vacuum spheres for space "launching"
Forgetu2
Hi all. I've read and heard some weird ideas for the future of launching
items into orbit. I was thinking however, that if one were to make spheres
from suitable materials in space and send them back to earth with returning
craft, these could be useful.
Vacuum spheres could be used like helium balloons to provide lift to LEO.
Is this way out of there, or might this be possible? For example, I know
of one high atmosphere helium balloon that broke up and is still in orbit now.
Jon
randome
Forgetu2 wrote:
>
> Hi all. I've read and heard some weird ideas for the future of
> launching items into orbit. I was thinking however, that if one
> were to make spheres from suitable materials in space and send
> them back to earth with returning craft, these could be useful.
Vacuum bubbles have a bad habit of imploding- structures under
compression can buckle and fail. The biggest limitation of vacuum
balloons is that they cannot expand- so as the air density declines
at higher altitude, the volume cannot be increased to maintain lift.
> Vacuum spheres could be used like helium balloons to provide lift
>to LEO.
No, they could lift to some modest height in the atmosphere. Nearly
9 Km/s of delta-v would still be needed to reach orbit. No joy.
> Is this way out of there, or might this be possible? For example,
> I know of one high atmosphere helium balloon that broke up and is
> still in orbit now.
That is flatly wrong- any lifting balloon that breaks falls to earth
quickly, it does not magically accelerate into orbit. Some inflated
devices have been placed in orbit by the usual means aboard various
rocket launchers, and then inflated, but generally have short orbital
lifetimes because of their large area with small mass.
> Jon
(Floating high in the sky) != (being in orbit)
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Henry Spencer
In article <19970912014...@ladder01.news.aol.com>,
Forgetu2 <forg...@aol.com> wrote:
>Vacuum spheres could be used like helium balloons to provide lift to LEO.
Unfortunately, this isn't a useful approach. Vacuum provides only
slightly more lift than helium, and the walls have to be much thicker to
withstand the outside pressure. It's easier to just use a slightly larger
helium balloon.
(Lift is the weight of the displaced air, less the weight of the balloon
and its filling. Helium weighs less than 1/7 of the weight of the same
volume of air, so it's pretty close to vacuum already.)
--
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next year from Microsoft. -- Mark Weiser | he...@zoo.toronto.edu
Jason C Goodman
Forgetu2 wrote:
>
> Hi all. I've read and heard some weird ideas for the future of launching
> items into orbit. I was thinking however, that if one were to make spheres
> from suitable materials in space and send them back to earth with returning
> craft, these could be useful.
First, there's no reason to do this in space: we can make much better
vacuum
right here on Earth. The problem with vacuum balloons is structural:
all known
materials strong enough to hold a vacuum at sea level are far too heavy
to make
the whole structure lighter than air. There was some discussion in this
group earlier on using aerogels to make lighter-than-air structures;
check
DejaNews.
> Vacuum spheres could be used like helium balloons to provide lift to LEO.
Not a chance. A balloon exerts lift equal to the weight of the fluid it
displaces minus its mass. Suppose the balloon weighed absolutely
nothing.
At 100 km altitude, the density of the 'air' is roughly .004 grams per
cubic
meter. You'd need a balloon the size of a football field to lift a
single
kilogram... and of course any real balloon would weigh more than one
kilogram,
leaving nothing for payload.
Even if you could get the balloon to orbital altitude (100 km), it
wouldn't
be in orbit. You need to get it moving around the Earth at 8 kilometers
per
second to make centrifugal force equal gravity -- that's the definition
of
being in orbit.
> For example, I know
> of one high atmosphere helium balloon that broke up and is still in orbit now.
That's impossible for the reason I just gave. Can you be more specific
about
this statement?
--
Jason Goodman
Homepage (PGP Key, too) http://www.mit.edu/people/goodmanj/goodmanj.html
Remove AS_ when replying via email.
RBynum3965
forg...@aol.com wrote:
>Hi all. I've read and heard some weird ideas for the future of launching
>items into orbit. I was thinking however, that if one were to make spheres
>from suitable materials in space and send them back to earth with returning
>craft, these could be useful.
>
>Vacuum spheres could be used like helium balloons to provide lift to LEO.
>Is this way out of there, or might this be possible? For example, I know
>of one high atmosphere helium balloon that broke up and is still in orbit
>now.
>
>
Balloons work by displacing air. If the mass of the balloon, lifting gas
and payload is less than the mass of a similar volume of air the ballon
will rise. Vacuum balloons require a shell that can withstand the pressure
of the atmosphere in order to displace a volume of air. As of yet I havent
heard of any material that can enclose a vacuum in a practical size for
lifting a payload. Theoretically a solid stiff shell of almost anything can
be used if a large enough volume of air is replaced with vacuum.
I dont have the correct numbers at hand for the mass of air but lets use
10 kg per 1000 cu meters of volume. Thus a sphere weighing 10 kg displacing
1000 cu meters would be neutrally bouyant. A sphere massing 5 kg and
displacing 1000 cu meters would rise.
As the sphere rises the air it is displacing becomes thinner. So the
volume it displaces is not 10kg of air but less. The sphere ceases to rise
when the volume it displaces is 5 kg per 1000 cu meters.
Unless the material enclosing the vacuum is massless the vacuum balloon
will have a ceiling on how high it can climb based on the mass of the shell
and payload being lifted.
As for orbiting, this is a matter of delta v a different problem than just
attaining height. Balloons by themselves will not put a sattelite in orbit.
Robert Bynum
RBynum3965
Joseph J. Strout
In article <19970912014...@ladder01.news.aol.com>,
forg...@aol.com (Forgetu2) wrote:
>Vacuum spheres could be used like helium balloons to provide lift to LEO.
>Is this way out of there, or might this be possible?
I did a study on this concept in seventh grade. It turns out that vacuum
doesn't give you a LOT more lift than helium or hydrogen balloons. And in
fact, with any material I've ever heard of, it's much worse; you can
contain helium in a thin bag, but to contain a vacuum, you need rigid
airtight shell (read: very heavy.
And what's worse, it really doesn't gain you very much. You can get way up
to the top of the atmosphere, but altitude really isn't the problem; it's
velocity that's the problem. You've got to get to Mach 26 to reach orbit,
and a balloon bobbing in the stratosphere with velocity 0 still has a long
way to go. You avoid some costs from air resistance, but that's all.
>For example, I know
>of one high atmosphere helium balloon that broke up and is still in orbit now.
I really doubt this -- there must be some misunderstanding somewhere. The
helium molecules might be in orbit, but the balloon would fall as soon as
it broke open.
,------------------------------------------------------------------.
| Joseph J. Strout Department of Neuroscience, UCSD |
| jst...@ucsd.edu http://www-acs.ucsd.edu/~jstrout/ |
`------------------------------------------------------------------'
Simon Read
forg...@aol.com (Forgetu2) wrote:
>Vacuum spheres could be used like helium balloons to provide lift to LEO.
>of one high atmosphere helium balloon that broke up and is still in orbit now.
This is surprising to say the least. You don't just have to get
up there, you have to be travelling at 18,000 miles per hour or
something along those lines. The helium balloon shouldn't just
burst, it also has to leap sideways at 18,000 miles per hour.
Then it might have a chance of being in orbit.
Simon
Dr John Stockton
In article <19970914185...@ladder02.news.aol.com> of Sun, 14
Sep 1997 14:56:21 in sci.space.tech, RBynum3965 <rbynu...@aol.com>
wrote:
>I dont have the correct numbers at hand for the mass of air but lets use
>10 kg per 1000 cu meters of volume.
Easy enough to calculate - 80% N2 MW=2*14, 20% O2 MW=2*16, so the
average MW is 28.8; 1 gram-mole is 24 litres @ room temp & pressure;
hence 28.8/24 = 1.2 grams per litre = 1.2 kg per cubic metre.
Air is heavier than most people realise - have you ever seen people
moving a hot-air balloon and basket with the balloon empty?
--
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