# Skydiving from Space?

02 December 2007

## Question

If an astronaut is stuck in space, would it be possible for them to project themselves towards Earth and re-enter the atmosphere with only a spacesuit? Could their spacesuit handle the re-entry temperatures?

We put this question to Dr Phil Rosenberg from the Open University, who worked on the Huygens probe:

"OK so our astronaut bails out of his rocket. What would happen then? Assuming he's in orbit around the Earth, actually not a lot! Both the astronaut and the rocket are in orbit around the Earth going at about 11km/s or 24,000m/h. They basically both orbit together. If the atmosphere there was a vacuum, there's no atmosphere at all then that would mean the astronaut would stay in orbit forever. It happens that there's a little bit of atmosphere up there. A tiny amount about a thousand, trillion, trillion times thinner atmosphere than there is at the surface of the Earth. That tiny amount of atmosphere will put a tiny bit of drag on the astronaut and as time went on that drag would slow the astronaut down. As he slowed down he would start to descend until eventually the atmosphere is thick enough that he could just fall to Earth.

Unfortunately, it's not great news for the astronaut because the atmosphere's so thin it would take him about a year to get slow enough that he would just fall to Earth. Because the astronaut's travelling so quickly, 24,000m/h, as he starts to slow down and go into the thicker atmosphere the friction caused by the drag will heat him up and burn him in the atmosphere. In order to avoid that essentially what you'd have to do is slow yourself down from that 24,000m/h to essentially 0. Even the shuttle can't do that at the moment. The shuttle has a special thermocoating on the underneath it to re-enter the atmosphere. As it enters the atmosphere, it's travelling at 17,000 m/h. Even the shuttle can't slow itself down enough. Having said that, the astronaut is a little bit lighter than the shuttle so a decent sized rocket engine will slow him down enough but unfortunately most astronauts aren't equipped with such devices.

Unfortunately for our stranded astronaut I think it's pretty close to impossible, or at least very difficult in our space suit that we have to survive re-entry. I think our astronaut's going to need some sort of escape pod or some sort of space vehicle to get back down form space to earth and survive the really difficult conditions that are involved in that." We also spoke to Cheryl Stearns, Pilot and record-breaking skydiver:

"You could do this if you're only going to 100-110,000 feet, that's a project that I'm working on right now. I'm not re-entering into the atmosphere. You can freefall from that altitude and you're going to get up to a speed of 900m/h but you will not feel that speed because the atmosphere is so thin. You'd only feel maybe 150m/h of actual wind resistance against your body. The outside layers of your suit would only be maybe 200 degrees temperature with the friction that you have in the thin air. So yes, that is possible to do, a parachute jump from that height, but definitely not possible to do a parachute jump or exiting out of a space craft. You'll never be able to enter back in."