Return-path: X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson Received: from hogtown.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 ; Fri, 14 Jun 91 06:00:39 -0400 (EDT) Message-ID: <4cK9D2S00WBw03ok5P@andrew.cmu.edu> Precedence: junk Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Fri, 14 Jun 91 06:00:34 -0400 (EDT) Subject: SPACE Digest V13 #645 SPACE Digest Volume 13 : Issue 645 Today's Topics: Re: Galileo Antenna (was Re: Amputation) Re: SPACE Digest V13 #556 Re: Self-sustaining infrastructures Re: Galileo Antenna (was Re: Amputation) Re: Extra Terrestrial Intelligence Re: SPACE Digest V13 #541 Re: Fred vs. Exploration: head-to-head competition Beginner's guide to space plasma physics wanted Re: Self-sustaining infrastructures What Kennedy forgot to say... (was: Re: SPACE Digest V13 #556) Refueling satellites (was Re: Self-sustaining infrastructures) Re: satellite refuelling Administrivia: Submissions to the SPACE Digest/sci.space should be mailed to space+@andrew.cmu.edu. Other mail, esp. [un]subscription requests, should be sent to space-request+@andrew.cmu.edu, or, if urgent, to tm2b+@andrew.cmu.edu ---------------------------------------------------------------------- Date: 27 May 91 02:37:09 GMT From: world!ksr!clj%ksr.com@uunet.uu.net (Chris Jones) Subject: Re: Galileo Antenna (was Re: Amputation) In article <2416@qusuna.queensu.CA>, akerman@qucis (Richard Akerman) writes: >In article <0094915E.41E11340@KING.ENG.UMD.EDU> sysmgr@KING.ENG.UMD.EDU (Doug Mohney) writes: >> >>You are implying that Galileo's antenna deployment problems are a direct >>result of the trajectory. or that flying it on Shuttle damaged it. Could you >>please produce some direct evidence of this? I wasn't aware that JPL had >>figured out why the antenna was gorked. >> >>Could be just a part which failed. Could be a lot of things. I'm sure both sci. >>space and JPL would appreciate the documentation of failure and why. > >Well, certainly the high-gain antenna cover was necessary because of the Venus >flyby, but I guess the question is whether the "umbrella" design of the >HG antenna was used because of the flyby or if it had been intended for the >spacecraft even if it had been launched by a Centaur upper stage from the >shuttle. Anyone know? I believe any high gain antenna with Galileo's data rate and operating from Jovian distances is going to be larger than will fit into any standard payload fairing. It's pretty much a given that it will require some sort of compact stowage and subsequent deployment. This particular design is the same as is used for TDRS satellites, I recall. It wasn't changed between the Shuttle-Centaur direct flight plan and the Shuttle-IUS VEEGA flight plan, save for the addition of the sun shield and the delay in deploying it. The unusual aspect of Galileo's mission is the length of time the antenna is kept undeployed, and I'm sure there is concern that this caused or contributed to the deployment problem. As has been pointed out, though, there are many possibilities, and JPL seems to be taking a very cautious approach to resolving the problem (as well they might, since they do have time, and don't want to make things worse by hasty action). -- Chris Jones clj@ksr.com {uunet,harvard,world}!ksr!clj ------------------------------ Date: Sun, 26 May 91 03:50 EDT From: Mike Bishop Subject: Re: SPACE Digest V13 #556 .....special session of Congress May 25, 1961 "I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man in the moon and returning him safely to earth." - John F. Kennedy ------------------------------------------------------------- Mike Bishop "If your on the right track, you'll get run over if you just sit there" SAS Institute Inc. Cary, NC - Will Rogers -------------------------------------------------------------- ------------------------------ Date: 26 May 91 17:51:58 GMT From: swrinde!cs.utexas.edu!sun-barr!newstop!exodus!concertina.Eng.Sun.COM!fiddler@ucsd.edu (Steve Hix) Subject: Re: Self-sustaining infrastructures In article <1991May26.011322.19893@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes: >In article <1991May26.002647.22594@agate.berkeley.edu> fcrary@lightning.Berkeley.EDU (Frank Crary) writes: >>On this note, I would like to mention that the lifetime of a satellite in >>Low Earth orbit is limited by its fuel supply... > >Another issue here, by the way, is that satellites fuelled by hydrazine also >suffer from slow degradation of the catalysts they use to break it down in >their thrusters. So just refuelling them has limits. > >>... Can anyone comment on the viability of a >>for-profit Low Earth orbit infrastructure for the purpose of re-fueling >>satellites? > >constellation. Refuelling geostationary comsats would be much more promising. >Getting from one side of Clarke orbit to the other is not quick, but it *is* >relatively cheap, and there usually is plenty of advance warning that a bird >is running low. Of course, you'd have to convince the comsat builders to >start providing for refuelling. Don't just refuel them: build the comsats with removable attitude-control packs. Pop out the old one, pop in the new one, and take the old one back for refurbishing and refueling (so as to deal with the catalyst degradation problem, etc. at the same time). Btw, would it make sense to build Clarke-orbit comsats with gravity-gradient stabilization? Or do they *really* have to have station-holding capability? -- ------------ The only drawback with morning is that it comes at such an inconvenient time of day. ------------ ------------------------------ Date: 27 May 91 01:22:11 GMT From: agate!lightning.Berkeley.EDU!fcrary@ucbvax.Berkeley.EDU (Frank Crary) Subject: Re: Galileo Antenna (was Re: Amputation) In article <2416@qusuna.queensu.CA> akerman@qucis.queensu.CA (Richard Akerman) writes: > ...but I guess the question is whether the "umbrella" design of the >HG antenna was used because of the flyby or if it had been intended for the >spacecraft even if it had been launched by a Centaur upper stage from the >shuttle. Anyone know? The high gain antenna was designed and built long before the Challenger accident. No one at the time had ANY idea that a Venus fly-by would be involved. The addition of the fly-by had NOTHING to do with the antenna design. Frank Crary ------------------------------ Date: 26 May 91 18:27:39 GMT From: agate!earthquake.Berkeley.EDU!fcrary@ucbvax.Berkeley.EDU (Frank Crary) Subject: Re: Extra Terrestrial Intelligence In article <1991May26.030900.20569@nntp-server.caltech.edu> steinly@zeppo.tapir.Caltech.EDU (Steinn Sigurdsson) writes: >Open clusters would be fairly bad for a civilization with a long term >view, too violent and too short lived. If the halo population has >planets it would be the best bet, although the stars may be too red >and dim. In either case there are plenty of second generation G >dwarfs, and we _know_ they can suffice. Clusters are only violent and short lived on an astrononical time scale. On the scale of a civilization, they are quite constant. Remember, ALL human civilization is less than 10,000 years old. As long as a cluster doesn't change much on a scale of 100,000 to 1,000,000 years (which it doesn't, unless it is VERY young and still has alot of O and B stars...) I don't think colonists would mind. (Note this is based on a extrapolation of social behavior resulting from a single data point, e.g. mankind.) Along a similar line, ALL teraforming concepts are "short lived:" they create a Earth-like environment on Mars or Venus or whatever that will last at most 10 million years. People still talk about them as if they were perminant. Halo population stars are, in general, metal-poor and would not, in all probability, have any planets. Frank Crary ------------------------------ Date: 26 May 91 18:22:53 GMT From: usc!jarthur!nntp-server.caltech.edu!hamlet.caltech.edu!carl@ucsd.edu (Lydick, Carl) Subject: Re: SPACE Digest V13 #541 In article , waltdnes@w-dnes.UUCP (Walter Dnes ) writes... > So we no longer burn a hydrogen-oxygen mixture in the shuttle's >rockets... instead we react hydrogen & oxygen in a fuel cell to >generate electricity to power the motor that reels/unreels the >tether. I still fail to see the difference. Now, how do you get the >hydrogen/oxygen up to the station ? > >> >shuttle will tend to remain in the same orbit as the station, *UNLESS >> >IT FIRES ITS ROCKET ENGINES TO DE-ORBIT*. That's what the shuttle has >> >to do right now. >> >> It doesn't have to fire it's engines. It has to expel enough mass at >> high enough speed to match the momentum change it wants. Rockets are >> traditional, but in this case, you could use the station itself as >> 'reaction mass'. > > Assuming that the station can maintain its structural >integrity through several years of heavy-duty jolting to kick >the shuttles out, *WHERE DOES THE ENERGY FOR THE "KICK" COME >FROM* ? A magnetic-repulsion launcher would require electricity, >which would take us back to fuel cells. The energy comes from lowering the shuttle back to the lower orbit prior to reentry. This, of course, requires that you have some way to store the energy. There will, of course, be losses. But using maneuvering rockets, the losses are 100%, so you're bound to save SOMETHING using a tether. You don't have to kick the shuttle hard enough to drop it all the way to the lower orbit; just hard enough that tidal forces can maintain a tension on the tether. -------------------------------------------------------------------------------- Carl J Lydick HEPnet/NSI: SOL1::CARL Internet: CARL@SOL1.GPS.CALTECH.EDU ------------------------------ Date: 26 May 91 17:53:57 GMT From: swrinde!sdd.hp.com!spool.mu.edu!news.nd.edu!mentor.cc.purdue.edu!pop.stat.purdue.edu!hrubin@ucsd.edu (Herman Rubin) Subject: Re: Fred vs. Exploration: head-to-head competition In article <4238@polari.UUCP>, crad@polari.UUCP (Charles Radley) writes: ................ > The makeup of comets......I would rather have skin makeup for my > wife. Really Mr. Szabo, your attempts at justifying space science > as being somehow more worthwile than manned spaceflight are > absolutely parochial to the point of silliness. Radley and Szabo have illustrated my point that the government should not be in the business at all. Different people want different things, and have different priorities, and it is important that governments not decide what should and should not be done. Let those who wish to support exploration support exploration, those who wish to support man is space support it, and those who wish to support welfare project support them. We need diversity, and not direction by bureaucrats or ignorant Congress- people. The funding should not come from taxes, but from those who wish to invest or donate to the cause. There will be cooperation between the various groups, as there is now, and there will not be the problem of trying to get majority support, or even convince politicians. -- Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907-1399 Phone: (317)494-6054 hrubin@l.cc.purdue.edu (Internet, bitnet) {purdue,pur-ee}!l.cc!hrubin(UUCP) ------------------------------ Date: 26 May 91 22:49:52 GMT From: agate!spool.mu.edu!uwm.edu!zaphod.mps.ohio-state.edu!wuarchive!rex!rouge!pc.usl.edu!dlbres10@ucbvax.Berkeley.EDU (Phil Fraering) Subject: Beginner's guide to space plasma physics wanted I'm looking for a good book on plasma physics for a senior level Physics student that can at least partially explain magnetic fields entrailed in plasmas and their behavior. I'd also like a good introduction to the work of Hannes Alfven (please excuse the plain ascii...). Thanks a lot!!! Post or e-mail, depending on your preference. Phil Fraering || Usenet (?):dlbres10@pc.usl.edu || YellNet: 318/365-5418 Standard disclaimer, whatever a disclaimer is, applies. ''It hardly mattered now; it was, in fact, a fine and enviable madness, this delusion that all questions have answers, and nothing is beyond the reach of a strong left arm.`` - Larry Niven and Jerry Pournelle, _The Mote in God's Eye_ ------------------------------ Date: 27 May 91 01:33:44 GMT From: agate!lightning.Berkeley.EDU!fcrary@ucbvax.Berkeley.EDU (Frank Crary) Subject: Re: Self-sustaining infrastructures In article <14033@exodus.Eng.Sun.COM> fiddler@concertina.Eng.Sun.COM (Steve Hix) writes: > >Don't just refuel them: build the comsats with removable attitude-control packs. >Pop out the old one, pop in the new one, and take the old one back for refurbishing >and refueling (so as to deal with the catalyst degradation problem, etc. at the >same time). > I think refueling would be easier to do, even if it might be a less effecient way to extend the lifetime of satellites. Replacing the station keeping system would invlove, at least, screwing in bolts. Refueling just requires connecting a hose. This would be easier to do teleroboticly, and may even be possible with a satellite not designed for refueling (or failing that, it would require very little re-design.) >Btw, would it make sense to build Clarke-orbit comsats with gravity-gradient >stabilization? Or do they *really* have to have station-holding capability? > They REALLY need station keeping. This is to keep the same position in orbit. Without this, the satellite would wind up in a geostationary orbit over the Indian Ocean (the gravitational minimum potential point in the geostationary orbit.) Gravity-gradient stabilization would only effect the attitude of the spacecraft, not its orbit. In any case, this effect, as well as other "tidal" forces, decreases with the CUBE of distance. As a result, it is VERY weak at geostationary heights. Frank Crary ------------------------------ Date: 27 May 91 00:41:05 GMT From: usc!zaphod.mps.ohio-state.edu!uwm.edu!csd4.csd.uwm.edu!markh@apple.com (Mark William Hopkins) Subject: What Kennedy forgot to say... (was: Re: SPACE Digest V13 #556) In article <9105260752.AA10074@mozart.unx.sas.com> SNOMCB@mvs.sas.com (Mike Bishop) writes: > May 25, 1961 > > "I believe that this nation should commit itself to achieving >the goal, before this decade is out, of landing a man in the >moon and returning him safely to earth." > > - John F. Kennedy "... and we should follow it up with sustained exploration of the moon, leading eventually to the establishment of lunar bases. With this experience, I believe that we shall have the capacity to forge ahead to land a man and woman on Mars BEFORE THE END OF THIS CENTURY, and settle the first colonies shortly thereafter." This is what he would have ultimately said if he had lived... America lost its sense of direction in the 1960's. As a people, we no longer knew why we were in Vietnam, we no longer knew why we were going into space, Congress no longer knew how to maintain finances properly :), pluralism becamse a curse on the future instead of a cause for future celebration. All this could be traced, in one significant stroke of insight, to the loss of vision ... ultimately to the loss of the man in '63. Hey, that's what you get for overreliance on someone else's vision! It might be called leadership addiction. :) ------------------------------ Date: 27 May 91 03:47:05 GMT From: news-server.csri.toronto.edu!helios.physics.utoronto.ca!aurora.physics.utoronto.ca!neufeld@uunet.uu.net (Christopher Neufeld) Subject: Refueling satellites (was Re: Self-sustaining infrastructures) On the subject of refueling satellites, can anybody tell us whether the fuel tank is usually kept in the spun or despun section of a satellite with both? Some tanks are equipped with a forcing membrane to feed the fuel. Are any fed centrifugally, possibly with a gas injector to maintain a constant pressure? In short, would there be any difficulties with putting the fuel system on an inertially fixed platform? If some of the thrusters have to go on the spun section this must result in some fancy plumbing at the bearing. -- Christopher Neufeld....Just a graduate student | There no place like $FC58 neufeld@aurora.physics.utoronto.ca Ad astra! | They're $FF69-ing my cneufeld@{pnet91,pro-cco}.cts.com | every word! Send for a "Don't edit reality for the sake of simplicity" | free $A56E. ------------------------------ Date: 27 May 91 22:20:54 GMT From: swrinde!zaphod.mps.ohio-state.edu!rpi!news-server.csri.toronto.edu!utzoo!henry@ucsd.edu (Henry Spencer) Subject: Re: satellite refuelling In article dlbres10@pc.usl.edu (Fraering Philip) writes: >\new development (pun unintentional) in comsat thrusters is using resistance >/grids or electric arcs to superheat the exhaust from a hydrazine thruster. > >Couldn't an electric heating element be used as a catalyst? I'd expect so -- the stuff does decompose if you heat it enough -- but there may be some problem with that. The resistojet-boosted hydrazine designs I've seen do seem to make catalysis and heating separate steps, if memory serves. I don't know why offhand. Actually, I can think of one possibility -- the conditions of decomposition influence the chemical composition of the exhaust, and hence the exhaust velocity -- but I don't know whether that applies. -- "We're thinking about upgrading from | Henry Spencer @ U of Toronto Zoology SunOS 4.1.1 to SunOS 3.5." | henry@zoo.toronto.edu utzoo!henry ------------------------------ End of SPACE Digest V13 #645 *******************