@S1-A.ARPA:host.MIT-MC.ARPA (05/08/85)
From: Tony Guzzi <tonyg%uconn.csnet@csnet-relay.arpa> This topic of "What do you do if you find yourself floating with nearly no velocity in a place where you can not reach anything?" This is a topic that I think few of us will ever have the possiblity of dealing with but it is an interesting "thought experiment" (as Albert Einstein calls them). In the past, a number of homemade experiments have been suggested here on SPACE (the paper airplane in zero-g for one), so here is another one. The topic could be called "Personal Propulsion Devices". The experiment would center around the idea of how to add velocity to a "stationary" astronaut. This first one may sound very silly, but I am wondering what the effect of giving a good, hard, long blow in the opposite direction will do. I do know that the direction is crucial and may just result in a summersaulting, stationary astronaut. The second involves a common, ordinary balloon. The balloon is blown up, placed near the astronauts center of gravity/mass and the air let out in the opposite direction the astronaut wants to go. The third is to use a pressurized container in place of the balloon (even though some people would consider balloon as pressurized containers). The containers could be re-filled using an ordinary bicycle tire pump. All these ideas center around the standard principle that all rockets work by so I think they are theorectically sound, but as for practicallity, well, I think only "field testing" can really tell. Tony Guzzi tonyg%uconn.csnet@csnet.arpa (If you are wondering why I mentioned using a balloon, a balloon can be easily carried around in a pocket. The pressurized container may be bothersome.)
@S1-A.ARPA:host.MIT-MC.ARPA (05/08/85)
From: Rick McGeer (on an aaa-60-s) <mcgeer%ucbkim@Berkeley>
Jerry Pournelle (POURNE@MIT-MC) has suggested ("What's it Like Out
There?" and "Spirals" <with Larry Niven>) that the most popular mode of
transportation in an O'Neill colony would be flying. Of course, in the
O'Neill colony there would be gravity...
I can't understand why swimming motions wouldn't work (and didn't,
according to recent postings). After all, motion in a fluid (air) should be
much the same as motion in another fluid (water), and I assure you that it's
possible for buoyant force to just match the gravitational force on a scuba
diver. Comments from anyone?
Rick.@S1-A.ARPA:host.MIT-MC.ARPA (05/08/85)
From: Martin D. Katz <katz@uci-icse> I understand that most attempts at throwing something fail to induce the desired motion because the astronaut doesn't know his center of mass. Baloons, etc. would have the same problem. One person suggested blowing. Because the mouth is near the end of the body, most of the energy would be converted into rotation unless the person could blow almost straight up. Throwing a ball would impart some momentum (mostly rotation). If the ball is caught on a single bounce, the momemtum would be almost cancelled. Catching the ball on a double bounce might double ones momentum (but, the chances of throwing from the center of mass and then catching to the center of mass are nearly nil). In general, I would say that if one wanted to throw something, it would be better to throw it upward. The best approach would probably be to swim -- one might be able to use a shirt as either a fin or a sail. Of course, it would be hard to actually get stuck for long -- the cabin air is kept in constant motion. The air flow would eventually move you toward an air intake.
ems@amdahl.UUCP (ems) (05/11/85)
> an ordinary bicycle tire pump. All these ideas center around the > standard principle that all rockets work by ...ically Er, one could, um, auh, ynow, use a, er liquid jet. After coffee one has at least a pint or so of 'reaction mass'. Just a thought ... and only in an emergency ... -- E. Michael Smith ...!{hplabs,ihnp4,amd,nsc}!amdahl!ems Tilapia Zilli is the way and the light. This is the obligatory disclaimer of everything.
jkw@lanl.ARPA (05/13/85)
> > an ordinary bicycle tire pump. All these ideas center around the > > standard principle that all rockets work by ...ically > > Er, one could, um, auh, ynow, use a, er liquid jet. After coffee > one has at least a pint or so of 'reaction mass'. Just a thought ... > and only in an emergency ... > -- > > E. Michael Smith ...!{hplabs,ihnp4,amd,nsc}!amdahl!ems > > Tilapia Zilli is the way and the light. > > This is the obligatory disclaimer of everything. ...Not to mention that the, er, uh, spigot or um, nozzle, is fairly near the center of gravity...
swift@reed.UUCP (Theodore Swift) (05/17/85)
Keywords:buoyancy, flatulance > I can't understand why swimming motions wouldn't work (and didn't, >according to recent postings). After all, motion in a fluid (air) should be >much the same as motion in another fluid (water), and I assure you that it's >possible for buoyant force to just match the gravitational force on a scuba >diver. Comments from anyone? > > Rick. Yeah, but I believe humans have a density close to that of water, not air (unless you consider the bean-fed solutions posted :-) ). I suppose you could have people strapped to big dirigibles, but, again, you have space problems (no pun intended...). Buoyant forces are at least partially dependant on the local force of gravity, so to get much buoyancy out of things, you'd need both a big dirigible and a reasonable gravitational field, as well as some atmosphere. Another problem someone else in the Terminal Ward here pointed out is though both air and water are fluids, air is easily compressible, so you will not be able to just "scale up" the effects of water motions to air. The best idea I've seen so far is forcibly throwing some mass away, like a shoe, thrown underhand, probably.