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 ; Tue, 31 Oct 89 04:23:06 -0500 (EST) Message-ID: Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Tue, 31 Oct 89 04:22:45 -0500 (EST) Subject: SPACE Digest V10 #179 SPACE Digest Volume 10 : Issue 179 Today's Topics: Re: Galileo boost from Venus Re: PowerSat Options Galileo boost from Venus Re: Space Shuttle SRB exhaust gas makeup. Re: finally! SRB exhaust pollution Re: Asteroids as weapons of mass destruction Re: Galileo Schedule Cleaning up LEO Re: TDRS vs military Conference: Reducing the Cost... Re: Exhaust velocity Re: Radar astronomy MACSat ---------------------------------------------------------------------- Date: 24 Oct 89 15:55:21 GMT From: gem.mps.ohio-state.edu!ginosko!aplcen!aplvax.jhuapl.edu!jwm@tut.cis.ohio-state.edu (Jim Meritt) Subject: Re: Galileo boost from Venus In article <619@zip.eecs.umich.edu> brian@dip.eecs.umich.edu (Brian Holtz) writes: }Let me ask this again: } }If the attraction between Galileo and, say, Venus is the same }when Galileo is coming and going, how does the encounter speed }up the craft? Does it have something to do with the fact that it's }passing Venus as they both orbit the the sun? It doesn't from the viewpoint of venus. Note: That is not the viewpoint you postulated. That that is is that that is. That that is not is that that is not. That that is is not that that is not. That that is not is not that that is. And that includes these opinions, which are solely mine! jwm@aplvax.jhuapl.edu - or - jwm@aplvax.uucp - or - meritt%aplvm.BITNET ------------------------------ Date: 25 Oct 89 03:30:57 GMT From: rochester!dietz@cu-arpa.cs.cornell.edu (Paul Dietz) Subject: Re: PowerSat Options In article <22510002@hpcvia.CV.HP.COM> 10e@hpcvia.CV.HP.COM (Steven_Tenney) writes: >Please forgive a novice's ignorance on this subject but I thought I read >somewhere about a powersatellite collecting solar power and passing it >down to receiving stations either as microwave or even as a laser beam. I >knew that microwave energy was a viable option but what about laser energy? It wouldn't make much sense to use PV cells at a powersat to drive a laser -- the efficiency is just too low. For laser powersats to work, you want to chuck the light--> electricity--> light conversion, and go with a laser pumped directly by sunlight. Some varieties of solar pumped lasers do exist, but I don't know how durable or efficient they are. The big advantage of a laser powersat is that it can be much smaller, at fixed beam power density; megawatt scale satellites are possible. Technologies that require you jump immediately to gigawatt scale plants are very hard to develop. But clouds would be a problem. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: 24 Oct 89 10:38:32 GMT From: mailrus!sharkey!umich!dip.eecs.umich.edu!brian@tut.cis.ohio-state.edu (Brian Holtz) Subject: Galileo boost from Venus Let me ask this again: If the attraction between Galileo and, say, Venus is the same when Galileo is coming and going, how does the encounter speed up the craft? Does it have something to do with the fact that it's passing Venus as they both orbit the the sun? ------------------------------ Date: 24 Oct 89 16:31:14 GMT From: cs.utexas.edu!mailrus!jarvis.csri.toronto.edu!utgpu!utzoo!henry@tut.cis.ohio-state.edu (Henry Spencer) Subject: Re: Space Shuttle SRB exhaust gas makeup. In article <8910231952.AA14411@decwrl.dec.com> klaes@wrksys.dec.com (N = R*fgfpneflfifaL 23-Oct-1989 1549) writes: > Could someone please post information concerning the exhaust > gases from the Space Shuttle's solid rocket boosters during takeoff. > Does it contain hydrogen oxide? I.e., water? Yes, among other things. Lots of other things. SRB fuel, if I recall correctly, is ammonium perchlorate (NH4ClO4) plus a dash of aluminum powder for extra heat, a demitasse of synthetic rubber for mechanical strength, and an assortment of minor odds and ends to control burn rate and such. So the exhaust will contain water, alumina (Al2O3) particles, carbon dioxide (from the rubber), and a witches' brew of nitrogen and chlorine compounds and partially burnt ickiness. -- 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: 21 Oct 89 22:38:46 GMT From: ubc-cs!alberta!calgary!cpsc!rossd@beaver.cs.washington.edu (David Ross) Subject: Re: finally! In article <1437@syma.sussex.ac.uk> andy@syma.sussex.ac.uk (Andy Clews) writes: >Thanks for the information, Henry, but, uh, haven't you slipped into the >"I must be the first person in the world to announce this" trap? I'm >sure most of us heard about the launch etc. on TV and radio before >your posting got around. Andy, while I see what you are saying, I feel it is only fair to tell you where _I_ first heard about the Atlantis launch. Right here. I don't know about you, but I did NOT spend the last two weeks huddled in front of the TV and radio waiting for news of the launch. Having spent almost all of that time either studying myself silly or writing exams. I didn't have the time. The whole point of this meaningless tirade is, in short, that even if Mr. Spencer is NOT the absolutely first person to tell _YOU_ about something, and even if he is not the first person to tell most people, there are still going to be a few of us who do appreciate hearing about it from SOMEBODY. If people only announced things when they could be sure that they were the first to do so, things could get pretty dull. -D ------------------------------ Date: 24 Oct 89 16:24:50 GMT From: cs.utexas.edu!mailrus!jarvis.csri.toronto.edu!utgpu!utzoo!henry@tut.cis.ohio-state.edu (Henry Spencer) Subject: SRB exhaust pollution In article <1989Oct23.230054.26802@jarvis.csri.toronto.edu> hogg@db.toronto.edu (John Hogg) writes: >Shuttle SRBs have their problems, but orbiting exhaust isn't one of them. Upper-atmosphere exhaust is, however, and I think that's what the original reference was to. High-altitude atmosphere sampling does find a significant number of alumina particles, almost certainly from solid-rocket exhausts. -- 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: 24 Oct 89 16:16:50 GMT From: cs.utexas.edu!mailrus!jarvis.csri.toronto.edu!utgpu!utzoo!henry@tut.cis.ohio-state.edu (Henry Spencer) Subject: Re: Asteroids as weapons of mass destruction In article kr0u+@andrew.cmu.edu (Kevin William Ryan) writes: > If the asteroid is already in an elliptical orbit crossing Earths, then the >delta vee needed is that which changes the period of the asteroids orbit just >enough so that it crosses Earths orbit when the Earth is there, some time in >the future. I'm not knowledgeable enough to say how much delta-vee this >requires... Potentially almost zero. Potentially zero, in fact, given that there is a significant chance of a natural impact if you wait long enough. Humans do tend to be impatient, however... :-) > Second, concerning propulsion of said asteroid - nobody has mentioned mass >drivers! ... Probably because (a) they are slow, and (b) they're not a fully-developed technology yet. Just kicking the thing with H-bombs can be done with off-the-shelf technology, and the thrust-to-weight ratio is better. -- 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 Oct 89 14:47:56 GMT From: bunny!krs0@husc6.harvard.edu (Rod Stephens) Subject: Re: Galileo Schedule In article <1940@jato.Jpl.Nasa.Gov> baalke@mars.jpl.nasa.gov (Ron Baalke) writes: > > > Galileo Schedule of Events : : > 02/15/90 - Venus Flyby > 10/**/90 - Venus Data Playback : : What is "Venus Data Playback?" Why is it so long after the Venus flyby? Rod Stephens GTE Laboratories, Inc 40 Sylvan Rd Waltham, MA 02254 (617)466-4182 ------------------------------ Date: 24 Oct 89 00:27:04 GMT From: gem.mps.ohio-state.edu!wuarchive!mailrus!jarvis.csri.toronto.edu!utgpu!radio.astro!helios.physics!griffin@tut.cis.ohio-state.edu (Prof. A. Griffin) Subject: Cleaning up LEO Disclaimer: I am NOT professor Griffin. If you use "F", please check the attribution against the signature. 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 1.6 hours of exposure to the beam, or roughly two days, where the orbit passes into the beam every ninety minutes for four minutes. The same flake in a Clarke orbit would enter atmosphere after about twenty months. 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. If anyone finds these results unlikely, send me e-mail and I'll send you the parameters I used. I checked the results a few different ways, so I don't think they're wrong. -- Christopher Neufeld....Just a graduate student | "Scotty..now _would_ cneufeld@pro-generic.pnet01.crash | be a good time!" griffin@helios.physics.utoronto.ca | - Pavel Chekov "Don't edit reality for the sake of simplicity" | ------------------------------ Date: 24 Oct 89 03:00:54 GMT From: mailrus!jarvis.csri.toronto.edu!db.toronto.edu!hogg@tut.cis.ohio-state.edu (John Hogg) Subject: Re: TDRS vs military In article <2852@harrier.ukc.ac.uk> has@ukc.ac.uk (H.A.Shaw) writes: > Of the tens of thousands of small particles collected by the NASA U-2 >flights very few (about 10 ??) were of space origin. That was BEFORE the smoke >the Shuttle spews out got up there. (Yet one more reason for BANNING SOLID >FUEL ROCKETS) Shuttle SRBs have their problems, but orbiting exhaust isn't one of them. The SRBs themselves don't reach orbit by a *long* shot (remember that you can see SRB staging on launch coverage) and the exhaust is pointed somewhat down. The only thing that stops it from going right to the surface immediately is our thick atmosphere. Which brings up one comment on polluting ourselves out of space: we'd have a hard time doing that totally. Atmospheric drag is a function of the mass-to-projected area ratio. Our old friend the square-cube relationship says that small particles will be swept out of very low orbits quite quickly, while spacecraft will barely notice the drag. So we can always launch short-lifespan vehicles. This is not to say that being confined to low orbits only is at all acceptable... -- John Hogg hogg@csri.utoronto.ca Department of Computer Science, University of Toronto ------------------------------ Date: 24 Oct 89 21:17:33 GMT From: frooz!cfashap!willner@husc6.harvard.edu (Steve Willner) Subject: Conference: Reducing the Cost... A conference brochure has just landed on my desk. The full title is "Reducing the Cost of Space Infrastructure and Operations." Dates are 1989 November 20-22, registration requested by Nov. 6 but perhaps acceptable later. Location is Gaithersburg, MD. Sponsors are National Institute of Standards and Technology (formerly National Bureau of Standards); Office of Space Commerce (Dept. of Commerce); and The Space Foundation. Registration information: Lori Phillips, 301-975-3881 Technical information: Bill Stone, 301-975-6075 Cary Gravatt, 301-975-3850. [I am merely passing along the information in the brochure and know very little more; please contact one of the people listed if you have questions or want to attend.] ------------------------------------------------------------------------- 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: 24 Oct 89 21:45:35 GMT From: crdgw1!crdos1!davidsen@uunet.uu.net (Wm E Davidsen Jr) Subject: Re: Exhaust velocity In article <1989Oct23.203306.24154@brutus.cs.uiuc.edu>, zweig@brutus.cs.uiuc.edu (Johnny Zweig) writes: | I can't quite hack all the Isp, TC/m, and other mumbo-jumbo. I think it boils | down to the fact that the mass-flow (Kg/S) out the back of the motor gives | you part of your thrust, and the interaction between what comes out the back | "pressing against" the atmosphere is another. So if I have two rockets that | spit out the same mass of stuff per second, but one has higher nozzle | pressure, that one will give me somewhat more thrust off the launchpad (once | up in space there should be no difference since there's no atmosphere). Let me try to explain how this works. Picture a sphere filled with a pressurized fluid. Call it a ballon full of hot air. If you bisect the sphere with a plane (like, cut it in half), the pressure against each half will be equal. No thrust. Now open a hole in the sphere and let pressure escape (let go of the next of the balloon). If you think about the sphere pressure now, the inner pressure is P (say 10 psi), and the diameter of the nozzle is D (say 1/4 inch). That's an area of .785 square inches, which would have had a pressure of 7.85 pounds against it. Therefore the "front" of the balloon (or combustion chamber) has 7.85 lb more pressure on it than the back. There are also action/reaction effects which are independent of the pressure. Note that atmospheric pressure didn't come into any of this, except that it raises the pressure in the combustion chamber by a tiny amount and therefore raises the thrust. Since lack of atmosphere will effect either of the rockets you mentioned, there will still be more thrust for the higher pressure. Since you said the samme mass per unit time, the *velocity* may well be higher, as well, depending on the density of the exhaust. Correct or expand on this as appropriate. The guy said he wasn't a physicist so I didn't use metric. -- bill davidsen (davidsen@crdos1.crd.GE.COM -or- uunet!crdgw1!crdos1!davidsen) "The world is filled with fools. They blindly follow their so-called 'reason' in the face of the church and common sense. Any fool can see that the world is flat!" - anon ------------------------------ Date: 24 Oct 89 15:25:05 GMT From: crash!orbit!pnet51!schaper@nosc.mil (S Schaper) Subject: Re: Radar astronomy sounds good to me. As a separate comment, what about Masers? For the purposes of radio astronomy, John Roberts suggestion would probably be better, but what about masers for probe-based radar imaging? Whatever happened to this technology? It even penetrates clouds:-) UUCP: {amdahl!bungia, uunet!rosevax, chinet, killer}!orbit!pnet51!schaper ARPA: crash!orbit!pnet51!schaper@nosc.mil INET: schaper@pnet51.cts.com ------------------------------ Date: 24 Oct 89 16:45:33 GMT From: hao!murphy@handies.ucar.edu (Graham Murphy) Subject: MACSat Could someone either send me a binhex'd copy of MacSat or the address to obtain it. Alas, my old copy 'twas blown away in a bad disk crash ... :-( Graham ---------- INTERNET: murphy@hao.UCAR.EDU solarNET: gmurphy@solar.STANFORD.EDU HAO/NCAR, P.O. Box 3000, Boulder, CO 80307-3000. (303) 497-1565. ------------------------------ End of SPACE Digest V10 #179 *******************