Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!linus!philabs!seismo!hao!hplabs!sri-unix!katz.uci-750a@Rand-Relay From: katz.uci-750a%Rand-Relay@sri-unix.UUCP Newsgroups: net.space Subject: Re: rocket "belt" backup recovery Message-ID: <14435@sri-arpa.UUCP> Date: Thu, 8-Dec-83 12:44:36 EST Article-I.D.: sri-arpa.14435 Posted: Thu Dec 8 12:44:36 1983 Date-Received: Sun, 11-Dec-83 02:03:44 EST Lines: 62 From: Martin D. Katz ...!orca!warner: The idea of throwing objects (such as the jet pack itself) is a bit expensive to say the least. Probably not that effective in any case. As someone mentioned on the net, actually throwing something propel oneself would be a great feat without a lot of training. I would say that it is an "If all else fails" alternative. I really only suggested it because it takes advantage of what is already there. As to expense, in an emergency, the cost of the propulsion unit is trivial compared to the cost of the astronaut and suit. My original idea of a spring loaded gun shooting a magnet that is connected by a wire to the astronaut seems more direct. The use of a spring loaded gun is probably a better alternative. Shooting a magnet and wire might work except that I understand that there is little exposed ferromagnetic material on the shuttle (even with the cargo bay doors open), and I understand that an attempt is made to limit the carrying of magnets on the shuttle because some equipment is sensitive to them. Thus, there is little place for the magnet to stick. I also think that aiming might be a problem, and so several shots might be needed (thus, a spring loaded unit sounds like an advantage). Would there be a problem with the line tangling between shots? Maybe instead of a magnet, one could use a wad of very sticky putty. It might even be an epoxy precurser which would react with the surface of the tiles (much like some suit patches which have been proposed). As to tangling, maybe a wrapped fiber which is thin, yet stiff might help. Also is there any orbital mechanics that are being over looked? What would be the orbit of an astronaut that had projected himself radially outward from the shuttle? Would he eventually intersect the orbit of the shuttle at a later time? As I understand it, the orbit of an astronaut who projected himself radially outward from the shuttle would be an ellipse which (because the dV is low) is approximately that of the original orbit. The actual effect depends on the direction of the shove, the dV, the original orbit, and the position in the orbit. Since the dV (change in momentum) is small, in most cases, the astronaut's orbit would intersect the orbit of the shuttle. Unfortunately, because the orbits don't match, the shuttle might not be at the intersection point when the astronaut is. If the difference is small enough, the shuttle might have moved little enough relative to the intersection point that it will effectively still be there for the astronaut. A problem is if the astronaut matches orbit with a satellite in a slightly different orbit from the shuttle. In this case, he might fall far behind because if the satellite is in a higher orbit, its orbital period is larger. In a one orbit EVA, this could be several hundred meters. As to whether we forgot something in orbital mechanics of throwing or shooting things -- definitely. Actually, everything in orbit moves approximately in an ellipse with one focus at the center of the earth. A propulsion changes which ellipse one follows, and the motion is not straight line to the astronaut. In fact, I understand that the most efficient way to move into an orbit further out is to propel oneself tangentially to the current orbit (speeding up ones motion propels one into a higher orbit). This is why "retro rockets" work. These effects are not large for an EVA because the orbits are similar, but the astronaut will need training and might need some navigational help on a long EVA.