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Astronauts Pull Off Risky Spacewalk
dylanduck writes "A pair of NASA astronauts overcame an issue with a loose jet pack to make crucial repairs to the International Space Station, according to a story on New Scientist Space. No jet pack means not getting home if you inadvertently push yourself away from the space station and into space. That's a long goodbye that doesn't bear thinking about."
NASA haven't used jet packs since the Challenger disaster (because of the inherent risk). It's simply his life support systems.
I jumped in and actually read this article because I couldn't bear not knowing if they had actually used duck tape to strap the jetpack to the astronaut. The sad fact is that they did not and NASA insists that it was in no danger of actually coming free... just a couple latches on the sides had come loose and the pack was both tethered to the astronaut and relatched while the astronauts were still in space actively pursuing their mission.
Gravity Sucks
It really doesn't matter what way you push off - down or 'back' (oppostite orbital direction), you end up going lower & slower, up or 'forward', higher & faster. You're still screwed, either way, but it won't be quick. (Well, unless you pop the suit open. That's quick.)
Have you been touched by his noodly appendage?
All astronauts are tethered to the station on spacewalks, there was never any risk. This is just stupid sensationalism, as usual.
How we know is more important than what we know.
Right. This is why each participant in the EVA is attached to 2 thethers at all times. Either 50' or 85', depending on where they are and where they're going.
The backpack is a tritary backup in case both tethers are released.
The item they are referring to is the SAFER (Simplified Aid For EVA Rescue) backpack.
SAFER is not an integral part of the EMU, rather it is a derivative of the MMU which is exclusively for emergency (loss of tether) use.
SAFER can provide an adrift astronaut with about 10m/s Delta-V ie: If you're travelling away from the station at less than 10m/s you have a chance of getting back (although the closer you are to 10m/s the longer it takes to get back)
Ripping an new rectum in the fabric of spacetime.
Link
With that out of the way, let's take a look at orbital dynamics. You can't actually throw anything (or yourself) out of orbit--all you can do is throw an object, or move yourself, from one orbit to another. If you want to go to a higher orbit, you need to increase your speed in the direction you're traveling. If you want to go to a lower orbit, you need to decrease your speed. Just trying to thrust straight up or down won't work too well: Thrusting down, for instance, will lower you temporarily, but now you're going too fast to stay in that lower orbit, and you'll end up oscillating back above your original orbit. As science fiction author Larry Niven put it, "East takes you out, out takes you west, west takes you in, and in takes you east."
To get those baseballs to earth, you want to throw them back from the shuttle. Now they're traveling slower. The effect of this is to put them into an elliptical orbit, whose apogee--the point furthest from the center of the earth--is at the same height as the shuttle. If the orbit is elliptical enough, then its perigee--the point closest to the earth's center--will be closer than the surface of the earth, and the ball will collide with the earth after half an orbit or less. But if it doesn't hit the earth (and if we ignore atmospheric friction for the moment), it'll stay in that nice comfortable elliptical orbit indefinitely.
Now for the specific problem of astronauts throwing fastballs: The space station is at a height of about 390 km over the surface of the earth, for a total distance of 6,768 km from the center, and it's traveling at about 7,674 m/s. Our 93 MPH pitch translates to about 42 m/s, so the total speed of the ball is then about 7,632 m/s. Given that energy and angular momentum are conserved, it's straightforward (if a bit tedious) to calculate that, at perigee, the ball will be 6,623 km from the center of the earth, which is still a comfortable 245 km above the surface.
But this is all figured without the atmosphere. Won't friction from the topmost layers of the atmosphere cause the ball's orbit to decay, and eventually bring it down? Yes, but that would happen even without pitching the ball. If left on its own, the space station itself would eventually fall to earth, but they boost the orbit every so often to prevent that. In fact, that's why Mir was deliberately brought down: The Russians didn't want to keep boosting it any more, and they knew that eventually it would come down on its own.
Or rather tethers.
Whenever the Astronauts are on EVA, they keep themselves tethered to either the station, the shuttle or a hardpoint on a robotic arm.
The 'SAFER' backpack in question is strictly for emergency use should the worst happen and an astronaut go adrift. SAFER is normally only employed when there is no vehicle readily available to effect a rescue (ie the Shuttle is docked so it cannot persue a drifting astronaut in a hurry).
Ripping an new rectum in the fabric of spacetime.
To sum it up, though, the total distance from the center of the orbited body and the orbiting object is proportional to the square of the velocity. Small change in velocity = not-quite so small, but still pretty small, change in orbital distance.
Have you been touched by his noodly appendage?
In the prologue to his autobiography Apollo 13 (formerly titled "Lost Moon"), Jim Lovell writes:
So according to him the stories are false.
You can read the book online at Amazon (go to "Search inside", do a search for "Prologue", then click on the only result you get). The first three pages are also available at ImageShack: page 1, page 2, page 3.
Here's your answer (for what's it's worth, I work for NASA).
The shuttle airlock is in the cargo bay at the base of the docking system. It's literally the tunnel between the vehicles. In order to go out the shuttle airlock, the hatches must be closed between the vehicles and both crews have to go back to their "home" spacecraft (since otherwise they'd be isolated from their rides home). Obviously we don't want the entire shuttle crew hanging out all day in the orbiter when there is work to do on ISS. Additionally, the folks doing most of the robotic arm work in ISS are actually shuttle crew members (since they can be trained on flight specific tasks very close to the mission) and they need to be able to go between the vehicles.
Quest doesn't suffer from this problem since it's hanging off the side. Additionally, depressurizing the shuttle airlock sometime introduces some control system challenges because it loses it's rigidity somewhat and it's part of the structural backbone of the vehicle, so that's nice to avoid.
That being said, the capability remains to go out the shuttle airlock if need be.
Worst...sig...ever!
In theory you could move the space station, in practice you could not. The space station isn't really designed to be maneuvered in real time by the crew (or the ground, for that matter). Attitude maneuvers can be accomplished fairly quickly (less than an hour if you really had to), but translational maneuvers (which would be required to go grab an astronaut) take in excess of a day to put together and execute. Space station normally bores holes in the sky, so it that capability was never designed in (like it was on the orbiter or Soyuz). The orbiter can't undock quickly enough to go get them, either - at least not without compromising the safety of the rest of the crew and the vehicles themselves.
Which is the whole reason why SAFER was developed. Back in the shuttle-only days, going and grabbing the lost crew member on a double tether failure was a viable option, today it isn't.
Worst...sig...ever!
It doesn't work that way. Orbital mechanics often works counterintuitively. There are no figures in this article, but it states that a good push off from the ISS would send you perhaps 3 kilometers away from the ISS, inot an orbit that would intersect with the station one or twice per 90 minute orbit. The space suits are good for 7+ hours, so provided you didn't do it at the end of the EVA there would be plenty of time to pick you up.
If you slowly push away from the space station, you won't keep moving away from it in a straight line, because you and the space station are both orbiting the earth. In 46 minutes or so you may find yourself passing by it again.
:)
The parent actually has an interesting point but is simply bad at explaining himself, stop modding him down
1) The height of one's orbit is directly related to the speed - the higher the speed, the higher your orbit
2) If you push yourself away so that your earth-relative speed changes (e.g. forward or backward), you will get to a higher or lower orbit, and cannot get back to the station
3) However, if your earth-relative speed doesn't change (e.g. if you push yourself off perpendicularly), you will keep orbiting the Earth at the same height as before. So we'll have two orbits (ISS and you) with
a) same height and speed
b) slightly different angles
c) you were at the same point at some point in time
These orbits will keep intersecting in two points, the original point, and one right across the Earth, so it's actually possible to get back.
When men used to be men
The jet pack is great, but the astronauts don't put their lives entirely on them. Actually, what really make the EVA safe are two tethers, linking the astronauts to the ISS. The issue with the jet pack was that the danger of it becoming space debris, what could put the ISS in danger. Check it out at space.com or any really serious space news site.
I grew up in a (canadian) military family, and we always had a supply of that army-green duct tape handy. The old man referred to it as "gun tape" because it was often used for field repair of training weapon stocks (which were often in poor repair).