Return-path: X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson Received: from sushi.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 ; Thu, 11 Jan 90 01:39:57 -0500 (EST) Message-ID: <8Zf2com00WCNQAok5r@andrew.cmu.edu> Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Thu, 11 Jan 90 01:39:49 -0500 (EST) Subject: SPACE Digest V10 #413 SPACE Digest Volume 10 : Issue 413 Today's Topics: Re: March 1990 ANALOG article on self-refueling vehicles Cosmonauts successfully install star sensors on Mir Greenhouse effect ADDITION TO SUBSCRIPTION LIST Re: Nuclear Reactors in Space NSS' DIAL-A-SHUTTLE Standardized payloads Re: Red Shifts through Random Media Re: Mars rovers ---------------------------------------------------------------------- Date: 10 Jan 90 19:32:39 GMT From: frooz!cfa.HARVARD.EDU@husc6.harvard.edu (Steve Willner, OIR) Subject: Re: March 1990 ANALOG article on self-refueling vehicles > In article <5264@sequoia.UUCP> jkg@sequoia.UUCP () writes: >>I don't see what difference it makes that the reactor is not operational >>until after departure, From article <1990Jan5.200226.12324@cs.rochester.edu>, by dietz@cs.rochester.edu (Paul Dietz): > The halflife of U-235 is eight million times the halflife of Pu-238 > (the stuff used in RTGs), so, pound for pound, it is about 8 million > times less radioactive. Uranium also lacks plutonium's tendency to accumulate in the blood forming tissues (i.e., bone marrow and such), so the radiation from uranium isotopes is on average delivered to less vulnerable targets. Also, uranium is less chemically poisonous than plutonium, though chemical toxicity is probably not much of an issue in this context. ------------------------------------------------------------------------- Steve Willner Phone 617-495-7123 Bitnet: willner@cfa 60 Garden St. FTS: 830-7123 UUCP: willner@cfa Cambridge, MA 02138 USA Internet: willner@cfa.harvard.edu ------------------------------ Date: Wed, 10 Jan 90 19:17:53 EST From: <@ll-vlsi.arpa:glenn@vdd> (Glenn Chapman) To: biro%hydra.enet.dec.com@decwrl.dec.com, isg@bfmny0.uu.net, klaes%wrksys.dec@decwrl.dec.com, lepage%vostok.dec.com@decwrl.dec.com, space-editors-new@andrew.cmu.edu, yaron@astro.as.utexas.edu Subject: Cosmonauts successfully install star sensors on Mir This year's major space activities on board the Russia's Mir space station have begun with cosmonauts Alexander Viktorenko and Alexander Serebrov making a space walk. On Jan 8th they opened the hatch at 23:23 Moscow time (15:23 EST), about one hour latter than intended. They then brought out two 80 Kg (176 lbs.) stellar sensors which were attached to Kvant 1's scientific equipment sections (the astrophysical module at the back end of Mir). These star sensors will enable more accurate orientation of the station which has been made more difficult with the addition of the Kvant 2 module to the side docking port. These transducers were mounted in place and the electrical connections made to the stations external signal bus. In addition the Viktorenko and Serebrov retrieved some samples left on the hull in earlier walk. Which EVA started that experiment was as not stated but my records show that on Dec. 9, 1988 Alexander Volkov and Jean-Loup Chretien (the French visitor) placed some French samples on Mir's surface originally intended to be retrieved some in six months (June '89). However, Mir had been closed down on Apr. 27 '89 so the decision must have been made to leave the samples until now, about 13 months later. Distance traveled from the hatch in this EVA was about 35 meter (114 ft.). It was not stated in the announcements which airlock which airlock was used, the older one on Mir or the new larger system on Kvant 2. However, 35 meters would be about the distance from the end of Kvant 2 to the Kvant 1 section. Also the TASS announcement made a point of calling this the longest distance traveled away from the airlock on the outside of the station, and many cosmonauts have walked up to the Kvant 1 section from Mir's port. The total time for this space walk was 2 hours 56 min. Rather surprisingly the next EVA is scheduled for Thursday Jan 11 (no time released as of yet). An additional 3 more space walks are planed for before Feb. 24th, when Viktorenko and Serebrov will be replaced on Mir with a new crew. A least this decade begins with a manned space station in orbit, something the 70' and 80's did not. Hopefully the turn of the century will show zero G facilities from two or more nations/organizations permanently manned. Glenn Chapman MIT Lincoln Lab ------------------------------ Date: Wed, 10 Jan 90 20:27:17 EST From: John Roberts Disclaimer: Opinions expressed are those of the sender and do not reflect NIST policy or agreement. Subject: Greenhouse effect >From: trident.arc.nasa.gov!yee@ames.arc.nasa.gov (Peter E. Yee) >Subject: NASA Headline News for 12/22/89 (Forwarded) >The Washington Post reports that scientists have scaled back >predictions of a significant sea level rise in the next 100 years >because of global warming. The latest prediction is based on a >noticeable accumulation of snow and ice in Greenland and >Antarctica. Data from Greenland was gathered by scientists at >NASA's Goddard Space Flight Center using satellites. A >University of Wisconsin polar research center study indicated >similar snow and ice accumulation in Antarctica. Ha! I knew it! Everybody's worried about the greenhouse effect, and we could be heading for another ice age! Here in Maryland, our last two summers were significantly cooler than usual (though nobody but the meteorologists believe it), and this past December was the coldest on record. (Purely by coincidence, I greatly prefer hot weather to cold weather, and live ~600 feet above sea level. :-) Just think how bad it would have been if we had stopped burning coal and used nuclear reactors for power generation. :-) John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ Date: Wed, 10 Jan 90 12:44 CST From: FRANCEY%ccm.UManitoba.CA@vma.cc.cmu.edu To: Subject: ADDITION TO SUBSCRIPTION LIST Could you please add to your mailing list of space digest. ------------------------------ Date: 10 Jan 90 22:53:35 GMT From: rochester!dietz@pt.cs.cmu.edu (Paul Dietz) Subject: Re: Nuclear Reactors in Space In article <6732@lynx.UUCP> neal@lynx.UUCP (Neal Woodall) writes: >Sure, there is a fundamental similarity: both use nuclear processes to "store" >their energy (as opposed to chemical proceses in a battery). Beyond this, they >are dissimilar. Wrong; both also convert heat to electricity. >1) The reactor uses a fissionable form of Plutonium which emits fast neutrons >and is capable of sustaining a nuclear reaction, As far as I know, all space reactor designs will use U-235, not plutonium. > while the RTG uses a non- >fisionable form of plutonium which emits only (I believe) beta particles..... Alpha particles. >which you you rather be hit by, a bunch of fast neutrons or a bunch of beta >particles? Of course, if the reactor breaks up, it *stops* making neutrons. The RTG continues to emit alpha particles even if it disintegrated down to component atoms. >2) The nuclear reactor gets its power from a sutained nuclear reaction, and >as such has the potential to get out of hand, while the RTG gets its power >strictly from nuclear decay...no chance of a runaway chain reaction here. Runaway chain reactions are not a problem. If the chain reaction uses thermal neutrons, the most a runaway reaction can do is disperse the core with about the energy yield of the same mass of chemical explosives. > 3) Because the nuclear reactor actually has a sustained nuclear > reaction going on inside of it, it needs active control systems to > dampen the reaction....thus, it is much more complex. A properly engineered reactor has inherent negative feedback. As the core heats up, the thermal neutrons get hotter, and the chance a neutron will cause a fission goes down. You do need to adjust for buildup of neutron poisons (xenon, for example), but this is a slow process. >In all, the RTG is an excellent trade-off of safety and power: because it uses >nuclear fuel, it has a very high energy density....much higher than chemical >batteries. However, because the fuel is not fissionable, it is much safer. >Also, because there is no nuclear chain reaction, it is safer than a reactor. Not safer. A reactor contains much less radioactivity before it is turned on. An RTG is already radioactive at launch time. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: 10 Jan 90 22:45:24 GMT From: EWTILENI@pucc.princeton.edu (Eric William Tilenius) Subject: NSS' DIAL-A-SHUTTLE DIAL-A-SHUTTLE 1-900-909-NASA Listen to the astronauts! Plus updates and features, 24 hours a day, from Launch to Landing. Sponsored by the National Space Society. ($2.00 first minute; $.45 each additional minute.) CALL 1-900-909-NASA - ERIC - (__) Eric W. Tilenius (oo) /-------\/ President, Princeton Planetary Society / | || * ||----|| 609-734-7677 // ewtileni@pucc.Princeton.EDU ------------------------------ Date: Wed, 10 Jan 90 20:51:00 EST From: John Roberts Disclaimer: Opinions expressed are those of the sender and do not reflect NIST policy or agreement. Subject: Standardized payloads >From: ibmpa!szabonj@uunet.uu.net (Nick Szabo) >Subject: Cargo: costs and standards >>In article <3332@ibmpa.UUCP> szabonj@ibmpa.UUCP (Nick Szabo) writes: >>>Unmanned strikes again! Delta launches cost probably one-fifth to >>>one-tenth of a Shuttle launch, depending on whose accounting you want >>>to believe. >Of course, I was talking about absolute cost, not cost per pound. >Delta launch versus Shuttle launch, is what I said. Therefore, obviously, the Shuttle should not be used to launch small payloads that do not require human presence. This is the "window of opportunity" being used by the startup launch companies - very small payloads at a low price, so "medium-sized" organizations can afford to buy launch services. >Hopefully, we will soon have a set of standards for space cargo. In fact, I >can foresee somebody like AMROC making a "Delta clone": a launch vehicle with >the same exact cargo hold as the Delta, with the same lift capability, but >using the new AMROC engine technology. That way, satellite makers can >design their satellites for the standard without have to commit to any >specific launch vehicle. Also, implementers of new technologies like >EML or laser-launch would be well-advised to scale the machines to >existing payloads. So I should design my payload so that it can be blasted into space at ~10000G, or wafted gently upward at ~5-10G, depending on which service is the cheapest at the time, and that will save money? :-) I agree with Henry, who pointed out that exotic new launch services will probably be most useful (at least at first) in entirely new applications. I agree that coming up with several discrete classes of standardized payloads is probably a good idea. John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ Date: 11 Jan 90 01:39:00 GMT From: shelby!siegman%sierra.Stanford.EDU@decwrl.dec.com (Anthony E. Siegman) Subject: Re: Red Shifts through Random Media The work is by Professor Emil Wolf at the University of Rochester and you should be able to find it by looking through the indexes of the various journals of the Optical Society of America for the past several years. (At least I think this is what you're referring to.) Might look into Phys. Rev. Letters also. I don't think you'll find the discussion awfully understandable, however. In my opinion, the essence of Wolf's work is not that the light gets red-shifted, but that when a broad light spectrum passes through certain scattering processes a greater fraction of the red end of the spectrum (and a lesser fraction of the blue end) gets scattered toward the observer, with the result that the light received by the observer appears red-shifted compared to the original light spectrum before scattering. ------------------------------ Date: Wed, 10 Jan 90 22:17:46 EST From: John Roberts Disclaimer: Opinions expressed are those of the sender and do not reflect NIST policy or agreement. Subject: Re: Mars rovers >From: zephyr.ens.tek.com!tektronix!percy!parsely!bucket!leonard@uunet.uu.net (Leonard Erickson) >Subject: Re: Mars rovers >[long argument for getting around the time-lag and AI problems of >a Mars rover by slowing it down deleted] >Fine, the rover is creeping along at the feet feet per hour that you >suggest is safe. Now something unexpected happens. The surface shifts. >(loose rocks hidden by dust, a dust pocket, whatever] >The rover *must* make a real time response. If it isn't autonomous, it >can't. You can handle some things be designing in recovery gear (like >those levers for righting it that you mentioned) but the odds are >against you. What do you do it it manages to "high center" itself? >or if it is traversing a slope and starts to slip? Autonomy and real-time control are good as far as it goes, but they are not sufficient. Suppose the rover moves out over a thin-shelled volcanic bubble, which suddenly collapses. Or suppose the rover travels halfway down a slope of loose rubble, then triggers an avalanche. In either case, even an immediate response is far too late, and the rover will be destroyed. That's where the propagation of information backward in time comes into play. (The technique is described in the novel Thrice upon a Time, by James P. Hogan.) If the rover receives continual status updates from a future version of itself, say over a 5-10 minute span, then it will perceive upcoming dangers, and thus avoid the bubble or the unstable slope. This approach is clearly so vital to the safety of the rover, that we must hold off rover deployment until this technology has been perfected. :-) (Disclaimer: OK, maybe I'm being a little sarcastic, but I'm trying to make a point.) In the message I posted 1-2 months ago, it should not be construed that I was promoting remote control as a *goal* - I suggested it merely as an *expediency*. (This is comparable to the popular misconception of RISC computer design - that reducing the instruction set somehow improves performance. In fact, the goal is to improve the performance of the individual instructions, which usually means that the instruction set has to be trimmed down to limit chip complexity.) Sure, feel free to include as much local autonomy as you can manage, but I feel it is counterproductive to deliberately hold up deployment for many years while searching for a perfect "fully" autonomous control algorithm. This greatly increases the complexity and cost of the project, as well as the time before the first rover data is obtained. The rover design proposal that I have been most impressed by is the CMU rover, which uses a laser rangefinder to build up a model of its surroundings, and walks on pivoting legs. It will supposedly be "mostly" autonomous. Note that the proposed rate of motion (a few centimeters per second) is not much faster than the rate at which I think a "more remote- controlled" rover would be able to move, given local feedback and the ability to follow a fairly complex set of instructions. (In either case, maximum safe speed will be affected by the "roughness" of the terrain.) I think that autonomous land rovers that can bound along at 40 miles per hour are several decades away. In the case of the CMU rover, I suspect that the hardware will be done before the software is perfected. If that turns out to be the case, I would recommend that the project push for launch as soon as possible, based on the following argument: It is not necessary that the rover be "fully" autonomous before it can be useful. At worst, it can operate under close human supervision, and while its rate of travel will be reduced, it can still collect a considerable amount of data. In the meantime, development of autonomous control software can proceed at essentially the same rate that it would if the rover were sitting back on earth doing nothing. When this development is complete, the internal program of the rover can be updated. Moreover, software development can continue over the ~2-year trip from Earth to Mars. There are precedents for this situation. The hardware of the Space Telescope was essentially complete long before the control software was ready. The control algorithms of the Voyager spacecraft were considerably enhanced years after they had been launched. I agree with your contention that the first target for local autonomy should be in safety systems, such as avoidance of large rocks and holes, slip detection, and antenna pointing. Once these systems are in place, it is time to concentrate on performance enhancement. The arguments about interruptions in communications and bandwidth required must also be considered. John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ End of SPACE Digest V10 #413 *******************