On reentry, why doesnt a space vehicle slow down to avoid friction and burning?

Question

A space vehicle on reentry faces burning away like a meteor due to intense atmospheric friction because of which heat shields come into play. Now if it slowed down using onboard motors and leftover fuel, it could avoid atmospheric friction. Why does not this happen?

Answer 1

Well the heat generated would travel up the canals of the boosters and blow up the gas tank. if they cam in to slow they would have to be at a different reentry pitch. that would be a lower pitch and the shuttle would bounce off the atmospher.
I know beacuse my son took space camp for a summer school. They brought in a space shuttle simulator.

Answer 2

Well, first off, it reenters at that speed because it doesn't *have* any fuel left to slow down - just to manuever. In order to slow a space craft (say, the shuttle) down, you'd need to loft *two* external fuel tanks along with the ship, manuever around in orbit with a 17 million gallon bomb strapped to the underbelly, then burn it all so you could fall easier.

Although reentry is hot, dangerous, and hard on the astronauts, it's the preferred method to bleeding off speed when coming home. It would be very, very difficult to boost the fuel needed to slow down a reentering space craft enough to avoid external heating.

Answer 3

It would need a huge amount of fuel to slow down enough to avoid the frictional heating. The shuttle uses all the fuel in the external tank, plus the two solid rocket boosters, plus a bit of manoeuvring fuel to get into orbit, at a speed of 17,500mph (any slower and it would not orbit). In order to slow down enough to avoid atmospheric frictional heating it would need almost as much fuel again. Imagine trying to get that into orbit as well. It is far cheaper and more efficient to use the atmospheric friction to slow down.

Answer 4

I agree with ioerr. Imagine a single stage rocket sent into orbit. Theoretically, if it was refueled in orbit, it could descend from orbit and decelerate to 0 velocity just as it touched down -- just visualize the launch in reverse -- using the same amount of fuel each way.
Of course, since we don't have refueling rigs in orbit, it would have to carry the fuel up. That would increase the payload of the the launch vehicle by a factor of at least 10 (http://en.wikipedia.org/wiki/Single_stage_to_orbit).
So we'd need one enormous launch vehicle, or re-enter with heat shields the way we do now.

Answer 5

It would take a lot of fuel to slow them down that much.

The extra fuel would weigh a lot, and they would have to haul it up with them at takeoff in order to have it available for this manuver.

So the launch vehicle would in turn have burn an even greater amount of fuel to push all that extra weight into orbit.

They use the atmosphere as a brake in order to avoid all that. The launch vehicles are already ridiculously large (and expensive) as it is.

Answer 6

Basically because altitude for a space vehicle is a function of speed. In order to be in an orbit, the vehicle must be going a certain speed. There is no way to stop dead in orbit. An orbiting object will go into a higher orbit as its speed increases and into a lower orbit as it decreases. As the speed decreases and the altitude decreases, eventually the object will transition from space travel to atmospheric travel.

Space vehicles do fire retro rockets to slow down. This is how the vehicle begins to re-enter the atmosphere in the first place and leave orbit.

Answer 7

IOERR is correct...

In fact, it would take as much fuel to slow down for full vertical decent as it takes now to take off.

Then consider that you now have to carry all that fuel (full sized rocket) with you into orbit. Now the launch vehicle is 3 times as large as before... massive! Enough fuel to lift payload and earth return rocket fully fueled into space.... BIG!

Re-entry friction may seem like a hardship to you, but it a very fortunate situation for earthly space travel. Without an atmosphere as thick as ours we would have to carry this massive slow down fuel with us into space every trip... we use atmospheric friction as the breaks, and even though it heats up the spacecraft, we would be screwed without it.

For Apollo, we used powered decent because there is no atmosphere to speak of around the moon. Slowing down from atmospheric friction was not possible. Here we were lucky again because the moon's very low gravity made this possible without bringing millions of pounds of fuel to land and take off.

We will only be partially as lucky on mars... Enough atmosphere to slow down for landing, but also allot of gravity so that we will have to bring or have or make enough fuel to take off like we do here on earth (big big rocket).

Answer 8

"His was the first mathematical analysis of the evolution of Earth's Moon. He suggested that since the effect of the tides has been to slow the Earth's rotation and to cause the Moon to recede from the Earth, then by extrapolating back 4.5 billion years ago the Moon and the Earth would have been very close, with a day being less than five hours. Before this time the two bodies would actually have been one, until the Moon was torn away from the Earth by powerful solar tides that would have deformed the Earth every 2.5 hours."

Answer 9

It would first have to bring all that fuel and second imagine having this heavy lump of metal going slow thrue the air. It would fall down like a block of concrete wouldn't it

Answer 10

I think they use all that left over fuel just to get into the right angle so they don't burn up.