Return-path: X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson Received: from beak.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl@andrew.cmu.edu (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests) ID ; Sat, 31 Mar 90 01:28:41 -0500 (EST) Message-ID: Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Sat, 31 Mar 90 01:28:12 -0500 (EST) Subject: SPACE Digest V11 #202 SPACE Digest Volume 11 : Issue 202 Today's Topics: Space-tech excerpt: Orbital debris Progress-M Alan Shepherd in Australia ---------------------------------------------------------------------- Date: Fri, 30 Mar 1990 16:57-EST From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU Subject: Space-tech excerpt: Orbital debris I recently went through and excerpted some of the most informative discussions from the space-tech mailing list, which I run. Here's one of them; expect a couple more over the next week or so. Space-tech is a mailing list for discussing concepts for space development, with emphasis on the technical problems and and how to solve them. To join, send mail to space-tech-request@cs.cmu.edu. Bring a pencil! /////////////////////////////////////////////////////////////////////// /// Marc Ringuette /// Carnegie Mellon University, Comp. Sci. Dept. /// /// mnr@cs.cmu.edu /// Pittsburgh, PA 15213. Phone 412-268-3728(w) /// /////////////////////////////////////////////////////////////////////// Space-tech excerpt: Orbital debris [270 lines, fall '89] The topic: how to reduce or eliminate orbital debris, which may become a serious practial problem in low orbit? ------------------------------ From: Steven Deterling I am working on a project here at A&M this semester and am wondering if this group has any suggestions or information to offer. We are trying to design a mission (or set of mission) for the purpose of removal of orbital debris. Any ideas would be greatly appreciated. ------------------------------ From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU My first idea is to have a very-large-surface-area setup where you try to vaporize small bits of debris by putting an obstacle in front of it. For instance, a mylar sheet or some sort of ultra-light foam. The critical factor for that kind of scheme would be whether a thin film would do something useful with the debris - presumably you'd like to vaporize it so it wouldn't have a destructive impact if it hit somebody. Maybe vaporizing it would also decrease its decay time. Actually, I have a better idea than a single film: two or three mylar films spaced far enough apart that when debris strikes one, if it breaks up at all, the fanned-out secondary debris hits the second sheet, and again for the third. It may allow you to destroy much larger chunks of stuff because it forces each object to come into contact with a larger surface area of the sheet (as opposed to just punching a tiny little hole). This is assuming objects break up, as opposed to just lose a few molecules off the surface. I wonder if you take your average small object and run it into a film at a few km/s, what happens? What's a representative sample of debris? (My guess: chips of paint, metal shavings, bits of rubber, metal bolts, entire assemblies; probably biased toward the really small stuff, but you care more about the big stuff). === Or maybe you were thinking of bigger pieces of debris that you can track and predict the orbit of. One option would be to chase the debris with a low-acceleration tug and put it in your garbage bag. But this is probably prohibitively expensive except for the very largest objects - it may take weeks or months per object, and each craft needs propulsion, power, and communications. A second tactic: put something in the object's way that vaporizes it. I wonder how much foam you'd have to put in the way of a chunk of metal before it was destroyed? The better you can predict the orbit, the more stuff you can stack in its path. If you can't get the orbit down pat, maybe you can use on-board radar and shoot a gun at it - a small solid projectile may be able to break up a large object; I wonder if this isn't worse than nothing. === Another line of thought: how do you cheaply contain the debris before it is generated? For instance, some sort of foam or glue or something that prevents an object from breaking up before it burns up completely. You carry a small amount of this gunk along on your mission, and wire it so that when you eject something, it foams up. But probably most debris is generated by accident, in small quantities. Or is it? Do you have figures? How about putting a plastic bag around the vehicle after it injects into orbit? :-} ------------------------------ From: Steven Deterling We also are basically keen on the idea of vaporizing debris. I do not know enough about hypervelocity collisions to say whether or not a small piece of junk running into a mylar sheet will generate enough heat to be destroyed. We have considered some form of encapsulation for bigger pieces of junk. Not too sure about what to yet, however. The scenario we are starting to look at real closely is to have some sort of craft with an engine on the back and a high power laser of some sort attached to vaporize small particles. The front of the craft would be a collector for larger, "non-vaporizeable" particles. When the collector was full, it could be started on a trajectory toward the Sun and the rear of the craft could be separated for re-use. We are looking at possible using an ion engine for our craft. We are not too concerned with the time span, a mission of 5 years or so would not be bad. As long as we are decreasing the amount of debris in orbit, we are being beneficial. Comments on this scheme from everyone would really be helpful. ------------------------------ From: Joe Beckenbach As for encapsulation: for anything too big to vaporize but too small to grab easily, perhaps spray on some foam concrete or let it plow through layers of foam metal, something either to increase its size or to slow it down so it will either embed or decay. I think this is the basic idea that everyone's been trying to figure out how to do. ------------------------------ From: KEVIN@A.CFR.CMU.EDU (Kevin Ryan) Cleaning orbital junk, eh? If only the atmosphere did a better job of slowing them down, at least for a little while... Enter the little men in white shirts and wire-frames, with little plastic pocket protectors. They smile at the brass hats. "We have a solution to the orbital debris problem. Detonate a large, clean (relatively clean, of course - all things are relative) thermonuclear device in the upper atmosphere. It will cause a large and temporary 'hump' in the atmosphere, thus greatly slowing the orbital junk, which will soon reenter. After the 'hump' subsides, relaunch the satellites of your choice. This cleans out debris in _all_ orbits which intersect this rather large 'hump.' If you don't get them all, use a larger device, or do it repeatedly." Slowly, the brass hats start to smile. This would mean getting to use some of their BIG toys... I wish I was spinning this out of imaginary cloth. I have seen serious (!) suggestions for creating such an atmospheric 'hump' to slow/divert/destroy ICBM's - and if it works for high suborbital missiles, it should work for LEO debris, which should be at the very least less aerodynamic. Before I'm flamed, let me emphasize - "Not on MY planet, monkey boy!" Just thought I'd chuck it in for amusement... ------------------------------ From: henry@utzoo.uucp (Henry Spencer) Jordin Kare has observed that the kind of 1MW laser that would be used as a feasibility-test system for a laser launcher could also be quite useful in sweeping up debris. It could vaporize very small pieces, and could de-orbit larger ones by blowing pulses of gas off their leading surfaces (a laser retrorocket). ------------------------------ From: neufeld@helios.physics.utoronto.ca (Christopher Neufeld) Over the past couple of weeks we've seen a few ways to clean dust and grit out of low earth orbit, where it could damage satellites, shuttles, or the space station. Two of the more memorable ones were the ice cube in an opposing orbit, and the giant flypaper. I submit that there is an easier and more selective way to do the same thing. According to some calculations I made this afternoon, and which I'm still having trouble believing, it's very easy, assuming that most of the grit is going spinward, in the direction of most satellite launches. This grit goes from west to east as seen by an observer on the ground. A mirror is placed in the sunlight in the east as seen by a terrestrial observer. The mirror reflects sunlight across the sky, from east to west, so that it is shining directly into the path of the orbiting grit. The scenario I used was a mettalic flake 1mm in diameter, and 0.1mm thick, in a circular orbit 300km above the surface of the earth. It turns out that the photon pressure on the flakes lowers the perigee of the orbit to 100km, at which time it can be said to be braking in the atmosphere and out of our way, in only 50 hours of exposure. If we have 5% coverage, this is 1000 hours real time, or roughly six weeks. The advantage to this approach is that it works best on small objects. A communication satellite would suffer a delta-v of only about 1m/s, which I presume is within the tolerance of the onboard thrusters to compensate. An alternative solution is to put a giant sunshade which blocks light reaching orbit as they cross from day to night, while still letting the particles get the sun in their faces as they go from night to day. I favor the first approach because it is easier to stabilize the mirror than a sunscreen, since solar pressure on the mirror acts to oppose the earth's gravity, while solar pressure on the sunshade adds to the earth's gravity. Also, a mirror can be easily aimed to sweep different orbits, while a sunshade or a retrograde ice cube would require a lot of effort and time to do the same. Here are the calculations: I used the following parameters for the solution of the great cosmic vacuum cleaner: Particle is a cylinder: 1 mm in diameter 0.1 mm thick Particle's specific gravity: exactly 7x10^3 kg/m^3 Particle orbiting at exactly 300 km in a circular orbit Mass of the earth: exactly 6x10^24 kg Earth has no higher order gravitational moments. Gravitational constant: exactly 6.67x10^-11 N m^2/kg^2 Gravitational acceleration at the earth's surface: exactly 9.81 m/s^2 Radius of the earth: 6.387x10^6 m Radius of the orbit: 6.687x10^6 m Orbital velocity: 7.736x10^3 m/s For purposes of momentum transfer from the particle: I used the effective area of the particle as 1/2 the area of an end cap, and assumed that all radiation incident on the (tumbling) flake was absorbed. This is actually a conservative estimate, since the actual figure goes from 1/2 for a perfectly absorbing slab to 2/3 for a perfectly reflecting slab. This under-estimation of the area will absorb any inefficiencies in the mirror, since I am still using a power flux at the particle of 1.4 kW/m^2, the solar flux in space at one astronomical unit. Force on the particle is Psolar/(speed of light) * area of particle. This gives an acceleration of 3.333x10^-4 m/s^2 for as long as the particle is in the beam. Now, it is necessary to find the delta-v on a particle orbiting at 300 km to drop the perigee to 100 km. This turns out to be about 60 m/s. See the note at the end of this article for the math behind this calculation. The acceleration will provide this impulse in only 50 hours. If we have 5% coverage, this is 1000 hours real time, or roughly six weeks. Now, I have to justify my assumption that hitting the particle several times will result in the lowering of the perigee, but will not change the apogee, which will stay at 300 km. Assume that the orbit is initially circular. I hit it with the beam as it traverses some 15 degrees of its orbit. The particle slows down by some small amount, then continues in its orbit as a free particle. From classical mechanics, a gravitational orbit is closed (no precession). So, the particle must return to the point at which it received the initial impulse. This argument then repeats for each orbit. So, after giving it a delta-v of 60 m/s, the apogee is at 300 km while the perigee is at 100 km. It is now hitting atmosphere, and will quickly be removed from worry. For a Clarke orbit, the delta-v is 1500 m/s, which takes quite a bit longer, but the algebra is essentially the same. In this case, though, the mirror has to rotate to track the sun as it moves relative to the orbit over a period of one year. The mirror must shine into the orbits always at apogee to get the efficiency I've postulated, and apogee will precess with respect to the earth and sun, since it will always point to the same fixed stars. ------------------------------ From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU I like this approach a lot! However, I'm concerned about two questions: 1. How big a mirror do we need? What is the size of the cross section through which most of the grit goes? 2. What are the magnitudes of the forces involved on the mirror itself, and how much of its time can be spent usefully? My guess is that the mirror would have to be very large and that it would have somewhat less than a 25% duty cycle because it would probably want to remain in a single orientation throughout its orbit. However, I don't really trust my guesses on this at all. ------------------------------ From: Christopher Neufeld I'm still working out the orbital dynamics for the mirror, but I usually have a pretty good feel for the orbits without doing the math (that's why I suspected my initial erroneous results). The situation I'm looking at is a dynamically unstable SOLAR orbit leading the earth by a bit. I would choose the position of the mirror and its angle so that the light pressure from the reflection exactly balances the earth's pull. If it drifted away from the earth a bit, the pull would be weakened, and it would tend to drift further, so the mirror would have to be furled slightly to lower the outward solar pressure and bring it back into line. If it drifted toward the earth, the pull would be strengthened, and extra mirror kept in reserve for that eventuality would be unfurled until it is back where it belongs. The feedback scheme shouldn't be impossible. Anyway, in a while I'll work out the details of the sail: its mass per unit area, position with respect to the earth, and a typical size. I expect that the mirror can be shining in a useful direction at least 90% of the time. More details as they become available. ------------------------------ [ End of excerpt ] ------------------------------ Date: 22 Mar 90 06:37:58 GMT From: munnari.oz.au!csc!ccadfa!usage!metro!ipso!mjl@uunet.uu.net (Mathew Lowry) Subject: Progress-M Can anyone tell me about the Progress-M, launched on August 23 by the USSR? International number 1989-66-A, the only ref I've got is "First of a new series of automatic carge spacecraft" Perigee 191 km, Apogee 235 km Period 88.5 minutes Inclination 51.6 degrees (Information from Telecommunication Journal, Satellite Launchings section) Probably best to email, and I'll summarise, Thanks in advance Mathew ------------------------------ Date: 23 Mar 90 00:34:21 GMT From: munnari.oz.au!csc!ccadfa!usage!metro!ipso!stcns3!dave@uunet.uu.net (Dave Horsfall) Subject: Alan Shepherd in Australia Just heard an interview on the radio this morning with Rear Admiral Alan Shepherd Jr, first American in space. [ Actually, I could have sworn the interviewer said "first man in space" at least once, but I digress... ] Anyway, apparently he is a director of Kwik Copy Corporation (sp?), and is in Sydney for a company convention. -- Dave Horsfall (VK2KFU) Alcatel STC Australia dave@stcns3.stc.oz.AU dave%stcns3.stc.oz.AU@uunet.UU.NET ...munnari!stcns3.stc.oz.AU!dave ------------------------------ End of SPACE Digest V11 #202 *******************