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 ; Thu, 2 Nov 89 04:22:33 -0500 (EST) Message-ID: Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Thu, 2 Nov 89 04:22:09 -0500 (EST) Subject: SPACE Digest V10 #189 SPACE Digest Volume 10 : Issue 189 Today's Topics: Re: Wood in space News of the Week, Oct 26 Re: PowerSat Options Asteroid Collisions Administrator Truly gives boost to reading program (Forwarded) Re: Mach - what does it really mean? Re: Mach - what does it really mean? Re: Wood in space Re: Computer Virus ---------------------------------------------------------------------- Date: 26 Oct 89 16:51:34 GMT From: swrinde!cs.utexas.edu!mailrus!jarvis.csri.toronto.edu!utgpu!utzoo!henry@ucsd.edu (Henry Spencer) Subject: Re: Wood in space In article wmartin@STL-06SIMA.ARMY.MIL (Will Martin) writes: >...Anyway, one of the features of the equipment hung on >the spacesuits' belts are a number of wood-handled tools...... what >would happen to wood exposed to space? Consider the effects of vacuum, >temperature, and radiation from the sun -- would wood dry up, crumble, >and disintegrate in a matter of seconds or minutes, or would it remain >strong enough to use for a reasonable length of time? It will definitely last for at least a modest length of time. The Chinese use wooden heatshields (thick oak) on their recoverable capsules. (They say it works just as well as sexy aerospace materials and is much cheaper and easier to work with.) Eventually you'd run into trouble with cracking due to dehydration, I'd expect. Overall, though, wood is fairly tough stuff. >Was any wood put on the LDEF? ... Not that I know of. Pity. -- 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: 26 Oct 89 18:23:07 GMT From: frooz!cfa250!mcdowell@husc6.harvard.edu (Jonathan McDowell) Subject: News of the Week, Oct 26 Jonathan's Space Report Oct 25,1989 (no.28) Pressure of various kinds of work means that I will be behind on analysing data for these reports for the next few weeks... --------------------------------------------------------------------- Atlantis/STS-34 was launched on Oct 18 and landed on Oct 23. It deployed the Galileo probe into a Venus transfer orbit. Viktorenko and Serebrov continue to work on the Soyuz TM-8/Mir/Progress M complex. The D module launch has been delayed. The fourth Block II Navstar GPS satellite was launched by Delta 6925 from Canaveral on Oct 21. The Czechoslovak Magion-2 satellite was released from the IK-24 magnetospheric research satellite on Oct 3. Kosmos-2047, launched on Oct 3, and Kosmos-2048, launched Oct 17, are GRU photo reconnaissance satellites. The Uosat-1 amateur radio satellite reentered on Oct 13. (c) 1989 Jonathan McDowell ------------------------------ Date: 27 Oct 89 01:46:49 GMT From: crash!orbit!pnet51!schaper@nosc.mil (S Schaper) Subject: Re: PowerSat Options Because the energy density is so low, aht is why they have to have large antenna farms to collect the energy, I don't think that there is any danger to birds flying through. I probably wouldn't want to build a house at that location, though. But that doesn't mean that it might not be safe. SPS has three main problems that I know of. 1) Politics - lack of vision, 2)Getting them built, we know how, but then we know how to build shuttles, too. 3), and in my mind most important :-) , a constellation of solar power sats is said to seriously degrade `seeing' for professional and amatuer astronomers. UUCP: {amdahl!bungia, uunet!rosevax, chinet, killer}!orbit!pnet51!schaper ARPA: crash!orbit!pnet51!schaper@nosc.mil INET: schaper@pnet51.cts.com ------------------------------ Date: 27 Oct 89 15:48:45 GMT From: frooz!cfa.HARVARD.EDU@husc6.harvard.edu (Steve Willner) Subject: Asteroid Collisions As part of an excellent article <2643@ibmpa.UUCP> on possible uses and dangers of Earth-approaching asteroids, szabonj@ibmpa.UUCP (Nick Szabo) asks: > Question: if two asteroids collide at high speed, do they shatter, > vaporize, or remain for the most part intact? There is a partial observational answer. The IRAS satellite discovered several "dust belts" above and below the ecliptic. These are attributed to dust generated by asteroid collisions. This observation doesn't give the whole answer, though. First of all, it applies only to main belt asteroids, and the Earth-approachers may be different. Second, the shattering may happen only for some, not all, collisions and/or some, not all, asteroid types. (In particular, I would not expect metallic asteroids to shatter. I don't think the composition of the dust belts is known, though.) And third, even where shattering occurs, it may not affect all of the original mass. (I.e., largely intact chunks could go flying off as well as the dust.) Or finally, of course, the explanation for the observed dust belts might simply be wrong (though it certainly seems plausible enough to me). In spite of these cautions (and maybe others I haven't thought of), it seems fair to say that at least some of the time, collisions must result in substantial shattering. ------------------------------------------------------------------------- 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: 27 Oct 89 21:00:12 GMT From: trident.arc.nasa.gov!yee@ames.arc.nasa.gov (Peter E. Yee) Subject: Administrator Truly gives boost to reading program (Forwarded) [Not strictly space, just your space agency working on the broader picture.-PEY] Jeff Vincent Headquarters, Washington, D.C. October 27, 1989 RELEASE: 89-166 ADMINISTRATOR TRULY GIVES BOOST TO READING PROGRAM NASA Administrator Richard H. Truly took his launch skills to an elementary school today and personally helped a new reading program get off the ground. It was a successful mission. Meeting with about 340 students at the Rock Creek Forest Elementary School, Montgomery County, Md., Admiral Truly helped initiate the "Launch into a Good Book" program, which is designed to encourage reading among elementary school children. The program features audio cassettes with prominent people reading book passages. The students can read along and practice their skills. Admiral Truly presented the students with an audio tape on which he read a passage from "Album of Spaceflight" by Tom McGowen. He also spoke briefly with them about the importance of reading and how it is an essential skill for achieving their goals, including those who aspire to space travel. Just yesterday, at a speech to the National Press Club, Admiral Truly said: "There is a new determination across our land to improve our educational system." He said there are certain themes that are particularly effective in reaching children. "Ghosts can do it, dinosaurs can do it, and space can do it. I predict that no other benefit from our future space endeavors will loom so large." The NASA Administrator also participated in the President's recent education summit with the nation's governors in Charlottesville, Va. ------------------------------ Date: 26 Oct 89 16:14:49 GMT From: skipper!shafer@ames.arc.nasa.gov (Mary Shafer) Subject: Re: Mach - what does it really mean? In article <4656@fy.sei.cmu.edu> krvw@sei.cmu.edu (Kenneth Van Wyk) writes: In article Mach - what does it really mean? of 25 Oct 89 19:49:22 GMT clj@ksr.com (Chris Jones) writes: > Mach 1 is the speed of sound (under ambient conditions, > I would guess). I understand the usefulness of saying that something > is going more or less than the speed of sound, since aerodynamic > characteristics change passing through that speed, but hearing that > the shuttle enters the atmosphere at, say, Mach 24 is so much hooey in > my opinion. What does it mean when I hear some NASA spokesperson say > that? Well, it's been a few years since I took Thermodynamics (my degree is in M.E.), but... "Mach 1" indeed means the speed of sound and yes, the speed of sound varies with temperature, pressure, etc. However, it's not impossible that "they" are referring to N times the speed of sound at Standard Atmospheric Conditions. In other words, if the speed of sound is 700 mph at standard atmosphere, and the shuttle is ^^^^^^^^ I think you mean sea level doing 7000 mph, then they might (incorrectly) refer to this as "Mach 7". We're smarter than that. :-) Of course, this wouldn't be as accurate as saying N m/sec or some other speed relative to the earth's surface, since it wouldn't count for the fact that the speed of sound is *significantly* different at these very high altitudes. We've noticed. But, then, perhaps they actually mean "Mach N" literally, in which case they should be supplying local atmospheric conditions along with "Mach N" so that viewers can take out their HP calculators and figure out the speed of sound under those conditions... :-) The Standard Atmosphere takes care of this problem. If you know the altitude (pressure altitude, corrected for temperature) then you know density, speed of sound, etc. The Shuttle air data is all Standard Atmosphere. So instead of your HP you get out your bright yellow 1966 Standard Atmosphere and discover that at 373,685 ft at 60 deg North in January, for example, the speed of sound is 1165.2 ft/sec. The Standard Atmosphere is really quite accurate. The tapeline altitude (from radar) and the pressure altitude agree quite well during the Shuttle flights. The Standard Atmosphere is so standard (sorry!) that it probably doesn't get explained. The theory is probably that if you don't know about it, you don't care, and if you do know about it, you don't need an explanation. Extra information because I don't have nearly enough lines for this to get sent follows: The Mach number is really about 24 when it first enters the atmosphere. The stability and control derivatives, particularly lateral-directional, are functions of Mach number, for example. Actually the longitudinal derivatives are usually functions of angle of attack, but angle of attack ties into Mach through the lift coefficient, although it's not linear. I can't remember if this is true for the high Mach numbers for the Shuttle and I can't find the papers right now. If you can't live without knowing, let me know and I'll keep searching to give you a citation. Another document of interest is NASA Reference Publication 1046, "Measurement of Aircraft Speed and Altitude" by William Gracey, 1980. However the Standard Atmosphere tables in this only go up to 100,000 ft. -- Mary Shafer shafer@elxsi.dfrf.nasa.gov ames!elxsi.dfrf.nasa.gov!shafer NASA Ames-Dryden Flight Research Facility, Edwards, CA Of course I don't speak for NASA -- Mary Shafer shafer@elxsi.dfrf.nasa.gov ames!elxsi.dfrf.nasa.gov!shafer NASA Ames-Dryden Flight Research Facility, Edwards, CA Of course I don't speak for NASA ------------------------------ Date: 26 Oct 89 16:53:12 GMT From: agate!sag4.ssl.berkeley.edu!daveray@ucbvax.Berkeley.EDU (David Ray) Subject: Re: Mach - what does it really mean? In article Mach - what does it really mean? of 25 Oct 89 19:49:22 GMT clj@ksr.com (Chris Jones) writes: > > Mach 1 is the speed of sound (under ambient conditions, > I would guess). I understand the usefulness of saying that something > is going more or less than the speed of sound, since aerodynamic > characteristics change passing through that speed, but hearing that > the shuttle enters the atmosphere at, say, Mach 24 is so much hooey in > my opinion. What does it mean when I hear some NASA spokesperson say > that? Good question, in other words, why talk about speed in terms of Mach numbers instead of actual distance/second? My guess is that the Mach number tells the propulsion experts what kind of mathematical model to use when calculating maneuvers. The effects of atmospheric drag, lift, etc., are profoundly affected by Mach number more than distance per second, and as a result different models and calculations are used for atmospheric/orbital maneuvers. -Dave ------------------------------ Date: 26 Oct 89 21:41:10 GMT From: swrinde!gem.mps.ohio-state.edu!ginosko!shadooby!mailrus!jarvis.csri.toronto.edu!db.toronto.edu!hogg@ucsd.edu (John Hogg) Subject: Re: Wood in space In article <1989Oct26.165134.4994@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes: >>what would happen to wood exposed to space? > >It will definitely last for at least a modest length of time. The Chinese >use wooden heatshields (thick oak) on their recoverable capsules. (They >say it works just as well as sexy aerospace materials and is much cheaper >and easier to work with.) > >Eventually you'd run into trouble with cracking due to dehydration, I'd >expect. Overall, though, wood is fairly tough stuff. This shouldn't be a problem if proper construction techniques are used. First, use small pieces of wood. (In fact, almost any reasonable application will involve laminated veneers.) Radial cracks appear in drying wood due to tangential contraction being greater than radial contraction. This is minimized if the dimensions are small. Secondly, dry it right out to begin with, and don't let it reabsorb moisture before launch. (I.e., coat it with the same epoxy used in lamination.) A lot of furniture cracking is not due so much to low humidity as to cyclic humidity. When the wood absorbs moisture, it swells, comes up against some restraining limit, and crushes slightly. This sets it up for a crack the next time that the humidity drops again, and it shrinks. (And this, incidentally, is the main reason that hammer heads loosen over time: the handle has been exposed to moisture or high humidity, and has been crushed by the head.) Leaving aside the protective coating, a piece of wood in space is absolutely, positively guaranteed not to absorb moisture. If it starts out dry, it will stay that way. Cracking will not be an issue. And finally, in many applications, minor cracking along the grain is not particularly serious anyway, although it may let in undesirable things (like bugs, moisture, or monatomic oxygen.) Take a close look at the next large wooden mast you see. If it's not built up, it's cracked. Another problem that might arise, though, is outgassing of adhesives. Again, epoxy is *probably* OK, once thoroughly cured. But don't build your imperial battlecruiser out of lumberyard plywood---the formaldehyde adhesive will not agree with the space cadets living inside. Wood is nice stuff. Don't underrate it. -- John Hogg hogg@csri.utoronto.ca Department of Computer Science, University of Toronto ------------------------------ Date: 26 Oct 89 17:40:49 GMT From: lightsabre!kenobi@sun.com (Rick Kwan) Subject: Re: Computer Virus In article <1908@jato.Jpl.Nasa.Gov> baalke@mars.jpl.nasa.gov (Ron Baalke) writes: > > >I just hope the new computer that they are replacing on the Space Shuttle >is not infected with the "Friday the 13th" computer virus...... When I first read this, I was infected by a simultaneous giggle and a shudder. As I recall, the Command and Data Systems (CDS) computer(s) on Magellan and Galileo are rad-hard, CMOS RCA 1802 chips. There was talk at the time (about 4 years ago) about moving to 8086-type processors manufactured by Harris (again, rad-hard requirements). Of course, this would make it really easy to use IBM PCs, running MS-DOS, to do development. Given larger memories coming, and standard tools to play with, one could imagine writing routines in "C" and doing final unit testing of the code on the PC, taking the resulting binaries, and integrating it into the spacecraft computer. Now, of course, we couldn't possibly expect a virus to show up in a future interplanetary/interstellar CDS, and go forth to infect the universe... could we? I mean... the thought of such contamination... A more serious question: what will be used for computing power on such probes in the near future? Is it Harris or what? Rick Kwan (aka Obi-Kwan Kenobi) Sun Microsystems - Intercontinental Operations kenobi@sun.UUCP or kenobi%lightsabre@sun.COM ------------------------------ End of SPACE Digest V10 #189 *******************