Date: Wed, 15 Jan 1992 16:05-EST From: space-tech-request@cs.cmu.edu To: "~/st/lists/stdigest" Subject: Space-tech Digest #93 Sender: mnr@DAISY.LEARNING.CS.CMU.EDU Contents: Space elevators: shielding with air???, avoiding collisions (22 msgs) ------------------------------------------------------------ From: henry@zoo.toronto.edu Date: Mon, 16 Dec 91 14:48:24 EST To: space-tech@cs.cmu.edu Subject: beanstalks with atmosphere :-) Wild idea of the week... Assume a classical beanstalk, with a permanent connection to the ground. Run an air hose up it, connected to spray rings at intervals. How much air would you have to pump to maintain a permanent thin atmosphere around it? It's clearly ridiculous to try to maintain an atmosphere that would be biologically useful, but incoming meteors burn up at *very* high altitude in very thin air. If you could maintain something that dense for some modest number of km around the beanstalk, this would make a very effective debris shield. It would also be a quick and clean way of sweeping up space junk, since the atmosphere column has a far larger cross-section than the beanstalk itself. If you were concerned primarily about the man-made debris hazard, it would suffice to do this up to, say, 1000km rather than all the way up. Apart from the question of whether the pumping rate is prohibitive, the one problem I see is that it makes big problems for legitimate satellites, which now have to avoid a much larger volume of space. (Implementation note: clearly you need booster pumps at regular intervals to avoid needing a ridiculous pressure at the ground end of the hose.) Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ To: space-tech@cs.cmu.edu Subject: Re: beanstalks with atmosphere :-) Reply-To: jerbil@ultra.com Date: Mon, 16 Dec 91 14:13:11 -0800 From: Joseph Beckenbach > Wild idea of the week... Assume a classical beanstalk, with a permanent > connection to the ground. Run an air hose up it, connected to spray rings > at intervals. I've heard of air showers, but this is ridiculous! :-) > (Implementation note: clearly you need booster pumps at regular intervals > to avoid needing a ridiculous pressure at the ground end of the hose.) An interesting addition would be controlled release of selected contaminants at some levels, such as ozone, and removal of selected other contaminants, such as dust and oxides of nitrogen. Perhaps the bottom pumpstation could do the bulk of the filtering.... Joseph Beckenbach Fnord: "Hey, Zorkk, remember that little aqueous planet we explored a couple hundred years back, the one with the flying fish and the dorky-looking tool-using bipeds?" Zorkk: "Yeah." Fnord: "I think they're losing it. They're trying to pump all their ground-level air out into space." Zorkk: "Huh. Well, that's bipeds for you." ------------------------------ To: w@ames.arc.nasa.gov From: mvp@hsv3.UUCP (Mike Van Pelt) Subject: Re: beanstalks with atmosphere :-) Date: 17 Dec 91 03:03:29 GMT In article <11889@hsv3.UUCP> ames!zoo.toronto.edu!henry@hsv3.UUCP writes: >=Fnord: "I think they're losing it. They're trying to pump all their >= ground-level air out into space." > >Definitely an issue, if the mass flow is large. As somebody or other >said in another connection: "The Sierra Club can be expected to object >to this." No doubt the Sierra Club (and all the other usual suspects) will object, regardless. However, all that air is moving at substantially less than orbital velocity (i.e., stationary, or nearly so) so it's all going to be coming down. Hmmm... if the mass flow is large, you're using up a good bit of your "export" capacity. It helps that you're not taking it all the way up to geosync. Even if it wasn't enough to stop the offending objects, it would turn them into nice, bright IR targets for terminal targeting! -- Mike Van Pelt Without objective evidence, "bell ringing" Headland Technology/Video 7 is indistinguishable from "crying wolf". ...ames!vsi1!hsv3!mvp -- Steve Emmerson mvp@hsv3.lsil.com ------------------------------ From: henry@zoo.toronto.edu Date: Mon, 16 Dec 91 19:14:25 EST To: space-tech@cs.cmu.edu Subject: Re: beanstalks with atmosphere :-) >Fnord: "I think they're losing it. They're trying to pump all their > ground-level air out into space." Definitely an issue, if the mass flow is large. As somebody or other said in another connection: "The Sierra Club can be expected to object to this." Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ From: henry@zoo.toronto.edu Date: Mon, 16 Dec 91 19:15:48 EST To: space-tech@cs.cmu.edu Subject: Re: beanstalks with atmosphere :-) >... As somebody or other said in another connection: "The Sierra Club >can be expected to object to this." Memory just clicked in... Dani Eder, talking about running one of his Kevlar catapults across the Grand Canyon. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: Mon, 16 Dec 91 19:38:04 EST From: dietz@cs.rochester.edu To: henry@zoo.toronto.edu Subject: Re: beanstalks with atmosphere :-) Cc: space-tech@cs.cmu.edu Henry proposed pumping air up a beanstalk in order to provide a temporary atmosphere to shield against micrometeorites. I think this idea can be fairly easily shot down. The effectiveness of gas for shielding goes as the column density seen by an incoming meteoroid. A fair approximation would be to consider gas more than a couple of cable diameters away to be useless (actually, the integral of gas density with distance from the cable diverges logarithmically, at least until other effects remove the gas, but never mind). Gas released into space will expand at a speed proportional to the speed of sound in the gas. Even in a very cold gas, however, this rate will be considerable, say 100 m/s. For reasonable sized cables, then, the gas escapes in much less than a second. Unless the time it takes for a load of replacement gas to reach the release points is less than the active time of that gas, the "dead load" of gas being transported up the cable will be greater than the effective mass of shielding gas. It would be more effective, then, to simply use stationary meteoroid shields. To be most effective, these shields should be close to the cable. Here's another idea.... I've read that the military has been looking at electromagnetic armor for tanks. In this concept, a capacitor is hooked into the armor. When a (shaped charge?) hits, the capacitor discharges, and the heating/magnetic fields divert/disrupt the plasma jet. Could a similar concept work for meteoroid protection? Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Mon, 16 Dec 1991 19:01:54 -0600 From: Fraering Philip G To: henry@zoo.toronto.edu, space-tech@cs.cmu.edu Subject: Re: beanstalks with atmosphere :-) Actually, I figure it's a conspiracy between Tibet and the former Incan Empire to reducd atmospheric pressure to the point where they will have a military advantage over the rest of us. More seriously, don't pump air, pump water. It's a nice tie-in to any rise in sea level we may have due to the Greenhouse effect or infalling mini-comets :-) (You should have known it was coming)... Surround the Beanstalk with a cloud of water snow, falling back to Earth... Hey, this should also cool the area near the beanstalk. Another counter to the Greenhouse effect! Greenpeace REALLY isn't going to like this. :-) Phil ------------------------------ Date: Tue, 17 Dec 91 00:37:34 EST From: John Roberts Disclaimer: Opinions expressed are those of the sender and do not reflect NIST policy or agreement. To: space-tech@cs.cmu.edu Subject: Meteroid shield >Date: Mon, 16 Dec 91 19:38:04 EST >From: dietz@cs.rochester.edu >To: henry@zoo.toronto.edu >Subject: Re: beanstalks with atmosphere :-) >Cc: space-tech@cs.cmu.edu >Here's another idea.... >I've read that the military has been looking at electromagnetic >armor for tanks. In this concept, a capacitor is hooked into >the armor. When a (shaped charge?) hits, the capacitor discharges, >and the heating/magnetic fields divert/disrupt the plasma jet. >Could a similar concept work for meteoroid protection? > Paul F. Dietz > dietz@cs.rochester.edu Do meteoroids act like shaped charges? The key factor of a shaped charge is that it creates a very precisely calculated wavefront (jet) which can pierce a much greater thickness of armor than a random explosion of the same magnitude would be expected to. A relatively minor force, correctly applied, can disrupt this wavefront. There are operational tanks in Israel (and perhaps elsewhere) that are covered with plates of explosive to defeat shaped charges. The proposed meteoroid shield made of a thin plate with a gap then a thicker plate might be considered approximately equivalent. John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ Date: Tue, 17 Dec 91 08:52:50 -0500 From: "Allen W. Sherzer" To: henry@zoo.toronto.edu, space-tech@CS.CMU.EDU Subject: Re: beanstalks with atmosphere :-) >Wild idea of the week... Assume a classical beanstalk, with a permanent >connection to the ground. Run an air hose up it, connected to spray rings >at intervals. How much air would you have to pump to maintain a permanent >thin atmosphere around it? How about a series of balloons roughly four km across and ten km long? Start them at 200 km to 1000 km to protect from man made junk. That way you need not constantly replenish the supply, just repair holes at your leisure. If the balloons are filled with something light (like He) they might even support themselves in the lower and denser parts of the atmosphere. Allen ------------------------------ Reply-To: davidsen@crdos1.crd.ge.com Date: Tue, 17 Dec 91 09:43:41 EST X-Mailer: Mail User's Shell (6.5 4/17/89) From: davidsen@crdos1.crd.ge.com To: space-tech@cs.cmu.edu Subject: Re: beanstalks with atmosphere :-) > (Implementation note: clearly you need booster pumps at regular intervals > to avoid needing a ridiculous pressure at the ground end of the hose.) I'm not sure I follow this. Surface level is only <15 psia, a fairly modest pressure of a few hundred psi should pump to the top of a reasonable structure. I'm just not sure what volume you would need, and how much of the air you pumped would be permanently lost to the planet. Meteors burn over miles of atmosphere, so you won't want just a few hundred feet around your stalk. My first thought is that this doesn't scale to a practical size, and that reactive armor would be easier, if you really want to protect the stalk. ------------------------------ To: space-tech@cs.cmu.edu Reply-To: munck@STARS.Reston.Unisys.COM Subject: Re: Tubular fullerine / Space elevator Date: Tue, 17 Dec 91 10:10:32 -0500 From: Bob Munck jbh55289@uxa.cso.uiuc.edu (Joshua B. Hopkins) writes: > Keep in mind that there won't _be_ any safe orbit for > satellites though (at least not below GEO altitudes) because the > beanstalk will be over the equator. 'af-a-mo, there's an assumption that can be questioned. Sure, if the beanstalk is a single strand, it has to be rooted very close to the equator, with the concomitant problems of getting those monks to move (literary allusion). HOWEVER, suppose the beanstalk is in the form of an inverted Y, with two connections to the Earth. Put them far enough north and south, and their joining high enough, and the popular LEO equatorial orbit is left empty. Taken to the extreme, put the anchors at the N and S poles and don't have them join at all until they get out to the counterweight - well beyond geosynch orbit. This leaves clear all but the tiniest fraction of popular orbits, including geosynchronous. Even if something in polar orbit hits one of the legs, it'll hit at an extreme angle and might just bounce off. (Next step: make each leg twice as long, and have another counterweight on the other side of the Earth. Now you don't need anchors at the poles, as the stalks just lie on the ground. Humm, what if the counterweights are moving just a tad faster than the Earth turns?...) Bob Munck ------------------------------ From: henry@zoo.toronto.edu Date: Tue, 17 Dec 91 13:26:05 EST To: Fraering Philip G Cc: space-tech@cs.cmu.edu Subject: Re: beanstalks with atmosphere :-) >More seriously, don't pump air, pump water... Nah, don't pump it at all. Use asteroidal or cometic [is that a word?] water brought down from the top. Put a turbogenerator every kilometer or two and we get housekeeping power as well -- a hydroelectric beanstalk! Talk about the ultimate hydro project... the hydro engineers normally think a hundred meters of drop is wonderful for a power plant... we've got them beat by six orders of magnitude... Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: Tue, 17 Dec 1991 12:29:36 -0600 From: Fraering Philip G To: henry@zoo.toronto.edu, pgwres01@ucs.usl.edu Subject: Re: beanstalks with atmosphere :-) Cc: space-tech@cs.cmu.edu You're right, but I think the proper term is cometary. Phil ------------------------------ Date: Tue, 17 Dec 91 10:43 PST From: trost@reed.edu (Bill Trost) To: munck@STARS.Reston.Unisys.COM Subject: Get your beanstalk away from my spy satellite! cc: space-tech@CS.CMU.EDU (Next step: make each leg twice as long, and have another counterweight on the other side of the Earth. Now you don't need anchors at the poles, as the stalks just lie on the ground. Humm, what if the counterweights are moving just a tad faster than the Earth turns?...) (Always wanted to play a game of limbo legs at the north pole...) Doesn't this have the same problem as a ring -- wouldn't it want to fall down? You'd have to have at least a minimal anchor to keep it drifting out of its unstable orbit. Anyhow, the poles probably aren't the best place to "launch" things from. Although there is something to be said for anchoring such a structure in, say, New York harbor -- avoids surface transport costs. By the way, does anyone have a good notion of how you would anchor a tether? I've tended to visualize a large bag of water/rocks, depending on what was more plentiful on the given object. ------------------------------ To: space-tech@cs.cmu.edu Subject: Re: Get your (polar) beanstalk away from my spy satellite! Reply-To: munck@STARS.Reston.Unisys.COM Date: Tue, 17 Dec 91 14:45:16 -0500 From: Bob Munck trost@reed.edu (Bill Trost) says: >Doesn't this have the same problem as a ring -- wouldn't it want to >fall down? You'd have to have at least a minimal anchor to keep it >drifting out of its unstable orbit. Fall down? Which way? The counterweight(s) are out beyond geosynch orbit and moving faster than orbital speed; they're trying to fall up! The weight of the beanstalk and tension on it hold them in place. How is the orbit unstable? >Anyhow, the poles probably aren't the best place to "launch" things >from. Although there is something to be said for anchoring such a >structure in, say, New York harbor -- avoids surface transport costs. Once we're really into beanstalks (and have given up free-falling satellites and cleaned up cis-Earth space), we could have them coming down all over the place. Our blue marble might become a fuzzy blue marble. >By the way, does anyone have a good notion of how you would anchor a >tether? I've tended to visualize a large bag of water/rocks, >depending on what was more plentiful on the given object. The Earth-side end could just hang there a foot off the ground. You really need it anchored only so that you can give it enough tension to counteract the weight of the payloads hanging on it. (This is true only at the Equator.) The counterweight end has to be attached to the counterweight strongly enough to hold the entire weight of the beanstalk, a more difficult job. Bob Munck ------------------------------ Reply-To: davidsen@crdos1.crd.ge.com Date: Tue, 17 Dec 91 13:19:16 EST X-Mailer: Mail User's Shell (6.5 4/17/89) From: davidsen@crdos1.crd.ge.com To: space-tech@cs.cmu.edu Subject: Re: beanstalks with atmosphere :-) > The reason you would need booster pumps is that at > 15 psi, the air could only be pumped on the order of tens of > kilometers up. Gravity confines an atmosphere > with a base pressure of 1 bar, you know. Exactly so, which is why I don't understand why the pressure needed to push air is all that big a deal. The volume needed to do anything useful would be a problem no matter how you do it, I suspect. This is LEO rather than GEO, right? So to get the "thin atmosphere" mentioned we should need something in the ballpark of 5-10k psi, depending on volume, actual height, and whatever design parameters we pick. Assuming the technology to raise a stalk, I think assuming we can handle up to, say, 40k psi with light wall tubing is pretty safe. The pressure and wall thickness will drop with altitude, of course. ------------------------------ Date: Tue, 17 Dec 91 13:01 PST From: trost@reed.edu (Bill Trost) To: munck@STARS.Reston.Unisys.COM Subject: Re: Get your (polar) beanstalk away from my spy satellite! cc: space-tech@cs.cmu.edu munck@STARS.Reston.Unisys.COM hath written: trost@reed.edu (Bill Trost) says: >Doesn't this have the same problem as a ring -- wouldn't it want to >fall down? You'd have to have at least a minimal anchor to keep it >drifting out of its unstable orbit. Fall down? Which way? The counterweight(s) are out beyond geosynch orbit and moving faster than orbital speed; they're trying to fall up! The weight of the beanstalk and tension on it hold them in place. How is the orbit unstable? For the same reason Larry Niven's Ringworld is unstable. Something "solid" (the cables with tension is solid enough) placed in an orbit is at a point of highest potential energy. If one counterweight were to become closer in than the other, it would be pulled in while the other is pulled out, eventully ending with one counterweight crashing to the surface. Ah, I finally remember the terminology. A ring orbital is known as a "repulsive fixed point" (like L1-L3), and what you really want is an "attractive fixed point" (like L4 & L5). The Earth-side end could just hang there a foot off the ground. You really need it anchored only so that you can give it enough tension to counteract the weight of the payloads hanging on it. (This is true only at the Equator.) I was thinking there would be a problem with the payload pulling the beanstalk down. One way to prevent this would be to have the beanstalk under tension, by putting more weight at the end than is needed to simply hold the stalk up. The stalk would then be pulling on the mount on the ground, and, as long as your payload doesn't go up to fast, the centrifugal force will keep the counterweight out where it should be. ------------------------------ To: davidsen@crdos1.crd.ge.com Cc: space-tech@cs.cmu.edu Subject: Re: beanstalks with atmosphere :-) Date: Tue, 17 Dec 91 16:41:29 EST From: John Carr >> Assuming the technology to raise a stalk, I think assuming we can >> handle up to, say, 40k psi with light wall tubing is pretty safe. The >> pressure and wall thickness will drop with altitude, of course. Would internal pressure help resist buckling under compressive load? ------------------------------ Date: Tue, 17 Dec 91 16:57:21 EST From: fpaterra@ra.cta.com (Frank Paterra) To: space-tech@cs.cmu.edu Subject: beanstalks with atmosphere :-) The internal pressure can also be used to raise the beanstalk. Just don't open the spray valves before the thing locks in place. Frank Paterra fpaterra@cta.com [ Yikes. The forces involved are wrong by a few orders of magnitude. --MNR ] ------------------------------ Date: Tue, 17 Dec 91 17:49:51 EST From: John Roberts Disclaimer: Opinions expressed are those of the sender and do not reflect NIST policy or agreement. To: space-tech@cs.cmu.edu Subject: Space elevator >To: space-tech@cs.cmu.edu >Subject: Re: Tubular fullerine / Space elevator >Date: Tue, 17 Dec 91 10:10:32 -0500 >From: Bob Munck >'af-a-mo, there's an assumption that can be questioned. Sure, if >the beanstalk is a single strand, it has to be rooted very close to >the equator, with the concomitant problems of getting those monks to >move (literary allusion). >HOWEVER, suppose the beanstalk is in the form of an inverted Y, with >two connections to the Earth. Put them far enough north and south, >and their joining high enough, and the popular LEO equatorial orbit is >left empty. >Taken to the extreme, put the anchors at the N and S poles... Interesting idea. One factor that should be taken into account when contemplating non-equatorial elevators: since the cable is no longer completely vertical with respect to the Earth's surface, the cable will sag (especially at the poles, where it starts out horizontal). I don't know to what extent this will effect the design, but it's probably worth considering. .................. Anyhow, the poles probably aren't the best place to "launch" things from. Although there is something to be said for anchoring such a structure in, say, New York harbor -- avoids surface transport costs. Of course, at the poles, you might not have to deal with the Longshoremen's Union. :-) .................. Henry has pointed out to me that the elevator is really a device for transfer of angular momentum. A payload going up gets some of its energy by slowing the Earth's rotation a little bit. A payload coming down speeds the Earth's rotation by a corresponding amount. Unless the traffic going up matches the traffic going down, you need a firm anchor. Elevators attached at the poles can't take advantage of this, so you need rocket engines or equivalent mounted on the elevator. John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ Reply-To: davidsen@crdos1.crd.ge.com Date: Wed, 18 Dec 91 08:03:38 EST X-Mailer: Mail User's Shell (6.5 4/17/89) From: davidsen@crdos1.crd.ge.com To: space-tech@cs.cmu.edu Subject: Re: Space elevator Assuming you ever get it up, and use anchors at the poles, you could put a *big* swivel in place, and if the orbit was a hair off, so what? The big problem with anchors at the poles is that we only have two of them. ------------------------------ Date: Wed, 18 Dec 91 08:47:34 EST From: John Roberts Disclaimer: Opinions expressed are those of the sender and do not reflect NIST policy or agreement. To: space-tech@cs.cmu.edu Subject: Re: Space elevator Even with swivels, you need a long-term balance between things going up and things going down, or the elevator will fall out of the sky (or some other catastrophe). If more things go down than come up, the excess energy might be dissipated by wind resistance rather than by pulling the elevator apart. John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ End of Space-tech Digest #93 *******************