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AJ
2002-Nov-14, 10:55 PM
I was watching a History Channel show about Aircraft Carriers. Part of the show explained the catapults and how they accelerated the planes. This led me to think about a verticle catapult for Space Shuttle launches. Assuming that we could get the Shuttle, SRB and fuel up to a speed of 25 meters/second how much less fuel (% less or Kg less) would it need to carry to get into orbit? What about 50 meters/sec, 100 meters/sec? Not being familiar with the equations I was wondering if anyone would know?

Now thinking about accelerating the Shuttle how long with the catapult have to be to get it up to these speeds. I guess to determine that you would need to know the maximum number of g's astronauts can take before blacking out and the maximum number of g's the Shuttle and it's components could take. The smaller of those two values would give the max acceleration. Ok enough rambling… please reply if you can fill in any of the values/answers.

Thanks,
AJ

mallen
2002-Nov-15, 01:41 AM
In fact, there are proposed systems to put satellites into orbit using only such a catapult (actually, a linear-induction cannon). Putting delicate cargo (ie people) into space this way tends to be a problem due to the g forces.

However, using a catapult + a launch vehicle has its merits. I wonder, though if the size of the rockets makes it prohibitively difficult to build a system large enough to assist them.

Colt
2002-Nov-15, 03:14 AM
They are thinking of designing an electromagnetic rail, built on a slope that would help accelerate the next-generation shutttles. It will probably never happen with the current Orbiter. -Colt

calliarcale
2002-Nov-15, 07:05 PM
There are two basic problems to these kinds of ground-based assists.

1) Land. Your rail or catapult has to be VERY long. Otherwise you need to subject the payload to enormous G-forces, which is unacceptable if the payload happens to include crew! This may be acceptable for unmanned payloads, however, as they can be built to tolerate much higher G-loads.

2) Aim. You need some way to aim where the rail points, or you are constrained to a narrow range of orbital inclinations. (Traditional rockets veer off into the desired inclination within moments of clearing their launch towers.) This means either building quite a lot of rails to accomodate different orbital inclinations, or making some sort of complicated mechanism to rotate the rail into the desired inclination. Otherwise, I suppose you could load up the second stage with a lot more propellant to acheive a later plane shift, but then you're back to square one and might as well just stick with the old-fashioned rockets.

Colt
2002-Nov-15, 08:27 PM
They are developing (I think at least) new acceleration couches for the NG shuttle, you would basically sink into them as it acclerated. Think of a gelpad, but human sized. -Colt

Kaptain K
2002-Nov-17, 12:27 AM
I've said this several times in the last year, but for the benefit of new readers, I'll repeat it.

All of this was figured out by SF writers long before Sputnik.

Most of the fuel used to launch the shuttle is used just pushing the fuel straight up off the ground. To get around this, you need to leave the first stage fuel on the ground. So:

1) Use a catapult (railgun or linear induction motor) as a first stage.
A 4 kilometer run at 1g will get you to high subsonic speed (don't want to go supersonic on the ground /phpBB/images/smiles/icon_smile.gif ). With higher acceleration, the catapult can be propotionally shorter (i.e. for 2g's, the run will be less than 2 km). The big advantage is that all of the fuel for this first stage stays on the ground and no energy is needed to accelerate it. In fact, with solar power and capacitive storage, no fuel is needed at all for this stage.
2) Second stage, winged SCRamjet (or throttle-able rocket) to near space and near orbital speed. This can be either manned or remotely piloted.
3 Third stage to orbit. can be either winged (for re-entry i.e. crew shuttle) or not (for one way i.e. cargo transport).

This system has a much higher mass to orbit/total mass ratio than the current "boot-straps" approach.

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<font size=-1>[ This Message was edited by: Kaptain K on 2002-11-16 19:30 ]</font>