When space shuttles exit the atmosphere, they seem to do so traveling along a (relatively) straight line… that is to say, it seems they’re primarily going up. Yet, when returning into the earth’s atmosphere it’s so important that they come in at a given angle, and less than a degree’s difference.
Do shuttles exit the atmosphere at the same angle they have to enter it in? If not, why don’t they risk burning up on departure? You’re going through the same conditions regardless of which direction you’re going? Or, is it just a matter that you can’t re-enter with the same force and speed you exited because you just don’t have the booster rocket anymore in space… and with sufficient power you could come straight in?
No, shuttles enter the atmosphere at a different angle than they exit. They don’t risk burning up on exit because the shuttle is traveling much more slowly.
The shuttle accelerates out of the atmosphere as it burns fuel (gets lighter) but the atmosphere is getting thinner the higher it goes. However, on reentry it accelerates much faster due to gravity while the atmosphere is getting thicker ( increasing friction ). Controlling this acceleration and friction are the reasons while the reentry angle is critical.
The Shuttle seems to go straight up. In reality it inserts intself into a low earth orbit. To stay in low earth orbit, it needs to be travelling at about 17000mph. Any slower and it would reenter the atmosphere.
If the Shuttle was to come straight down, it would have to decelerate from 17000mph to a much lower speed, very quickly. To do this, it would have to have a few hundred tons of fuel lying around to burn its engines in the opposite direction.
The Shuttle doesn’t have a few hundred tons of spare fuel, it spent it all to get up there. It has enough fuel to fire retros that slow it down enough to reenter the atmostphere. I believe that the speed is reduced by only a couple of hundred mph.
That is why the Shuttle comes in shallow and fast.
If you had a fully-fueled, launch-ready space shuttle (or any other orbital rocket assembly) in orbit, I suppose you could land it by flying the liftoff in reverse. That’s in theory. In practice:
You’d be flying backwards. The rockets would be pointing in the direction of travel, and using their thrust to slow down. I doubt the existing shuttle would be stable in that configuration. (Think of a dart or badminton shuttlecock trying to fly with the pointy end in back.)
Controlability would be a huge issue. There are dry lakebeds that have miles of solid, flat ground, but coming back to an area the size of the launch pad would be damn tricky. And the shuttle, as it’s currently built, wouldn’t stand on its tail without the launch pad and various attachments to keep it upright.
The shuttle has solid-fuel rockets. Those can’t be controlled. You design them to operate a certain way (the cross-section of the fuel changes the burn rate), and once you light them, that’s what they’ll do. On liftoff, you have a certain acceptable variability, and it looks like the solids are still burning a little when they’re jetisoned. For landing, the tolerances are much less forgiving, and you’d need a clean shutdown.
Weight is the killer. The full shuttle stack weighs 4.5 million pounds at liftoff, and the empty orbiter is about 150 thousand. It takes several pounds of fuel to put one pound of anything into orbit. To get ready for this reverse descent, it would take the equivalent of dozens of shuttle launches to get the vehicle and all its fuel into orbit in the first place. Re-entry is different from launch in that you’re trying to lose kinetic energy, not gain it. You can do that by firing rockets against your direction of travel (requires lots of fuel and weight), or you can let friction and heat take it away essentially for free.
And a real rocket scientist could probably give fifty more reasons not to do it.
In principle a shuttle could land straight down if it had the fuel and control to “stand” on it’s rocket and land (like the lunar module did). But this would take essentially the same amount of fuel as it took to launch it* which the shuttle does not have. Recall that the shuttle is really launched by an external rocket that drops off. In fact the shuttle lands like a glider with essentially no fuel at all.
*Of course if the shuttle had this fuel it would take even more fuel to launch to carry the weight of the fuel into orbit.
I think this is an important point. You can go into orbit with rocket power because a minor discrepancy when you arrive at your destination is not a big deal. You’re aiming at outer space so it doesn’t matter if you’re a meter or two off; you just adjust your orbit. When your destination is a planet however, you have to be more in control. If you’re a little off-target then, you crash.
Just trying to head off a potential question here.
When you see a rocket launch, it starts by going straight up. But that’s just so it can’t get up where the air is thin, and then start doing the real work. Here’s how orbit is usually explained to physics students:
Imagine you’re on top of a mountain, at the edge of a cliff, and you have a cannonball. Drop that cannonball, and it will fall straight down until it hits the ground. Now imagine you have a huge slingshot. You load the cannonball into the slingshot, pull back, and let go. If you were standing to the side, you’d see the cannonball start out horizotally, and the pull of gravity would make it curve downward, and it would hit the ground, too. So now you have a cannon, and you aim it perfectly level and fire that cannonball. Gravity will pull on that, too, and it will hit the ground, but it will travel farther than either of the first two attempts. Gravity pulls the cannonball into a curved path, but the Earth is curved, too. If you could build a bigger cannon, that cannonball would go even farther, and might be over the horizon, out of sight, before it hit the ground. Build a big enough cannon, and fire your cannonball fast enough, and it will keep going over the horizon forever; gravity will keep it going in a circle around the Earth. That’s orbit.
When John Glenn became the first American in orbit, he took off, went around the Earth three times, and splashed down, in less than five hours. You may think the shuttle is going straight up, but that’s the easy part. Going fast enough that you don’t fall straight back down again is the hard part.
So the shuttle is not really shooting itself into space but actually shooting itself into orbit.
So if the shuttle did shoot in a straight line away from earth what would happen when the boosters ran out?
Would it be far enough away from earth’s gravitational pull that it would slowly float away from the earth…
or,
Earth’s gravitational pull would slowly pull the shuttle back down and into a freefall.
When the fuel tanks of a shuttle fall off, do those just burn up at re-entry? I guess I’ve always assumed that but now that I think of it, it seems a monumental waste
However unlike the early boosters, the main external fuel tank jettisoned at 97% of orbital speed does burn up since it cannot practically be returned for reuse. The remnants land in a remote section of the Indian Ocean.
The shuttle doesn’t have enough fuel for escape velocity, so it has to come back down eventually. If it just went straight up, I’m not sure how high it would get. A typical shuttle orbit is about 300 miles up. (Plus whatever energy it spent getting to orbital velocity.) Geostationary orbit is 22,300 miles. The moon is about 230,000 miles, and that’s clearly within the Earth’s gravitational influence, so the shuttle would have a long way to go.
There’s four parts to the shuttle. There’s the orbiter (the part with the wings that glides back to the ground), the external tank, and two solid rocket boosters.
The solids are jetisoned about 2 minutes after launch. They descend under parachutes and are recovered in the Atlantic, taken apart, and reused.
The external tank stays attached to the orbiter until about 8 minutes after launch. It burns up over the Indian Ocean and is not recovered, but there’s not much to it. The fuel and oxidizer it carries are fed through tubes to the engines on the orbiter. So the engines get reused and it’s just the tank that’s expendable.
(2), if it went straight up it would come down. This is how the private space plane does it. In order to stay up it would have to accelerate to orbit velocity as Newton had demostrated mathematically with his "cannonball"thought experiment.
You can think of it as a problem in energy management. The orbiter, when in orbit around the Earth, has a huge amount of kinetic energy. To be able to land on the Earth, it has to get rid of almost all of its kinetic energy. One way to do that is to convert the kinetic energy to heat at a controlled rate via atmospheric friction.
I can confirm that the shuttle pretty rapidly books off to the east after about 3 minutes in. I followed the red glow of the exhausts for at least 10-15 minutes one night in very clear weather, and only lost sight of them once they dropped “under” the horizon.