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Escape timelines for my interstellar ark

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Abdul Ahad

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Apr 15, 2006, 3:31:46 PM4/15/06
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This is one of those difficult topics that isn't strictly science fact,
nor is it completely science fiction, so I am hoping this posting is
not going to be thought of as inappropriate by this group. Assuming it
isn't, here goes. Suppose that through a long number of decades of
on-orbit engineering in a future era, humanity has managed to patch
together an interstellar ark of the sort of dimensions and mass I have
outlined in my sci-fi concept 'First Ark to Alpha Centauri'.

Now, suppose this object is orbiting above the Earth at around 28,000
miles (just past the Geostationary satellite belt) and it grosses a
final mass of some 1.8 x 10^14 kg (circa 10% of Deimos - the smaller
moon of Mars). Now, since no science authority has yet modelled such a
large-scale interstellar vehicle, I'm wondering if the timescales and
the dynamical sequences for departure from our solar system that I'm
visualising - or hypothesising - sound "about right"?!

I don't have answers for the total amount of energy that's going to be
required nor the precise kind of propulsion or specific impulse of the
engines to hand, but I still want to project some kind of a realistic
timescale in order to get this craft booted out of our solar system...
on its way to Alpha Centauri. I have managed to patch together an
article here that I think (and hope) looks right:-

http://www.astroscience.org/abdul-ahad/firstarktoalphacentauri/escape-sequence.htm

Now, I want some views from experts here if they see any major flaws or
have a violent disagreement with my projections. Thanks for any serious
thoughts. :-)

AA

ytyour...@p.zapto.org

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Apr 15, 2006, 5:19:23 PM4/15/06
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Abdul Ahad wrote:
> This is one of those difficult topics that isn't strictly science fact,
> nor is it completely science fiction,

It is completely science fiction. 100 percent. There is not a shred of
science fact to it.

> I don't have answers for the total amount of energy that's going to be
> required nor the precise kind of propulsion or specific impulse of the
> engines to hand,

In other words you have none of the items that might infuse "science
fact" into the story. You merely have a big thing and you say "it'll be
propelled by somehting I don't know and I want you folks tell me how
that's going to work or how long it'll take".

You have already chosen to just make up some numbers. No science fact
informed them. That's OK, mind you -- that makes it science fiction.
Nothing wrong with science fiction.. Nothing wrong with any fiction.
But there is something radically wrong whenever\wherever fiction is
misrepresented as fact.

As long as your invented craft is propelled by invented propulsion,
you'll be stuck with inventing the timescales involved. If you want
realistic dynamics, you'll have to start with a realistic craft and
realistic propulsion mechanisms.

Do you know the escape velocity for the solar system? How much
propellant you'd have to burn to attain it with chemical rockets? How
long it would take to reach it with ion engines? There's a *reason*
that this is strictly fiction.


cordially

Y.T.

--
Remove YourClothes before you email me.

George Dishman

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Apr 15, 2006, 5:46:22 PM4/15/06
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"Abdul Ahad" <abdul...@ntlworld.com> wrote in message
news:1145129506....@z34g2000cwc.googlegroups.com...

> This is one of those difficult topics that isn't strictly science fact,
> nor is it completely science fiction, so I am hoping this posting is
> not going to be thought of as inappropriate by this group. Assuming it
> isn't, here goes. Suppose that through a long number of decades of
> on-orbit engineering in a future era, humanity has managed to patch
> together an interstellar ark of the sort of dimensions and mass I have
> outlined in my sci-fi concept 'First Ark to Alpha Centauri'.
>
> Now, suppose this object is orbiting above the Earth at around 28,000
> miles (just past the Geostationary satellite belt) and it grosses a
> final mass of some 1.8 x 10^14 kg (circa 10% of Deimos - the smaller
> moon of Mars). Now, since no science authority has yet modelled such a
> large-scale interstellar vehicle, I'm wondering if the timescales and
> the dynamical sequences for departure from our solar system that I'm
> visualising - or hypothesising - sound "about right"?!
>
> I don't have answers for the total amount of energy that's going to be
> required nor the precise kind of propulsion or specific impulse of the
> engines to hand, but I still want to project some kind of a realistic
> timescale in order to get this craft booted out of our solar system...

Your departure speed of around 29km/s at 20AU is comparable
to current deep space craft. The energy would be stupidly
high if you use engines so instead you would need to use
multiple gravitational slingshots like Cassini. 20AU assumes
a final boost from Uranus. It would take many years but that
doesn't matter given the context. Whether you could design a
path to achieve that is another matter.

> on its way to Alpha Centauri. I have managed to patch together an
> article here that I think (and hope) looks right:-
>
> http://www.astroscience.org/abdul-ahad/firstarktoalphacentauri/escape-sequence.htm
>
> Now, I want some views from experts here if they see any major flaws or
> have a violent disagreement with my projections. Thanks for any serious
> thoughts. :-)

I'm not an expert by any means but two points are obvious.
First the path in part three should be a straight line since
there is no possibility of mid-course adjustments. The other
big problem is how you stop when you arrive. We don't have
the detailed knowledge that would be needed to reverse the
slingshot technique unless you could use the binary pair in
that way. For that you might need them to be in just the
right configuration which might mean waiting a few more
thousand years.

George


Michael Rhino

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Apr 15, 2006, 9:36:15 PM4/15/06
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"George Dishman" <geo...@briar.demon.co.uk> wrote in message
news:e1rouh$vf4$1...@news.freedom2surf.net...

>
> I'm not an expert by any means but two points are obvious.
> First the path in part three should be a straight line since
> there is no possibility of mid-course adjustments. The other
> big problem is how you stop when you arrive. We don't have
> the detailed knowledge that would be needed to reverse the
> slingshot technique unless you could use the binary pair in
> that way. For that you might need them to be in just the
> right configuration which might mean waiting a few more
> thousand years.
>
> George

You don't necessarily have to stop. One possibility:
a. Half the people stay on the ark and sail right past Alpha Centauri
b. Half the people board life boats and use some form of propulsion to slow
down.

Propulsion possibilities:
1. Anti-matter
2. Hydrogen fusion
3. Fission
4. Solar Sail

It would be hard to move something that massive with a solar sail. A solar
sail could be used to slow down the life boats. Storing fuel for the first
3 for 50,000 years would be risky or difficult. If the ark is sturdy enough
to last 50,000 years, you can hope that technology advances and somebody
figures something out. I think that technological advance works better with
millions of people and might not work well on the ark. If Earth lasts
another 2000 years, then perhaps Earthlings could send a message about what
to do.


Michael Rhino

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Apr 16, 2006, 1:25:24 AM4/16/06
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"Michael Rhino" <news...@alexanderpics.com> wrote in message
news:jch0g.4203$543....@tornado.socal.rr.com...

One other stray thought. You could have two arks, one in Earth orbit and
one constructed in the asteroid belt out of asteroid material. At launch,
the Earth ark will be full of the people while the other one will be 90%
empty. Surviving 50,000 years would require tons of supplies. Why not get
some of your supplies from the asteroid belt? The spare ark would also
provide room for expansion (babies). If one ship uses Venus for gravity
assist, while the other uses Jupiter, synchronizing the two ships could take
20 years.


Abdul Ahad

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Apr 16, 2006, 3:06:12 AM4/16/06
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George Dishman wrote:

> I'm not an expert by any means but two points are obvious.
> First the path in part three should be a straight line since
> there is no possibility of mid-course adjustments. The other
> big problem is how you stop when you arrive. We don't have
> the detailed knowledge that would be needed to reverse the
> slingshot technique unless you could use the binary pair in
> that way. For that you might need them to be in just the
> right configuration which might mean waiting a few more
> thousand years.
>

Just to clear any misunderstandings, this is a *fictional* concept.

I have pitch/yaw, roll and retro thrusters on the ark for 3-axis
maneouverability. Regarding deceleration at Alpha Centauri, isn't it a
case of turning around and firing the main engines to deliver thrust in
the opposite direction? Then there is also the possibility of planets
in that system that could be used for gravity-assisted slow down
(opposite to sling shot?).

AA

Mark McIntyre

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Apr 16, 2006, 5:08:08 AM4/16/06
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On Sun, 16 Apr 2006 01:36:15 GMT, in uk.sci.astronomy , "Michael
Rhino" <news...@alexanderpics.com> wrote:

>"George Dishman" <geo...@briar.demon.co.uk> wrote in message
>news:e1rouh$vf4$1...@news.freedom2surf.net...
>>
>> I'm not an expert by any means but two points are obvious.
>> First the path in part three should be a straight line since
>> there is no possibility of mid-course adjustments.

Its worth pointing out that there's no possibility of travelling in a
straight line. Quite aside from the fact that a slingshot path is a
hyperbola at best, gravitational effects from the Rest of the Galaxy
will cause your path to curve to and fro. Look at the paths the
various outer system exploration vehicles took, and remember they too
had no serious intra-course correction mechanism.

>One possibility:
>a. Half the people stay on the ark and sail right past Alpha Centauri
>b. Half the people board life boats and use some form of propulsion to slow
>down.

Difficulty is, the energy required to do this is pretty enormous.

>to last 50,000 years, you can hope that technology advances and somebody

If, in 50K years, technology hasn't advanced enough /on earth/ to
solve this problem, then its no longer worth worrying about. Compare
50K years ago with today.

Mark McIntyre
--

Peter Lynch

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Apr 16, 2006, 5:23:22 AM4/16/06
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On 2006-04-15, ytyour...@p.zapto.org <ytyour...@p.zapto.org> wrote:
>
> Do you know the escape velocity for the solar system? How much
> propellant you'd have to burn to attain it with chemical rockets? How
> long it would take to reach it with ion engines? There's a *reason*
> that this is strictly fiction.
>
My understanding of escape velocity is that it assumes that it is
reached (relatively) quickly) and once the "burn phase" is over there
is no more significant force applied in direction of travel.
If you are able to _sustain_ your velocity (not your acceleration)
by powering your engines to overcome the effects of the sun's gravity
you could escape the solar system at any speed.
Obviously, the slower you go the longer it takes.

The reason escape velocity is loved by 1960s genre sci-fi (and therefore
most films) is that when you have to carry your chemical propellant, there
are huge advantages to high acceleration for a short time.

If the mass of your propellant is only a small proportion of your
total mass, the balance changes and it's not necessary to reach
escape velocity to escape from the sun's gravity well.

Pete

p.s. since this is fiction, I'd suggest dreaming up some form of
warp-drive or jump-gate. Failing that, you may be able to form an
argument that newtonian mechanics only applies inside a gravity
well.

--
..........................................................................
. never trust a man who, when left alone ...... Pete Lynch .
. in a room with a tea cosy ...... Marlow, England .
. doesn't try it on (Billy Connolly) .....................................

Mark McIntyre

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Apr 16, 2006, 5:52:04 AM4/16/06
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On Sun, 16 Apr 2006 09:23:22 GMT, in uk.sci.astronomy , Peter Lynch
<pe...@freyr.local> wrote:

>On 2006-04-15, ytyour...@p.zapto.org <ytyour...@p.zapto.org> wrote:
>>
>> Do you know the escape velocity for the solar system? How much
>> propellant you'd have to burn to attain it with chemical rockets? How
>> long it would take to reach it with ion engines? There's a *reason*
>> that this is strictly fiction.
>>
>My understanding of escape velocity is that it assumes that it is
>reached (relatively) quickly) and once the "burn phase" is over there
>is no more significant force applied in direction of travel.

Indeed. Escape velocity is the velocitry an _unpowered_ object needs
to be travelling at to escape the gravitational field it is in.
Provided you pick the right course /and/ have power to maintain it,
you can escape at any speed you like.

>The reason escape velocity is loved by 1960s genre sci-fi (and therefore
>most films) is that when you have to carry your chemical propellant, there
>are huge advantages to high acceleration for a short time.

Well, the reason sci-fi films love it is because it makes for good
spectacle... :-)

The point is that you don't need any particular velocity to escape,
just to provide enough extra energy. EV as a concept assumes you need
to provide that energy in short order at lift-off, you can just as
easily supply it in tiny amounts.

Mark McIntyre
--

George Dishman

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Apr 16, 2006, 6:09:17 AM4/16/06
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"Abdul Ahad" <abdul...@ntlworld.com> wrote in message
news:1145171172.4...@e56g2000cwe.googlegroups.com...

> George Dishman wrote:
>
>> I'm not an expert by any means but two points are obvious.
>> First the path in part three should be a straight line since
>> there is no possibility of mid-course adjustments. The other
>> big problem is how you stop when you arrive. We don't have
>> the detailed knowledge that would be needed to reverse the
>> slingshot technique unless you could use the binary pair in
>> that way. For that you might need them to be in just the
>> right configuration which might mean waiting a few more
>> thousand years.
>>
>
> Just to clear any misunderstandings, this is a *fictional* concept.

In that case pick any numbers you like. However you asked

>>> This is one of those difficult topics that isn't strictly science fact,

>>> nor is it completely science fiction, ... I still want to project some


>>> kind of a realistic timescale in order to get this craft booted out of
>>> our solar system...

I answered on that basis since this is a science group,
not SF, and though I love good SF, it spoils a story
for me if unrealistic mistakes are made in those stories
that try to be credible.

> I have pitch/yaw, roll and retro thrusters on the ark for 3-axis
> maneouverability.

Of course, that would be necessary for fine adjustments
to take account of minor gravitational effects of others
stars en route that couldn't be predicted sufficiently
accurately before launch, but they would allow only a
fraction of a degree course change over the trip if you
want to be anywhere near realistic. Otherwise your
"thrusters" would be as poweful as main engines, just
consider the delta-V needed for a significant change of
course, and that means you are into pure fiction so you
don't need to bother asking here.

> Regarding deceleration at Alpha Centauri, isn't it a
> case of turning around and firing the main engines to deliver thrust in
> the opposite direction?

Sure, but you need to same energy for the same delta-V
and that's pure fiction.

> Then there is also the possibility of planets
> in that system that could be used for gravity-assisted slow down
> (opposite to sling shot?).

That's what I suggested. The possibility is there if
there are planets but they would need to detect them
in advance and carefully tailor the course to arrive
exactly at the right point relative to the first
slingshot target which would almost certainly mean
waiting for the right 'launch window'. That might be
centuries of delay but it is a realistic way to do it.

George


George Dishman

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Apr 16, 2006, 8:30:30 AM4/16/06
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"Michael Rhino" <news...@alexanderpics.com> wrote in message
news:jch0g.4203$543....@tornado.socal.rr.com...
> "George Dishman" <geo...@briar.demon.co.uk> wrote in message
> news:e1rouh$vf4$1...@news.freedom2surf.net...
>>
>> I'm not an expert by any means but two points are obvious.
>> First the path in part three should be a straight line since
>> there is no possibility of mid-course adjustments. The other
>> big problem is how you stop when you arrive. We don't have
>> the detailed knowledge that would be needed to reverse the
>> slingshot technique unless you could use the binary pair in
>> that way. For that you might need them to be in just the
>> right configuration which might mean waiting a few more
>> thousand years.
>>
>> George
>
> You don't necessarily have to stop. One possibility:
> a. Half the people stay on the ark and sail right past Alpha Centauri
> b. Half the people board life boats and use some form of propulsion to
> slow down.

The population that stays on board eventually die since
the craft wouldn't be any more likely to stop at any
future star and on-board fuel is finite. Better to have
them all leave but you need a pre-existing habitable
planet.

> Propulsion possibilities:
> 1. Anti-matter

See previous discussions in the group, it's not really
credible though perhaps OK in SF.

> 2. Hydrogen fusion

No, but use Deuterium.

> 3. Fission

Probably not useful due to engine mass for controlled
release or protective shielding for the "Daedelus"
concept. Lifeboats need to be low mass if they are to
be of benefit.

> 4. Solar Sail

That works but again only for a very low mass payload.

> It would be hard to move something that massive with a solar sail. A
> solar sail could be used to slow down the life boats. Storing fuel for
> the first 3 for 50,000 years would be risky or difficult.

It's not something that can be avoided, you need energy
throughout the 50k years just to maintain life and the
ark's environment (growing crops etc.).

> If the ark is sturdy enough to last 50,000 years, you can hope that
> technology advances and somebody figures something out. I think that
> technological advance works better with millions of people and might not
> work well on the ark. If Earth lasts another 2000 years, then perhaps
> Earthlings could send a message about what to do.

Technology isn't the problem, it is the energy needed
to run it. If someone figures out how to manufacture
stable anti-matter after they leave, they still don't
have the fuel on board and there's no source of energy
to manufacture it en route.

George


bombardmentforce

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Apr 16, 2006, 8:32:21 AM4/16/06
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Here's some numbers based on Dyson's 1968 article.
"Interstellar Transport," Physics Today, 41 (1968)

http://spacebombardment.blogspot.com/2005/06/navigators-log-uss-taylor.html

Jaxtraw

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Apr 16, 2006, 12:02:12 PM4/16/06
to

Talking SF blue-sky technologies, another possibility is a small black hole.
The advantage: total conversion of your fuel into energy. Your black hole
will radiate proportional to its mass, so your fuel is actually fed into it
to keep the mass constant and prevent it running away and exploding.
Disadvantages: several :)

You have to keep feeding it or the output goes up until it explodes, so
running out of fuel is inherently disastrous. You may be able to dump it
overboard but whether you can accelerate away afterwards is questionable :)
The simple engineering problems of fixing the thing inside the ship, also.
Biggest problem is, for reasonably low mass black holes the energy output is
too high, so you need some kind of handwavium technology that feeds most of
its output back into it immediately (you can use this to control the
engine's output tho, which solve your runaway problem). If you're prepared
to use the handwavium to deal with that (superduper magnetic fields?) then
creating one is no big problem (you could compress the matter with a massive
nuclear explosion in space, perhaps).

There's also the question of how you use the output (a mixture of
electromagnetic radiation and high energy particles) to actually push the
ship forwards.

Still, you get as much energy as a matter/antimatter reaction without having
to create a large amount of antimatter as fuel. And if you need an
auto-destruct, as fitted on all quality starships, it's a winner :)

For the OP, this site might be useful-

http://www.projectrho.com/rocket/index.html

It discusses real and futuristic technologies for rocketry from the SF
writer's POV.

Ian

--
www.jaxtrawstudios.com
science fiction comics with shagging in


Abdul Ahad

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Apr 16, 2006, 1:52:11 PM4/16/06
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George Dishman wrote:
> >
> > Just to clear any misunderstandings, this is a *fictional* concept.
>
> In that case pick any numbers you like.

Well, it's fictional in the sense "this is hypothetical. It's in the
future. It may or may not happen like this." But the factual
perspective is "if we were to do this... here's what might be required
in terms of the physics and the math..." that's why I posted it on
*sci* groups as opposed to *sci-fi* groups. Hope you catch my drift?

>From my perspective, this is definitely *aspirational*. Something we
could work towards, if global support was there for it to be done. So
don't let anyone here feel their efforts are being expended over a
"thin air" fantasy concept. ;-)

AA

Abdul Ahad

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Apr 16, 2006, 2:31:03 PM4/16/06
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ytyour...@p.zapto.org wrote:
> Abdul Ahad wrote:
> > This is one of those difficult topics that isn't strictly science fact,
> > nor is it completely science fiction,
>
> It is completely science fiction. 100 percent. There is not a shred of
> science fact to it.
>
It's a human interstellar craft with a purpose, physical dimensions,
internal engineering with biosphere/ecosystem, estimate of total mass,
orbital location from where it is departing, an optimally defined
projectile-shape for deflecting any interstellar debris, a firm
destination goal, with broad mission timelines and intervening
distances mapped out, ... plus countless other *facts* that are in my
novel, which even includes draft outline for orbital assembly.

The propulsion and the dynamics for realising this dream are all that's
missing, and I was only hoping to fill those in...

cheers,

AA

George Dishman

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Apr 16, 2006, 4:01:51 PM4/16/06
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"Abdul Ahad" <abdul...@ntlworld.com> wrote in message
news:1145209931.4...@z34g2000cwc.googlegroups.com...

> George Dishman wrote:
>> >
>> > Just to clear any misunderstandings, this is a *fictional* concept.
>>
>> In that case pick any numbers you like.
>
> Well, it's fictional in the sense "this is hypothetical. It's in the
> future. It may or may not happen like this." But the factual
> perspective is "if we were to do this... here's what might be required
> in terms of the physics and the math..." that's why I posted it on
> *sci* groups as opposed to *sci-fi* groups. Hope you catch my drift?

Sure, that's why I made the positive suggestion of
using slingshots to achieve your launch speed, it
takes only a minimal amount of energy to get the
process started and for a high mass craft that is
important.

However, you seem to neglect that when I noted the
path should be a straight line as if you wanted to
choose which bits would be realistic and just go
fictional if it was inconvenient. Thrusters might
give you a few metres per second though more likely
it would be much less than that. Compared to the
28km/s main speed, that's a negligible deviation.
A lateral delta_v of 1m/s at the mid point is still
enough to make a change of 788 million km at the
destination but it is only 2 thousandths of a
degree course change, 7 arc seconds or less than a
pixel on your chart.

If you use slingshots to launch and stop and a
straight line path with a course correction of a
few arc seconds then your flight dynamics won't
be too far out. You need someone who understands
slingshot calculations to say what maximum speed
you might achieve or I just found this site:

http://www.orbitersim.com/

It looks as though you can try it out yourself,
I'm off to have a go. :-)

> From my perspective, this is definitely *aspirational*. Something we
> could work towards, if global support was there for it to be done. So
> don't let anyone here feel their efforts are being expended over a
> "thin air" fantasy concept. ;-)

Well the flight stuff has been discussed but one
of the biggest problems is providing power for
basic life support. You can't stick enough food
in the freezer for 50000 years of a significant
population so you need a fully self-sustaining
system. Take the poulation, work out how much
arable land you need, then find out how many kW
hours it takes per acre per year and consider
where that will come from. If you can crack that
problem you have a chance of being realistic.

George


George Dishman

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Apr 16, 2006, 5:55:26 PM4/16/06
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"Jaxtraw" <j...@knickersjaxtrawstudios.com> wrote in message
news:4442695c$0$676$fa0f...@news.zen.co.uk...

Why inside? You need a large mass to get the temperature
down to a usable level, much larger than the mass of the
ship, so put the ship in orbit round the hole.

> Biggest problem is, for reasonably low mass black holes the energy output
> is
> too high, so you need some kind of handwavium technology that feeds most
> of
> its output back into it immediately (you can use this to control the
> engine's output tho, which solve your runaway problem).

Choose the mass to maximise the fraction of the output
that is in a usable band and keep a reasonable distance
from it. The ship doesn't need to be as close as say the
solar cells used to extract power.

> If you're prepared
> to use the handwavium to deal with that (superduper magnetic fields?) then
> creating one is no big problem (you could compress the matter with a
> massive
> nuclear explosion in space, perhaps).

If it is supposed to be realistic, creating the hole is
the key problem of course.

> There's also the question of how you use the output (a mixture of
> electromagnetic radiation and high energy particles) to actually push the
> ship forwards.

If you have matter available to feed the hole, you just
use a fraction as reaction mass. The key is getting
high exhaust velocity so run an accalerator with the
available power.

George


Dr John Stockton

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Apr 16, 2006, 4:04:45 PM4/16/06
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JRS: In article <slrne443g...@freyr.local>, dated Sun, 16 Apr
2006 09:23:22 remote, seen in news:uk.sci.astronomy, Peter Lynch
<pe...@freyr.local> posted :

>On 2006-04-15, ytyour...@p.zapto.org <ytyour...@p.zapto.org> wrote:
>>
>> Do you know the escape velocity for the solar system?

If the OP had not cross-posted to so many newsgroups, his article would
have been auto-killed by fewer people.

The escape velocity for the Solar System is as low as one likes,
provided that one starts from far enough out and is not significantly
influenced by outside bodies.

The escape velocity from any point within the Solar System (outside Sol,
and ignoring nearby planets, moons, etc.) is Root2 times the circular
orbit speed at that point; and, for Earth, that speed is two pi AU per
year which I think is nearly 30 km/s. But if escaping from circular
orbit, one only needs to add (Root2-1) * circular speed.

Orbit calculators in gravity2.htm; travel calculators in astron-3.htm;
enter via <URL:http://www.merlyn.demon.co.uk/astron-1.htm>.

--
© John Stockton, Surrey, UK. ?@merlyn.demon.co.uk Turnpike v4.00 MIME. ©
Web <URL:http://www.merlyn.demon.co.uk/> - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

William Mook

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Apr 17, 2006, 12:23:44 AM4/17/06
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The consumer electronics revolution came about by a dedication of
engineers to maintaining a continuous exponential increase in the
number of circuits built for a dollar.

A revolution in space travel can come about by a similar dedication to
maintaining a continuous exponential increase in the momentum that can
be attaned for a dollar invested in rockets.

The cost of momentum dropped dramatically through the 1950s through the
1960s - then, in the 1970s, cost of momentum remained relatively
constant, and the space program stalled. This is the result of how we
manage our space industry and how we fund it, not the result of any
fundamental technical limit.

So, should we change the way we approach rocketry on this planet, we
can expect radical increases in its impact on our daily lives. Here is
the development arc we can expect to see;

1) 1950s - suborbital small payloads - ICBMs - end of global warfare -
threat of global thermonuclear war creates mutual assured destruction
of any combatants enforcing an uneasy peace between them - intelligence
operations, advertising and propaganda come to dominate international
relations.

2) 1960s - small orbiting payloads - infosats - global communications
- create broad access to the international market across the globe.

3) 1970s - large cislunar payloads - manned flight - lunar travel -
global awareness, environmental movement - high quality images of earth
alone in space release new ideas about a Earth as a single entity, Gaia
Theory and Environmental Movement are a few of the practical results.
Suggested but never implemented were Solar Power Satellites that beam
energy captued in space to users on Earth, and to users around the
solar system.

Major spending on space development ended when the US went to the moon
and the developmetn arc stopped. Concerns over missile proliferation
and nuclear weapns proliferation have made broad use of rocket and
nuclear technologies impossible. Certainly improvements were made, but
further improvements are possible; Had research continued we could
have expected (but did not achieve) the following;

4) 1980s - very large interplanetary payloads - asteroidal movement,
planetary colonization - asteroids on collision paths with Earth are
deflected. Rich asteroids are identified and returned to Earth orbit.
Automated and remotely controlled factories making use asteroidal
materials, solar power - and delver them to users directly on Earth, or
anywhere in cislunar space.. This starts out with rare metals and other
hard to locate materials but eventually grows more complex with
industrial goods, consumer goods, and even, with the creation of large
pressure vessels on orbit, farms and forests in space to deliver food
and fiber to people on Earth and everywhere,

Practical interstellar travel requires massve momentum changes far
greater than that required for interplanetary travel. So, further
reductions in cost of momentum do not lead directly to star travel.
They lead to traversing the development arc described above a second
time, but this time, at a far lower cost - a cost that permits the
ownership or use of individual spacecraft;

5) 1990s small suborbital payloads - personal ballistic transport -
micromachinery based rocket arrays create propulsive skins powered by
solar pumped lasers placed on orbit. These propulsive skins, powered
by solar pumped lasers are very simple, safe, and easy to use - once
developed. Starting out as simple easy to use braking rockets these
systems grow ever more complex and capable, leading to the ability of
anyone to travel anywhere in 42 minutes or less. They unite the Earth
into a single political and economic entity - making good on the 1950s
promise of a Global Village. Large metropolitan areas unravel as
people spread far and wide, obtaining information, energy, consumer
goods, and even employment - by virtual presence - on orbit.

6) 2000s larger orbital payloads - personal orbiter - based on a the
ballistic transporter described above. When combined with remotely
controlled and automated production on orbit, to create large
personally owned space stations - based on the farm and forest sats of
an earlier generation.

7) 2010s very large interplanetary payloads - personal interplanetary
traveller - personally owned space stations moved by a combination of
laser powered rockets and laser light sails - move large personal
spacestations throughout the solar system.

8) 2020s - to support a growing energy demand by humanity, solar power
companies develop sun hovering powersat arrays that ultimately enshroud
and collect and direct the entire energy output of the sun. 10^25
elements held 1 million km from the surface of the sun, by photon
pressure and solar wind are controlled by structured controlling laser
pulses to deliver massive controlled pulses of laser energy safely and
reliably to billions of users around the solar environment from a cloud
surrounding the sun. , Each element is microns thick and only
millimeters wide. They are produced by millions of laser powered and
automated production cells operated throughout the asteroid belt and
each element uses solar energy, laser energy, and solar wind to
navigate to a postion 1 million km above the solar surface. THIS IS A
SOURCE OF ENERGY CONTROLLED AND LARGE ENOUGH TO POWER INTERSTELLAR
EXPEDITIONS - along with billions of privately owned interplanetary
space colonies and millions of industrial centers located throughout
interplanetary space.

9) 2030s - First Interstellar Wave - Multi-staged solar sails move
lightweight space colony 'seeds' at 1/8 th light speed from star to
star - Once arrived at the target star in about 40 years - the colony
seed identifies asteroidal feedstocks that might bre useful, and
exploits those, along with the remote star's output to create.star
hovering shrouds surrounding the target star. Once well established,
these star powered lasers allow the operation of Single-staged solar
sails moving fully functioning family owned space colonies at 1/2 light
speed from star to star in 10 years or less, the target star also
constructs and send forward another colony seed further removed from
Sol to repeat the process. .

10) 2070s - Second Interstellar Wave - Single staged soalr sails move
full weight space colonies at 1/2 light speed from star to star - Once
arrived at the target star, in about 10 years - the colony directs to a
point withing the target star, or to another star system further
removed.

THIS IS THE LEVEL AT WHICH YOUR QUESTION IS DIRECTED - To answer your
question, you need to know a few things. How much does your colony
ship mass? How fast do you want to accelerate it? How fast do you
want it to go? How are you accelerating it? ANSWERS BELOW

11) 2100s - Third Interstellar Wave - multiple star systems with
multiple energy shrouds can send copious materials from star to star at
1/2 light speed. THis is useful in trade, but it can also be used to
create a new generation of interstellar collider that takes very large
payloads and collides them to create engineered black holes - over
time, these experiments could lead to revolutionary technologies that
permit superuminal travel and time travel- if we're lucky! lol.


At 1/8th light speed you'll have around 1/64th the rest mass energy
tied up as kinetic energy - relativistic effects though measurable
don't count for much at these speeds At 1/2 light speed - over 1/4 of
the rest mass energy is tied up as kinetic energy.

But a 1/2 light speed, you do have relativistic effects - so 1/3 of the
rest mass energy is needed as kinetic energy at this speed.

Now, if you use photon rockets to push your spacecraft you would have
to expend more energy than this

To quote from;

http://en.wikipedia.org/wiki/Relativistic_rocket

The mass of the fuel tanks and the pion rocket engine can not exceed
450 t, and the maximum mass of the crew habitat, and any other vehicles
based on it will be limited to 300 t. This pion rocket will be capable
of accelerating up to 0.5c two times before all the fuel is used.
Maximum round trip velocity for a one stage vehicle is thus limited to
1/4th of light velocity. One way decelerated velocity is limited to
0.5c. One way undecelerated cruising velocity will be about 0.9c to
0.99c for a one stage vehicle. A minimum of a two-stage (4/1) mass
fraction pion rocket is required to achieve a round trip cruising
velocity of 0.5c. If 4 stages were used a round trip cruising velocity
of up to 0.87c is theoretically possible. These figures show that the
best starship designs are based on a non-rocket systems such as light
sails, interstellar ramjets, interstellar rairs, or laser-maser
electric propulsion interstellar vehicles. This is because all of
rocketry is limited by the rocket equation, and also limited by the
maximum amount of energy that can be released from the rocket fuel.

So, 750 t rocket must mass 3,000 t at liftoff - 'burning' through 2,250
t of matter and anti-matter.

A solar sail doesn't need to carry the propellant along. And you can
have combinations - a solar sail at take off and an anti-matter rocket
to slow down.- to save fuel.

Sail weights are likely to be nearly what the anti-matter weights would
be. We know how to make big sails we don't know how to make lots of
anti-matter. But that could change with research.

One interesting possibility is to have a solar sail that absorbs rather
than reflects laser energy. Then use the absorbed laser energy to make
matter/anti-matter. THis antimatter can then be used to slow the
spacecraft down, at the end of the journey.

Such a sail/engine would be very interesting.

Another possibility is to create engineered black holes. Black holes
are very very dense, so even a large quantity of material can be put
into a tiny volume.

Black holes are not completely black either. They have a temperature
because they emit Hawking Radiation. The temperature of a black hole
is inversely proportional to the fourth power of their mass. So, very
tiny black holes are very intense energy sources and have very short
lifetimes. Depending on the details, this energy can takemany forms -
the easiest would be gravity waves.

Collections of very tiny black holes can be postulated that orbit
around one another in such a way as to absorb and re-emit intense
bursts of gravity radiation very efficiently with zero leakage.

These black holes are then charged so they are manipulated with
electrostatic fields in such a way as to emit controlled bursts of
highly directed intense gravity radiation - converting the rest mass of
the black hole into a rocket burst.

A payload can be gravitationally bound to such a collection of black
holes by merely falling toward it. If the surface gravity of the black
hole cloud is 100 gees for example, and the space colony falls towards
the black hole as the cloud is accelerating at 100 gees - the colony
would feel no force - it would be in free fall.

This seems an ideal sort of propulsion system if it could be built.

Refueling would be a cinch, just feed it regular matter and it would
get sucked into the black hole dust. Electromagnetic radiation would
be produced by a single black hold sucking in regular matter. But,
with an appropriately engineered cloud - all radiation could be
efficiently absorbed by the cloud by controlling the pattern of the
black holes that made up the cloud and the pattern of infalling matter.

http://www.nas.nasa.gov/About/Education/SpaceSettlement/75SummerStudy/Table_of_Contents1.html

Space Colonies are probably a good place to start in engineering a
colony ship. I'd go for an active shield.

A torus, a cylinder, and a sphere are studied here. A torus

http://www.nas.nasa.gov/About/Education/SpaceSettlement/75SummerStudy/5appendA.html

A torus - donut shape - consisting of a tube 130 m in diameter bent
into a circle 1800 m in diameter masses 229,000 tonnes.

http://www.nas.nasa.gov/About/Education/SpaceSettlement/75SummerStudy/figure5.1.gif

I can imagine something like this with a laser light sail

http://en.wikipedia.org/wiki/Light_sail

That would be nearly 100 km in diameter - So,the center of the colony
would be attached by cable to a very large light sail, and that would
be illuminated by laser beam. The colony would have daylight by
reflected flight from the laser, and would also be powered by laser
too.

Alternatively the cloud of interacting engineered black holes would
hover above the colony as shown,and emit gravity waves so that the
colony wouldn't fall in. The could would be controlled by
remotecontrol. The cloud could also emit light in controlled amounts
so that the colony had heat, light and power - the could would also
absorb radiation and matter ahead of the colony as it accelerated.
When slowing the colony wouldn't have this protection.

Accelerating at 100 gees the rocket for a 229,000 tonne station would
be as bright as a star! lol. But it would only take a day and a half
to get up to 1/2 light speed.

Even at half light speed time would be slowed by only 15%- but still,

Say with 300,000 tonnes overall, The black hole cloud would be composed
of 900,000 tonnes of material, and it would all be radiated away in two
36 hour bursts!

At the end of the journey, the black hole cloud would have to be fed
another 900,000 tonnes of material. If it were rock at 3 g/cc - it
would be an asteroid 83 meters in diameter - absorbed into a cloud of
interacting black holes that would be invisible to the naked eye -
except when operating to produce visible light.

600,000 tonnes of matter converted to energy - on the first burst, to
get it up to speed - and 300,000 tonnes converted to energy on the
second burst - to slow it down, all within 36 hours - or 129,600
seconds

A kilogram of matter has

E = mc2 = 1 * (3e8)^2 joules = 9e16 joules/kg

600,000 tonnes of matter has;

E = 6e8 * 9e16 = 5.4e25 joules

Divide this by the number of seconds;

P = 5.4e25 / 1.3e5 = 4.2e20 Watts

The sun puts out 3.86e26 Watts -

Which is about 1/1,000,000th the entire output of the sun.

Laser sail based starships would be be limited to about 1/10th gee -
which is a power level 1/1,000th this level - and it would take 1,500
days, not 1.5 days to get up to speed - that's a little over 4 years of
acceleration- each time - so, that's 8 years - added to an 8 year trip.
but, with the ENTIRE SUN being harvested, 1 billion starships could be
dispatched over this 4 year period - which means if each family owned
one, they could all fly using the sun's output, no problem.

George Dishman

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Apr 17, 2006, 6:35:56 AM4/17/06
to

"Abdul Ahad" <abdul...@ntlworld.com> wrote in message
news:1145129506....@z34g2000cwc.googlegroups.com...

> Now, suppose this object is orbiting above the Earth at around 28,000
> miles (just past the Geostationary satellite belt) and it grosses a
> final mass of some 1.8 x 10^14 kg (circa 10% of Deimos - the smaller
> moon of Mars). Now, since no science authority has yet modelled such a
> large-scale interstellar vehicle, I'm wondering if the timescales and
> the dynamical sequences for departure from our solar system that I'm
> visualising - or hypothesising - sound "about right"?!
>
> I don't have answers for the total amount of energy that's going to be
> required

It's of the order of 54 million megatons just for the
final kinetic energy of the craft and ignoring escaping
from Earth orbit and any sort of engine inefficiency.

> nor the precise kind of propulsion or specific impulse of the
> engines to hand, but I still want to project some kind of a realistic
> timescale in order to get this craft booted out of our solar system...

With realistic engines you are into the billions of
megatons or worse. Consider an Orion style propulsion
using ten million of the biggest hydrogen bombs we could
produce as an over-optimistic minimum.

George


Peter Lynch

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Apr 17, 2006, 8:42:54 AM4/17/06
to
On 2006-04-17, George Dishman <geo...@briar.demon.co.uk> wrote:
>
> With realistic engines you are into the billions of
> megatons or worse. Consider an Orion style propulsion
> using ten million of the biggest hydrogen bombs we could
> produce as an over-optimistic minimum.
>
My understanding of orion engines is that they use atomic/nuclear
detonations as the energy source to (explosively) heat air uunder
the vehicle. It's the rapid expansion of the heated air that actually
provides the thrust, not the detonation itself.
On that basis, they wouldn't work outside the atmosphere.

Pete

Abdul Ahad

unread,
Apr 17, 2006, 9:47:40 AM4/17/06
to
George Dishman wrote:
> "Abdul Ahad" <abdul...@ntlworld.com> wrote in message

> It's of the order of 54 million megatons just for the


> final kinetic energy of the craft and ignoring escaping
> from Earth orbit and any sort of engine inefficiency.
>

Let us consider a more tangible scenario that's easier to visualise. We
have a 300-kg mass spacecraft orbiting at LEO (circa 250 miles altitude
above the Earth, where incidentally the gravity well is dramatically
more steep for an escape departure, compared to the 28,000 mile
projected altitude of my ark).

Now, we want to propel this spacecraft to break out of its closed orbit
around Earth and head off towards the moon ("trans-lunar injection" or
TLI is the technical term in old Apollo language).

How much fuel do we need to achieve this? Well, I believe the ratio is
3.15 times for propellant mass to payload mass in that scenario, if
we're using conventional chemical rockets.

(See my comments on this old thread here:
http://groups.google.com/group/sci.space.shuttle/msg/406ccb7616dcc21a?hl=en&
)

In other words, to push that 300-kg spacecraft out of Earth's gravity
well, we need 645-kg of rocket fuel that's additionally over and above
the 300-kg spacecraft mass to achieve this.

Now, suppose that 300-kg spacecraft was orbiting where the ark is - at
28,000 miles above Earth ("HEO"). From this point further up above the
gravity well, I reckon the fuel requirement will be substantially less
than 645-kg for an escape to TLI. Without doing the calculations, I
would guess less than half that. For the sake of argument, let's say
the propellant/payload ratio is just 1.5 (as opposed to 3.15 if it were
departing from LEO, as noted above).

On that basis, we need a separate ark-sized fuel tank of (1.8 x 10^14 *
1.5 = 2.7 x 10^14 - 1.8 x 10^14 = 9 x 10^13 kg ) mass to break "First
Ark to Alpha Centauri" out of Earth orbit and achieve a provisional
orbit around the Sun.

Indeed that is a very very steep fuel requirement! But that's assuming
we're using a hypothetical mixture of LOX/RP-1 in a chemical engine
adapted for vacuum that burns in a single impulse.

However, the scenario I am proposing for my ark is not "a single
impulse". It is a *gradual* application of thrust over many years, so
that the thing eases it's way out of the closed orbit around the Earth,
and eventually achieves a heliocentric path that's perhaps
significantly elliptical.

That's the first part.

The next part is where the possibility of gravity-assisted swing by's
of bodies like Venus, Mars, or the Earth becomes feasible to propel it
out of the *inner* solar system toward the *outer* solar system. The
timescale for this is going to be into several *decades* I reckon,
since we're using a myriad of low thrust, multiple impulses.

Does all of this sound "plausible" to people here?

cheers,
AA

George Dishman

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Apr 17, 2006, 11:14:19 AM4/17/06
to

"Peter Lynch" <pe...@freyr.local> wrote in message
news:slrne473a...@freyr.local...

> On 2006-04-17, George Dishman <geo...@briar.demon.co.uk> wrote:
>>
>> With realistic engines you are into the billions of
>> megatons or worse. Consider an Orion style propulsion
>> using ten million of the biggest hydrogen bombs we could
>> produce as an over-optimistic minimum.
>>
> My understanding of orion engines is that they use atomic/nuclear
> detonations as the energy source to (explosively) heat air uunder
> the vehicle. It's the rapid expansion of the heated air that actually
> provides the thrust, not the detonation itself.
> On that basis, they wouldn't work outside the atmosphere.

There would need to some reaction mass involved
of course but I see that as technology, not a
fundamental limitation. I wanted to convey the
sort of energy levels involved.

George


George Dishman

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Apr 17, 2006, 11:27:13 AM4/17/06
to

"Abdul Ahad" <abdul...@ntlworld.com> wrote in message
news:1145281660.8...@t31g2000cwb.googlegroups.com...

Using a solar sail to gradually boost the orbit would
take no effort but many years. Using many ion engines
would also take some time but be a better compromise.
Power isn't a problem since you can use solar energy
while in Earth orbit, the limitation would be reaction
mass. Simply manufacturing your ark in the asteroid
belt would solve the initial problem of leaving Earth
and also the cost of lifting that much mass to orbit.

> That's the first part.
>
> The next part is where the possibility of gravity-assisted swing by's
> of bodies like Venus, Mars, or the Earth becomes feasible to propel it
> out of the *inner* solar system toward the *outer* solar system. The
> timescale for this is going to be into several *decades* I reckon,
> since we're using a myriad of low thrust, multiple impulses.
>
> Does all of this sound "plausible" to people here?

A decades is probably right but you can't do lots of
small changes since there is a limit to how fast you
can pass a planet and still choose your departure
trajectory without getting too close. You need to
look at the maximum that could be achieved on the
final series but 27km/s doesn't sound unreasonable.

George


Peter Lynch

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Apr 17, 2006, 1:29:17 PM4/17/06
to
On 2006-04-17, Abdul Ahad <abdul...@ntlworld.com> wrote:

> "First
> Ark to Alpha Centauri"

It might be the first ark to _leave_ for Alpha Centauri, but if it's going
to take 50,000 years to get there (or wherever it end up) the advances in
technology made on earth during the trip means that when they get there,
they'll probably meet humans who stayed behind and developed a faster
means of transport. Read Niven+Pournelle wrt. pupetteers leaving the galaxy.

> However, the scenario I am proposing for my ark is not "a single
> impulse". It is a *gradual* application of thrust over many years, so

requires even more fuel, as you have to accelerate the fuel you'll
burn later. Plus (and this is a biggie) there's a limit to the final
speed that a chemical rocket can get you to. It's related to the
velocity of the exhaust gases. LOX + H2 won't get you to solar escape
velocity, it doesn't burn fast enough. You'll need something more.

> That's the first part.
>
> The next part is where the possibility of gravity-assisted swing by's
> of bodies like Venus, Mars, or the Earth becomes feasible to propel it
> out of the *inner* solar system toward the *outer* solar system.

Probably not. Given the size of your craft, it can't get too close
to a gravity well or the stresses imposed by the change in direction
will tear it apart. We've seen what happens to comets when they get
too close to a planet: they break up.

>
> Does all of this sound "plausible" to people here?
>
> cheers,
> AA
>

mme...@cars3.uchicago.edu

unread,
Apr 17, 2006, 6:31:59 PM4/17/06
to
In article <slrne47k3...@freyr.local>, Peter Lynch <pe...@freyr.local> writes:
>On 2006-04-17, Abdul Ahad <abdul...@ntlworld.com> wrote:
>
>> "First
>> Ark to Alpha Centauri"
>
>It might be the first ark to _leave_ for Alpha Centauri, but if it's going
>to take 50,000 years to get there (or wherever it end up) the advances in
>technology made on earth during the trip means that when they get there,
>they'll probably meet humans who stayed behind and developed a faster
>means of transport. Read Niven+Pournelle wrt. pupetteers leaving the galaxy.
>
>> However, the scenario I am proposing for my ark is not "a single
>> impulse". It is a *gradual* application of thrust over many years, so
>
>requires even more fuel, as you have to accelerate the fuel you'll
>burn later. Plus (and this is a biggie) there's a limit to the final
>speed that a chemical rocket can get you to. It's related to the
>velocity of the exhaust gases. LOX + H2 won't get you to solar escape
>velocity, it doesn't burn fast enough. You'll need something more.

No, this is quite incorrect. The final speed of a rocket is not
limited to the velocity of the exhaust gases. Else, you couldn't even
launch a satellite to LEO. Granted, getting better than, say, factor
3 above the exhaust velocity requires rather unrealistic fuel mass to
total mass ratios.

Mati Meron | "When you argue with a fool,
me...@cars.uchicago.edu | chances are he is doing just the same"

Jaxtraw

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Apr 17, 2006, 8:10:29 PM4/17/06
to

I can't see that working (even in sci-fi :) You have to attach the engines
to the ship; if the ship's mass is small compared to the black hole and it's
orbiting around it, firing the engines simply breaks the ship out of orbit.
The black hole won't follow.

That's why I suggested some handwavium technology which will allow a small
black hole to emit far too much energy; if you can push the energy back into
the black hole you're okay. You could just let it escape but then the black
hole rapidly loses mass, energy goes up, and you're sitting on a very big
bomb.

I did do some calculations on this at one point (I draw an adult sci-fi
comic strip and it's not been explicitly stated but this is how the
starships are powered) and concluded that realistic energy outputs equate
to unfeasibly massive black holes. It seems I didn't keep the calculations
however :(

Anyway, as I said, I don't see how you make the black hole stay with the
ship, if the ship's mass is tiny compared to it. Having said that, I'm not
sure how you'd do so anyway. Obviously you can't physically attach anything
to the black hole. So you need either a magic artificial gravity field or
something electromagnetic (my relativity's a bit blurry, but IIRC a
sufficiently unfeasibly powerful magnetic field would curve spacetime...)

Ian


Jaxtraw

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Apr 17, 2006, 8:16:45 PM4/17/06
to

I don't understand this. Surely a rocket engine can accelerate a rocket
regardless of the rocket's velocity? After all, "at rest" is an arbitrary
statement; one can define whatever velocity one likes as "at rest"- i.e. a
ship moving at any constant velocity defines an inertial frame. To say
otherwise means an astronaut can test what speed his rocket ship is going at
relative to some universal reference frame, in clear violation of
relativity.

I don't see what fixed reference frame you're measuring the velocity of the
rocket compared to. The only meaningful measure of the speed of the exhaust
gases is relative to the rocket, and that's going to stay the same for as
long as the engine is firing, regardless of the speed of the rocket relative
to, say, the Earth (or indeed the sun, the galactic centre, or somebody
whizzing by at half the speed of light).

Ian


Greg D. Moore (Strider)

unread,
Apr 17, 2006, 8:24:07 PM4/17/06
to

"Peter Lynch" <pe...@freyr.local> wrote in message
news:slrne473a...@freyr.local...
> On 2006-04-17, George Dishman <geo...@briar.demon.co.uk> wrote:
> >
> > With realistic engines you are into the billions of
> > megatons or worse. Consider an Orion style propulsion
> > using ten million of the biggest hydrogen bombs we could
> > produce as an over-optimistic minimum.
> >
> My understanding of orion engines is that they use atomic/nuclear
> detonations as the energy source to (explosively) heat air uunder
> the vehicle. It's the rapid expansion of the heated air that actually
> provides the thrust, not the detonation itself.
> On that basis, they wouldn't work outside the atmosphere.

Your understanding is wrong.

Orion was designed for interplanetary operations.

mme...@cars3.uchicago.edu

unread,
Apr 17, 2006, 10:29:03 PM4/17/06
to

Certainly. That's why I said "... not limited to the velocity of the
exhaus gases".

> After all, "at rest" is an arbitrary
>statement; one can define whatever velocity one likes as "at rest"- i.e. a
>ship moving at any constant velocity defines an inertial frame. To say
>otherwise means an astronaut can test what speed his rocket ship is going at
>relative to some universal reference frame, in clear violation of
>relativity.

Yep.

>
>I don't see what fixed reference frame you're measuring the velocity of the
>rocket compared to. The only meaningful measure of the speed of the exhaust
>gases is relative to the rocket, and that's going to stay the same for as
>long as the engine is firing, regardless of the speed of the rocket relative
>to, say, the Earth (or indeed the sun, the galactic centre, or somebody
>whizzing by at half the speed of light).
>

I fully agree. So, what is it in what I said that your "I don't
understand this" refers to?

Michael Rhino

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Apr 17, 2006, 10:33:45 PM4/17/06
to
"Jaxtraw" <j...@knickersjaxtrawstudios.com> wrote in message
news:44442ec5$0$214$db0f...@news.zen.co.uk...

At one time, I proposed a system for getting up to half the speed of light
with chemical rockets. Somebody pointed out that the total amount of fuel
needed would exceed the mass of the universe.

Suppose you start off with 16 rockets and they accelerate. When they are
half full, you transfer fuel to 8 rockets and those 8 continue. When they
are half full, you transfer fuel to 4 and continue. That gets you up to 3
times the speed of a single rocket, but it still isn't close to the speed of
light.


bombardmentforce

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Apr 17, 2006, 11:35:18 PM4/17/06
to
>My understanding of orion engines is that they use atomic/nuclear
>detonations as the energy source to (explosively) heat air uunder
>the vehicle.

http://spacebombardment.blogspot.com/2005/10/orion-isp-at-low-altitude.html


There are two modes, as you described up to 300,000 feet then a switch
to larger pulse units above.

Here's a diagram of the internal propellant pulse unit, with a tungsten
disk providing thrust. The low altitude unit's diagrams are still
classified.

http://spacebombardment.blogspot.com/2006/03/pulse-unit-extract-from-page-23-of-ga.html

Abdul Ahad

unread,
Apr 18, 2006, 3:03:56 AM4/18/06
to
George Dishman wrote:
>
> However, you seem to neglect that when I noted the
> path should be a straight line as if you wanted to
> choose which bits would be realistic and just go
> fictional if it was inconvenient. Thrusters might
> give you a few metres per second though more likely
> it would be much less than that. Compared to the
> 28km/s main speed, that's a negligible deviation.
> A lateral delta_v of 1m/s at the mid point is still
> enough to make a change of 788 million km at the
> destination but it is only 2 thousandths of a
> degree course change, 7 arc seconds or less than a
> pixel on your chart.

Alpha Centauri is currently drifting across our night skies with a
total proper motion of 3.7 arc-seconds per year. In 50,000 years, it
will have moved 51.4 degrees. Are you saying I shoot the ark toward a
spot in the sky that's 51.4 degrees "in front" of the star?

Given that the Milky Way is a rotating system and that gravitational
perturbations from high-mass nearby systems like Sirius, Altair,
Procyon, Vega, etc. are not fully quantified, I believe some interim
course corrections will be necessary. Projecting a straight-line
trajectory will have to dismiss all the other unknown factors, such as
the tenuousness (is that the right word?) of the Oort cloud, it's
composition, the amount of interstellar "drag" (if any) that the ark
might encounter, etc... these are all totally unknown in this voyage.

> basic life support. You can't stick enough food
> in the freezer for 50000 years of a significant
> population so you need a fully self-sustaining
> system.

With a self-sustaining ecosystem, there's a flourishing and vibrant
community living inside the ark! Check this movie trailer ;-) >>>

http://www.astroscience.org/abdul-ahad/firstarktoalphacentauri/chapter3.htm

AA

Peter Lynch

unread,
Apr 18, 2006, 6:49:25 AM4/18/06
to
On 2006-04-18, Jaxtraw <j...@knickersjaxtrawstudios.com> wrote:
> mme...@cars3.uchicago.edu wrote:
>> In article <slrne47k3...@freyr.local>, Peter Lynch
>> <pe...@freyr.local> writes:
>>> On 2006-04-17, Abdul Ahad <abdul...@ntlworld.com> wrote:
>>>
>>> requires even more fuel, as you have to accelerate the fuel you'll
>>> burn later. Plus (and this is a biggie) there's a limit to the final
>>> speed that a chemical rocket can get you to. It's related to the
>>> velocity of the exhaust gases. LOX + H2 won't get you to solar escape
>>> velocity, it doesn't burn fast enough. You'll need something more.
>>
>> No, this is quite incorrect. The final speed of a rocket is not
>> limited to the velocity of the exhaust gases. Else, you couldn't even
>> launch a satellite to LEO. Granted, getting better than, say, factor
>> 3 above the exhaust velocity requires rather unrealistic fuel mass to
>> total mass ratios.
>>
>
> I don't understand this. Surely a rocket engine can accelerate a rocket
> regardless of the rocket's velocity? After all, "at rest" is an arbitrary
> statement; one can define whatever velocity one likes as "at rest"- i.e. a
> ship moving at any constant velocity defines an inertial frame. To say
> otherwise means an astronaut can test what speed his rocket ship is going at
> relative to some universal reference frame, in clear violation of
> relativity.
>
OK, I admit my fingers got ahead of my brain. The _rocket equation_
tells you that if your exhaust leaves at (say) 4000 m/s and you want
to reach (say) 40,000 m/s then the ratio of fuel to payload is given
by V = Vexhaust * ln (starting mass / final mass) so for a V : Ve ratio of
10 : 1 the ratio of masses is something like 20,000 : 1, i.e. you
need about 20,000 times as much fuel as payload.
I should've said a _practical_ limit to the final speed.

Obviously from the equation, if you have a faster burning fuel, the
ratio changes, but chemical fuels are still too slow for a practical
solution.

Hope that clears it up a bit

Pete

Jaxtraw

unread,
Apr 18, 2006, 9:44:59 AM4/18/06
to

I'm sorry, it was a mixture of lack of understanding and confabulating your
post with the one you were replying to. I've re-read your post and got what
you were talking about this time :)

If I understand correctly, you're merely saying that a factor 3 is a
practical rule of thumb, kind of thing based on realistic engineering
constraints.

Ian


mme...@cars3.uchicago.edu

unread,
Apr 18, 2006, 12:05:28 PM4/18/06
to
Yep, right on.

>Obviously from the equation, if you have a faster burning fuel, the
>ratio changes, but chemical fuels are still too slow for a practical
>solution.

Indeed. They're good enough for near Earth operation, barely good
enough for Solar system exploration (unmanned), perhaps nearest
planets manned flights. Beyond this, they're inadequate.


>
>Hope that clears it up a bit
>

Sure.

mme...@cars3.uchicago.edu

unread,
Apr 18, 2006, 12:52:42 PM4/18/06
to
Yes, exactly. You do need some tanks to hold the fuel, plumbing to
move it around etc. Not to mention payload. All of this carries some
mass. In fact even factor 3 is very optimistic, for launch from Earth
(where significan accelerations are involved) it is more like 2. Mind
you, you can improve on this a bit by throwing away dead mass as soon
as it is not needed (which is what multistage rocket is). Still, I'm
not aware of any chemical rocket, so far, that got beyond factor 4 or
so.

George Dishman

unread,
Apr 19, 2006, 2:42:48 PM4/19/06
to

"Abdul Ahad" <abdul...@ntlworld.com> wrote in message
news:1145343836.6...@i39g2000cwa.googlegroups.com...

> George Dishman wrote:
>>
>> However, you seem to neglect that when I noted the
>> path should be a straight line as if you wanted to
>> choose which bits would be realistic and just go
>> fictional if it was inconvenient. Thrusters might
>> give you a few metres per second though more likely
>> it would be much less than that. Compared to the
>> 28km/s main speed, that's a negligible deviation.
>> A lateral delta_v of 1m/s at the mid point is still
>> enough to make a change of 788 million km at the
>> destination but it is only 2 thousandths of a
>> degree course change, 7 arc seconds or less than a
>> pixel on your chart.
>
> Alpha Centauri is currently drifting across our night skies with a
> total proper motion of 3.7 arc-seconds per year. In 50,000 years, it
> will have moved 51.4 degrees. Are you saying I shoot the ark toward a
> spot in the sky that's 51.4 degrees "in front" of the star?

Of course, ever tried to shoot a moving target?
You launch on a line that should achieve a
perfect rendezvous. That minimises the fuel you
needto carry for the inevitable course corrections.

> Given that the Milky Way is a rotating system and that gravitational
> perturbations from high-mass nearby systems like Sirius, Altair,
> Procyon, Vega, etc. are not fully quantified, I believe some interim
> course corrections will be necessary.

Those are valid but probably small in comparison to
the uncertainty in your launch vector.

> Projecting a straight-line
> trajectory will have to dismiss all the other unknown factors, such as
> the tenuousness (is that the right word?) of the Oort cloud, it's
> composition, the amount of interstellar "drag" (if any) that the ark
> might encounter, etc... these are all totally unknown in this voyage.

Obviously you would use computer modelling with
the best data available at the time to predict
the course and not launch until you were sure
the maximum possible error could be corrected
within the thruster fuel you planned to carry.

What I _am_ saying is that those effects from
other bodies are sufficiently small that they
would probably not cause a deflection of more
than a couple of pixels from a straight line
given the limited resolution of your graphic.

If you want to be sure, you could find the mass
of say Sirius and work out how much acceleration
it would produce and from that see how much the
line would be bent.

>> basic life support. You can't stick enough food
>> in the freezer for 50000 years of a significant
>> population so you need a fully self-sustaining
>> system.
>
> With a self-sustaining ecosystem, there's a flourishing and vibrant
> community living inside the ark! Check this movie trailer ;-) >>>
>
> http://www.astroscience.org/abdul-ahad/firstarktoalphacentauri/chapter3.htm

Looks big, what is the internal surface area of
the ark? Multiply by around 1.3kW/m^2 to get
your power requirement. There's no sunlight so
you need an alternative, fission I would guess.

George


George Dishman

unread,
Apr 19, 2006, 2:50:19 PM4/19/06
to

"Jaxtraw" <j...@knickersjaxtrawstudios.com> wrote in message
news:44442d4c$0$216$db0f...@news.zen.co.uk...

> George Dishman wrote:
>> "Jaxtraw" <j...@knickersjaxtrawstudios.com> wrote in message
>> news:4442695c$0$676$fa0f...@news.zen.co.uk...
...

>>>
>>> Talking SF blue-sky technologies, another possibility is a small
>>> black hole.
>>> The advantage: total conversion of your fuel into energy. Your black
>>> hole will radiate proportional to its mass, so your fuel is actually
>>> fed into it
>>> to keep the mass constant and prevent it running away and exploding.
>>> Disadvantages: several :)
>>>
>>> You have to keep feeding it or the output goes up until it explodes,
>>> so running out of fuel is inherently disastrous. You may be able to
>>> dump it overboard but whether you can accelerate away afterwards is
>>> questionable :)
>>> The simple engineering problems of fixing the thing inside the ship,
>>> also.
>>
>> Why inside? You need a large mass to get the temperature
>> down to a usable level, much larger than the mass of the
>> ship, so put the ship in orbit round the hole.
>>
>
> I can't see that working (even in sci-fi :) You have to attach the engines
> to the ship; if the ship's mass is small compared to the black hole and
> it's
> orbiting around it, firing the engines simply breaks the ship out of
> orbit.
> The black hole won't follow.

Yes it will, gravity works both ways, but you have to
make sure the exhaust misses the hole. Just keep
hovering in front of it.

> That's why I suggested some handwavium technology which will allow a small
> black hole to emit far too much energy; if you can push the energy back
> into
> the black hole you're okay. You could just let it escape but then the
> black
> hole rapidly loses mass, energy goes up, and you're sitting on a very big
> bomb.

A surrounding spherical mirror might work for optical
wavelengths but you aren't going to reflect the
majority of the output, gamma for example.

> I did do some calculations on this at one point (I draw an adult sci-fi
> comic strip and it's not been explicitly stated but this is how the
> starships are powered) and concluded that realistic energy outputs equate
> to unfeasibly massive black holes. It seems I didn't keep the calculations
> however :(

Shame, but you need more than the mass of the Sun to
create on in the first place so it's a bit limited
anyway. The trick would be to hitch a lift with a
passing primordial hole on a parabolic trajectory.

> Anyway, as I said, I don't see how you make the black hole stay with the
> ship, if the ship's mass is tiny compared to it. Having said that, I'm not
> sure how you'd do so anyway. Obviously you can't physically attach
> anything
> to the black hole. So you need either a magic artificial gravity field or
> something electromagnetic (my relativity's a bit blurry, but IIRC a
> sufficiently unfeasibly powerful magnetic field would curve spacetime...)

Just dangle a smaller mass in front of the hole
on a long piece of handwaving string, I hear
black holes like carrots.

George


Abdul Ahad

unread,
Apr 19, 2006, 4:20:30 PM4/19/06
to
George Dishman wrote:
> > Alpha Centauri is currently drifting across our night skies with a
> > total proper motion of 3.7 arc-seconds per year. In 50,000 years, it
> > will have moved 51.4 degrees. Are you saying I shoot the ark toward a
> > spot in the sky that's 51.4 degrees "in front" of the star?
>
> Of course, ever tried to shoot a moving target?

I was afraid there'd be some shooting involved... that's why I designed
the body of the craft from a titanium alloy... and made it a bullet
shape. LOL!

> >
> > With a self-sustaining ecosystem, there's a flourishing and vibrant
> > community living inside the ark! Check this movie trailer ;-) >>>
> >
> > http://www.astroscience.org/abdul-ahad/firstarktoalphacentauri/chapter3.htm
>
> Looks big, what is the internal surface area of
> the ark? Multiply by around 1.3kW/m^2 to get
> your power requirement. There's no sunlight so
> you need an alternative, fission I would guess.

There's a lot of uranium onboard, which works the lighting system
across the cylindrical interior. The ship hits a potential shortage of
that en-route though, which has the MMC's mining team step off the ark
onto a dark ice world - SNIP! (That's the sequel to my first novel).

Abdul Ahad

unread,
Apr 20, 2006, 3:06:44 AM4/20/06
to
Peter Lynch wrote:

>
> It might be the first ark to _leave_ for Alpha Centauri, but if it's going
> to take 50,000 years to get there (or wherever it end up) the advances in
> technology made on earth during the trip means that when they get there,
> they'll probably meet humans who stayed behind and developed a faster
> means of transport. Read Niven+Pournelle wrt. pupetteers leaving the galaxy.

That's an assumption on the part of some sci-fi writers. And one
assumption is as good as another :-)

> Probably not. Given the size of your craft, it can't get too close
> to a gravity well or the stresses imposed by the change in direction
> will tear it apart. We've seen what happens to comets when they get
> too close to a planet: they break up.

A comet is a flimsy aggregation of gas, dust, ice and rock. The
Centauri Princess is a tough, precision engineered projectile with a
solid metallic outside and *hard* asteroidal material of roughly 1-km
thickness(!) all the way round on the inside.

To compare the ark to a comet, in terms of stress withstanding ability
when moving at high speed through a planetary gravity field is simply
not right. It's like saying "Here's a feather, and here's a steel nail.
Let's blow some air onto the two and see which one drifts off first..."

Incidentally, on a slightly different topic, I'm curious as to how much
material we have lifted off the Earth since the start of the Space Age
back in the 1950s in total. Does anyone here know, if we added up every
single payload, from every single rocket launch, by every single
nation, on every single orbital, lunar, planetary, and interplanetary
mission... what the cumulative mass (in kg) would be to date?

The shuttle orbiters would be a special case I guess, as they come
back. The calculation will include Sputniks, Rangers, Mariners,
Eutelsats, Iridium, every single spy satellite, TV/telecom satellite,
Viking, Surveyors, Magellan, Vostok, Apollo, Soyuz/Salyut, Mir space
station, Skylab, the International Space Station, Apollo CSM, all the
geostationary satellites, Cassini-Huygens, Pioneers and Voyagers, etc
etc...

That number would no doubt still be a far cry from my 1.8 x 10^14 kg
ark mass!?

AA

George Dishman

unread,
Apr 22, 2006, 4:44:36 AM4/22/06
to

"Abdul Ahad" <abdul...@ntlworld.com> wrote in message
news:1145478030....@i39g2000cwa.googlegroups.com...

> George Dishman wrote:
>> > Alpha Centauri is currently drifting across our night skies with a
>> > total proper motion of 3.7 arc-seconds per year. In 50,000 years, it
>> > will have moved 51.4 degrees. Are you saying I shoot the ark toward a
>> > spot in the sky that's 51.4 degrees "in front" of the star?
>>
>> Of course, ever tried to shoot a moving target?
>
> I was afraid there'd be some shooting involved... that's why I designed
> the body of the craft from a titanium alloy... and made it a bullet
> shape. LOL!

:)

OK, point is yes, your trajectory would be an almost
straight line from launch to landing with no chance
of any deviation other than a tiny course correction
in flight to make sure the ark was gravitationally
captured at the destination.

>> > With a self-sustaining ecosystem, there's a flourishing and vibrant
>> > community living inside the ark! Check this movie trailer ;-) >>>
>> >
>> > http://www.astroscience.org/abdul-ahad/firstarktoalphacentauri/chapter3.htm
>>
>> Looks big, what is the internal surface area of
>> the ark? Multiply by around 1.3kW/m^2 to get
>> your power requirement. There's no sunlight so
>> you need an alternative, fission I would guess.
>
> There's a lot of uranium onboard, which works the lighting system
> across the cylindrical interior.

OK, it might be useful to calculate how much of
your mass that takes.

> The ship hits a potential shortage of
> that en-route though, which has the MMC's mining team step off the ark
> onto a dark ice world - SNIP! (That's the sequel to my first novel).

No way! The chances of your course passing within
a billion miles of anything bigger than a grain
of sand are ludicrously small and you can't change
course.

It reminds me of one of my favourite "B" movies, the
hero is piloting a "flying city" of billions of tons
between the stars intending to ram the bad guys base
when they are attacked by fighters. The line "Quick,
take evasive action!" breaks me up every time ;-)

Stepping on to anything at 28km/s makes a large bang,
you don't have fuel or engines to slow down or
accelerate again and you couldn't catch up afterwards.
Think how far the ark would travel at that speed while
you setup up run the mining operation.

Finally, the composition of KBOs and Oort cloud
material is probably all volatile material so
you wouldn't find any fissionable material there
anyway.

That suggestion is by far the most unrealistic you
have made so far. The whole basis of an ark approach
is that it is completely sealed and self-sufficient
for the duration of the journey. The inhabitants
have no option but to live within their energy
budget, something we here on Earth have to learn
over the next couple of centuries too. There would
be no reason to have craft on board or way to launch
anything unless they plan on abandoning the ark as
it flies through the Centauri system and then their
engine/fuel design would not allow the delta-v
needed for stopping and then catching up.

George


Abdul Ahad

unread,
Apr 22, 2006, 5:59:20 AM4/22/06
to
George Dishman wrote:

> >
> > There's a lot of uranium onboard, which works the lighting system
> > across the cylindrical interior.
>
> OK, it might be useful to calculate how much of
> your mass that takes.

I'd love to work it out, but only if we were serious about building
this thing!
I can't say I never tried, though... see this:

http://www.physicsforums.com/archive/index.php/t-86371.html

>
> > The ship hits a potential shortage of
> > that en-route though, which has the MMC's mining team step off the ark
> > onto a dark ice world - SNIP! (That's the sequel to my first novel).
>
> No way! The chances of your course passing within
> a billion miles of anything bigger than a grain
> of sand are ludicrously small and you can't change
> course.
>
> It reminds me of one of my favourite "B" movies, the
> hero is piloting a "flying city" of billions of tons
> between the stars intending to ram the bad guys base
> when they are attacked by fighters. The line "Quick,
> take evasive action!" breaks me up every time ;-)
>
> Stepping on to anything at 28km/s makes a large bang,
> you don't have fuel or engines to slow down or
> accelerate again and you couldn't catch up afterwards.
> Think how far the ark would travel at that speed while
> you setup up run the mining operation.

Yes, too right! The ark itself does not have to stop. There is a small
ship option, which is discussed in my first novel, and dramatised fully
in my second novel. You'll have to wait for that one... it's coming
soon. :)

>
> Finally, the composition of KBOs and Oort cloud
> material is probably all volatile material so
> you wouldn't find any fissionable material there
> anyway.

Well, we don't know that for a fact. Why is Sedna 'red'? Why is
Enceladus venting vapor clouds off into space? These are only recently
discovered perplexing facts that are hinting at internal and external
compositions that are at odds with our previous assumptions about these
icy objects. And why are we continually discovering all these
substantial sized far-off worlds at distances scores of times farther
out from the Sun than Pluto?

Sol's gravitational field stretches way past Alpha Centauri in its
reach, and it can trap and hold many weird and wonderful objects in
between.

There are trillions of comets and small icy planetoids floating around
Sol, according to the picture on this page and countless other articles
on the Oort cloud:

http://en.wikipedia.org/wiki/Oort_Cloud

>
> That suggestion is by far the most unrealistic you
> have made so far. The whole basis of an ark approach
> is that it is completely sealed and self-sufficient
> for the duration of the journey.

Yes, you are right of course. Mostly it is self-sufficient. But this
voyage is relying on the *possibility* of topping-up resources along
the way, *if* the need arises... and *if* those resources materialise
in front of the ship en-route. They could be real or they could be no
less illusive than just a mirage, which is what makes this part of the
voyage a leap of the imagination...

George Dishman

unread,
Apr 22, 2006, 8:16:11 AM4/22/06
to

"Abdul Ahad" <abdul...@ntlworld.com> wrote in message
news:1145699960.0...@i39g2000cwa.googlegroups.com...

> George Dishman wrote:
>
>> >
>> > There's a lot of uranium onboard, which works the lighting system
>> > across the cylindrical interior.
>>
>> OK, it might be useful to calculate how much of
>> your mass that takes.
>
> I'd love to work it out, but only if we were serious about building
> this thing!
> I can't say I never tried, though... see this:
>
> http://www.physicsforums.com/archive/index.php/t-86371.html

You say in that "the interior surface area of my ark
will be of approx. 600 square kilometres" or 6*10^8 m^2.
During the day it needs about 7*10^11 W to grow crops
or half that with a night cycle. Current power plants
produce up to about 1GW so you would need about 300 of
them though advances in technology would reduce that to
a reasonable number, say 30 producing 10GW each.

Each plant would use about 288 tonnes of fuel per
year so you need 430 millions tonnes of pre-processed
fuel rods for the flight, produced from 8000 billion
tonnes of uranium-rich ore.

http://www.wise-uranium.org/nfcm.html

Fast breeder technology would help but I don't have
the time to dig into that today.

>> > The ship hits a potential shortage of
>> > that en-route though, which has the MMC's mining team step off the ark
>> > onto a dark ice world - SNIP! (That's the sequel to my first novel).
>>
>> No way! The chances of your course passing within
>> a billion miles of anything bigger than a grain
>> of sand are ludicrously small and you can't change
>> course.
>>
>> It reminds me of one of my favourite "B" movies, the
>> hero is piloting a "flying city" of billions of tons
>> between the stars intending to ram the bad guys base
>> when they are attacked by fighters. The line "Quick,
>> take evasive action!" breaks me up every time ;-)
>>
>> Stepping on to anything at 28km/s makes a large bang,
>> you don't have fuel or engines to slow down or
>> accelerate again and you couldn't catch up afterwards.
>> Think how far the ark would travel at that speed while
>> you setup up run the mining operation.
>
> Yes, too right! The ark itself does not have to stop. There is a small
> ship option, which is discussed in my first novel, and dramatised fully
> in my second novel. You'll have to wait for that one... it's coming
> soon. :)

But your not talking of a small ship. If it is
to be of any use, it needs to haul thousands of
tone of Uranium containing ore back to the ark,
and you have all the same problems that meant
it was necessary to use slingshots to launch
the ark. You can't process in situ because you
need a huge amount of energy to refine the ore.

Your ship would burn the uranium from about
2 million tonnes of ore per year. The largest
craft launched to date from Earth is Cassini
which had a mass of 5.8 tonnes, of which 3.1
was thruster propellant and it had to use
multiple slingshots. 5.8 tonnes of uranium ore
would fuel the ark's power plants for 89 seconds.

>> Finally, the composition of KBOs and Oort cloud
>> material is probably all volatile material so
>> you wouldn't find any fissionable material there
>> anyway.
>
> Well, we don't know that for a fact. Why is Sedna 'red'?

Most likely the same reason as Titan is orange,
methane.

> Why is
> Enceladus venting vapor clouds off into space?

Because it is made of material that vaporises
easily, i.e. elements of low atomic weight.

> These are only recently
> discovered perplexing facts that are hinting at internal and external
> compositions that are at odds with our previous assumptions about these
> icy objects. And why are we continually discovering all these
> substantial sized far-off worlds at distances scores of times farther
> out from the Sun than Pluto?

Because we expect at least tens of thousands to be
out there but they are so small and far apart we
have only found a handful since Pluto even with
dedicated searches using powerful telescopes.

> Sol's gravitational field stretches way past Alpha Centauri in its
> reach, and it can trap and hold many weird and wonderful objects in
> between.

The gravitational influence extends to infinity in
theory but it becomes small in comparison to others
ong before that. Beyond the Oort cloud, disruption
from other stars means it's unlikely there are
objects with stable orbits beyond a third of the
distance to Alpha Centauri, even long period comets.

> There are trillions of comets and small icy planetoids floating around
> Sol, according to the picture on this page and countless other articles
> on the Oort cloud:
>
> http://en.wikipedia.org/wiki/Oort_Cloud

The key words being "small icy", no heavy metals.
Even on Earth uranium ore is scarce.

>> That suggestion is by far the most unrealistic you
>> have made so far. The whole basis of an ark approach
>> is that it is completely sealed and self-sufficient
>> for the duration of the journey.
>
> Yes, you are right of course. Mostly it is self-sufficient. But this
> voyage is relying on the *possibility* of topping-up resources along
> the way, *if* the need arises... and *if* those resources materialise
> in front of the ship en-route.

You cannot "rely" on something that has "if"s
and in this case those "if"s are virtually
impossible. No sane person is going to get on
such a vessel, let alone fund its construction.

> They could be real or they could be no
> less illusive than just a mirage, which is what makes this part of the
> voyage a leap of the imagination...

If you want any sort of credibility, the people
paying for the creation of the ship must believe
it can get there without impossible re-fuelling
in the plan. That part is totally nuts.

George


Abdul Ahad

unread,
Apr 22, 2006, 3:13:08 PM4/22/06
to
George Dishman wrote:
> You say in that "the interior surface area of my ark
> will be of approx. 600 square kilometres" or 6*10^8 m^2.
> During the day it needs about 7*10^11 W to grow crops
> or half that with a night cycle. Current power plants
> produce up to about 1GW so you would need about 300 of
> them though advances in technology would reduce that to
> a reasonable number, say 30 producing 10GW each.
>
> Each plant would use about 288 tonnes of fuel per
> year so you need 430 millions tonnes of pre-processed
> fuel rods for the flight, produced from 8000 billion
> tonnes of uranium-rich ore.
>

I haven't checked these yet, but I will take them "under advisement" :)
so thanks!

> >
> > Well, we don't know that for a fact. Why is Sedna 'red'?
>
> Most likely the same reason as Titan is orange,
> methane.

Titan's atmosphere has photochemical reactions from sunlight, which
creates the orange smog. Sedna is too far out from the Sun and too
small to possess an atmopshere. If it did have an atmosphere, its gases
will likely have frozen solid onto its surface, so I think the two are
radically different.

> in the plan. That part is totally nuts.

It makes for great fiction though :)

I did not invent the Oort cloud surrounding Sol nor one hypothetically
existing around Alpha Centauri and for them to be overlapping in the
middle. They're probably there for a reason. We cannot ignore these
clouds, as it would be perilous to do so, but we might be able to take
advantage of them...

Fred J. McCall

unread,
Apr 22, 2006, 3:46:04 PM4/22/06
to
Peter Lynch <pe...@freyr.local> wrote:

:On 2006-04-17, George Dishman <geo...@briar.demon.co.uk> wrote:
:>
:> With realistic engines you are into the billions of
:> megatons or worse. Consider an Orion style propulsion
:> using ten million of the biggest hydrogen bombs we could
:> produce as an over-optimistic minimum.
:>
:My understanding of orion engines is that they use atomic/nuclear
:detonations as the energy source to (explosively) heat air uunder
:the vehicle. It's the rapid expansion of the heated air that actually
:provides the thrust, not the detonation itself.
:On that basis, they wouldn't work outside the atmosphere.

Your understanding is incorrect.

--
"Ignorance is preferable to error, and he is less remote from the
truth who believes nothing than he who believes what is wrong."
-- Thomas Jefferson

George Dishman

unread,
Apr 22, 2006, 6:16:55 PM4/22/06
to

"Abdul Ahad" <abdul...@ntlworld.com> wrote in message
news:1145733188.6...@j33g2000cwa.googlegroups.com...

> George Dishman wrote:
>> You say in that "the interior surface area of my ark
>> will be of approx. 600 square kilometres" or 6*10^8 m^2.
>> During the day it needs about 7*10^11 W to grow crops
>> or half that with a night cycle. Current power plants
>> produce up to about 1GW so you would need about 300 of
>> them though advances in technology would reduce that to
>> a reasonable number, say 30 producing 10GW each.
>>
>> Each plant would use about 288 tonnes of fuel per
>> year so you need 430 millions tonnes of pre-processed
>> fuel rods for the flight, produced from 8000 billion
>> tonnes of uranium-rich ore.
>>
>
> I haven't checked these yet, but I will take them "under advisement" :)
> so thanks!

They are very rough but hopefully you can see
how to go about working out the numbers for
yourself with a bit of digging on the internet
for alternative technology.

>> > Well, we don't know that for a fact. Why is Sedna 'red'?
>>
>> Most likely the same reason as Titan is orange,
>> methane.
>
> Titan's atmosphere has photochemical reactions from sunlight, which
> creates the orange smog. Sedna is too far out from the Sun and too
> small to possess an atmopshere. If it did have an atmosphere, its gases
> will likely have frozen solid onto its surface, so I think the two are
> radically different.

It is still exposed to cosmic radiation which
produces similar photochemial reactions. Being
so far out, there's little to disturb the result
so there is probably a thin layer of hydrocarbon
products on the surface.

>> in the plan. That part is totally nuts.
>
> It makes for great fiction though :)

So do dragons but how realistic do you want it
to be?

> I did not invent the Oort cloud surrounding Sol nor one hypothetically
> existing around Alpha Centauri and for them to be overlapping in the
> middle. They're probably there for a reason. We cannot ignore these
> clouds, as it would be perilous to do so,

That' depends on your religious beliefs. I see no
reason to take that sort of attitude to them, they
are just aggregate that didn't get swept up when
our system formed.

> but we might be able to take
> advantage of them...

If you want to send a probe to Sedna, fine, but
your ark's trajectory has got to be aimed at the
Centauri system and it will be travelling too fast
to collect anything so as I said it isn't realistic
in any sense. If you had engines effective enough
to make it possible, you probably wouldn't need an
ark in the first place.

What is the point of taking the time to ensure you
are realistic in one part of the story and then
just ignoring the limitations and going to complete
fantasy in another part?

George


Alex Terrell

unread,
Apr 22, 2006, 6:25:38 PM4/22/06
to

Michael Rhino wrote:

>
> Propulsion possibilities:
> 1. Anti-matter
> 2. Hydrogen fusion
> 3. Fission
> 4. Solar Sail

Check out Magnetic Sail, devised by Zubrin. This is more effective than
a solar sail in slowing down craft coming into a solar system.

Peter Munn

unread,
Apr 23, 2006, 5:04:40 PM4/23/06
to
Leafing through uk.sci.astronomy, I read George Dishman's message of
Wed, 19 Apr 2006:

>> Alpha Centauri is currently drifting across our night skies with a
>> total proper motion of 3.7 arc-seconds per year. In 50,000 years, it
>> will have moved 51.4 degrees. Are you saying I shoot the ark toward a
>> spot in the sky that's 51.4 degrees "in front" of the star?
>
>Of course, ever tried to shoot a moving target?
>You launch on a line that should achieve a
>perfect rendezvous. That minimises the fuel you
>needto carry for the inevitable course corrections.

He'll also need to allow for Alpha Centauri approaching us at an angle
of about 45 degrees to head-on. I believe its current motion works out
at about 23 km/sec across our line of sight, and 22 km/sec towards us, a
total relative motion of about 32 km/sec. If this is correct, the ark
will have to travel less than 4 light years to get there in 50000 years'
time.

These values seem to bring A Cen close to 3 light years away in about
30000 years' time - aiming the ship here could shorten the voyage time.
However, it would require more delta-v on arrival as the ark would be
travelling at right angles to its destination star (in the Solar System
reference frame), whereas their relative directions would be more
similar in 50,000 years time (both receding from the Solar System).


[I've removed sci.physics - hopefully neither George nor Abdul are
reading this thread there - it would be helpful if posters indicate the
group they are reading.]
--
,---. __ E-mail replies: please simply reply
_./ \_.' without altering the subject line.
'..l.--''7 If this newsgroup message is over
|`---' two months old, or you meet other
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| Staffordshire UK @pearce-neptune... instead.

Sander Vesik

unread,
Apr 23, 2006, 7:10:40 PM4/23/06
to
George Dishman wrote:
> You say in that "the interior surface area of my ark
> will be of approx. 600 square kilometres" or 6*10^8 m^2.
> During the day it needs about 7*10^11 W to grow crops
> or half that with a night cycle. Current power plants

Well, you are allocating over 1.1KW per square meter, which I would say
is a dubious number. Earth receives that much from sunlight, and the
actual numbers needed for growing crops are much less. Especially if
you provide the right wavelengths. And what do you need the night cycle
lightning at half power for?

> produce up to about 1GW so you would need about 300 of
> them though advances in technology would reduce that to
> a reasonable number, say 30 producing 10GW each.
>
> Each plant would use about 288 tonnes of fuel per
> year so you need 430 millions tonnes of pre-processed
> fuel rods for the flight, produced from 8000 billion
> tonnes of uranium-rich ore.

It would be seriously odd if such a nuclear powered ark did not use a
thorium based power cycle and rather suggest that in such a case
abundant reserves of highly enriched uranium ore were somehow found.
You are also using 0% reprocessing which is extremely unlikely in a
closed environment.

The larger problem with expending such enormous amounts of energy over
a superextensive period of time, all of it derived from nuclear energy
is that it would make far more sense to use that enormous amount of
energy to propel the spacecraft along faster to to Alpha Centaury and
not spend it on ligtning the interior ;-)

> George

Peter Webb

unread,
Apr 24, 2006, 10:04:47 AM4/24/06
to
"Alex Terrell" <alext...@yahoo.com> wrote in message
news:1145744738.5...@e56g2000cwe.googlegroups.com...

I googled, but couldn't find a clear explanation. Got a link?


Jaxtraw

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Apr 24, 2006, 12:40:21 PM4/24/06
to

The back of my envelope suggests that, ignoring loses (heh) you can get the
same amount of energy from around 50,000 metric tonnes of matter/antimatter
fuel. If you can find a way to contain the 25,000 tonnes of anti-matter.
OTOH, if you're relying on the microscopic chance of encountering something
like an asteroid along the way, that can be used for fuel, that's only
25,000 tonnes of fuel you have to take with you to light the plants...

Ian

--


kha...@hotmail.com

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Apr 24, 2006, 12:51:17 PM4/24/06
to
I guess I don't see the problem here. The only thing really unusual
about the ark is its mass. It's traveling at a reasonable velocity. The
travel time seems long. A society stable over 2,000 generations seems
improbable unless something, which can survive most of the trip, keeps
things together. But I really don't see big issues with resource
consumption (aside from the energy source). Virtually all of it can be
recycled.

Something like an ion drive coupled with the power output from fission
plants that supposedly is meant to power agriculture in the place, ie,
on the order of 0.1 to 1 TW of generating capacity (according to George
Dishman's post earlier in this thread) seems to be ample for
decellerating such a thing over 10,000 or more years. I recommend
dropping most of the agriculture (at least till you no longer need to
decellerate!) in favor of acceleration.

IYou might need to wring a lot more than the 2500 m/s or so of ISP that
current ion drives can muster in order to keep reaction mass down. And
you'd have to be able to use reaction mass that is more common than
xenon or mercury.

Gravity based momentum transfer sounds very feasible. Even though we
don't yet know of planets in the system, we have three stars in that
system that we can use.

Finally, I think some care needs to be taken to explain why the ark is
so massive. It probably is more feasible to ship frozen eggs and sperm
than living humans. And more feasible to ship manufacturing equipment
and make a colony on site than it would be to ship the colony from Sol.

Having said that, it's not that much of a stretch to think that one of
these could get built. A gigantic ark could be the future's equivalent
of the Pyramids (perhaps some particularly wealthy group sees this as a
means to gain everlasting fame) except that a few thousand generations
might have to compensate for the ill-thought though luxurious plans of
the first group.


Karl Hallowell
kha...@hotmail.com

Peter Munn

unread,
Apr 24, 2006, 4:16:17 PM4/24/06
to
Leafing through uk.sci.astronomy, I read Abdul Ahad's message of Mon, 17
Apr 2006:

>The next part is where the possibility of gravity-assisted swing by's
>of bodies like Venus, Mars, or the Earth becomes feasible to propel it
>out of the *inner* solar system toward the *outer* solar system. The
>timescale for this is going to be into several *decades* I reckon,
>since we're using a myriad of low thrust, multiple impulses.

I've had time to have a good look at this now.

Using gravity assists to get out of the inner solar system to Jupiter is
a well-known procedure. I'd recommend researching how the Voyagers did
it, because that is more similar to your requirement. (In contrast,
Galileo needed to arrive at Jupiter as slowly as practical, because it
needed to stop there, and Cassini similarly needed to arrive at Saturn
as slowly as possible).

You are also correct to assert that you should be able to engineer your
ark not to be torn apart by such gravity assists - solid rock bodies of
20km diameter may have problems, but rock lacks tensile strength, and
presumably you will be using materials with high tensile strength.

The more novel requirement is leaving the solar system with the velocity
your scenario requires, and for that you will need a velocity of 25
km/sec after getting out of Jupiter's gravity well. As Jupiter moves
around its orbit at 13 km/sec, this equates to a velocity of 12km/sec
relative to Jupiter. (Fortunately for you, I believe Alpha Centauri
will be comparatively near the ecliptic in 50,000 years' time, otherwise
this figure would be significantly larger and your task more difficult
still.)

To leave at a relative velocity of 12km/sec, you need to approach at 12
km/sec, and that is not trivial - I don't believe there is a way using
gravity assists from Earth, Venus and Mercury for you to achieve this
(and Mars will hardly help at all).

I think the best bet is a gravity assist from Jupiter, sending your ark
hurtling towards Saturn faster than either Voyager did. Saturn is then
used to tip your ark's orbit out of the ecliptic, but back inward
towards Jupiter. (This style of manoeuvre has been used before, when
Jupiter was used to send the Ulysses probe out of the ecliptic to study
the Sun from far above its poles.)

I haven't done the detailed calculations for this, but it may be
possible to achieve another rendezvous with Jupiter one and a half
orbits later (if not, then two and a half orbits, or half a century,
later). This time your ark will be approaching Jupiter's orbit from the
North or South and you will have the 12km/sec relative approach speed
that you need.

This final assist will need to occur when Jupiter is in the part of its
orbit where its velocity is directed in the general direction of where
Alpha Centauri will be in 50,000 years' time. (George is correct to
point out you will lack the energy resource to make more than trivial
changes of course afterwards.) This needs a more thorough analysis, but
I would be very surprised if an appropriate alignment of Jupiter and
Saturn occurs every century.

HTH

Peter

Abdul Ahad

unread,
Apr 25, 2006, 5:59:38 AM4/25/06
to
Peter Munn wrote:
>
> I haven't done the detailed calculations for this, but it may be
> possible to achieve another rendezvous with Jupiter one and a half
> orbits later (if not, then two and a half orbits, or half a century,
> later). This time your ark will be approaching Jupiter's orbit from the
> North or South and you will have the 12km/sec relative approach speed
> that you need.
>
> This final assist will need to occur when Jupiter is in the part of its
> orbit where its velocity is directed in the general direction of where
> Alpha Centauri will be in 50,000 years' time.

Hi Peter,
Thanks very much for these pointers, really appreciated.
They should come in handy if someone actually decides to build this
thing (for real!) one day... who knows!?

Abdul

George Dishman

unread,
Apr 25, 2006, 2:50:07 PM4/25/06
to

"Sander Vesik" <san...@haldjas.folklore.ee> wrote in message
news:1145833840.1...@e56g2000cwe.googlegroups.com...

> George Dishman wrote:
>> You say in that "the interior surface area of my ark
>> will be of approx. 600 square kilometres" or 6*10^8 m^2.
>> During the day it needs about 7*10^11 W to grow crops
>> or half that with a night cycle. Current power plants
>
> Well, you are allocating over 1.1KW per square meter, which I would say
> is a dubious number. Earth receives that much from sunlight,

That's where my number comes from.

> and the
> actual numbers needed for growing crops are much less. Especially if
> you provide the right wavelengths.

True, though you are debating a factor that is probably
less than an order of magnitude and the type of reactor
used could make a much larger change.

> And what do you need the night cycle
> lightning at half power for?

I think you misunderstood, I meant half the ark lit,
half in darkness at any time.

>> produce up to about 1GW so you would need about 300 of
>> them though advances in technology would reduce that to
>> a reasonable number, say 30 producing 10GW each.
>>
>> Each plant would use about 288 tonnes of fuel per
>> year so you need 430 millions tonnes of pre-processed
>> fuel rods for the flight, produced from 8000 billion
>> tonnes of uranium-rich ore.
>
> It would be seriously odd if such a nuclear powered ark did not use a
> thorium based power cycle and rather suggest that in such a case
> abundant reserves of highly enriched uranium ore were somehow found.
> You are also using 0% reprocessing which is extremely unlikely in a
> closed environment.

Yes, I mentioned that briefly but didn't have any
figures available. You seem to know a bit about the
subject so could you revise the numbers?

> The larger problem with expending such enormous amounts of energy over
> a superextensive period of time, all of it derived from nuclear energy
> is that it would make far more sense to use that enormous amount of
> energy to propel the spacecraft along faster to to Alpha Centaury and
> not spend it on ligtning the interior ;-)

Unless I made some silly mistakes, I get a reduced
trip time of about 11k years with a peak speed of
about 840km/s assuming 300GW available for propulsion
and 1% of the ark used as reaction mass. That assumes
constant steady thrust with a mid-point turn round.
Again just toy numbers though.

George


Peter Munn

unread,
May 6, 2006, 5:40:18 PM5/6/06
to
Leafing through uk.sci.astronomy, I read Abdul Ahad's message of Tue, 25
Apr 2006:
>Peter Munn wrote:
[...]

>> This final assist will need to occur when Jupiter is in the part of its
>> orbit where its velocity is directed in the general direction of where
>> Alpha Centauri will be in 50,000 years' time.
>
>Thanks very much for these pointers, really appreciated.
>They should come in handy if someone actually decides to build this
>thing (for real!) one day... who knows!?

Thankyou, but I doubt the world needs my help to calculate gravity
assists - there are plenty of others more capable. And, my own best bet
is we will get to nearby star-systems by sending nano-robots to do the
colonising (and their journey velocity will be perhaps 5% light speed),
and our descendants will follow on somewhat later, but at the speed of
light, as codified DNA sequences.

However, I am prepared to offer help with your story-line for the heck
of it. For instance, the orbits you show on
http://www.astroscience.org/abdul-ahad/firstarktoalphacentauri/escape-
sequence.htm would take over 300 years to complete. (So "several
decades", as you put it, could be read as a significant underestimate.)
The final orbit which loops out beyond Neptune, to nearly 50 AU it
seems, would take about 125 years.

The Real Chris

unread,
May 9, 2006, 4:06:35 AM5/9/06
to
Hello,

Get a better starship engine, like mine! Go faster, get their sooner, go
further.

Chris.

"Peter Munn" <pmun...@pearce-neptune.demon.co.uk> wrote in message
news:DN7uYFAC...@pearce-neptune.demon.co.uk...

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