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Reaching orbit cheaply through riding airstreams



 
 
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  #1  
Old July 31st 11, 06:33 PM posted to alt.sci.physics,sci.physics,sci.astro
Andrew Usher[_3_]
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Posts: 64
Default Reaching orbit cheaply through riding airstreams

dlzc wrote:

Actually that's about 1000 mph, even greater and about 6%
of the velocity needed.


But still only 0.3% of the energy required, and a single propensity
for final orbital momentum.


But rocket propellant needed for a single burn is (more than)
proportional to delta-v, so you really do save that much fuel.

The other problem is that rockets are pretty complicated
pieces of machinery and lots can go wrong that would
require significant infrastructure to fix before a launch. =A0You
would have to bring all that (people, equipment,
infrastructure, etc) =A0along with you to the platform.


Which could use an elevator.


An elevator that high would be some feat, tethered only to a
moving platform!

Such a 'platform', if ever built, would not be a balloon but a
real tower, which is practical to at least 100,000 ft if you can
spend enough money.


Fuller's "Cloud Nines" could be used, should such be better than a
fixed terrorist target.


Actually, a 100,000 foot tower would have to be so heavy at the
base that most terrorist bombs would hardly damage it, I think.
I looked up those 'cloud nines' - interesting, a kind of rigid
balloon. But they do need to be very large to work, and I'm not
sure how vulnerable they'd be to a single point of damage.

But such a structure (either tower or balloon) should only be the
starting point. Landings should not be attempted there.


If only for safety reasons, yes. So it is necessary to have some
kind of elevator to bring them back up.

Yes, this is probably the ideal way to get to space. Wasn't it
the first concept for the Space Shuttle, that was then abandoned
for developement cost reasons? The rocket stage should probably
also be reusable.


I still don't understand why we don't use a catapult, for maximum
efficiency (shy of a space elevator).


Obviously, the g-force would be too high for humans (and some
machines, too). But beyond that, a catapult can't go faster than
the speed of sound in the material it's made of, I believe,
which is not enough for orbit.

Andrew Usher


  #2  
Old August 1st 11, 07:45 PM posted to alt.sci.physics,sci.physics,sci.astro
Dr J R Stockton[_123_]
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Default Reaching orbit cheaply through riding airstreams

In sci.astro message , Sun,
31 Jul 2011 21:33:19, Andrew Usher posted:


Obviously, the g-force would be too high for humans (and some
machines, too). But beyond that, a catapult can't go faster than
the speed of sound in the material it's made of, I believe,
which is not enough for orbit.


One can make a two-stage catapult, though. One needs to worry, rather
more than usual, about where the first stage lands.

To get, on any body with unimportant rotation, to low-orbit speed from
the surface takes half a radian at one local gee of horizontal
acceleration. On Earth, that's about 3200 km. It reduces in proportion
to the increase of acceleration.

The rocket has the advantage that it does not need a structure that big,

--
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Web http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms and links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
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