could you use solar sail to make a ship hover around in the atomsphere of earth if the ship had powerfull lights
Magnum 360
in are atomsphere with solars sails as the means to do it. I would
start with saying that new carbon fiber mesh sails should be used. I
think these are 0.3 grams a square meter. And of course the more
imporant part of this whole thing is that you have powerfull lights to
push on the sails.
John F. Eldredge
It sounds like you are talking about having the lights that provide the
lift to the sails be mounted on the ship itself. This means that the
sail would both be having to lift the lights and be lifted by the lights.
This won't work, just as you can't pick yourself up and hover in mid-air
by pulling upwards on your belt.
--
John F. Eldredge -- jo...@jfeldredge.com
"Reserve your right to think, for even to think wrongly is better
than not to think at all." -- Hypatia of Alexandria
Mike Dworetsky
news:71e3b267-42da-4c0b...@d9g2000prh.googlegroups.com...
No, but nice try at inventing a perpetual motion machine.
If the ship is carrying the lights, then the emission of the light would
have an equal and opposite reaction on the ship (I'm not allowing for losses
on reflection). It wouldn't move. Lights that powerful would be useful as
"rockets" all by themselves.
And doing this in an atmosphere is a no-no. Real winds would be far more
powerful than any sort of light pressure effect.
Some sort of ground-based laser could make a ship hover, perhaps. I've
heard about experiments to do something like that.
--
Mike Dworetsky
(Remove pants sp*mbl*ck to reply)
Greg Goss
I've seen a proposal to push on a "pseudo-satellite" using radio
waves. Any such proposal would have to be outside the atmosphere. If
it can take the winds, it's too heavy for this idea.
Active components are easier. Propellor plane with solar cells
perhaps supplemented by microwave feed.
--
apart from one noisy guy up in Canada, no-one wants
a three-cylinder tissue box on bicycle tires.
Robert Martinu
> No, but nice try at inventing a perpetual motion machine.
>
> If the ship is carrying the lights, then the emission of the light would
> have an equal and opposite reaction on the ship (I'm not allowing for
> losses on reflection). It wouldn't move. Lights that powerful would be
> useful as "rockets" all by themselves.
No perpetual motion!
Think of reflection as a seperate absorbtion and reemission event, you
get twice the impulse of the photon emission from the light source.
The absorbtion would cancel the impulse from the lights.
But the self illuminated light sail would accelerate - with just the
same impulse a photon rocket would have on its own.
Your worse of none the less because you have to carry the sail...unless
you also plan to use a radiation source thats independent of the ship.
Robert
Jim Burns
> Magnum 360 <magnu...@rock.com> wrote:
>
>> so the Idea here is how hard would it be to make a ship hover around
>> in are atomsphere with solars sails as the means to do it. I would
>> start with saying that new carbon fiber mesh sails should be used. I
>> think these are 0.3 grams a square meter. And of course the more
>> imporant part of this whole thing is that you have powerfull lights to
>> push on the sails.
>
> I've seen a proposal to push on a "pseudo-satellite" using radio
> waves. Any such proposal would have to be outside the atmosphere. If
> it can take the winds, it's too heavy for this idea.
Once you're outside the atmosphere, combining a solar sail with
the more usual satellite dynamics will allow you to "hover"
over any spot on Earth, up to and including the poles.
This kind of device was named a "statite" and patented in 1993
by Dr. Robert L. Forward (who just passed away this September,
I'm sorry to learn).
http://en.wikipedia.org/wiki/Statite
However, the height of the statite would be far outside the
atmosphere, not even low Earth orbit, so this may not be what
the original poster had in mind.
A quick calculation, very optimistic, got me an acceleration
of 3.0 cm/sec^2 using the Sun's light at Earth's orbit
with the 0.3 g/m^2 figure mentioned above for the sail
and no payload. This compares to 980 cm/sec^2 from Earth's
gravitational attraction near the surface of the Earth.
Move farther away from the Earth and it's attraction will
decline as 1/r^2, while the force from the sunlight will
remain essentially unchanged. Somewhere out beyond 18 Earth radii,
the two forces will be comparable, and hovering looks
feasible.
If you use light from an installation on Earth instead
of the Sun, then I suppose the statite could hover lower,
but if it were low enough to be thought of as just outside
the atmosphere, the light supplied would have to be more
than 300 times as bright as the noonday sun at the statite,
so that, if it were 100 km straight up, the beam would have
to be that bright after spreading out while traveling
at least the 100 km of height. Very impressive.
> Active components are easier. Propellor plane with solar cells
> perhaps supplemented by microwave feed.
Or just a balloon? If all you want to do is hover, why not?
Jim Burns
Magnum 360
>
> >> so the Idea here is how hard would it be to make a ship hover around
> >> in are atomsphere with solars sails as the means to do it. I would
> >> start with saying that new carbon fiber mesh sails should be used. I
> >> think these are 0.3 grams a square meter. And of course the more
> >> imporant part of this whole thing is that you have powerfull lights to
> >> push on the sails.
>
> > I've seen a proposal to push on a "pseudo-satellite" using radio
> > waves. Any such proposal would have to be outside the atmosphere. If
> > it can take the winds, it's too heavy for this idea.
>
> Once you're outside the atmosphere, combining a solar sail with
> the more usual satellite dynamics will allow you to "hover"
> over any spot on Earth, up to and including the poles.
>
> This kind of device was named a "statite" and patented in 1993
> by Dr. Robert L. Forward (who just passed away this September,
Thank you very much for this comment. That was almost exactaly what I
was thinking about I was just not sure how to do the math on the
subject.
But now how about we make the subject a bit harder. Lets say I had a
20,000 ton warship that I wanted to hover with many masts of solar
sails in
the 1st couple miles of the atomsphere. So I guess the new question
would be how much sail area would be required and how many mega watts
of power
would it need for its lights to lift 20,000 ton warship and let it
hover.
Your caulation realy shows well what current solar sails can do.
Jim Burns
> Thank you very much for this comment. That was almost
> exactaly what I was thinking about I was just not sure
> how to do the math on the subject.
>
> But now how about we make the subject a bit harder.
> Lets say I had a 20,000 ton warship that I wanted to
> hover with many masts of solar sails in the 1st couple
> miles of the atomsphere. So I guess the new question
> would be how much sail area would be required and how
> many mega watts of power would it need for its lights
> to lift 20,000 ton warship and let it hover.
>
> Your caulation realy shows well what current solar sails
> can do.
It looks to me like my calculation shows what current
solar sails cannot do, but your mileage varies, apparently.
I'm not familiar with the solar sail material, but
my guess is that the 300 suns' worth of light necessary
to make this gossamer-thin material float near the
Earth's surface would also be enough to vaporize it.
This is not even taking into account the very optimistic
assumptions I was making, like 100% reflectivity.
Also, let me point out I was assuming the light
beams' source was down on the planet.
Your last question, about "floating" a warship on
light beams, is actually very easy.
(warship)*(Earth gravity) = (power)/(speed of light)
or
Mg = P/c
thus
P = 59,000 Terawatts = 59,000,000,000 Megawatts
The factor of the speed of light converts the energy
transferred by the super-beam to the momentum transferred.
I'm assuming that the light leaves the warship and does
not return -- in which case, I don't know what the
lightsails are for. There is another possibility,
that the warship is over a ginormous mirror that
reflects all that light back to the ship
and then from there to the ground again, and so on.
Maybe you could reduce the power needed by a factor
of 1/2, but that would be at the cost of carrying along
these lightsails -- extra mass, and delicate as all
get out, an odd design choice for a warship.
59,000 Terawatts is such an awe-inspiring number
that it deserves a little attention.
http://en.wikipedia.org/wiki/Orders_of_magnitude_(power)
-- 15 TW [Terawatt] - average total power consumption
of the human world in 2004
-- 75 TW - global net biomass production
via photosynthesis
-- 4 PW [1,000 Terawatts] - estimated total heat flux
transported by earth's atmosphere and oceans away
from the equator towards the poles.
-- 10 to 100 PW - estimated total power output of
a Type-I civilization on the Kardashev scale
(that is, a civilization that is able to harness
all of the power available on a single planet).
-- 59 PW - the power required to float your warship
-- 174 PW - total power received by the earth from the sun
So, maybe, someday, if we all are very, very fortunate,
if the only thing our civilization wanted to do was
float that warship, we would have enough power to
do so.
Jim Burns
Robert Martinu
> -- 59 PW - the power required to float your warship
> -- 174 PW - total power received by the earth from the sun
>
> So, maybe, someday, if we all are very, very fortunate,
> if the only thing our civilization wanted to do was
> float that warship, we would have enough power to
> do so.
But please do it on the other side of the planet.
(Or could you think of a different, sufficient radiation shield?)
Robert
Greg Goss
>> Active components are easier. Propellor plane with solar cells
>> perhaps supplemented by microwave feed.
>
>Or just a balloon? If all you want to do is hover, why not?
You need to hover at station. Balloons tend to wander away.
Greg Goss
Doing it on the other side of the planet? Inconstant Moon won a Hugo
for describing something like that.
Magnum 360
> -- 15 TW [Terawatt] - average total power consumption
> of the human world in 2004
> -- 75 TW - global net biomass production
> via photosynthesis
> -- 4 PW [1,000 Terawatts] - estimated total heat flux
> transported by earth's atmosphere and oceans away
> from the equator towards the poles.
> -- 10 to 100 PW - estimated total power output of
> a Type-I civilization on the Kardashev scale
> (that is, a civilization that is able to harness
> all of the power available on a single planet).
> -- 59 PW - the power required to float your warship
> -- 174 PW - total power received by the earth from the sun
>
> So, maybe, someday, if we all are very, very fortunate,
> if the only thing our civilization wanted to do was
> float that warship, we would have enough power to
> do so.
>
> Jim Burns
Well while I think you have proven your point fairly well I think your
math may be wrong. I am not super good at math or anything but those
figures still did not seems quite right to me thou I think they are
probly close enough anyway. Well I looked on the net a bit more to see
what math they use to caulate the solar sail with, and something that
was not overcomplacated like red shift and all that mess
anyway here is what I found
Using the following equations and values, you can calculate the force
of sunlight on and acceleration of the spacecraft:
•Force (F) = 2(P x A)/c
•Acceleration (a) = F/M
At 1 astronomical unit (AU), the power of sunlight is about 131 watts/
foot2 (1,400 watts/meter2). Our spacecraft weighs 2.2-lb (1-kg) and
has a sail area of 0.38 mi2 (1 km2 or 1-million m2), so:
•P (power) = 1,400 watts/m2
•A (area) = 1-million m2
•c (speed of light) = 3x108 m/s
•M (mass) = 1 kg
This works out to a force (F) of about 2 lb or 9 newtons (N). This
force leads to an acceleration (a) of about 29 ft/s 2 (9 m/s2),
slightly less than the acceleration due to Earth's gravity. In
comparison, a space-shuttle main engine can produce 367,000 lb (1.67-
million N) of force during liftoff and 462,000 lb (2.1-million N) of
thrust in a vacuum
here is the address of the site
http://science.howstuffworks.com/solarsail2.htm
I will have to do the math for the 20,000 ton ship latter but I don't
think it will come out much better, of course I could be wrong.
Mike Dworetsky
news:7lpgdaF...@mid.individual.net...
> Jim Burns <burn...@osu.edu> wrote:
>
>>> Active components are easier. Propellor plane with solar cells
>>> perhaps supplemented by microwave feed.
>>
>>Or just a balloon? If all you want to do is hover, why not?
>
> You need to hover at station. Balloons tend to wander away.
Add a motor, like a dirigible.
Mike Dworetsky
news:c9493$4af6ff61$557f6d00$92...@news.inode.at...
Indeed. I was thinking, I suppose, of proposals to power sailboats caught
in a dead calm, by carrying fans to blow air and fill the sails. Still, why
not just carry the "photon rockets" and avoid the sails and their weight?
Of course, this would have the unfortunate side effect of toasting any part
of the Earth you happened to be hovering over...after all, you could only
hover by shining the light downwards, whether directly or via one total
reflection off the light sail. Unless mass destruction was intended, this
sounds like an unfortunate side-effect of the proposal.
Mike Williams
>Some sort of ground-based laser could make a ship hover, perhaps. I've
>heard about experiments to do something like that.
There have been several laser propulsion experiments that were able to
lift objects, but they didn't work by using radiation pressure.
One experiment used a laser to heat the lower surface of the object,
causing it to ablate. The expansion of the resulting plasma created the
lift.
Leik Myrabo's Lightcraft has a parabolic mirror on the underside of the
vehicle. Pulses from a ground based laser are focussed by the mirror and
heat the air at the focus. The air expands violently, pushing the craft
upwards.
--
Mike Williams
Gentleman of Leisure
Dr J R Stockton
2009 13:59:55, Jim Burns <burn...@osu.edu> posted:
>
>This kind of device was named a "statite" and patented in 1993
>by Dr. Robert L. Forward (who just passed away this September,
>I'm sorry to learn).
>http://en.wikipedia.org/wiki/Statite
Your calendar is stuck; it's 2009! September 21, 2002 (2002-09-22)
--
(c) John Stockton, nr London, UK. ?@merlyn.demon.co.uk Turnpike v6.05 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.
James Burns
> In rec.arts.sf.science message <4AF7152B...@osu.edu>, Sun, 8 Nov
> 2009 13:59:55, Jim Burns <burn...@osu.edu> posted:
>
>>This kind of device was named a "statite" and patented in 1993
>>by Dr. Robert L. Forward (who just passed away this September,
>>I'm sorry to learn).
>>http://en.wikipedia.org/wiki/Statite
>
> Your calendar is stuck; it's 2009! September 21, 2002 (2002-09-22)
Ah HAH! That would explain a lot.
But where are all the flying cars?
Jim Burns
James Burns
> Well while I think you have proven your point fairly well I think your
> math may be wrong. I am not super good at math or anything but those
> figures still did not seems quite right to me thou I think they are
> probly close enough anyway. Well I looked on the net a bit more to see
> what math they use to caulate the solar sail with, and something that
> was not overcomplacated like red shift and all that mess
>
> anyway here is what I found
>
> Using the following equations and values, you can calculate the force
> of sunlight on and acceleration of the spacecraft:
> �Force (F) = 2(P x A)/c
> �Acceleration (a) = F/M
> At 1 astronomical unit (AU), the power of sunlight is about 131 watts/
> foot2 (1,400 watts/meter2). Our spacecraft weighs 2.2-lb (1-kg) and
> has a sail area of 0.38 mi2 (1 km2 or 1-million m2), so:
I've checked your math, and it looks fine,
but you need to keep the importance of the
mass-per-area of the lightsail material in mind.
The figure you gave earlier (and that I used) was 0.3 g/m^2,
while the figure you use for this calculation is 0.001 g/m^2.
This seems fine: you get about 300 times more acceleration,
because the fabric you use is about 300 times lighter.
> �P (power) = 1,400 watts/m2
> �A (area) = 1-million m2
> �c (speed of light) = 3x108 m/s
> �M (mass) = 1 kg
> This works out to a force (F) of about 2 lb or 9 newtons (N). This
> force leads to an acceleration (a) of about 29 ft/s 2 (9 m/s2),
> slightly less than the acceleration due to Earth's gravity. In
> comparison, a space-shuttle main engine can produce 367,000 lb (1.67-
> million N) of force during liftoff and 462,000 lb (2.1-million N) of
> thrust in a vacuum
>
> here is the address of the site
> http://science.howstuffworks.com/solarsail2.htm
>
> I will have to do the math for the 20,000 ton ship latter but I don't
> think it will come out much better, of course I could be wrong.
How reasonable are the figures 0.3 g/m^2 and 0.001 g/m^2
for the mass-per-area of the light sail material?
If we assume that the material has the same density as
graphite (2.09 to 2.23 g/cm^3) then we get
0.3 g/m^2 ==> 144 nm [1e-9 m]
0.001 g/m^2 ==> 0.48 nm
Compare to the wavelength of visible light (380 to 750 nm)
and the carbon-carbon bond length (0.12 to 0.154 nm).
The thicker material is less than a wavelength thick.
I don't know, but I wonder whether it becomes difficult
for it to be opaque at this thickness.
The thinner material looks like it's only a couple of
layers of atoms thick. Again, I have the concern about
opacity, only more so, of course.
Jim Burns
Magnum 360
> -- 15 TW [Terawatt] - average total power consumption
> of the human world in 2004
> -- 75 TW - global net biomass production
> via photosynthesis
> -- 4 PW [1,000 Terawatts] - estimated total heat flux
> transported by earth's atmosphere and oceans away
> from the equator towards the poles.
> -- 10 to 100 PW - estimated total power output of
> a Type-I civilization on the Kardashev scale
> (that is, a civilization that is able to harness
> all of the power available on a single planet).
> -- 59 PW - the power required to float your warship
> -- 174 PW - total power received by the earth from the sun
>
> So, maybe, someday, if we all are very, very fortunate,
> if the only thing our civilization wanted to do was
> float that warship, we would have enough power to
> do so.
>
> Jim Burns
Ok so using light is out of the question to achive such an effect, I
mean 59,000,000,000 megawatts of power is something no one could ever
put into a small ship. So I was still trying to figure out a way to
get this concept to work. I thought well if the photons could be more
powerfull than maybe one could get a effect. So I looked up Gamma
rays, here is the site I looked up on
http://www.britannica.com/EBchecked/topic/183228/electromagnetic-radiation/59180/Forms-of-electromagnetic-radiation.
Any way Gamma-ray photons are 10,000 times to 10,000,000 times more
powerfull than light photons meaning instead of 59,000,000,000
megawatts only 5900 megawatts would be needed, now thats still way to
much power but its much better and closer to some resable goal. Now I
know that there is lots of radiation involved here but maybe instead
of the sails reflecting the radiation it would absorb the radiation.
Anyway seems like a better way than light photons.
Magnum 360
> Magnum 360 wrote:
> > Well while I think you have proven your point fairly well I think your
> > math may be wrong. I am not super good at math or anything but those
> > figures still did not seems quite right to me thou I think they are
> > probly close enough anyway. Well I looked on the net a bit more to see
> > what math they use to caulate the solar sail with, and something that
> > was not overcomplacated like red shift and all that mess
>
> > anyway here is what I found
>
> > Using the following equations and values, you can calculate the force
> > of sunlight on and acceleration of the spacecraft:
> > •Acceleration (a) = F/M
> > At 1 astronomical unit (AU), the power of sunlight is about 131 watts/
> > foot2 (1,400 watts/meter2). Our spacecraft weighs 2.2-lb (1-kg) and
> > has a sail area of 0.38 mi2 (1 km2 or 1-million m2), so:
>
> I've checked your math, and it looks fine,
> but you need to keep the importance of the
> mass-per-area of the lightsail material in mind.
>
> The figure you gave earlier (and that I used) was 0.3 g/m^2,
> while the figure you use for this calculation is 0.001 g/m^2.
> This seems fine: you get about 300 times more acceleration,
> because the fabric you use is about 300 times lighter.
>
>
>
>
>
> > •A (area) = 1-million m2
> > •c (speed of light) = 3x108 m/s
> > •M (mass) = 1 kg
> > This works out to a force (F) of about 2 lb or 9 newtons (N). This
> > force leads to an acceleration (a) of about 29 ft/s 2 (9 m/s2),
> > slightly less than the acceleration due to Earth's gravity. In
> > comparison, a space-shuttle main engine can produce 367,000 lb (1.67-
> > million N) of force during liftoff and 462,000 lb (2.1-million N) of
> > thrust in a vacuum
>
> > here is the address of the site
> >http://science.howstuffworks.com/solarsail2.htm
>
> > I will have to do the math for the 20,000 ton ship latter but I don't
> > think it will come out much better, of course I could be wrong.
>
> How reasonable are the figures 0.3 g/m^2 and 0.001 g/m^2
> for the mass-per-area of the light sail material?
>
> If we assume that the material has the same density as
> graphite (2.09 to 2.23 g/cm^3) then we get
> 0.3 g/m^2 ==> 144 nm [1e-9 m]
> 0.001 g/m^2 ==> 0.48 nm
> Compare to the wavelength of visible light (380 to 750 nm)
> and the carbon-carbon bond length (0.12 to 0.154 nm).
>
> The thicker material is less than a wavelength thick.
> I don't know, but I wonder whether it becomes difficult
> for it to be opaque at this thickness.
>
> The thinner material looks like it's only a couple of
> layers of atoms thick. Again, I have the concern about
> opacity, only more so, of course.
>
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -
Well for one I was wrong about 0.3 grams per square meter it is 3
grams instead. For one the carbon fiber material is not a mirror its a
mesh of nano like fibers and is about as stif and thick as cardboard.
Anyway here is a link to that http://www.space.com/businesstechnology/technology/carbonsail_000302.html
Now the other carbon sail I know of is very hard to make and is
currently not realy buildable. It is made from carbon nanotube I think
it is about 0.1 gram a square meter, they say if they can grow the
tubes to a meter long they could make it about 0.08 or 0.01 maybe but
this is very unlikely.
here is a link to that site, and be warned the site seems to be
giltchy http://nextbigfuture.com/2008/02/large-sheets-of-carbon-nanotube.html
anway even with all that said it seems like light sails will always be
small probes and nothing more which is to bad because I realy wanted
to do a whole age of space sail
maybe they can use something other than light.
Patok
> On Nov 8, 6:36 pm, Jim Burns <burns...@osu.edu> wrote:
>> So, maybe, someday, if we all are very, very fortunate,
>> if the only thing our civilization wanted to do was
>> float that warship, we would have enough power to
>> do so.
>
> mean 59,000,000,000 megawatts of power is something no one could ever
> put into a small ship. So I was still trying to figure out a way to
> get this concept to work. I thought well if the photons could be more
> powerfull than maybe one could get a effect. So I looked up Gamma
> rays, here is the site I looked up on
> http://www.britannica.com/EBchecked/topic/183228/electromagnetic-radiation/59180/Forms-of-electromagnetic-radiation.
> Any way Gamma-ray photons are 10,000 times to 10,000,000 times more
> powerfull than light photons meaning instead of 59,000,000,000
> megawatts only 5900 megawatts would be needed, now thats still way to
> much power but its much better and closer to some resable goal. Now I
> know that there is lots of radiation involved here but maybe instead
> of the sails reflecting the radiation it would absorb the radiation.
> Anyway seems like a better way than light photons.
You are wrong on that. The formula was for any kind of
electromagnetic radiation - it will be exactly the same, no matter if
radio waves, light, x-rays or gamma. You need to generate the same
power, if you want the ship to hover. The problem is that photons of any
stripe have no mass, and you must rely on their pure energy to achieve
the effect.
The whole concept is patently ridiculous - you are trying to waste
tremendous amounts of power, to achieve something that actually should
consume no power. If the ship was perched on a ledge, it would stay in
place, and no work would be performed. Better try to think of a way of
constructing a nonce scaffold out of thin air, whenever the ship feels a
need to hover, rest on that scaffold, and then discard it when done.
Several megawatts should be enough for that, I think. :)
If you absolutely need to hover using propulsion, better use
something that has mass - like air, or failing that - alpha particles.
--
You'd be crazy to e-mail me with the crazy. But leave the div alone.
Robert Martinu
> Any way Gamma-ray photons are 10,000 times to 10,000,000 times more
> powerfull than light photons meaning instead of 59,000,000,000
> megawatts only 5900 megawatts would be needed,
Thats a misconception!
The individual photon holds more energy, so you need less of them.
But you also need equally more energy to create every single one of them.
> much power but its much better and closer to some resable goal. Now I
> know that there is lots of radiation involved here but maybe instead
> of the sails reflecting the radiation it would absorb the radiation.
With absorbtion you loose half of the overall impulse you could get from
a light sail. Also you now have the whole energy dumped into the sail,
which should turn into plasma really fast.
That only works if you use the belly of your ship as a kind of ablation
drive. Have the burnt off mass double as a kind of rocket engine exhaust.
> Anyway seems like a better way than light photons.
Building a mirror for light is easy.
But with x-ray or gamma you first need to find a material they don't
simply pass through. To catch most of them you use inches of lead or
meters of concrete, basically it doesn't matter that much what kind
material it is, only how much mass the rays have to go through counts.
Bad news for anything thats supposed to be lightweight.
Robert
Mike Dworetsky
news:5QoM6pEg...@econym.demon.co.uk...
Indeed, that was what I was recalling. Still, it works as a source of
launch power without carrying a lot of fuel. But it isn't a light-pressure
device, nosirree.
James Burns
> anway even with all that said it seems like
> light sails will always be small probes and
> nothing more which is to bad because I realy
> wanted to do a whole age of space sail
> maybe they can use something other than light.
!!!
But, this is another question entirely!
Light sails -- /solar sails/ -- work fine as a way
to get from planet to planet or station to station,
as long as you don't have to launch them or land them.
Depending on the particulars they could be a lot faster
than rockets, for example. That 3 cm/sec^2 isn't
a lot compared to gravity, but it's free once you
have your sails (burns no fuel) and it is on
/all the time/. Every 24 hours, your sails produce
another 2.6 km/sec. Compare to the delta-vee from
low Earth orbit to escape orbit, 7.9 km/sec, or
Earth's orbital velocity around the Sun, 29.8 km/sec.
And a rocket-type minimum-fuel orbit between planets,
a Hohmann transfer orbit, will take months to years.
You just need a different way to get from the surface
of a planet to "the docks" (in orbit) and back down
again. This really isn't all that different from
bringing ships into port in the Age of Sail.
No one expected them to go anywhere we wanted
/on land/.
My personal favorite method to get to and from orbit
is the space elevator, but it's not the only possibility.
http://en.wikipedia.org/wiki/Space_elevator
The same material science (almost) that would
make space elevators feasible would make solar
sails inevitable -- superstrong materials.
There are also very interesting geopolitical
issues involved. Who controls cheap passage
to and from a planet?
Jim Burns
Magnum 360
yeah this is true, and I love the space elevator Idea alot I hope they
can make it happen. I have always wonder how they would lay the cable
thou. Anyway the solar sails do out do current rockets but it seems
like you would need a huge sail to move any good amount of cargo. This
is where I realy see the difficultly, a 1000 ton or 907184.74kg ship
would need a sail or sails that was about 11km by 11km which is 121
million square meters, all ready if sail was a 3 gram a square meter,
it takes up 399.3 tons or 362238.87kg of the ships weight. I would
think you would need at least 300 tons more to support the sail that
leaves you with 300.7 tons which is bigger than an space ship we have
but is not realy a good cargo amout, I mean I guess it would move a
lot of people so in that way it would work good. So the sail would
have about 1129.33 newtons of thurst and acceleration of about
1 millimeter per sec. which means it would take it about 3 to 4 months
to get to mars when launched at the right time. So yeah still better
than rockets but it does not seem to be a what you could build a
empire off of for a sci fi universe. And it does not seem like
something that a Power house like the USA or china would ever try to
build either. But better than rocket for sure.
yeah I have been think of leaning toward something more sci fi now
like a anti-gravity sail, it would be made out of a material that
would repel gravity but only on its surface. Of course this would have
disadvatages of its own, like you would need to stay in a certian
distance for a planet to get a good amount of force. Anyway still
think of Ideas
Jim Burns
> yeah this is true, and I love the space elevator Idea alot I hope they
> can make it happen. I have always wonder how they would lay the cable
> thou. Anyway the solar sails do out do current rockets but it seems
> like you would need a huge sail to move any good amount of cargo. This
> is where I realy see the difficultly, a 1000 ton or 907184.74kg ship
> would need a sail or sails that was about 11km by 11km which is 121
> million square meters, all ready if sail was a 3 gram a square meter,
> it takes up 399.3 tons or 362238.87kg of the ships weight. I would
> think you would need at least 300 tons more to support the sail that
> leaves you with 300.7 tons which is bigger than an space ship we have
> but is not realy a good cargo amout, I mean I guess it would move a
> lot of people so in that way it would work good. So the sail would
> have about 1129.33 newtons of thurst and acceleration of about
> 1 millimeter per sec. which means it would take it about 3 to 4 months
> to get to mars when launched at the right time. So yeah still better
> than rockets but it does not seem to be a what you could build a
> empire off of for a sci fi universe. And it does not seem like
> something that a Power house like the USA or china would ever try to
> build either. But better than rocket for sure.
I don't know about the 3 or 4 month travel times being a deal-breaker.
The British held together a world empire with sailing ships.
And at that time the fastest way to get a message from from
one side of the world to the other was to write a letter and put
it on the fastest ship you had. That would not be true of
your interplanetary empire. For radio, the travel time is
minutes in the inner system and still only about 4 hours
out to Neptune. Not comfortable for a conversation, but
plenty fast enough to say, "You guys settle down out there,
or we're coming out there to settle you down."
I think using the upper ends of space elevators as slings to get
most of the planet-to-planet delta-vee and using solar sails
to correct the flight path is a good combination of the
strengths of each technology. I think you will still
have flight times of months, though.
>
> yeah I have been think of leaning toward something more sci fi now
> like a anti-gravity sail, it would be made out of a material that
> would repel gravity but only on its surface. Of course this would have
> disadvatages of its own, like you would need to stay in a certian
> distance for a planet to get a good amount of force. Anyway still
> think of Ideas
Sounds like Cavorite.
http://en.wikipedia.org/wiki/Cavorite
That's quite a bit further from science fictional realism
than solar sails with a mass-to-area ration of 0.001 g.m^2.
Everything we currently know about gravity suggests that
Cavorite is impossible.
You might consider negative mass.
http://en.wikipedia.org/wiki/Exotic_matter#Negative_mass
We don't think negative matter exists either, but
we do have some ideas about how it would behave,
if it did exist.
One thing you might be able to do is build an
"inertialess drive" by balancing the normal,
positive mass of your payload with an equal
amount of negative mass. This is something you could
potentially fly right down onto the surface of a planet.
However, another interesting feature of negative matter
is that it would be extremely dangerous to have around.
With normal matter, if you push it away, it moves away,
at least a little bit. With negative matter, if you
push it away, it moves toward you, so you can easily
get into a positive feedback situation, with essentially
unlimited quantities of energy flowing, large chunks of
planets or stars blasting into space, etc.
Jim Burns
Magnum 360
> That's quite a bit further from science fictional realism
> than solar sails with a mass-to-area ration of 0.001 g.m^2.
> Everything we currently know about gravity suggests that
> Cavorite is impossible.
>
> We don't think negative matter exists either, but
> we do have some ideas about how it would behave,
> if it did exist.
>
> One thing you might be able to do is build an
> "inertialess drive" by balancing the normal,
> positive mass of your payload with an equal
> amount of negative mass. This is something you could
> potentially fly right down onto the surface of a planet.
>
> However, another interesting feature of negative matter
> is that it would be extremely dangerous to have around.
> With normal matter, if you push it away, it moves away,
> at least a little bit. With negative matter, if you
> push it away, it moves toward you, so you can easily
> get into a positive feedback situation, with essentially
> unlimited quantities of energy flowing, large chunks of
> planets or stars blasting into space, etc.
>
>
> - Show quoted text -
Yeah your right 3 to 4 months is not big deal at all realy. But the
problem that I was looking at more but did not realy bring it out was
moving vast amounts of cargo, mean to some effect the the space
elevators woulds solve this problem some what. But trying to go past
mars for example would become a difficult. But at any rate I was going
to go some what sci fi anyway I was going to have faster than light
drives but I was going to have two kinds and both are limited in
different ways. The main one would be a drive that could go any speed
given some time it works by waves of energy doubling there speed one
after the other. For example 2, 4, 8, 16, 32, 64, 128, but you cannot
stay at one speed its kind of a chain reaction effect. So basicly it
does not work good for short distances but could allow you to go to
another galaxy if wanted. The other would work on some kind of natural
effect between planets and stars, kind of like slip string theory but
different realy, the limits would be the ships have to be small and
made very strong and could only do inaccuarte jumps between planets
and stars, so a ship like that could hold may a 2tons of cargo or so
and would need very high enery fuels.
But yeah even with such sci fi things as these I realy did not want a
Cavorite. What I was thinking for a anti-gravity sail was a nano or
just a fine material, I would like it to be some what cloth like. I
was thinking of basing it off some of those anti-gravity experimants,
I know most of these are proably fruad but none the less I still think
some of them have worked but just not been practial for anything,
inotherwords did not work good. I heard about a simiple method for a
ex nasa scientist were you that some copper wire and and make 128
turns until you get a plate and he said if you run current thour that
it would hover. Now I guess he could be lieing but he realy was a ex
nasa scientist. But I was thinking you could make a sail cloth based
on this effect. I have also heard that some of those plasmas that they
expriment with have a anti-gravity effect also of course I have no
Idea how true that is either.
I know thats still kind of Cavorite but I wanted something at least
semi based on fact.
David Mitchell
> But yeah even with such sci fi things as these I realy did not want a
> Cavorite. What I was thinking for a anti-gravity sail was a nano or just
> a fine material, I would like it to be some what cloth like. I was
> thinking of basing it off some of those anti-gravity experimants, I know
> most of these are proably fruad but none the less I still think some of
> them have worked but just not been practial for anything, inotherwords
> did not work good. I heard about a simiple method for a ex nasa
> scientist were you that some copper wire and and make 128 turns until
> you get a plate and he said if you run current thour that it would
> hover. Now I guess he could be lieing but he realy was a ex nasa
> scientist. But I was thinking you could make a sail cloth based on this
> effect. I have also heard that some of those plasmas that they expriment
> with have a anti-gravity effect also of course I have no Idea how true
> that is either.
Not at all. Do you _really_ think that something so momentous would have
gone unnoticed?
Anti-gravity opens up the whole solar system, and that's the least of it.
It would, frankly, be the biggest invention since fire.
And we'd know about it.
>
> I know thats still kind of Cavorite but I wanted something at least semi
> based on fact.
Try again.
While I'm being so snarky, if you're ever going to write anything for
public consumption, get a spelling checker.
--
=======================================================================
= David --- If you use Microsoft products, you will, inevitably, get
= Mitchell --- viruses, so please don't add me to your address book.
=======================================================================
Magnum 360
well your proably right, but this is a sci fi. Anyway if you could
make Gravity sails ,basicly sails that reflect gravity, what would
there performance be like. I would guess great in the atomsphere of
the planet but when you get to the moon and beyond I think they may
not perform much better than a solar sail. So with that said its hard
to say which is better in the space lets say between mars and earth,
at close distance of course.
David Mitchell
>>
>> While I'm being so snarky, if you're ever going to write anything for
>> public consumption, get a spelling checker.
>
> well your proably right, but this is a sci fi.
Yep, and the "sci" part should be a clue. It's certainly true that
there's room for speculation; but, unless you want most of the better
educated of your readers to throw the book against the wall, the science
should at least be plausible, IMO.
Obviously, there are some SF tropes (such as FTL), which are no longer
believed to be plausible; but which are so well embedded in fandom's
collective consciousness (and so useful) that most authors feel free to
make use of them.
However, "Gravity sails ,basicly sails that reflect gravity" do not fall
into this category, IMO.
Damien Valentine
> well your proably right, but this is a sci fi. Anyway if you could
> make Gravity sails ,basicly sails that reflect gravity, what would
> there performance be like.
Your best bet is to look over the link to "negative mass" that Jim
Burns gave you a few posts upstream. Any kind of engine that
functions by manipulating gravity, it'll have to incorporate that
somehow. Technically, something that would "reflect gravity" would
violate all kinds of physical laws, since gravitational waves can't be
blocked (see http://en.wikipedia.org/wiki/Anti-gravity#Gravity_shields).
In other words, it's impossible even in theory, never mind in practice.
alie...@gmail.com
> On Nov 15, 4:59 pm, Magnum 360 <magnus_2...@rock.com> wrote:
>
> > well your proably right, but this is a sci fi. Anyway if you could
> > make Gravity sails ,basicly sails that reflect gravity, what would
> > there performance be like.
>
> Your best bet is to look over the link to "negative mass" that Jim
> Burns gave you a few posts upstream. Any kind of engine that
> functions by manipulating gravity, it'll have to incorporate that
> somehow. Technically, something that would "reflect gravity" would
> violate all kinds of physical laws, since gravitational waves can't be
> In other words, it's impossible even in theory, never mind in practice.
How about the three-kinds-of-mass thing partly covered by the
Equivalence Principle?
http://en.wikipedia.org/wiki/Mass
There's inertial mass (that which resists being accelerated)),
active gravitational mass (that which makes gravity fields) and
passive gravitational mass (that which feels gravity).
So far they're experimentally identical, but if ever an experiment
shows an exception, perhaps there's some quantity shared equally among
all three that can be redistributed as desired. Hence you could
decrease inertial mass while increasing the other two, which makes
driving your ship easier with the complication that it's more
sensitive to gravity fields and causes a stronger-than-normal field.
If the reallocated whatever is directionally polarizable instead of
being isotropic that might help the navigational complications, even
if you don't get to choose the anisotropy.
It's not gravity shielding, it's not "antigravity", but it _is_
nearly Smith's Bergenholm.
It would also make predicting one's course... interesting.
Mark L. Fergerson
Erik Max Francis
> How about the three-kinds-of-mass thing partly covered by the
> Equivalence Principle?
>
> http://en.wikipedia.org/wiki/Mass
>
> There's inertial mass (that which resists being accelerated)),
> active gravitational mass (that which makes gravity fields) and
> passive gravitational mass (that which feels gravity).
>
> So far they're experimentally identical, but if ever an experiment
> shows an exception, perhaps there's some quantity shared equally among
> all three that can be redistributed as desired. Hence you could
> decrease inertial mass while increasing the other two, which makes
> driving your ship easier with the complication that it's more
> sensitive to gravity fields and causes a stronger-than-normal field.
> If the reallocated whatever is directionally polarizable instead of
> being isotropic that might help the navigational complications, even
> if you don't get to choose the anisotropy.
It's a bit trickier than this. As to the first and third, Newton took
them as being equal and there's no evidence so far that they're not. In
general relativity, they're even more closely tied -- as objects follow
the shortest path through spacetime, they're not reacting to any passive
mass, they're just travelling along geodesics. In other words, general
relativistically, there isn't even in principle _a way_ to separate the two.
The second type (active gravitational mass) gets tricky as well. Take
photons (which have zero mass). It's not clear how these should be
treated in Newtonian mechanics, as Newton certainly was unaware of the
idea of a massless particle. In general relativity, a photon still
travels along the shortest path through spacetime available to it,
although it's generally a different path from a massive particle since a
photon is constrained to travel at c locally; such paths are called null
geodesics as opposed to timelike geodesics.
But photons, since they have energy, _do_ generate gravitational fields
(in general relativity, represented with the energy-momentum tensor) --
but since they're always on the move, they generate a different type of
field than massive particles even if they had the same equivalent
energy. Newtonian mechanics really wouldn't know how to deal with a
particle with zero active and passive mass. You'd at least have to
ignore the issue by acknowledging you've already cancelled them in the
differential equation, never minding that they involved division by zero ...
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 18 N 121 57 W && AIM/Y!M/Skype erikmaxfrancis
The color is red / Under my shoe
-- Neneh Cherry
Magnum 360
> San Jose, CA, USA && 37 18 N 121 57 W && AIM/Y!M/Skype erikmaxfrancis
> The color is red / Under my shoe
>
> - Show quoted text -
I must say by the current theroies and laws that reflecting gravity
should not be possible, but we however do not know how it all works
for sure. And there have been experiments by people that suggest that
you can reflect gravity. Here is a small article on that subject
http://www.technologyreview.com/blog/arxiv/23198/
Anyway whats say you could realy reflect gravity, if you could how far
could you go on it. Basicly gravity is stronger closer to the planet
and weaker further away you are.
So I would think that a ship that had this technolgy could accelerate
faster at surface of the planet and slower acceleration further away
it was. So real question is how fast could you get mars or jupiter
with a ship like this.
Erik Max Francis
> I must say by the current theroies and laws that reflecting gravity
> should not be possible, but we however do not know how it all works
> for sure. And there have been experiments by people that suggest that
> you can reflect gravity. Here is a small article on that subject
> http://www.technologyreview.com/blog/arxiv/23198/
> Anyway whats say you could realy reflect gravity, if you could how far
> could you go on it. Basicly gravity is stronger closer to the planet
> and weaker further away you are.
Those are gravitational waves, not the effects of spacetime curvature
itself.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 18 N 121 57 W && AIM/Y!M/Skype erikmaxfrancis
Give me chastity, but not yet.
-- St. Augustine
Magnum 360
> Magnum 360 wrote:
> > I must say by the current theroies and laws that reflecting gravity
> > should not be possible, but we however do not know how it all works
> > for sure. And there have been experiments by people that suggest that
> > you can reflect gravity. Here is a small article on that subject
> >http://www.technologyreview.com/blog/arxiv/23198/
> > Anyway whats say you could realy reflect gravity, if you could how far
> > could you go on it. Basicly gravity is stronger closer to the planet
> > and weaker further away you are.
>
> Those are gravitational waves, not the effects of spacetime curvature
> itself.
>
> --
> San Jose, CA, USA && 37 18 N 121 57 W && AIM/Y!M/Skype erikmaxfrancis
> Give me chastity, but not yet.
> -- St. Augustine
But gravitational waves are fluctuation in spacetime curvature. And if
you go by the theory of Quantum gravity or I should say the many
theories under that, that gravity must be some sort of radiant force
much like light from the sun or the electromagnetic field of a planet
or a sun, those are realy good examples but there the closest thing I
can compare it to. At any rate it must mean that gravity is radiant
type force that causes spacetime curvature, or is the spacetime
curvature. So based on this you should be able to make something that
could reflect gravity.
Wayne Throop
: But gravitational waves are fluctuation in spacetime curvature. And
: if you go by the theory of Quantum gravity or I should say the many
: theories under that, that gravity must be some sort of radiant force
: much like light from the sun or the electromagnetic field of a planet
: or a sun, those are realy good examples but there the closest thing I
: can compare it to. At any rate it must mean that gravity is radiant
: type force that causes spacetime curvature, or is the spacetime
: curvature. So based on this you should be able to make something that
: could reflect gravity.
For values of "should" which imply "based on a series of misleading
analogies, ignoring any competing analogies, with the addition of
extemely brisk handwaving to obscure any fine points", sure.
Consider a mountain slope. Vibrations on the surface of the slope
imply variations *in* that slope, and these vibrations can be reflected.
However that hardly supports the conclusion that one "should" be
able to reflect the slope itself.
Wayne Throop thr...@sheol.org http://sheol.org/throopw
Erik Max Francis
> On Nov 21, 8:32 pm, Erik Max Francis <m...@alcyone.com> wrote:
>> Magnum 360 wrote:
>>> I must say by the current theroies and laws that reflecting gravity
>>> should not be possible, but we however do not know how it all works
>>> for sure. And there have been experiments by people that suggest that
>>> you can reflect gravity. Here is a small article on that subject
>>> http://www.technologyreview.com/blog/arxiv/23198/
>>> Anyway whats say you could realy reflect gravity, if you could how far
>>> could you go on it. Basicly gravity is stronger closer to the planet
>>> and weaker further away you are.
>> Those are gravitational waves, not the effects of spacetime curvature
>> itself.
>
> you go by the theory of Quantum gravity or I should say the many
We have no such theory as of yet. The paper _you cited_ takes a
semiclassical approach, where one can deal with quantum mechanical
behavior in curved spacetime such that the curvature is not so big that
you'd have to worry about quantum gravitational effects.
Either way, even a quick scan of the paper -- or just the blog entry --
makes it pretty clear they're talking about gravitational waves only and
nothing about gravity itself. No mention of "reflecting gravity" is
made. At all. Not even indirectly.
And this is the blog entry (and paper) _you cited_.
> ... that gravity must be some sort of radiant force
> much like light from the sun or the electromagnetic field of a planet
> or a sun, those are realy good examples but there the closest thing I
> can compare it to.
These would have nothing to do with a quantum mechanical nature of
gravity, so even the argument you're putting forth doesn't make the
slightest bit of sense.
> At any rate it must mean that gravity is radiant
> type force that causes spacetime curvature, or is the spacetime
> curvature. So based on this you should be able to make something that
> could reflect gravity.
No, for the reason I already pointed out. Spacetime curvature and waves
in spacetime are not the same thing. The paper in question has nothing
to do with "reflecting gravity."
You can engage in technobabble if you wish, but be expected to get
called on it. The paper has nothing to do with what you're talking about.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 18 N 121 57 W && AIM/Y!M/Skype erikmaxfrancis
The mind is not a vessel to be filled but a fire to be kindled.
-- Plutarch
Brian Davis
> But gravitational waves are fluctuation in spacetime curvature.
I can reflect water waves very easily - holding the entire ocean at an
angle is something very different.
--
Brian Davis