Question for the aerospace gurus!!

[kerryin2004]

I have been watching these private companies send up aircraft and from what I understand to re-renter the atmosphere is a particularly tricky thing to do..


How are they able to so easily climb into space and then glide back down so easily??

[lil-petunia]

1. they need a drag queen

Someone or something to grab the whisps of air at the farthest reaches, and slow them down so they don't burn up.

Parachutes are great. Layered chutes, (open, drag, release the chute; open, drag, release the next chute) also work well, and anticipates the fact that one chute (or its lines) cannot last the stresses all the way to the ground. And failure is not an option.

But a good design doesn't need to stop the craft. It needs to slow down enough for normal airship designs to take over. Like airfoils, lifting surfaces. turning, yaw, pitch controls. As in glider control. Then, the air will slow you down on its own. Until you land safely.

[maine_raptor]

2. It's based on a badminton shuttlecock

Take one and throw it up, notice how it slows down on its way back down.

Burt Rutan based his design on that. The actual spacecraft is carried aloft by a carrier aircraft, then released, whereupon a solid fuel throttle-able rocket is ignited. By the way the fuel for that engine is made from old car tires, somewhat eco-friendly, eh?

Technically Space begins at 62 miles, so the carrier plane takes you to 8-10 miles high, and the rocket motor, pushing against less air get you higher. On the way back down the increasing air density and the shuttlecock design get you back down to the point where you can glide to a landing.

[kerryin2004]

3. From what I understand about re-entry...

Your window is very small, but the way I am hearing it these guys are going up and coming back down like an airplane, only with a shell that prevents burning up..Isn't it possible to somehow skip right off the earth if you miss your re-entry point(have I watched Apollo 13 too many times?), and how are they factoring for this?

[lil-petunia]

5. not high enough, nor fast enough, and not really approaching

Gaia from afar. 62 miles, although technically space, is still pretty damned close to a globe as big as this rock. Heck, Chicago's lake front is only 3/5 of that distance. Compare Chicago's size to a map of the US, and the scale takes on more reality.

[maine_raptor]

7. Re-entry does not have to be "hot"

What causes the heat on re-entry that everybody thinks is normal, is not due to entering the atmosphere per se; the heat is caused by the speed at which the spacecraft hits the air.

Orbital velocity is roughly 18,000 mph. If the shuttle, or any other orbital vehicle, could shed that speed, say slow down to 100 mph prior to entering the atmosphere, then there would be no real heating to worry about. Problem is that in order to shed that much energy, the shuttle would have to carry just about as much fuel has it did to et up there in the first place.

[Wilber_Stool]

4. I think you are missing an important point.

These are all sub-orbital flights. Re-entry is not a problem. Going into orbit is exponentially more difficult. (With all of these hyphens, I hope the grammer Nazis don't get me.)

[XNASA]

6. Ah yes. Orbital Mechanics.....fascinating subject.

I'm no rocket scientist, but I can give you a couple of hints.

Let's take the Shuttle for instance. As it climbs (ascent) it gets lighter and lighter because the fuel is being spent, and the air gets thinner and thinner. So by the time it gets to low earth orbit, about 175-225 miles up, it's travelling at about 17,500 MPH. It needs to be travelling that fast at that altitude to stay in orbit with no help.

Coming down (descent) is tricky, mostly because it's going so fast and needs to slow down. I don't think that coming down from low earth orbit is as critical as say, coming back from the Moon.

And the Orbiter (the airplane part of the Shuttle) doesn't exactly flutter back down. It's angle of approach is about 10 times as steep as a commercial jetliner, roughly 30 degrees. It flies like a brick with wings. Plus, the pilot only gets one chance. There is no way to reaccelerate once you're commited to landing.