klaes@mtwain.dec.com (CUP/ML, MLO5-2/G1 8A, 223-3283) (11/02/88)
For over thirty years now the human race has been launching all types of vehicles into the Universe, creating an immense "cloud" of human-made objects orbiting Earth and slowly expanding into the Solar System and interstellar space. While many of the satellites in space are of benefit to our society, many more are now inactive, floating around Earth serving no purpose at present. In addition to dead satellites and rocket boosters, there are also thousands of pieces of metal scrap and paint flecks from rockets and satellites which have disintergrated in orbit for one reason or another; and the satellite cloud is growing all the time. At present there is a one in thirty chance that a Space Shuttle could be struck by some man-made orbital debris; by 2010 the chances will be reduced to one in four. This cloud represents a danger on many levels: In space, this debris is orbiting Earth at eighteen thousand miles per hour (the minimum velocity needed to achieve and stay in orbit); while some of it will eventually be dragged into Earth's atmosphere and burn up, many more are in orbits which will last for millennia! As more functioning manned and unmanned vehicles are launched into orbit, the risk of being struck and killed/destroyed by this debris - no matter how small - grows constantly. Even a grain-sized particle could hit with the impact of a rifle bullet! And people and places on Earth's surface are not immune from the dangers of falling debris: If an object is large enough, it will not burn up completely and strike the surface. The Soviet nuclear-powered COSMOS satellite hitting Canada in 1978 and the United States SKYLAB space station hitting Australia in 1979 are good examples of debris too big to be burned up on reentry and the consequences which result. Satellite debris also interferes with astronomical observations. The incredibly sensitive instruments professional astronomers use can be "thrown off" by passing satellites and man-made debris. Even more threatening, just recently the French were stopped from launching a huge balloon ring satellite to commemorate Paris' Eiffel Tower's one hundredth anniversary. Many astronomers opposed the ring satellite, as it would have been the size and visual brightness of the full Moon as viewed from the ground and interfered with observations. They were also concerned that it might start companies advertising in space with huge satellite "billboards", which some *are* considering! Along with light pollution on the ground from ever-growing cities, astronomers - and those who just enjoy looking at the stars - are having their work cut out for them. The International Dark-Sky Association is an organization designed to help deal with our growing light pollution problem, while not compromising public safety in the process. For more details, write to: Dr. Dave Crawford Kitt Peak National Observatory PO Box 26732 Tucson, AZ 85726 You can also receive a brochure on an important meeting of astronomers and other scientists who discussed the problems of light pollution in Washington, DC, on August 13-16, 1988, by writing to Dr. Tomas Gergely, National Science Foundation, Dept. of Astronomy, 1800 G St., NW, Washington, DC 20550. Now I know some of you are probably asking yourselves: "How can I possibly stop and/or clean up space debris? I'm afraid I don't have much access to a Space Shuttle with a huge vacuum cleaner; also, I and other average citizens did not personally make the pollution now flying over our heads!" I am well aware of this, and naturally this is a project for a major government and/or corporation to handle; but as is always pointed out, such organizations won't do much of anything unless it personally affects them and/or the citizens they are supposed to serve say something about it - in other words, write to your Congressman; it does a lot more good than you might think. Tell them there should be a major program to start picking up the useless satellite and rocket debris orbiting Earth. It can be done using the Space Shuttle, or even relatively cheaply using robot satellites which can attain orbits where the Shuttle cannot; and what is even better is that the debris need not be returned to pollute Earth. For one thing, some old, deactivated satellites are now part of space history, and deserve to be returned to Earth for placement in our museums. Others still have valuable parts which can be reused and/or recycled; and as for the truly useless debris, if it is small enough it can be deorbited to burn up completely on reentry, or launched into the Sun with no harmful effects to our star. The debris can also be placed in safe containers and launched into solar orbit away from Earth, or even out of the Solar System, but I do not care for this plan, as it does not destroy the debris, and just leaves the hazard for future space travelers when humanity start to colonize this and other star systems. I would like to point out that I am aware these clean-up plans are not for the immediate future, as I understand the difficulties in orbital mechanics, such as trying to send an object towards the Sun, etc., but I hope they will inspire the start of such projects when it is more feasible. I am also aware of the recent Air Force project designed to deorbit booster rockets earlier than normal for previous missions, to make Low Earth Orbit (LEO) a bit less cluttered; I personally approve of this, but it might be more beneficial if we could recover the boosters and other debris for scrap metal, if nothing else. I just feel that *something* should be started relatively soon, so that it does not become too late for us to do anything about it by the time we are socially and technologically ready. It would be horrible to think that we might trap ourselves on this planet with our own space debris circling the globe, making space launchings too risky to attempt. This is an extreme view in some ways, but not impossible. Besides the fact that man-made debris is potentially dangerous to satellites and humans, why else should we "clean up" space? Because it will help the future of our space programs, which in turn benefits all of society. These very clean-up projects will get us more involved in space exploration and colonization. We will colonize the other planets and star systems someday, and we cannot continue to bring our pollution and poor management habits with us. Space leaves very little room for error and bad planning. What you say to those who will guide our future in space can have a lot of impact. Do not think of space as something separate from Earth and its concerns: We live on a planet in space, and if we ruin not only our world but the environment around it, then where can we go to live? Larry Klaes
karn@jupiter..bellcore.com (Phil R. Karn) (11/03/88)
The note on stopping space pollution is interesting, but one of the proposed solutions is, shall we say, a bit impractical. First of all, the main problem isn't intact payloads. The real problem is with the numerous small fragments in long-lived orbits, and these are not easily reached from the Shuttle. Debris, large or small, that *is* in a typical Shuttle orbit (about 300 km) re-enters within a few months anyway, so there's not much point in going up to get it. Second, there are so *many* small bits of debris, in so many different orbits, that even if you could reach them with the Shuttle you'd have to expend enormous amounts of fuel chasing them all. Third, the Shuttle itself generates a not-insignificant amount of debris through such things as waste dumps and loose parts. This would largely offset whatever debris it could pick up. I remember seeing the first on-orbit TV of the payload bay sent to earth during STS-1; clearly visible was a small piece of loose hardware spinning across the field of view, off into the blackness. If you're seriously interested in the space pollution problem, I believe you should advocate the following PREVENTIVE approaches: 1. An international treaty prohibiting deliberate collisions between or explosions of objects in earth orbit above a certain altitude, say 500 km. This would include both Soviet and American SDI and ASAT tests. Much existing orbital debris is the result of Soviet ASAT tests. The reduction of space debris is only one of many reasons that a complete ban on all ASAT testing would be to our mutual advantage. 2. An international treaty requiring launch agencies to vent excess liquid fuel from spent upper stages to render them incapable of exploding. Much existing orbital debris has come from upper stages that explode some time after deploying their payloads. This can happen in a cryogenic stage when the fuel vaporizes (e.g., the Ariane 3rd stage that launched SPOT-1) or it can happen in a hypergolic stage when the fuel and/or oxidizer corrode through the bulkhead and mix (e.g., some Delta 2nd stages). I believe that most launchers now vent as standard operating procedure, so it shouldn't be much of a burden to make this a formal requirement. 3. International guidelines for the design of orbital missions missions such that the fewest possible non-payload objects are deployed in long lived orbits. This would consist of several aspects: a. The use of short-lived transfer orbits whenever possible. For example, a standard Ariane geostationary transfer orbit has a perigee of about 200 Km. Spent Ariane third stages generally last in this orbit for a few years or so. intermediate earth orbits with "direct ascent" launches are the real problem, since the upper stage goes into the same orbit as the payload. If at all possible, spent stages should be designed to de-orbit themselves after deploying their payloads. b. Methods to control the amount of debris generated in long-lived orbits, with emphasis on payload deployment operations. Clamp bands, springs, fasteners, explosive bolt cutters and the like should be captive, i.e., they should be tethered so they don't go floating off on their own after separation. This is already standard procedure on most Western launches; it should be an international requirement. c. Integrity standards for external coatings on all objects deployed in long-lived orbits. The white paint used on Delta upper stages has been traced as the cause of some small craters found on Shuttle windows. Phil
henry@utzoo.uucp (Henry Spencer) (11/05/88)
In article <1379@thumper.bellcore.com> karn@jupiter.UUCP (Phil R. Karn) writes: >Second, there are so *many* small bits of debris, in so many different >orbits, that even if you could reach them with the Shuttle you'd have to >expend enormous amounts of fuel chasing them all. In fact, even if you had propulsion suitable to the job -- I once took a cursory look at the idea of a tiny satellite with electrodynamic propulsion, specifically as a garbage retriever -- the sheer size of the problem is just plain excessive. It's not the two-ton lumps that are the real problem: they are (relatively) few in number and collisions with them are fairly unlikely. The bad part of the problem is the coin-sized bits. They're too small for any practical retrieval scheme, too numerous to just trust to luck, too small *and* too numerous to just track and avoid, and too massive to just disregard. The best we can do is to protect major facilities against them and try hard to avoid creating more! >b. Methods to control the amount of debris generated in long-lived orbits, >with emphasis on payload deployment operations. Clamp bands, springs, >fasteners, explosive bolt cutters and the like should be captive, i.e., they >should be tethered so they don't go floating off on their own after >separation. This is already standard procedure on most Western launches... An alternative that is worth exploring for some types of object is photo- degradeable materials. De-spin weights, for example, *have* to be cut loose, but I would suspect that they and their cables could be made out of some plastic that would break down in sunlight, so eventually you'd have nothing but organic gas left. >c. Integrity standards for external coatings on all objects deployed in >long-lived orbits. The white paint used on Delta upper stages has been >traced as the cause of some small craters found on Shuttle windows. Those who are enthusiastic about using shuttle external tanks in orbit should note that the insulation on the tanks is likely to "popcorn" in vacuum as it outgases. The folks working on turning a tank into a gamma-ray telescope (the only NASA-funded external-tank work) plan to put an outer casing around the tank, partly to contain the debris. (The other reason for the casing is as a classic "meteor bumper" against both natural meteorites and space debris.) -- The Earth is our mother. | Henry Spencer at U of Toronto Zoology Our nine months are up. |uunet!attcan!utzoo!henry henry@zoo.toronto.edu
anand@amax.npac.syr.edu (Anand Rangachari) (11/07/88)
With all this talk about reducing the possibility of collision with debris, I am reminded of a scheme suggested in the book 'The songs of distant Earth' by Clarke. In this book, the ship Magellen pushes a shield made of ice ahead of it, sweeping a clean path. Maybe a similar shield could be made for the space shuttle from waste water and the water produced in the fuel cells. In fact it could be produced quite easily by creating a framework made from a shape memory alloy. Then, water could be sprayed on it to actually form the shield. R. Anand Internet: anand@amax.npac.syr.edu Bitnet: ranand@sunrise
bpendlet@esunix.UUCP (Bob Pendleton) (11/09/88)
From article <809@cmx.npac.syr.edu>, by anand@amax.npac.syr.edu (Anand Rangachari): > > With all this talk about reducing the possibility of collision with debris, > I am reminded of a scheme suggested in the book 'The songs of distant Earth' > by Clarke. In this book, the ship Magellen pushes a shield made of ice > ahead of it, sweeping a clean path. Maybe a similar shield could be > made for the space shuttle from waste water and the water produced in the > fuel cells. Not a bad idea, except that a starship traveling at some fraction of the speed of light and a space shuttle in LEO are very different physical systems. The shield would have to surround the shuttle, not just sit in front of it. Debris in the same orbit as the as the shuttle has very little (none if in the SAME orbit, going the SAME direction) difference in velocity relative to the shuttle and is not a threat. But debris in orbits that cross the shuttle orbit, and therefore have high velocities relative to the shuttle are the danger. A starship is moving quickly with respect to the interstellar dust and gases and can (maybe) get away with not worrying about material in trajectories that cross its path. > In fact it could be produced quite easily by creating a framework made > from a shape memory alloy. Then, water could be sprayed on it to actually > form the shield. In a vacuum ice sublimes. That is it converts directly from a solid to a gas. This fact has been used to get rid of heat on manned spacecraft for quite some time. I suppose that if the ice is cold enough this can be reduced to a point where the loss is insignificant, but in LEO the ice will be in sun light for about half of each orbit. The shield will slowly melt away. > R. Anand Question: Liquid water released in orbit tends to convert into a cloud of water vapor and ice cristals. The ice crystals later sublime to water vapor. Could large clouds of ice crystals be used to "sweep" orbits of small debris particles? Doesn't sound practicle, too large a volume, too few particles. But I haven't heard it suggested before. Might it be useful for sheilding a battle station from a kinetic engery attack using a bucket of b.b.s? Bob P. -- Bob Pendleton, speaking only for myself. UUCP Address: decwrl!esunix!bpendlet or utah-cs!esunix!bpendlet Reality is what you make of it.
henry@utzoo.uucp (Henry Spencer) (11/12/88)
In article <1068@esunix.UUCP> bpendlet@esunix.UUCP (Bob Pendleton) writes: >Question: Liquid water released in orbit tends to convert into a cloud >of water vapor and ice cristals. The ice crystals later sublime to >water vapor. Could large clouds of ice crystals be used to "sweep" >orbits of small debris particles? Unfortunately, you need to sweep a spherical shell, not just a single orbit, since anything at the same altitude will intersect your orbit. (Ignoring non-circular orbits for the moment...) That's a lot of volume. You also have to be careful about the possibility of making the problem worse. Hypervelocity impacts can behave in peculiar ways. It's quite possible for an impact to break both objects into pieces without doing much to decelerate or vaporize either one. Breaking the existing debris up into smaller bits is the *last* thing we want to do. -- Sendmail is a bug, | Henry Spencer at U of Toronto Zoology not a feature. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
bpendlet@esunix.UUCP (Bob Pendleton) (11/15/88)
From article <1988Nov11.213348.27877@utzoo.uucp>, by henry@utzoo.uucp (Henry Spencer): > In article <1068@esunix.UUCP> bpendlet@esunix.UUCP (Bob Pendleton) writes: >>Could large clouds of ice crystals be used to "sweep" >>orbits of small debris particles? > > Unfortunately, you need to sweep a spherical shell, not just a single orbit, > since anything at the same altitude will intersect your orbit. Depending on how long the cloud persists it would eventually sweep out a sherical shell. Especially if the cloud is in a polar orbit. The question is how long will the cloud persist? My guess is that it won't last long enough. > Breaking the existing > debris up into smaller bits is the *last* thing we want to do. Not really. Even a fairly heavy rain of microscopic particles can be stopped more easily than one large chunk. Bob P. -- Bob Pendleton, speaking only for myself. UUCP Address: decwrl!esunix!bpendlet or utah-cs!esunix!bpendlet Reality is what you make of it.
karn@ka9q.bellcore.com (Phil Karn) (11/17/88)
Henry is correct about hypervelocity impacts. SDI PR stun...um, er, "tests" have demonstrated what happens when two extremely fast-moving objects collide. The shock of initial impact fragments each object, and the resulting bits of debris fly past each other with very little exchange of momentum. The result is a pair of debris clouds moving away from each other, the center of gravity of each having almost the same velocity as the intact objects did before the collision. Unless you can build your debris catcher from material that can actually STOP objects moving at relative velocities many times that of a rifle bullet, you won't be able to clean up much of the orbital debris. Phil
henry@utzoo.uucp (Henry Spencer) (11/18/88)
In article <1084@esunix.UUCP> bpendlet@esunix.UUCP (Bob Pendleton) writes: >> Breaking the existing >> debris up into smaller bits is the *last* thing we want to do. > >Not really. Even a fairly heavy rain of microscopic particles can be >stopped more easily than one large chunk. *Microscopic* particles aren't that much of a problem. Macroscopic ones are. A fairly light rain of coin-sized particles is a WHOLE LOT harder to deal with than one large chunk, which can at least be tracked and avoided. If we can't utterly pulverize the debris, we don't want to break it up at all. Unfortunately, hypervelocity collisions are non-intuitive in some ways. Based on the SDI Delta experiment, if two fairly large chunks hit each other, the shock wave from the instant of first contact explodes both, and the debris clouds then pass through each other without interacting much. There is more than enough energy there to vaporize everything, but it doesn't get applied efficiently. Any plan to get rid of debris with collisions will have to be studied and tested *very* carefully to make sure that it isn't going to make things worse. -- Sendmail is a bug, | Henry Spencer at U of Toronto Zoology not a feature. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
bpendlet@esunix.UUCP (Bob Pendleton) (11/22/88)
From article <1988Nov17.173505.7601@utzoo.uucp>, by henry@utzoo.uucp (Henry Spencer): > In article <1084@esunix.UUCP> bpendlet@esunix.UUCP (Bob Pendleton) writes: >>> Breaking the existing >>> debris up into smaller bits is the *last* thing we want to do. >> >>Not really. Even a fairly heavy rain of microscopic particles can be >>stopped more easily than one large chunk. > > *Microscopic* particles aren't that much of a problem. Nice to hear that you agree with me. I think my assumptions came through quite well. [Restatement of the obvious deleted. Yes I agree with you too.] > Unfortunately, hypervelocity collisions are non-intuitive in some > ways. Based on the SDI Delta experiment, if two fairly large chunks hit > each other, the shock wave from the instant of first contact explodes > both, and the debris clouds then pass through each other without interacting > much. Yes, I read AW&ST too. My wife qualifies for the cheap rate. She doesn't mind that I read it first, and sometimes she even helps with the long words. Sarcasm aside; What is the average particle size resulting from hypervelocity collisions? And how does it vary for different materials? I don't know. If you know please tell me. That will settle the question. No one knows? Then I aggree that more testing is needed. Bob P. -- Bob Pendleton, speaking only for myself. UUCP Address: decwrl!esunix!bpendlet or utah-cs!esunix!bpendlet Reality is what you make of it.