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# Space Poma

Using heliocentric momentum to pull spaceships into low earth orbit.
 (+1) [vote for, against]

The idea is to use a spaceship with large mass, the "Poma", in a highly elliptical orbit around the sun that passes close to the earth. The Poma orbits the sun with a path like one of those flowers drawn by those spirax toys. The spaceship has a tail 1000s km long (carbon nano tube or something more mundane). At the end of each "petal" the tail passes close to the Earth (e.g. within say 100km) and one of the XPrize planes then grabs the tail with some grabbing implement on the front. The tail is moving at similar speed to the plane at this time. Momentum is transferred from the poma to the plane. After the plane achieves a certain height it releases the tail, trades off height for speed, and uses rockets for orbital insertion. The poma continues on its way picking up speed using a gravitational sling shot from the sun for its next pass.

The main (possibly insurmountable) problem, it seems to me, is to get the poma in an orbit where the tail is moving slow enough to be caught by the plane, and the Poma is far enough away or moving at enough speed not to be captured by Earths gravity. The tail might have to pass over one of the poles (or near to) to avoid being hit by the Earth to avoid this. It might not be possible to build a strong enough, and long enough tail.

A related problem is getting good enough geographical precision to allow the plane to be in the right place at the right time.

Other problems include the need to refuel the poma periodically so that it can fine tune its orbit, and radiation proofing for the electronics e.g. what kind of life expectancy could you expect from the thing if it were feasible?

A variation of this could involve a Poma that orbits the Earth building up height using one of the fancier new propulsion systems (HAL effect, ION drive etc) and then comes swooping in on a close orbit every now and again. I can't see how you can get the tail close enough *and* slow enough this way though - the diference is that the orbits speed up as you get close to the focus, so if you're orbiting the earth you're speeding up as you get closer).

This is similar to the "Space Tram" idea but this has got a means of pulling things into space instead of the tram approach where there is nothing to stop the trams from pulling the orbiting satelites out of orbit.

 — blaize, Jun 27 2007

rotating space tether http://www.tethers.com/MXTethers2.html
the catch & release works this way [the great unknown, Jun 27 2007]

3 body orbit http://www.upscale....Body/ThreeBody.html
Something along these lines? (~M1=1.3xM2) [quantum_flux, Jul 01 2007]

 //gravitational sling shot from the sun for its next pass.//

You can't get a gravitational boost from the object you are orbiting around. Sorry.
 — Galbinus_Caeli, Jun 27 2007

 Hmmm true if you don't change your orbit and you only have a two body interaction. But if you modify the orbit each time using small amounts of power you can get a boost by getting an additional heave from the Earths gravity as well. If they can do it for Voyager they should be able to do it for this.

 I think the problem really comes down to whether you can find an orbit that is appropriate and a way to get the tail moving slow enough with the poma getting captured.

 Another problem is that going to the sun takes a long time so it's a while before you can reuse the thing. So it might be better to orbit close in around the moon instead.

 The aim is really to try to use low thrust, high Isp engines to help get into LEO somehow. So I envisioned the thing as being potentially under constant low power (though I didn't say so) if that's required.

A space bolus :) One end being much heavier than the other. It spins in orbit around the earth with the small end coming close. After each sling shot the bolus uses its low power/high efficiency motors over a period of weeks to get back into its original orbit. No idea if that's original.
 — blaize, Jun 27 2007

Doesn't a bolus have something to do with cows and cud chewing? I'm all for milking this one.
 — normzone, Jun 27 2007

sp bolas..
 — blaize, Jun 27 2007

Someone has thought of it already (when you spell it correctly - though I think that with a u is an acceptable variant or a plural? ).
 — blaize, Jun 27 2007

I had an idea similar to this a ways back using Haleys Comet and a bungee cord.
 — 2 fries shy of a happy meal, Jun 27 2007

This sounds like the idea of having a rotating tether in orbit where stuff is picked up and flung to a higher orbit. a series of these could grab in tagum, like on a trapese. but this orbis the earth, not the sun.
 — the great unknown, Jun 27 2007

 I've been thinking on this a while... As far as I can see the orbiting around the sun approach buys you nothing. Although you can cross the Earths orbit at whatever speed you like you don't gain anything unless:

 i) you're going very fast (fast enough to escape the Earths gravitational pull >> 6km/s) then you get caught by Earths gravity, or

 ii) you have a tether long enough so that the heavy end of the Poma sits outside L1 (so longer than from here to the moon).

 Both of which strike me as infeasible..

 Done some homework on the bolus approach. I believe the Gemini project did this to transfer orbits from one LEO to another. So it seems a reasonable candidate to compete with other low impulse/high efficiency engine approaches.

 The big problem that it would be good to solve is getting stuff into LEO in the first place (which currently costs something like \$US8000-20000/kg depending on what you take to get there and inflation on these dated figures). So the cost of building anything is enormous.

 Say you're using the bolus to get stuff into LEO. What length cable do you need? What G forces do you need to handle etc? (I'm not an engineer - take these figures and calculations with a grain of salt).

 Centripetal acceleration (a m/s^2) is a function of angular velocity (w in rad/s) and the radius of revolution (r in m)..

 [1] a = -w^2r

 Angular velocity (w) is a function of velocity (v in m/s) and radius (r)..

 [2] w = v/r

 Substitute [2] into [1] and solve for r..

 a = v^2/r

 so

 r = v^2/a

 Now we're going to make some assumptions about v and a to estimate r...

 Assume a=3g = 30m/s^s (approx). A typical dude can handle 5g pilots 9g. and assume v=3000m/s^2 which is pretty fast - rocket speed - faster than a XPlane then

 r = 3000^2/30 = 300000m = 300km

 Assume a stays the same but v=6000m/s^2, in which case the near earth end of the bolus would be near stationary, then

 r = 6000^2/30 = 1200000m = 1200km..

 These values compare favourably with the space elevator.. Pearsons model is 144000km long. Because the cable is under greater tension it'd have to be stronger but only 4 times stronger (for 3g plus earths g) so equiv in strength to that needed for a cable of length 4800km.

That just leaves the problem of rendezvous with the bolus and tether harmonics (both really trivial problems :)
 — blaize, Jul 01 2007

wiki for "space tether" or google for rotovator for more info.. Note they seem to think that there is some issue with rotovator tether strength..
 — blaize, Jul 01 2007

Not a space puma, then? Damn.
 — imaginality, Jul 01 2007

Exactly what I was about to say [imaginality]. I'm rather disappointed.
 — hidden truths, Jul 01 2007

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