when coming back from space, why do astronauts don’t just use a parachute all the way down?
In: Engineering
Cause they’re in orbit, which means really really fast. They’ll burn up in the atmosphere slowing down.
Because:
1) you can’t jump out in space and expect to fall to the earth. The spacecraft uses thrusters to get out of orbit.
2) the spacecraft can be steered so they can precisely drop where they want to go.
3) the spacecraft protects the astronauts.
if you deployed a parachute in space, it won’t work because there’s no (read: very little) air to cause drag.
skipping that, once you do start reaching the edge of the atmoshpere proper, you’re moving at orbital speeds. i’m sure you’ve seen spacecraft descending, and they basically become a fireball once they hit the atmosphere. this is extreme heating caused by a lot of drag, causing significant decceleration. if you deployed a parachute here… it’s going to burn up immediately. by using the heatshield this is effectively doing the same job as a parachute, it’s just below rather than above, and it’s built to take the extreme heat.
First, you need to brake – orbital speed is like permanently „falling and missing the ground“. By braking you manage to hit ground. That is something a parachute won’t manage in „empty“ space in a reasonable time. Up there is just not enough, almost none, air to slow you down.
Then you are still traveling at HIGH speeds. Take a look at the latest starship „landing“. That rocket was not fully orbital, yet it was so fast everything, that was not perfectly prepared, started burning and melting. (Not by friction but by compressing the air in front of it)
A human would not survive that, you need a capsule.
And finally, when you take a look at Baumgartners jump from space (stationary in a balloon, not in any orbit with lateral speed), you will see that there is still not enough air at that relatively low height to control your own rotation. He started spinning an there was quite some risk that he would lose consciousness because the spinning got too fast.
TLDR; They don’t work in space, they and the body would never survive the reentry heat, manual control of reentry would be quite hard.
Edit: *break – no idea what autocorrect did to me here!
If they were just going straight up and falling back down, they absolutely could just use a parachute.
The problem is that they are moving very fast sideways; like 20x the speed of a normal passenger jet. Fast enough that when they hit the atmosphere, it ionizes the air. It’s hot enough to melt practically any parachute.
So instead, most spacecraft use a heat shield and simply the spacecraft’s body to slow down most of the way. It’s very effective for 90% of the slowing down; slow enough deceleration that it doesn’t melt anything or put too high of loads on the spacecraft and astronauts. Then they’ll deploy parachutes for the rest of the way.
When you’re in orbit, you’re not just gracefully floating up there like a balloon. You’re shooting around at about 27000 km/h (17000mph). There’s not a parachute or cord anywhere that could handle those speeds.
You have to smack your ship/capsule into the atmosphere to slow yourself down first.
Imagine sticking your hand out a car window on the highway, you can feel the air pushing hard against your hand. Highway speed is about 110km/h, imagine doing that at 27,000km/h, which is the speed the ISS moves to maintain orbit. You’d burn up from the air friction.
If you travel straight up with something like a balloon you can basically (with a pressure suit) jump out and skydive with a parachute. An astronaut stays in space by traveling so insanely fast around the earth that they don’t immediately fall back into it. When you are traveling that fast and hit air you burn up from the intense friction. So when re-entering atmosphere from orbit you have to slow down and hide behind a heat shield.
Orbits are very fast. You don’t want to hit the ground at that speed, you’ll get smashed.
You also don’t want to hit the air at that speed. You’ll melt.
So we use heat shields to kinda skip into the atmosphere. Kind of like a stone, and on each skip we get a little slower and deeper into the atmosphere until you get to the very dense part right above the ground. Then you use a parachute to finish bleeding off that speed.
To get to space you need to drive straight up for 4 hours.
To stay in space you need to drive sideways at 8 km/s or 5 miles per second.
So, the problem isn’t the drop, it’s the going sideways at ridiculous speeds that will do you in.
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