of him."
- the Goon Show
-- http://ciips.ee.uwa.edu.au/~joel ------------------------
Ian Davis
> To fly "outwards" from the sun, you angle your sail so that it pushes you _forward_
> along the direction of your orbit. Your orbital velocity increases, so you start moving
> too fast for your current orbit, and move "outwards" ie in a larger orbit. To travel
> "inwards" you do the opposite. Angle your sail so that it pushes you backwards
> against your orbit direction. Now you're not travelling fast enough for your current
> orbit, and fall towards the sun (actually you spiral inwards slowly).
This is the part I still don't understand. Without something to resist
lateral movement (equivalent to the keel pushing against water in a
boat), how can you resolve the vectors away from the direction of the
incident light (in this case, with or against your current orbit)? A
sail turned at an angle isn't enough to do this; all you do is present a
smaller surface to the incoming light. The keel in a boat adds two
sides to make the triangle:
_
/|^
/ |
wind / | desired direction of travel (orbit)
/ |
/ |
------>
force exerted on keel against water, perpendicular to direction
of travel.
The physics is additionally complicated in a boat, since the sail works
like a wing ie the boat is pulled by trimming the sail to the optimal
shape to allow aerodynamic flow over each surface of the sail. This is
unlikely to happen in vacuum where all that can happen is pushing by the
incident light.
I am probably missing something obvious here, but I can't work it out.
Ian, no rocket scientist.
Ian Davis
A solar yacht in orbit around the sun has its sail turned parallel to
the incoming light, ie no thrust at all.
At the appropriate time, the sail is turned towards the sun, and the
degree of thrust (in a line away from the sun) would depend on the angle
of the sail (ie the area of sail seen along the line from the sun).
This provides thrust away from the sun and would ultimately make the
orbit more elliptical. By furling the sail again, the spacecraft will
then accelerate towards the sun and deceleration due to increased
incident light is avoided. By unfurling on the way out you will be put
into an even higher orbit. Do this at the right times and for long
enough and perhaps the orbit might be elliptical enough to allow
transfer from Earth to Mars. How you decelerate at Mars orbit to do an
orbital insertion I don't know, but I suppose you plan your aphelion to
coincide with Mars.
I probably have this one wrong too!
Ian.
Knightod
With an angled _reflective_ sail, you get 2 forces acting on the sail. One
is the force applied by the incident light, which acts directly away from
the source (sun). The second is the force required to sent the light on it's
new vector. If the sail is perpendicular to the sun, the light is reflected
straight back, and the forces act in the same direction. If the sail is at
an angle, the second force acts at 180 degrees from where the light reflects
to, hence you move sideways with respect to the sun.
^
/ Resultant force on sail
\ /
reflected light \ /
<-------------------------\/
^ \
| \ sail
| \
|
| incident light
Hope this helps.
Knightod
Owen Godfrey
> Owen Godfrey wrote:
> > This is the best paper I could find on the subject. It goes directly against what you are
> > saying, and frankly, I believe it. Every paper I have read on the subject talks about
> > tacking. The paper is at <http://caliban.physics.utoronto.ca/neufeld/sailing.txt>.
>
> This link doesn't seem to be working, and I'm most interested in
> following it up. I have never quite understood how you tack in a medium
> where you are unable to resist or apply lateral force. In sailing, the
> keel allows a force vector to be split into forces at right angles to
> each other: you get movement at an angle to the incident wind, at a
> lower velocity than the incident wind and in the direction the boat is
> facing, while the remaining vector is applied perpendicular to the
> keel. The resistance of the water to sideways movemnt of the keel means
> that the end result is movement at an angle to the incident wind force.
> Movement upwind is possible by the same mechanism and by remembering
> that when tacking upwind sails aren't being pushed by the wind, but
> pulled due to their shape (think of an aeroplane wing). In vacuum, the
> only way to move in a direction other than the direction of the incident
> solar wind would seem to be by applying lateral thrust from onboard
> thrusters, which sort of defeats the purpose.
>
> Do I have this completely wrong? Is it ever possible to tack in vacuum,
> or will we always be running outsystem?
>
> Ian Davis.
The link works, but I have sent you a copy of the text. I don't want to post it, as I am wary
of copyright restrictions.
I wish we using HTML, then I would draw you a diagram, however, many people can't read that
format, so I'll struggle along without it.
First of all, it is important to realise that we are talking about VERY small accelerations
here. This method works best where both gravity and the solar wind are strongest. In orbit
around a planet with a good magnetic field, like the earth, I imagine things get more
interesting than in deep space.
First, your vessel is in orbit about a body. The trick is to change your orbital velocity. If
you speed up, you will move into a higher orbit, but if you slow down, you will move to a lower
orbit. If the wind is coming directly out from the body, then the sail should be inclined away
from the orbital path. Some of the energy will push the vessel higher, but overall you will
still be shedding velocity and so falling. Some careful manipulation of solar thrust and
orbital speed, and you can easily move any which way you want. However, you can't accelerate
inwards faster than gravitational acceleration at that distance, except by gravitational
slingshots, and you need solar flux in order to maneuver. I would not like to operate a solar
sail out beyond Jupiter. If the figures I've seen are correct, then to get a 1G acceleration
from your sail at 1AU, then your sail would have to have a mass of about 0.0005g/sqm, and would
have to be sufficiently strong enough to pull the vessel. If I recall, isn't the solar flux at
Jupiter about 1/64 of the flux at earth?
Mind you, I think it would be worth the trip for the view. :)
(Imagine : mahognoy chart table anchored to the wall. Lone sailor, bearded from many years in
space, checking his charts by the light of Jupiter, aligning his sails for his final slingshot
past Europa before his long voyage home.)
Ian Davis
> With an angled _reflective_ sail, you get 2 forces acting on the sail. ...
> Hope this helps.
It helps!
Ian.
Thorfinn
Ian Davis <da...@licre.ludwig.edu.au> wrote:
>Joel Kelso wrote:
>> To fly "outwards" from the sun, you angle your sail so that it
>> pushes you _forward_ along the direction of your orbit. Your
>> orbital velocity increases, so you start moving too fast for your
>> current orbit, and move "outwards" ie in a larger orbit. To travel
>> "inwards" you do the opposite. Angle your sail so that it pushes
>> you backwards against your orbit direction. Now you're not
>> travelling fast enough for your current orbit, and fall towards the
>> sun (actually you spiral inwards slowly).
>This is the part I still don't understand. Without something to resist
>lateral movement (equivalent to the keel pushing against water in a
>boat), how can you resolve the vectors away from the direction of the
>incident light (in this case, with or against your current orbit)? A
>sail turned at an angle isn't enough to do this; all you do is present a
>smaller surface to the incoming light.
[boat example snipped]
>I am probably missing something obvious here, but I can't work it out.
Gravity.
If I had "Integral Trees" by Larry Niven here, I'd snaffle the quote
about orbital mechanics from it.
Orbital mechanics is fun... I'm no physics type (I'm a discrete maths
geek, though) but this is my understanding of how it goes.
You're in orbit around an object (the sun).
This means, you are travelling at a constant speed at a tangent to the
orbit you are taking.
Gravity pulls you towards the sun (and the sun towards you, but this is
negligible).
As a result, you travel in a circle (yes, it's not a circle, but don't
ask me how to explain that. Ask a real physics type) around the sun, at
a particular distance from it.
If you slow the speed at which you are travelling, by causing your sail
to push you against your forward direction (and incidentally *slightly*
away from the sun, but only slightly), then gravity will have *more* of
an effect on your direction of travel.
You will then spiral slowly in towards the sun, until you return your
sail to edge on to the sunlight, at which point your orbit will settle
down.
If you want to change your orbit to be further out, you have to point
your sail to assist you in increasing your forward tangential speed...
this will allow you to travel further tangentially as gravity pulls
you towards the sun, which lets you go further *out*, orbitally.
I don't recall what happens if you point your sail directly at the sun.
You either "slow down" in your current orbit or "speed up" in your
current orbit, but I don't recall which, and my physics is not up to
scratch in working it out without lots of paper scribbling.
:) Ain't orbital mechanics fun?
Later,
Thorf
--
<a href="http://www.tertius.net.au/~thorfinn/">thor...@tertius.net.au</a>
GothCode3.1A: GoEn5$CS5$Sb2 TFeG5 PPeGMo =B10/21Bk!"1@ cBk-s8 V3s M3
ZGoClIpa C9o a24= n7 b54 H153 G7!??91A m@Z3 w6T v5R r4EBISP p55865Zz D66*
h5(PPeGMo) sM6P SrNy k7BdSMmDsFNRT =N0392JPFSLMCONEWH RsS$ LauVIC5]NSW5[
Owen Godfrey
> Owen Godfrey wrote:
> > This is the best paper I could find on the subject. It goes directly against what you are
> > saying, and frankly, I believe it. Every paper I have read on the subject talks about
> > tacking. The paper is at <http://caliban.physics.utoronto.ca/neufeld/sailing.txt>.
>
> This link doesn't seem to be working, and I'm most interested in
> following it up. <snip>
> Ian Davis.
<http://weber.u.washington.edu/~nebrich/solarsails/mechanics.html>
benjamin_k
the US and the Soviet Union actually dividing up the entire universe as a
boy. Perhaps that stupi idea has been quietly shelved....
Adam Burke <ad...@mailbox.uq.edu.au> wrote in article
<35EA61...@mailbox.uq.edu.au>...
og...@my-dejanews.com
Joel Kelso <jo...@ee.uwa.edu.au> wrote:
> <snip>
> And, while we're on the subject of orbital mechanics, can anyone explain
> why the "trojan" Legrange points (the ones 60 degrees in front
> of an behind the satellite) in a two-body system are stable ?
*sigh*
No good references for Lagrangian Points or trojan bodies. So as I can
figure, the answer is not simple. It goes soemting like this;
On the surface, the points are not stable. In the earth-moon system,
gravity from the moon pulls the body towards it. However, this also
shifts its orbit, and when you follow the path of the object, you
find that it forms a stable orbit that is sort of bone shaped. It is
the fact that objects keep falling back into these odd orbits that
make the L4 and L5 points stable.
Can anybody do any better please?
--
"...there is sometimes little to choose between
the reality of illusion and the illusion of reality."
Patrick White, The Aunt's Story , 1948
-----== Posted via Deja News, The Leader in Internet Discussion ==-----
http://www.dejanews.com/rg_mkgrp.xp Create Your Own Free Member Forum
og...@my-dejanews.com
Hmmm ... this is right ... (quick maths in head, rough guestimates)
... Any time you do intra-stellar travel, it is by plotting an orbit
within the system that intersects your starting point and ending
point. The orbit is modified by the other bodies in the system.
What you are describing is the high power path. You put on a
hard burn at the start, discard your excess mass, and then
coast to your destination.
This is essentially the same as we have discussed, except
that you are using the power of the sail to distort your
orbit and make it more eliptical, THEN adding the sails
power to work your way into a higher energy orbit.
However, solar sails are low power drives. With no need for
short burns, it operates for extended periods. Therefore, the
low energy, more circular path should be taken. You accelerate
constantly, moving outwards, but without the power needed to fight
gravity constantly. Over a long distance, this might actually be
fastest way to get there. After all, given enough time, the ship
that accelerates indefinitely ends up going fastest, regardless of
the difference in power.
CitizenJ
carry its own reaction mass, is still subject to the same limitation as
conventional rockets: the total change in velocity that it can produce is
determined by the "mass ratio" of the rocket and its exhaust velocity.
dV = Ve ln( Mi / Me )
where dV is the maximum possible change in velocity
if the rocket expends all its fuel or reaction mass;
Ve is the exhaust velocity of the rocket, i.e. the speed
with which the reaction mass or burnt fuel is expelled
from the back of the rocket;
Mf is the initial mass of the rocket including its
fuel or reaction mass and payload;
Me is the mass of the rocket with all its fuel or reaction
mass expended but including the payload.
This is for the simple case of a single stage rocket. It gets more
complicated for a multistage rocket, but the essence is the same. To achieve
a dV which is less than the exhaust velocity is not too hard, but to achieve
a dV which is several times Ve a tremendous amount of fuel or reaction mass
must be expended for a small payload. The key to effcient rockets is to
increase Ve, but unfortunately the energy required to accelerate the reaction
mass goes up as the square of Ve while the dV only goes up as the first
power.
Chemical rockets are limited to a Ve which is determined by the chemical
energy contained in the fuel. The fuel is both energy source and reaction
mass. If the chemical energy is converted to kinetic energy of the exhaust
with 100% efficieny, a certain Ve is achieved - you can't do better. The
laser powered rocket seperates the energy source from the reaction mass. It
could theoretically do better than a chemical rocket since there's no
fundamental limit on the laser power. There are some severe practical limits!
NASA "Deep Space One" project will be a solar powered, ion rocket. Here very
high Ve is achieved by accellerating the xenon reaction mass using electical
energy. Conceptually the energy could be supplied by solar panels or a
nuclear raector. The reaction mass is still finite, however. A more radical
approach is to use the momentum of light itself to provide the reaction. This
uses practically no reaction mass (still finite, though) but the energy
required to achieve a given dV is huge (the ratio is c, the speed of light).
The practical limitations here are also rather sever. The attraction of solar
sails is that they consume no reaction mass since the momentum of the Sun's
incident radiation provides the propulsive force. Also, they appear quite
practical with materials that now exist - you don't have to imagine the
existence of gigawatt lasers. (A one gigawatt continuous laser, i.e. 10^9
watts, would only generate a reaction force of 0.3 newtons, or about 1
ounce.)
--
CitizenJ
Robert Whyte
There was a study done back in the 1980's to look at the feasibility
of using a solar sail for a mission to Mars. They actually worked out
that it would be faster to use a sail as opposed to a burn and coast
method.
Robert Whyte
Chris Severn
> There was a study done back in the 1980's to look at the feasibility
> of using a solar sail for a mission to Mars. They actually worked out
> that it would be faster to use a sail as opposed to a burn and coast
> method.
Interesting.
Why haven't they done it then ?
Were they talking about a manned mission, unmanned or both ?
Do you know where to get any more information ?
Thanks.
Chris Severn.
--
Delete the 'x's to remove the spamblock.
og...@my-dejanews.com
sev...@iinetx.netx.aux wrote:
> <snip>
> Interesting.
>
> Why haven't they done it then ?
> Were they talking about a manned mission, unmanned or both ?
>
> Do you know where to get any more information ?
I think this relates directly to the paper I referd to in my earlier
posting <http://caliban.physics.utoronto.ca/neufeld/sailing.txt>.
Breifly, the Americans wanted to set up a solar sail race to Mars to
comemerate Christopher Columbus landing in America. The plans were
submitted, and it wasn't to have any government funding, but it
eventually fell through. As much history as i have is presented
in the abover report, which was created around 1990.
David Ralphs
: Joel Kelso wrote:
: > To fly "outwards" from the sun, you angle your sail so that it pushes you _forward_
: > along the direction of your orbit. Your orbital velocity increases, so you start moving
: > too fast for your current orbit, and move "outwards" ie in a larger orbit. To travel
: > "inwards" you do the opposite. Angle your sail so that it pushes you backwards
: > against your orbit direction. Now you're not travelling fast enough for your current
: > orbit, and fall towards the sun (actually you spiral inwards slowly).
: This is the part I still don't understand. Without something to resist
: lateral movement (equivalent to the keel pushing against water in a
: boat), how can you resolve the vectors away from the direction of the
: incident light (in this case, with or against your current orbit)? A
: sail turned at an angle isn't enough to do this; all you do is present a
: smaller surface to the incoming light. The keel in a boat adds two
: sides to make the triangle:
: _
: /|^
: / |
: wind / | desired direction of travel (orbit)
: / |
: / |
: ------>
: force exerted on keel against water, perpendicular to direction
: of travel.
Light reflects... and in doing so changes its momentum
and the momentum of the reflecting body.
Hmm lets try another cute diagram!
before hitting sail
(we will assume the sail is still, ie we are in its frame of reference)
light sail \
----> \
\
after hitting sail
sail \
\
\
light |
|
\/
Now the 'total momentum of the system' should be the same.
This was originally equal to the lights momentum in
the direction to our right.
So after the collision it should still be this.
Thus the sail must have momentum to the upper right,
such that:
the component up must cancel the final lights downwards momentum
the component to the right must be the original lights rightwards momentum.
Thus you "tack".
: Ian, no rocket scientist.
Neither am I, but I did do a few years of physics at uni.
DN
--
A snake you were when we met
I loved you anyway
Pulling out your poisoned fangs
The venom never goes away
D. Mustaine - "Poison Was The Cure"
The Wraith
wrote:
>
>Now the 'total momentum of the system' should be the same.
>This was originally equal to the lights momentum in
>the direction to our right.
>So after the collision it should still be this.
>Thus the sail must have momentum to the upper right,
>such that:
>the component up must cancel the final lights downwards momentum
>the component to the right must be the original lights rightwards momentum.
>
>Thus you "tack".
That's all very well, and quite correct, but tacking, as it is used in
sailing, uses rather different mechanics, which will actually allow
the ship in question to move into the wind (with a lot of to-ing and
fro-ing). What you describe doesn't result in the ship moving directly
away from the sun, but it still always requires the ship in question
to move to the "right" - possibly "up right" or "down right", but
still always "right", with the solar wind. This certainly doesn't
allow the same range of movement options as tacking (even if another
mechanic does).
--
Now, by popular demand, a new .sig!
I still can't think of anything witty to say, though.
The Wraith
Russell Dovey
<god...@ccis.adisys.zebra.com.au> wrote:
>
>
>Russell Dovey wrote:
>
>> On Thu, 27 Aug 1998 09:54:06 +1000,
>> mgib...@quondong.aus.fruit.and.vege () wrote:
>>
>> >Gregory Bond (g...@itga.com.au) wrote:
>> ><snip>
>> > Dyson wasn't just a futurist. He's also a physicist and contemporary
>> > of Richard Feynman. AFAIR the Star Trek representation of a Dyson sphere being
>> > a solid object is incorrect. It is supposed to be an interlinked array of
>> > satelites that generates a field effect. Consider that obtaining the materials
>> >to surround the outer atmosphere of a planet with a solid sphere would be
>> > horrendous in both time and materials.
>> > The best person to give an explanation would be a physicist....
>> > Is there a physicist in the house :-)
>>
>> Close enough....
>>
>> The Dyson Sphere could quite easily be a solid shell, because you'd
>> want to capture every last smidgen of energy, and the materials would
>> be a small problem. You'd need to be able to transmute gas to solid
>> metal, or to some kind of flexible polymer, and use Jupiter for the
>> construction material. If you don't have to live on the shell, then a
>> kind of opaque balloon would be ok.
>
>It could not work.
>
> 1. How do the "satelites" at the far northern and southern poles stay in place?
> Since the sphere is spinning, the poles must be stationary in respect, and so
> they should fall into the sun.
What kind of idiot would spin a Dyson Sphere? The entire thing would
stay up due to pressure from light and the solar wind.
> 2. If they don't fall, then they are applying pressure on the surounding
> "satelites". Add up the pressure at the equator for atht kind of diameter;
> nothing made of matter could support that.
If you don't spin the sphere (no point, IMO) there's no problem.
> 3. There isn't enough material in Jupiter to form any kind of shell at that
> distance, and the energy needed to shift that mass to another orbit would be
> prohibitive.
Nah. Simple Hohmann orbits, using even primitive solar sails would be
fine.
> 4. There is the problem of keeping ity stable. Things shift in orbit. Orbital
> forces would eventually rip the structure apart.
So you don't build it in orbit. As I said, the entire thing would be
like one huge solar sail.
>
>--
>Owen Godfrey - (08) 9333 8808 - <mailto:god...@ccis.adisys.com.au>
>"...there is sometimes little to choose between
> the reality of illusion and the illusion of reality."
> Patrick White, The Aunt's Story , 1948
>
>
--------------------------------------------------------
Fight for what you believe in!
"The most beautiful experience we can have is the
mysterious." - Albert Einstein.
"Pinky, are you pondering what I'm pondering?"
"Uh, I think so, Brain, but how are we going to get all
those computers to fail all at the same time?"
Russell "Not Just For Lepers Any More" Dovey, Australia.
ICQ:11780873 email:st...@dynamite.com.au
--------------------------------------------------------
og...@my-dejanews.com
You've missed the point. You have to use orbital mechanics to maneuver,
then you can use this method to get anywhere you like. As you increase
your orbital velocity, you move to a higher orbit. As you decrease it,
you move to a lower orbit. Maneuvers are easier within a planetary
system, so you use planets to maneuver mostly and then just drift between
them. But you have to give up the idea straight line flight between
bodies; you "tack" between orbits using the solar wind.
> --
> Now, by popular demand, a new .sig!
> I still can't think of anything witty to say, though.
>
> The Wraith
>
--
"...there is sometimes little to choose
between the reality of illusion and
the illusion of reality
-----== Posted via Deja News, The Leader in Internet Discussion ==-----
The Wraith
>
>You've missed the point. You have to use orbital mechanics to maneuver,
>then you can use this method to get anywhere you like. As you increase
>your orbital velocity, you move to a higher orbit. As you decrease it,
>you move to a lower orbit. Maneuvers are easier within a planetary
>system, so you use planets to maneuver mostly and then just drift between
>them. But you have to give up the idea straight line flight between
>bodies; you "tack" between orbits using the solar wind.
Fair enough, I can see that. I've never disputed that a ship with a
solar sail could approach the sun. (Heck, even discounting this
maneuvering, you could always just furl the sail and wait to fall back
towards the sun.) Nevertheless, it is still a very different mechanic
to that of nautical tacking. I'm not really sure the term properly
applies.
David Ralphs
: On Mon, 14 Sep 1998 03:10:33 GMT, og...@my-dejanews.com wrote:
: >
: >You've missed the point. You have to use orbital mechanics to maneuver,
: >then you can use this method to get anywhere you like. As you increase
: >your orbital velocity, you move to a higher orbit. As you decrease it,
: >you move to a lower orbit. Maneuvers are easier within a planetary
: >system, so you use planets to maneuver mostly and then just drift between
: >them. But you have to give up the idea straight line flight between
: >bodies; you "tack" between orbits using the solar wind.
: Fair enough, I can see that. I've never disputed that a ship with a
: solar sail could approach the sun. (Heck, even discounting this
: maneuvering, you could always just furl the sail and wait to fall back
: towards the sun.) Nevertheless, it is still a very different mechanic
: to that of nautical tacking. I'm not really sure the term properly
: applies.
Forget the "orbital" stuff for a moment.
The trick is "the sun sucks".
Gravity will pull you into the sun, its only when you
want to get away from the sun (or slow down your aproach)
do you need the sail.
The orbital stuff is just an example of an easy way to
balance between gravity and solar sailing.
You can approach the sun directly - not via orbital stuff.
Just use the sail to control how much force you want,
no sail = gravity = accelerate towards sun
full sail = overcome gravity = accelerate away from sun
DN
--
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| David N Ralphs |
| ATN - Channel 7 Phone: (02) 9877 7707 |
| Mobbs Lane Fax: (02) 9877 7894 |
| Epping, NSW Email: d...@atn.atn7.eggs.oz.au |
| (remove 'eggs' to unspam me!) |
----------------------------------------------------------
These views are mine.. no one else would agree with them!
I like the things that you try and fake
And your face when I see you break
And that you say you will pray for me
You realise you are prey for me
D. Mustaine - "Reckoning Day"
Viv
og...@my-dejanews.com wrote in message <6ti1fa$n3k$1...@nnrp1.dejanews.com>...
>In article <35fbb913...@news.powerup.com.au>,
> wra...@powerup.com.au (The Wraith) wrote:
>> On Tue, 8 Sep 1998 07:40:40 GMT, da...@atn.atn7.oz.au (David Ralphs)
>> wrote:
>You've missed the point. You have to use orbital mechanics to manoeuvre,
>then you can use this method to get anywhere you like. As you increase
>your orbital velocity, you move to a higher orbit. As you decrease it,
>system, so you use planets to manoeuvre mostly and then just drift between
>them. But you have to give up the idea straight line flight between
>bodies; you "tack" between orbits using the solar wind.
>> Now, by popular demand, a new .sig!
>> I still can't think of anything witty to say, though.
>>
>> The Wraith
>>
>
>
>"...there is sometimes little to choose
>between the reality of illusion and
>the illusion of reality
Nitpicker's point:
Your point regarding the use of orbital mechanics to manoeuvre is quite
correct in principle, but I think you have got the relative speeds reversed.
A lower orbit has a higher orbital velocity than a higher orbit if I
remember celestial mechanics correctly.
Larry Niven's novel (written with Steven Barnes) "The Descent of Anansi"
describes this principle of orbital mechanics quite nicely as his heroes use
a method based on this form of manoeuvring to escape from space-jackers. (No
lightsails however - sorry.)
Vivienne Smythe
viv_deleteme_@au._metoo_mensa.org (to reply remove the obvious)
++++++
Television: anagram => "novelise it"
og...@my-dejanews.com
You are aware that solar sails cannot generate enough thrust to defeat
gravity? You are also aware that solar winds are no constant, but vary
constantly throughout the year? You are also aware that there are massive
quantities of gass and matter out there that are orbiting and will
constantly impact on these structures?
Not possible.
> > 2. If they don't fall, then they are applying pressure on the surounding
> > "satelites". Add up the pressure at the equator for atht kind of
diameter;
> > nothing made of matter could support that.
>
> If you don't spin the sphere (no point, IMO) there's no problem.
If it were possible, you structure would be a few atoms thick over
thousands of square kilometers. Hard to imagine living on the surface.
> > 3. There isn't enough material in Jupiter to form any kind of shell at that
> > distance, and the energy needed to shift that mass to another orbit
would be
> > prohibitive.
>
> Nah. Simple Hohmann orbits, using even primitive solar sails would be
> fine.
>
> > 4. There is the problem of keeping ity stable. Things shift in orbit.
Orbital
> > forces would eventually rip the structure apart.
>
> So you don't build it in orbit. As I said, the entire thing would be
> like one huge solar sail.
My argumnent still applies. Your sail may be trying to stay staionary, but
everything else is moving. Tidal forces, stellar gass and particle collisions,
these things will still act on it.
And what is the gain? A huge helium baloon. Someone going to a party?
--
"...there is sometimes little to choose
between the reality of illusion and
the illusion of reality
-----== Posted via Deja News, The Leader in Internet Discussion ==-----