From @PO2.ANDREW.CMU.EDU:ota+space.mail-errors@andrew.cmu.edu Tue Jul 31 03:13:49 1990 Return-Path: <@PO2.ANDREW.CMU.EDU:ota+space.mail-errors@andrew.cmu.edu> Received: from po2.andrew.cmu.edu by FED.EXPRES.CS.CMU.EDU (NeXT-1.0 (From Sendmail 5.52)/NeXT-1.0 jgm1.0) id AA06150; Tue, 31 Jul 90 03:13:49 EDT Received: by po2.andrew.cmu.edu (5.54/3.15) id ; Tue, 31 Jul 90 01:52:06 EDT Received: via switchmail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl@andrew.cmu.edu; Tue, 31 Jul 90 01:52:01 -0400 (EDT) Received: from andrew.cmu.edu via qmail ID ; Tue, 31 Jul 90 01:37:19 -0400 (EDT) Received: from beak.andrew.cmu.edu via qmail ID ; Tue, 31 Jul 90 01:32:56 -0400 (EDT) Message-Id: Precedence: junk Reply-To: space+@ANDREW.CMU.EDU From: space-request+@ANDREW.CMU.EDU To: space+@ANDREW.CMU.EDU Date: Tue, 31 Jul 1990 01:29:47 -0400 (EDT) Subject: SPACE Digest V12 #150 SPACE Digest Volume 12 : Issue 150 Today's Topics: Re: What if? RE: SPACE Digest V12 #143 Info need on rovers Re: Space Junk velocities Re: Model Rockets become more space junk Re: Galileo Update - 07/27/90 Re: HST testing (followup) Re: slowing the earth unusual sighting last evening Re: Omni magazine on Mars Re: space news from June 11 AW&ST Administrivia: Submissions to the SPACE Digest/sci.space should be mailed to space+@andrew.cmu.edu. Other mail, esp. [un]subscription notices, should be sent to space-request+@andrew.cmu.edu, or, if urgent, to tm2b+@andrew.cmu.edu ---------------------------------------------------------------------- Date: 30 Jul 90 19:44:16 GMT From: sdd.hp.com!hp-pcd!hpcvia!kas@ucsd.edu (ken_scofield) Subject: Re: What if? From: dil@mace.cc.purdue.edu (Perry G Ramsey) Message-ID: <5186@mace.cc.purdue.edu> >To really accomplish what you want, you would have to send the angular >momentum somewhere else. Example: > >A big linear accelerator facing west. Pick up some rocks and shoot them >into space. Chuck enough rocks out fast enough and you could make a dent. >I'll get you some numbers. > >And here they are! >Angular momentum of earth: 6.3 e33 kg m^2 s^-1 >Slowing to 25 hr rotation is 4% reduction, = 2.5e32 >If you chucked the rocks out at 15 km/s, you would need > >m = delta angular momentum > ________________________ = 2.8 e21 kg of rock > radius of earth * velocity > >This amounts to a hole about 800 km on a side to quarry the rocks. This reminds me of a recurring thought I've had, to wit: If a wayward asteroid struck the Earth with enough mass/energy to appreciably affect the rotation rate, would anybody survive to notice it? I haven't checked your numbers above, but one might assume that "catching" an 800 km cube would have roughly the same effect as "throwing" the cube -- except that "catching" it all at once is obviously going to wreak havoc. So, has anyone heard or read anything about what happens to us if this should occur? (Again, I'm interested in the case where the Earth's rotation and/or orbit are affected to a significant degree.) To a rough approx- imation, how big a "rock" would it take to do this? Ken Scofield C-9355 SSI #453890085 ^ Hewlett-Packard, ICO Phone: (503)750-2426 |----/-\----| 1020 NE Circle Blvd. (kas@hpcvia.CV.HP.COM) | Gone | Corvallis, OR 97330 (ucbvax!hplabs!hp-pcd!kas) | Divin' or | | Jumpin' | Cute Disclaimer: Nobody ever listened to me before, |-----------| so why start now? ------------------------------ Date: Mon, 30 Jul 90 09:56 EST From: "ADMIRAL AQUILONE, GREAT ALLIANCE" Subject: RE: SPACE Digest V12 #143 I have read your messages on this bulletin. and I am wondering. although I think jet propolsion and stuff is fun is there any information or discussion on aliens and the effects on us or the events, sightings and so forth????? decnet splava::aqui4156 bitnet aqui4156@snyplava ------------------------------ Date: Mon, 30 Jul 90 18:09 CDT From: Astronomers Do It At Night!! Subject: Info need on rovers X-Envelope-To: space+@andrew.cmu.edu ------------------------------ Date: 31 Jul 90 02:44:51 GMT From: usc!jarthur!nntp-server.caltech.edu!deimos.caltech.edu!krs@ucsd.edu (Karl Stapelfeldt) Subject: Re: Space Junk velocities Two objects in a 28.5 degree inclination circular orbit CAN impact each other with a relative velocity almost as large as the orbit velocity. Case in point: when the two orbits have a 180 degree difference between the longitudes of their ascending nodes. In this case, the orbits have the same inclination to the Earth's equator but their planes intersect at a 2*(28.5)= 57 degree angle. The relative velocity of two colliding particles in this case is (17,500 mph)*sin(57)= 14,700 mph !!! This represents the maximum possible relative velocity; a typical collision will occur at somewhat lower velocities. The equatorial bulge of the Earth perturbs low orbits in such a way that the longitude of the ascending node is always changing (`regressing'). This regression, combined with the constant influx of new debris sources, essentially guarantees that there will be some piece of junk in the a 28.5 orbit that can eventually realize the maximum impact velocity with any given spacecraft. Remember : Two orbits with the same inclination do not, in general, lie in the same plane. Karl Stapelfeldt krs@deimos.caltech.edu ------------------------------ Date: 30 Jul 90 20:17:11 GMT From: talos!kjones@uunet.uu.net (Kyle Jones) Subject: Re: Model Rockets become more space junk David E. Jenkins writes: > Many people have been discussing a contest to put a model > rocket on the Moon. > [...] > At orbital velocities even the smallest fragment can cause potentially > fatal damage to equipment and/or crew members. Do we really want to > contribute to this growing problem over a silly contest. Are these little bits of metal and whatnot a serious danger to LEO spacecraft? I would think that all the garbage and spacecraft would be orbiting in the same direction and at roughly the same speed, so the collisions wouldn't be as bad as if the garbage was in (say) retrograde orbit. ------------------------------ Date: 30 Jul 90 13:03:27 GMT From: cs.utexas.edu!sdd.hp.com!uakari.primate.wisc.edu!aplcen!warper.jhuapl.edu@tut.cis.ohio-state.edu (Ray Sterner) Subject: Re: Galileo Update - 07/27/90 In article <4410@jato.Jpl.Nasa.Gov> baalke@mars.jpl.nasa.gov (Ron Baalke) writes: > > GALILEO MISSION STATUS > July 27, 1990 > . . . > The flight team is now planning the remaining maneuvers and >cruise sequences, together with the Earth science activities for >the early December Earth gravity-assist flyby. Are there any concerns about Galileo's high speed dive so deep into the cloud of space debris around the earth? ------------------------------ Date: Mon, 30 Jul 90 18:12:03 EDT From: John Roberts Disclaimer: Opinions expressed are those of the sender and do not reflect NIST policy or agreement. Subject: Re: HST testing (followup) >From: zaphod.mps.ohio-state.edu!uwm.edu!ux1.cso.uiuc.edu!aries!mcdonald@tut.cis.ohio-state.edu (Doug McDonald) >Subject: Re: HST testing (followup) >In article <9007300049.AA21696@cmr.ncsl.nist.gov> roberts@CMR.NCSL.NIST.GOV (John Roberts) writes: [deleted] >This is a long quote. Sorry. I'll give it because the retort is so >simple: there was another mirror made. Thanks to Henry Spencer for pointing out that the second mirror was not completed, with most of the time and dollars still not put in. There have been conflicting reports in the media. Last week, CNN made some airhead comment about bringing HST back to earth and switching mirrors. >IF a real test had been done, >it is unlikely that the second mirror woudl have had a serious error. That's assuming NASA provided the correct specifications. They're pretty sure they did, but the investigation is not completed, so it's really not possible to make a definite statement now. >IF it did, of course, then money (not necessarily the taxpayer's) >would have been needed for fixing it. BUT if the second one was OK - >no more cost. AND we would have KNOWN about Perkin-Elmer's >incompetence earlier. You're forgetting the second (expensive) test, which almost certainly would have been demanded at that point. Component testing comes to be of decreasing utility as fabrication nears completion. At the time of completion of the mirrors, the expected cost to detect and fix an error apparently would not be dramatically less than the expected cost to fix it now. A reasonable conclusion is that the flaw *should* have been detected much earlier, when it would have been much cheaper to correct, and that's where the big mistake was made, not in the decision not to test upon completion. Two major areas of the current investigation are how the error was introduced in the first place, and why the testing didn't pick it up. For the second question, it could be an error in the testing methodology, or in the application of the tests, or a combination of the two. NASA and Perkin Elmer apparently both came up with portions of the test methodology, so either could be at fault. If the error was in the application of the tests, it is likely that PE would receive the bulk of the blame, since NASA has maintained that they were not able to have as much direct oversight as they would have liked. By the way, in reference to your comment that the testing could have been performed before coating, thus avoiding risk to the coating: the encyclopedia states that the thickness of a reflective coating (aluminum) should be at least 0.12 um for maximum reflectance. With a coating ~ 1/4 wave thick, and a tolerance of ~ 1/50 wave, unless they could be absolutely sure that the coating would be completely uniform, the definitive final testing (integrated or otherwise) would have to be performed after the coating process had been completed. Additional HST information (mostly from recollection of the HST telephone conference a few weeks ago): - Researchers are becoming increasingly confident that the error is fully in the primary mirror. That would be good, because it's the easiest type to correct. - If the error is purely a spherical aberration in the primary, then the blurring of star images should be fairly symmetric. If there is an error in the secondary, it is likely to produce coma (off-center blurring, i.e. comet-like tails on the stars), which will be more pronounced in instruments which are off the main optical axis of the telescope. - The wide field/planetary camera (WF/PC) is pretty much on the main optical axis. The faint object camera (FOC) is more off the axis. By comparing images from these two cameras, researchers can determine whether coma is present at the best focus, and thus deduce the nature of the aberration. - The people who are trying to find a fix for the problem are confident that they can deduce and compensate for at least 95% of the aberration based purely on images from space. (Would that be enough to put the optics fully within spec?) Nevertheless, determining the exact source and nature of the error by ground-based investigation (i.e. looking at the test equipment) would be a valuable check, and might improve the accuracy of the correction. - The magnitude of the error appears to be about four wavelengths of visible light. (Is 500nm the reference?) - With no further corrections or computer enhancement, image resolution is about as good as the best ground-based optical telescopes, or maybe a little better. Being above most of the atmosphere, HST is still very useful as an ultraviolet telescope before any fixes are made. Many of the other instruments are also usable. - The wide field / planetary camera is about the size of a telephone booth (younger readers can see old Superman episodes for reference :-). It contains eight tertiary reflectors, each about the size of a US 5 cent piece. Changing the curvature of these small mirrors can compensate for errors in the primary/secondary pair, as long as the big mirrors are sufficiently "smooth", which appears to be the case. John Roberts roberts@cmr.ncsl.nist.gov "We get 20 agents to memorize the book. That way, if something happens to 19 of them, we still have the information." - Maxwell Smart, Control Agent 86 (paraphrased) ------------------------------ Date: 30 Jul 90 16:50:28 GMT From: cs.utexas.edu!ut-emx!aoab314@tut.cis.ohio-state.edu (Srinivas Bettadpur) Subject: Re: slowing the earth In article <9007272338.AA20105@cmr.ncsl.nist.gov> roberts@CMR.NCSL.NIST.GOV (John Roberts) writes: > >>From: usc!samsung!noose.ecn.purdue.edu!mentor.cc.purdue.edu!mace.cc.purdue.edu!dil@ucsd.edu (Perry G Ramsey) > > >>To really accomplish what you want, you would have to send the angular >>momentum somewhere else. Example: > The nice thing about rigid body mechanics in 3-D is that you dont have to "send angular momentum" anywhere in order to change the angular velocity of the body, you can accomplish the same thing by a re-distribution of mass (due to the change in the Moments of Inertia). How about simply shifting the entire population of the earth to the equator so that the polar moment of inertia of the earth rises ? That should result in a drop in the spin rate about the Z axis to keep the net angular momentum in the Z direction constant. Corrections are welcomed. Srinivas Bettadpur ( aoab314 @ utchpc aoab314 @ emx.cc.utexas.edu ) ------------------------------ Date: 30 Jul 90 16:23:18 GMT From: usc!jarthur!nntp-server.caltech.edu!news@ucsd.edu (Horowitz, Irwin Kenneth) Subject: unusual sighting last evening I was wondering if the folks who read these newsgroups can help identify something that I saw last evening. At 7 p.m. I observed an object that appeared to be a very high flying aircraft (at first I thought it might have been an extremely bright star, and my curiousity was aroused by the fact that it was still an hour till sunset!). The unusual aspect of this object was that it was moving at an extremely slow rate, and I was able to follow it for nearly 30 minutes. Most normal aircraft, even flying that high, would move out of range in a matter of minutes. The object appeared due north at first, at an altitude between 70 and 80 degrees (ie-near the zenith), and was moving on a heading of around 300-310 degrees (towards the northwest). I looked at it through my binoculars, but was only able to discern that it wasn't point-like in appearance. Unfortunately, by the time that I set up my telescope, it had already moved out of visual range, and I couldn't recover it (this was around 7:40 p.m.). If anyone out there has a reasonable explanation to describe this object, I would appreciate hearing it. For readers of sci.aeronautics, I am cross posting this to your newsgroup, but I don't read sci.aeronautics, so please e-mail any responses that you have. ------------------------------------------------------------------------------- Irwin Horowitz |"Suppose they went nowhere?"-McCoy Astronomy Department |"Then this will be your big chance California Institute of Technology | to get away from it all!"-Kirk irwin@romeo.caltech.edu | from STII:TWOK ih@deimos.caltech.edu | ------------------------------------------------------------------------------- ------------------------------ Date: 30 Jul 90 13:59:07 GMT From: crdgw1!gecrdvm1!gipp@uunet.uu.net Subject: Re: Omni magazine on Mars In article <13986@shlump.nac.dec.com>, cook@vcsesu.enet.dec.com (Peter R. Cook) says: > > The July issue of Omni is dedicated to Mars, exploration, etc... > I found it very good reading. > > FYI > > /prc > Hmmm...I guess the reading was ok, but I'm still trying to figure out why the spacecraft on the cover has wings. For some truly informative reading, legible to the average joe, check out the July issue of "Aerospace America". The issue is dedicated to propulsion technology and is jammed with articles on stuff like ion thrusters, solar sails, laser propulsion, solid fuel rockets etc. It even addressed associated environmental concerns. fyi Pete G. >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >~ > Peter R. Cook -Don't DEC for my opinions. > Digital Equipment Corp. > Marlboro, MA. (MR01-3/SL1) > 508-467-6936 "1984 has past forget about Big Brother, > welcome to the 90's where the government's > your mother!" - Scatterbrain > Call your rep about HR 4079! ------------------------------ Date: 30 Jul 90 17:22:12 GMT From: mojo!SYSMGR%KING.ENG.UMD.EDU@mimsy.umd.edu (Doug Mohney) Subject: Re: space news from June 11 AW&ST In article , manning@arrester.caltech.edu (Evan Marshall Manning) writes: > >But a full production run will most likely not be made. I'm betting >no production craft will be made, giving us a divide by zero error >in calculations of unit cost. Comparable to the cost of a successful >Phobos, I guess ;-) Ahh, but 13 aircraft are already funded and paid for, regardless of what happens in the future. I'm not sure, but I think even the test article planes (1 & 2) will be able to take megatons to Moscow. ------------------------------ End of SPACE Digest V12 #150 *******************