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, 25 Nov 89 01:46:09 -0500 (EST) Message-ID: Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Sat, 25 Nov 89 01:45:38 -0500 (EST) Subject: SPACE Digest V10 #273 SPACE Digest Volume 10 : Issue 273 Today's Topics: Re: Steam powered solar power sats (SPSPS) NASA Space archive service now available Shuttle Book Re: Steam powered solar power sats (SPSPS) Re: Moon Colonies / Ant Tanks? Re: Why NASA wants to go to Mars Re: Viewing Earth w/the HST ---------------------------------------------------------------------- Date: 23 Nov 89 21:26:36 GMT From: daisy.learning.cs.cmu.edu!mnr@pt.cs.cmu.edu (Marc Ringuette) Subject: Re: Steam powered solar power sats (SPSPS) paj@mrcu (Paul Johnson) writes: > [Everybody] seem to be proposing solar power satalites > using square miles of solar cells. Why not use mirrors (cheap & > light: make them out of sodium) and run a steam turbine. Using a large mirror plus a high-temperature generator is a great idea for space power production, as far as I can tell. A turbine containing water or some other fluid is one possibility. An alternative to turbines is thermionic power conversion. Thermionic Power Conversion (TEC) --------------------------------- The idea of TEC is to heat up an electrode until electrons are moving so fast that some of them can jump across a potential gap. If you make sure the other electrode isn't as hot, so the electrons don't jump back, you can use this to drive an electrical load. It looks like a winner. It has no moving parts, turns a temperature difference directly into electricity, doesn't use up any material, and works at high temperatures for a good power-to-weight ratio. The research was mostly done at NASA Lewis. A 1981 article in Horton's book (references below) cited these figures: input power densities of up to 100 Wt/cm/cm (Wt = watts total) output power densities 10-40 We/cm/cm (We = watts electrical) operating temperatures 1300-1900K input 900-1500K output 500-1000K differential gives 10-40 We/cm/cm Note that the power densities are in watts per unit area, rather than watts per kilogram. I have figures for solar flux level in outer space of 0.1 to 0.15 W/cm/cm, so an input flux of 100 Wt/cm/cm is about 700-1000 times that of ambient sunlight. Another 1966 paper from the Szego book, from JPL, has a TEC working at 24 W/cm/cm, weighing 260g, producing 48W at 2000K emitter temperature. Pretty good power densities for that early stage. The Radiator ------------ Most space power systems are driven by a temperature difference. This difference must be maintained by some sort of radiator on the cool side of the generator. The radiator can often be the heaviest part of a system. However, the higher the temperature, the more energy you can radiate, which is an advantage for a TEC or turbine system. In fact, some TEC systems are configured so as not to need an external radiator; they operate at high enough temperature that the necessary temperature gradient can be maintained by merely keeping one side dark. One article is by Shimada and Ewell of JPL, in the Horton book; the power densities weren't spectacular, though. If you use a radiator, the basic design conducts heat to a set of radiating fins, by fluid flow or a heat pipe. There are some untested but interesting alternatives like the one Keith Henson pointed out, which use dust or gas to increase the ratio of surface area to weight in the radiator. References ---------- Finke, Electric Propulsion and its Application to Space Missions, AIAA, 1981 Horton, ed., Spacecraft Radiative Transfer and Temperature Control, AIAA, 1981 Szego & Taylor, Space Power Systems Engineering, AIAA, 1966 Summary ------- Cool stuff, and potential for orders of magnitude improvement in space power generation. If you like to think about this kind of stuff, you might want to join 'space-tech', a mailing list I run. We talk about all sorts of ideas for space transportation and exploration, with emphasis on working out the physics of what's going on. To join or ask for more info, send mail to 'space-tech-request@cs.cmu.edu' on the Internet. -- Marc Ringuette // CMU CS Dept, Pittsburgh // Internet: mnr@cs.cmu.edu ------------------------------ Date: 22 Nov 89 07:08:17 GMT From: trident.arc.nasa.gov!yee@ames.arc.nasa.gov (Peter E. Yee) Subject: NASA Space archive service now available I've added an extra directory to the archive server running on ames.arc.nasa.gov. Now, if you miss a status report posting, or you want to read back issues of NASA Headline News, you can! The archive is available via both anonymous ftp and archive-server mail response. Instructions: Anonymous FTP ftp to ames.arc.nasa.gov (128.102.18.3). Cd to pub/SPACE. Get any of the files you want. The file index contains a listing of what's available. Archive-server mail response Send a letter to archive-server@ames.arc.nasa.gov (or to ames!archive-server, or ames::archive-server). As the subject of your message you may send commands like: "send space index" or "send space STS-34.Press-Kit". Send the command "help" for more detailed instructions on how to use the archive-server. File names: Generally files are named by type and date. For example, the Shuttle Status report for this morning would be named ss11.21.89. Common prefixes are "ps" for Payload Status, "h" for NASA Headline News, "r" for Press Release, "ss" for Shuttle Status, "gs" for Galileo Status", "ms" for Magellan Status, "cs" for COBE Status, "la" for Launch Advisory, etc. There are also several other files with more descriptive names. Problems: Send me e-mail if you have problems accessing the archives. Start of Service: I started filling the archive yesterday, so there isn't much there yet. -Peter Yee yee@ames.arc.nasa.gov ames!yee ------------------------------ Date: 20 Nov 89 10:54:30 GMT From: mcsun!ukc!strath-cs!cs.glasgow.ac.uk!kww@uunet.uu.net (Mr Kevin Waite) Subject: Shuttle Book Can anyone recommend a good medium-level text on the Space Shuttle that concentrates on the technical issues rather than the political ones. By 'medium-level' I mean something between the "the Space Shuttle is a spaceship" level and the "design of turbopump turbine blades" level. Thanks in advance. Kevin -- Email: kww@uk.ac.glasgow.cs (JANET) kww%cs.glasgow.ac.uk@nsfnet-relay.ac.uk (INTERNET) Address: Dept. of Computing Science, University of Glasgow, 17 Lilybank Gardens, Glasgow, United Kingdom. G12 8QQ ------------------------------ Date: 23 Nov 89 17:45:43 GMT From: cs.utexas.edu!samsung!shadooby!mailrus!jarvis.csri.toronto.edu!ists!yunexus!utzoo!henry@tut.cis.ohio-state.edu (Henry Spencer) Subject: Re: Steam powered solar power sats (SPSPS) In article <264@oasis.mrcu> paj@mrcu (Paul Johnson) writes: >...he and everyone else seem to be proposing solar power satalites >using square miles of solar cells. Why not use mirrors (cheap & >light: make them out of sodium) and run a steam turbine... Actually, one would use aluminum rather than sodium. Just as good, if not better, as a mirror (most astronomical telescopes use it), and not nearly the hassle to handle. Aluminum mirrors can be very thin; 30nm of aluminum is still highly reflective. The main problems with solar-dynamic powersats are (a) moving parts and (b) greater sensitivity to structural distortions and inaccurate Sun-pointing. Also, there is very little experience with solar-dynamic power systems in space. A solar-dynamic powersat is probably a better design, but as of today it's also a riskier design. >BTW, how much would solar cell production by the square mile damage >the environment? Depends on the type of cell. Silicon is no big deal. Gallium arsenide is a bigger problem, due to highly toxic materials. The best place to build parts for power satellites is, in any case, either in space or on the Moon. >Similarly, for power down to Earth, everyone assumes microwaves. Why >not set up an antimatter factory in orbit and ship a few milligrammes >back down to Earth every so often? With current designs, antimatter production is *very* inefficient, and using antimatter for power production is not great either. The big advantage of microwaves is that the conversions to and from electricity are quite efficient. -- A bit of tolerance is worth a | Henry Spencer at U of Toronto Zoology megabyte of flaming. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ Date: 23 Nov 89 18:24:48 GMT From: mailrus!jarvis.csri.toronto.edu!ists!yunexus!utzoo!henry@uunet.uu.net (Henry Spencer) Subject: Re: Moon Colonies / Ant Tanks? In article <5341@mentor.cc.purdue.edu> f3w@mentor.cc.purdue.edu (Mark Gellis) writes: >... this means you have to have >carbon as an initial material. How common is carbon in the solar >system (not counting hard to reach places like the core of the sun)? Quite common, actually, although it tends to be associated with volatile compounds and hence isn't common on the Moon. Barring that, it is one of the half-dozen commonest elements for quite fundamental reasons. The solar system has lots of carbon dioxide and methane, although much of it is not in the most convenient places. There is, however, a useful amount of carbon in certain classes of meteorites and hence very probably in certain classes of asteroids. >Could it be, say, extracted from the ice/junk surfaces of the moons >of the gas giants? Reasonably likely, picking the colder moons, although it is difficult to be sure since our knowledge of the surface compositions of those moons is somewhat indirect. >Second, for anyone who knows anything about fusion reactions, also >related to carbon. If you have controlled fusion power (which we >should have sometime in the next hundred years), can you simply make >carbon from helium? ... Only with great difficulty. Controlled fusion will not be up to doing that in useful quantities for a long time, barring some major breakthrough. The helium->carbon reaction is geologically slow under conditions that are likely to be practical in the near future. (It's not exactly fast even in most stars. It requires *three* helium nuclei colliding in the right way, as there is no stable intermediate that could be formed by collision of two.) >Fourth, O'neill has his space habitat as a 6.4 km x 32 km. cylinder. >Is there any reason why a cylinder in space could not be made longer? >Could you build a 6.4 km. x 320 km. cylinder, for example... Ideally, no problem. But there are various non-ideal complications. Tidal forces need considering if you're doing this anywhere near the Earth or the Sun, for example. For another example, a spinning object generally prefers to spin end over end (formally: on the axis with the greatest moment of inertia). A rigid object is not capable of changing its spin axis... but no hollow cylinder kilometers across is rigid in any realistic sense. Spinning satellites have to be designed quite carefully to keep the spin axis where it belongs. I'm not sure O'Neill thought of this... The problems will get worse as the cylinder gets longer. -- That's not a joke, that's | Henry Spencer at U of Toronto Zoology NASA. -Nick Szabo | uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ Date: 23 Nov 89 05:14:12 GMT From: frooz!cfa.HARVARD.EDU@husc6.harvard.edu (Bill Wyatt) Subject: Re: Why NASA wants to go to Mars [...] < From "Aviation Week and Space Technology," Oct. 30, 1989 (p.15): < Franklin D. Martin, NASA's associate administrator for exploration, has a < host of reasons for sending humans to Mars. [...] < "Hey, Frank, you left off science," [...] < "Yeah, maybe so. Yeah," [...] "science is < one of the reasons you do these things, but it's not the driver." < < Am I the only one who nearly became physically ill after reading this? < Is this truly what our space program has become, a bunch of administrators < who are no longer aware that space exploration is meant for science? < [...] < If any of you hopeful ones needed proof of the final < collapse of the United States' space program, here it is. Yes, I agree the (U.S.) space program is near collapse, and YES I agree that sending men to Mars is not done because of science. If you want to do space research, there are a hell of a lot better and more productive ways to spend your money than by putting people up there. There's a small class of problems that would benefit by human presence, but there's a long way to go before you've exhausted the worthy unmanned projects. As an example: test the absurdity, given present levels of technology and more reasonable alternatives, of the following statement: `We must must embark on a program to send men to Pluto, since the Voyagers didn't get out there to take any pictures and give us a close-up view of the Pluto-Charon system.' I'm not against a manned space program, but I do think it's a crime the way NASA fixates on bloated projects at the expense of space science, and turns around and denys there's any alternative. Don't you believe that science has EVER been a driver for the manned space program; it has ALWAYS been primarily a politically and then technologically motivated operation. The scientific gains have been a bonus, not a driver, ever. Bill Wyatt, Smithsonian Astrophysical Observatory (Cambridge, MA, USA) UUCP : {husc6,cmcl2,mit-eddie}!harvard!cfa!wyatt ARPA: wyatt@cfa.harvard.edu SPAN: cfa::wyatt BITNET: wyatt@cfa Bill Wyatt, Smithsonian Astrophysical Observatory (Cambridge, MA, USA) UUCP : {husc6,cmcl2,mit-eddie}!harvard!cfa!wyatt ARPA: wyatt@cfa.harvard.edu SPAN: cfa::wyatt BITNET: wyatt@cfa ------------------------------ Date: 22 Nov 89 15:49:24 GMT From: gem.mps.ohio-state.edu!uakari.primate.wisc.edu!larry!sde@tut.cis.ohio-state.edu (Scott Ellington) Subject: Re: Viewing Earth w/the HST The sunlit earth is far too bright to be observed by any of the HST sensors. In any case, the guidance system cannot slew anywhere near fast enough to track a target on the surface of the earth. ------------------------------ End of SPACE Digest V10 #273 *******************