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Date: Fri, 4 Sep 92 05:03:59 From: Space Digest maintainer <digests@isu.isunet.edu> Reply-To: Space-request@isu.isunet.edu Subject: Space Digest V15 #167 To: Space Digest Readers Precedence: bulk Space Digest Fri, 4 Sep 92 Volume 15 : Issue 167 Today's Topics: Galileo Update - 09/03/92 Iridium Is NASA really planning to Terraform Mars? Laser distance record? (2 msgs) Mars Observer Press Kit (long) [Part 2] SAS Def. Subcom. vote on SDI->Single Stage to Orbit Senate vote on Freedom Shuttle traking progra Space Industries International Special Relativity Welcome to the Space Digest!! Please send your messages to "space@isu.isunet.edu", and (un)subscription requests of the form "Subscribe Space <your name>" to one of these addresses: listserv@uga (BITNET), rice::boyle (SPAN/NSInet), utadnx::utspan::rice::boyle (THENET), or space-REQUEST@isu.isunet.edu (Internet). ---------------------------------------------------------------------- Date: 4 Sep 92 07:40:50 GMT From: Ron Baalke <baalke@kelvin.jpl.nasa.gov> Subject: Galileo Update - 09/03/92 Newsgroups: sci.space,sci.astro Forwarded from Neal Ausman, Galileo Mission Director GALILEO MISSION DIRECTOR STATUS REPORT POST-LAUNCH August 28 - September 3, 1992 SPACECRAFT 1. On August 31, a NO-OP command was sent to reset the command loss timer to 264 hours, its planned value for this mission phase. 2. On September 3, the Dual Drive Actuator (DDA) pulse mini-sequence No. 3 was uplinked to the spacecraft. This mini-sequence covers spacecraft activities from September 8 to September 11, 1992. This mini-sequence includes two 2-second DDA motor turn on pulses, one shortly after turning to a 45-degree off-sun attitude and the other just before returning to a near sun-pointed attitude. (See Special Topic No. 2.) 3. On September 3, a routine sun vector update was performed. This sun vector is valid through October 5, 1992. 4. The AC/DC bus imbalance measurements exhibited some change. The AC measurement remained unchanged and reads 3.3 volts. The DC measurement has ranged from 120 DN (14.0 volts) to 132 DN (15.5 volts) and now reads 120 DN (14.0 volts). These measurement variations are consistent with the model developed by the AC/DC special anomaly team. 5. The Spacecraft status as of September 3, 1992, is as follows: a) System Power Margin - 70 watts b) Spin Configuration - Dual-Spin c) Spin Rate/Sensor - 3.15 rpm/Star Scanner d) Spacecraft Attitude is approximately 6 degrees off-sun (leading) and 27 degrees off-earth (lagging) e) Downlink telemetry rate/antenna-40 bps (coded)/LGA-1 f) General Thermal Control - all temperatures within acceptable range g) RPM Tank Pressures - all within acceptable range h) Orbiter Science- UVS, EUV, DDS, MAG, EPD, and HIC are powered on i) Probe/RRH - powered off, temperatures within acceptable range j) CMD Loss Timer Setting - 264 hours Time To Initiation - 256 hours UPLINK GENERATION/COMMAND REVIEW AND APPROVAL: 1. The Dual Drive Actuator (DDA) pulse mini-sequence No. 3 memory load was approved for transmission by the Project on September 2, 1992. (See Special Topic No. 2.) GDS (Ground Data Systems): 1. The D1.0 deliveries will continue thru October 1992 and will provide updates to uplink capabilities needed for Jupiter sequence planning and developments activities as well as updates to downlink capabilities needed for Earth 2 support. TRAJECTORY As of noon Thursday, September 3, 1992, the Galileo Spacecraft trajectory status was as follows: Distance from Earth 72,134,600 miles (.78 AU) Distance from Sun 145,608,000 miles (1.57 AU) Heliocentric Speed 53,600 miles per hour Distance from Jupiter 647,914,400 miles Round Trip Light Time 13 minutes, 2 seconds SPECIAL TOPIC 1. As of September 3, 1992, a total of 8113 real-time commands have been transmitted to Galileo since Launch. Of these, 3235 were pre-planned in the sequence design and 4878 were not. In the past week, 2 real time command was transmitted and pre-planned in the sequence design. In addition, 5677 mini-sequence commands have been transmitted since March 1991; 3519 were pre-planned and 2158 were not. In the past week, 250 mini-sequence commands were transmitted. Major command activities this week included commands to reset the command loss timer and to update the sun vector. 2. The Dual Drive Actuator (DDA) pulse mini-sequence No. 3 covers spacecraft activities from September 8 to 11, 1992. The warming turn to a 45-degree off-sun attitude along with the first DDA two second motor turn on pulse is scheduled for September 8. The spacecraft will remain at the warming attitude for approximately 28 hours. The second DDA two second motor turn on pulse is scheduled just prior to turning back to approximately a 6 degree off-sun attitude. Sun gate data will be collected on September 10. The star scanner checkout along with the collection of wobble data is scheduled for September 11. ___ _____ ___ /_ /| /____/ \ /_ /| Ron Baalke | baalke@kelvin.jpl.nasa.gov | | | | __ \ /| | | | Jet Propulsion Lab | ___| | | | |__) |/ | | |__ M/S 525-3684 Telos | Anything is impossible if /___| | | | ___/ | |/__ /| Pasadena, CA 91109 | you don't attempt it. |_____|/ |_|/ |_____|/ | ------------------------------ Date: 4 Sep 92 03:19:34 GMT From: John Roberts <roberts@CMR.NCSL.NIST.GOV> Subject: Iridium Newsgroups: sci.space -From: clarke@acme.ucf.edu (Thomas Clarke) -Subject: Re: With telepresence, who needs people in Earth orbit? -Date: 3 Sep 92 15:21:29 GMT -Organization: University of Central Florida -In article <1992Sep1.193908.25701@clipper.ingr.com> arnold@clipper.ingr.com -(Roger Arnold) writes: -> Build a necklace of -> co-orbiting microsats to relay signals from the facility to whichever -> satellite is currently in position to downlink. It's easiest if the -> orbit is equatorial, and so what if that means using Pegasus or Ariane -> for launches? -Easier still, use the Motorola Iridium constellation of 77 -satellites for teleoperation. Iridium should work just as -well for LEO as for "cellular phones" on the ground. The main question is whether Iridium can support a video link. I saw some Iridium people, and meant to ask them, but they were busy and I was in a hurry, so I didn't get a chance. Another question is whether it will allow you to set up a link with a guaranteed maximum transfer time. If the switching algorithm does not allow for this, and there is a risk that the feedback channel or the control channel will be automatically switched to a much longer path, you might lose control of whatever you're trying to operate. The other Clarke (Arthur C.) describes this scenario in the beginning of "Meeting with Medusa". John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ Date: 4 Sep 92 00:40:08 GMT From: Barry Kort <barry@chezmoto.ai.mit.edu> Subject: Is NASA really planning to Terraform Mars? Newsgroups: sci.space A colleague of mine, who claims to be knowledgeable in such matters tells me: A fairly large team <at NASA>, is planning the terraforming of Mars, which involves destroying the planet as we know it. Mars will be rasied 20 degrees C. And with minimal study of that planet it becomes clear what chain of events will occur. After this chain Mars will be 'polluted' with earth-based micro-organisms and rugged plant life. Can anyone confirm, deny, or refute the above, or otherwise elaborate on NASA's plans with respect to Mars? Barry Kort Visiting Scientist Educational Technology Research BBN Labs Cambridge, MA ------------------------------ Date: 3 Sep 92 22:11:57 GMT From: "Kevin W. Plaxco" <kwp@wag.caltech.edu> Subject: Laser distance record? Newsgroups: sci.space >To date, what is the farthest that a laser has been seen from? > >I recall a successful experiment sending a laser beam from the >Earth to a Surveyor lander on the Moon in the sixties. That would >make the current record approx. 384,400 km? With the use of one mirror and a rather large reciever signals are regularly sent and recieved at twice that distance. -Kevin ------------------------------ Date: 4 Sep 92 04:05:12 GMT From: David Knapp <knapp@spot.Colorado.EDU> Subject: Laser distance record? Newsgroups: sci.space In article <1992Sep3.193838.19912@sunova.ssc.gov> faught@redfox.ssc.gov writes: >In article <26059@dog.ee.lbl.gov> sichase@csa1.lbl.gov (SCOTT I CHASE) writes: >>In article <rabjab.77.0@golem.ucsd.edu>, rabjab@golem.ucsd.edu (Jeff Bytof) >writes... >>>To date, what is the farthest that a laser has been seen from? >>> >>>I recall a successful experiment sending a laser beam from the >>>Earth to a Surveyor lander on the Moon in the sixties. That would >>>make the current record approx. 384,400 km? *And* back. >> >>If you allow masers, then the answer is best measured in parsecs. Oh... you >>want man-made lasers. Never mind. >> >>-Scott >>-------------------- >>Scott I. Chase "The question seems to be of such a character >>SICHASE@CSA2.LBL.GOV that if I should come to life after my death >> and some mathematician were to tell me that it >> had been definitely settled, I think I would >> immediately drop dead again." - Vandiver > >I seem to recall reading something about natural lasers in the atmoshere of >Venus?????? Hmmm, I think that's Mars. I had read it was CO2 transitions which would be thermally crowed transitions in the Venutian atmosphere. Can anyone confirm? >-- >Ed Faught WA9WDM faught@psychosis.ssc.gov > Superconducting Super Collider Laboratory -- David Knapp University of Colorado, Boulder Perpetual Student knapp@spot.colorado.edu ------------------------------ Date: 4 Sep 92 06:02:03 GMT From: Ron Baalke <baalke@kelvin.jpl.nasa.gov> Subject: Mars Observer Press Kit (long) [Part 2] Newsgroups: sci.space,sci.astro via a project database at JPL. Using workstations and electronic communications links, scientists also will be connected to the mission planning activities at JPL. In the same way, data products returned to the JPL database from the home institution for each of the instruments will be sent electronically to other investigators at their home institutions. This will allow scientists to have ready access to science data without moving to JPL for the duration of the mission. More than 60 workstations will be connected to the project database at JPL, a centralized repository for downlink science and engineering telemetry data, ancillary data including navigation data, and uplink command and sequence data. This database, with about 30 gigabytes of on- line storage, will be electronically available to the science instrument investigators via NASCOM data links. During the mapping phase, the instrument investigations will return processed science data products to the database at JPL for access by the interdisciplinary scientists and the other investigation teams. Forty-two participating scientists from universities and scientific institutions in the United States, Russia, France, Germany and Great Britain will join the permanent Mars Observer science team once the mission is under way in October 1992. Investigators/spacecraft instrument graphic MARS OBSERVER INVESTIGATORS Gamma Ray Spectrometer (GRS) TEAM LEADER: William V. Boynton, University of Arizona James R. Arnold, University of California, San Diego Peter Englert, San Jose State University William C. Feldman, Los Alamos National Laboratory Albert E. Metzger, Jet Propulsion Laboratory Robert C. Reedy, Los Alamos National Laboratory Steven W. Squyres, Cornell University Jacob L. Trombka, Goddard Space Flight Center Heinrich Wnke, Max Planck Institute for Chemistry Johannes Brckner, Max Planck Institute for Chemistry Darrell M. Drake, Los Alamos National Laboratory Larry G. Evans, Computer Sciences Corporation John G. Laros, Los Alamos National Laboratory Richard D. Starr, Catholic University Yu A. Surkov, Russia Mars Observer Camera (MOC) PRINCIPAL INVESTIGATOR: Michael C. Malin, Malin Space Science Systems, Inc. G. Edward Danielson Jr., California Institute of Technology Andrew P. Ingersoll, California Institute of Technology Laurence A. Soderblom, U.S. Geological Survey Joseph Veverka, Cornell University Merton E. Davies, The RAND Corporation William K. Hartmann, Science Applications International Philip B. James, University of Toledo Alfred S. McEwan, U.S. Geological Survey Peter C. Thomas, Cornell University Thermal Emission Spectrometer (TES) PRINCIPAL INVESTIGATOR: Philip R. Christensen, Arizona State University Donald A. Anderson, Arizona State University Stillman C. Chase, Santa Barbara Research Center Roger N. Clark, U.S. Geological Survey Hugh H. Kieffer, U.S. Geological Survey Michael C. Malin, Malin Space Science Systems, Inc. John Pearl, Goddard Space Flight Center Todd R. Clancy, University of Colorado Barney J. Conrath, Goddard Space Flight Center R.O. Kuzmin, Russia Ted L. Roush, San Francisco State University A.S. Selivanov, Russia Pressure Modulator Infrared Radiometer (PMIRR) PRINCIPAL INVESTIGATOR: Daniel J. McCleese, Jet Propulsion Laboratory Robert D. Haskins, Jet Propulsion Laboratory Conway B. Leovy, University of Washington David A. Paige, University of California, Los Angeles John T. Schofield, Jet Propulsion Laboratory Fredric Taylor, University of Oxford Richard W. Zurek, Jet Propulsion Laboratory Michael D. Allison, Goddard Space Flight Center Jeffrey R. Barnes, Oregon State University Terry Z. Martin, Jet Propulsion Laboratory Peter L. Read, University of Oxford Mars Observer Laser Altimeter (MOLA) PRINCIPAL INVESTIGATOR: David E. Smith, Goddard Space Flight Center Herbert V. Frey, Goddard Space Flight Center James B. Garvin, Goddard Space Flight Center James W. Head, Brown University James G. Marsh, Goddard Space Flight Center Duane Muhleman, California Institute of Technology Gordon H. Pettengill, Massachusetts Institute of Technology Roger J. Phillips, Southern Methodist University Sean C. Solomon, Massachusetts Institute of Technology Maria T. Zuber, Goddard Space Flight Center H. Jay Zwally, Goddard Space Flight Center Bruce W. Banerdt, Jet Propulsion Laboratory Thomas C. Duxbury, Jet Propulsion Laboratory Radio Science (RS) TEAM LEADER: G. Leonard Tyler, Stanford University Georges Balmino, Centre National d'Etudes Spatiales (CNES), France David Hinson, Stanford University William L. Sjogren, Jet Propulsion Laboratory David E. Smith, Goddard Space Flight Center Richard Woo, Jet Propulsion Laboratory E. L. Akim, Russia John W. Armstrong, Jet Propulsion Laboratory Michael F. Flasar, Goddard Space Flight Center Richard A. Simpson, Stanford University Magnetometer and Electron Reflectometer (MAG/ER) PRINCIPAL INVESTIGATOR: Mario H. Acuna, Goddard Space Flight Center Kinsey S. Anderson, University of California, Berkeley Sigfried Bauer, University of Graz Charles W. Carlson, University of California, Berkeley Paul Cloutier, Rice University John E. P. Connerney, Goddard Space Flight Center David W. Curtis, University of California, Berkeley Robert P. Lin, University of California, Berkeley Michael Mayhew, National Science Foundation Norman F. Ness, University of Delaware Henri Reme, University of Paul Sabatier Peter J. Wasilewski, Goddard Space Flight Center M. Menvielle, Universit of Paris Sud, France Diedrich M hlmann, German Aerospace Research Establishment, Germany A.A. Ruzmaikin, Russia James A. Slavin, Goddard Space Flight Center A.V. Zakharov, Russia INTERDISCIPLINARY SCIENTISTS Raymond E. Arvidson, Washington University Bruce Fegley Jr., Washington University Michael H. Carr, U.S. Geological Survey A. T. Bazilevsky, Russia Matthew Golombek, Jet Propulsion Laboratory Harry Y. McSween Jr., University of Tennessee Andrew P. Ingersoll, California Institute of Technology Howard Houben, Space Physics Research Institute Bruce M. Jakosky, University of Colorado L.V. Ksanfomality, Russia Aaron P. Zent, Search for Extraterrestrial Intelligence (SETI) Institute James B. Pollack, Ames Research Center Robert M. Haberle, Ames Research Center V.I. Moroz, Russia Laurence A. Soderblom, U.S. Geological Survey Ken Herkenhoff, Jet Propulsion Laboratory Bruce C. Murray, California Institute of Technology MARS OBSERVER MANAGEMENT NASA HEADQUARTERS, WASHINGTON, D.C. Office of Space Science and Applications Dr. Lennard A. Fisk, Associate Administrator Alphonso V. Diaz, Deputy Associate Administrator Dr. Wesley T. Huntress, Director, Solar Systems Exploration Div. Douglas R. Broome, Deputy Director, Solar System Exploration Div. Dr. William L. Piotrowski, Chief, Flight Programs Branch and Mars Observer Program Manager William C. Panter, Mars Observer Deputy Program Manager Dr. Bevin M. French, Mars Observer Program Scientist Guenter K. Strobel, Planetary Flight Support Manager Charles R. Gunn, Director, Expendable Launch Vehicles Office B.C. Lam, Upper Stages Program Manager Office of Space Communications Charles T. Force, Associate Administrator for Space Communications Jerry J. Fitts, Deputy Associate Administrator for Space Communications Robert M. Hornstein, Director, Ground Networks Div. JET PROPULSION LABORATORY, PASADENA, CALIF. Dr. Edward C. Stone, Director Larry N. Dumas, Deputy Director John R. Casani, Assistant Laboratory Director, Flight Projects David D. Evans, Mars Observer Project Manager Glenn E. Cunningham, Mars Observer Deputy Project Director Dr. Arden L. Albee, Mars Observer Project Scientist Frank D. Palluconi, Mars Observer Deputy Project Scientist Thomas E. Thorpe, Mars Observer Science Manager George D. Pace, Mars Observer Spacecraft Manager Gary L. Reisdorf, Mars Observer Payload Manager Dr. Saterios S. Dallas, Mars Observer Mission Manager Joseph Shaffer, Mars Observer Launch Vehicle Manager Gail K. Robinson, Mars Observer Administration and Finance Manager T. David Linich, Multi-Mission Operations Support Manager Eugene S. Burke, Multi-Mission Operations Manager Marvin Traxler, Tracking and Telecommunications Data Systems Manager Dr. Peter Poon, Coordinator with Multimission Operations Systems Center KENNEDY SPACE CENTER, FLA. Robert L. Crippen, Director James A. "Gene" Thomas, Deputy Director John T. Conway, Director, Payload Management and Operations James L. Womack, Director, Expendable Vehicles George E. Looschen, Chief, Launch Operations Division David C. Bragdon, Launch Vehicle/Payload Integration Manager Floyd A. Curington, Chief, Project Planning and Support James W. Meyer, Tracking and Range Coordinator JoAnn H. Morgan, Director, Payload Projects Management Gayle C. Hager, Mars Observer Launch Site Support Manager Julie A. Scheringer, TOS Launch Site Support Manager LEWIS RESEARCH CENTER, CLEVELAND Lawrence J. Ross, Director Dr. J. Stuart Fordyce, Deputy Director Thomas H. Cochran, Director, Space Flight Systems John W. Gibb, Manager, Launch Vehicle Project Office Steven V. Szabo, Jr., Director, Engineering Directorate Edward G. Stakolich, Titan Mission Manager Edwin R. Procasky, Chief, System Engineering Office Edwin T. Muckley, Chief, Mission and Vehicle Integration Office MARSHALL SPACE FLIGHT CENTER, HUNTSVILLE, ALA. Thomas J. Lee, Director Dr. J. Wayne Littles, Deputy Director Sidney P. Saucier, Manager, Space Systems Projects Alvin E. Hughes, Manager, Upper Stage Projects Robert W. Hughes, Upper Stages Chief Engineer GODDARD SPACE FLIGHT CENTER, GREENBELT, MD. Dr. John Klineberg, Director Peter T. Burr, Deputy Director Dr. Dale W. Harris, Director, Flight Projects Directorate Jeremiah J. Madden, Associate Director of Flight Projects for Earth Observing System (EOS) Martin J. Donohoe, Project Manager for EOS Instruments Projects Dr. Douglas D. McLennan, Manager for Mars Observer GRS Bertrand L. Johnson, Jr., Manager for Mars Observer MOLA Previous Mars missions/1 (graphic) Previous Mars missions/2 (graphic) ___ _____ ___ /_ /| /____/ \ /_ /| Ron Baalke | baalke@kelvin.jpl.nasa.gov | | | | __ \ /| | | | Jet Propulsion Lab | ___| | | | |__) |/ | | |__ M/S 525-3684 Telos | Anything is impossible if /___| | | | ___/ | |/__ /| Pasadena, CA 91109 | you don't attempt it. |_____|/ |_|/ |_____|/ | ------------------------------ Date: Fri, 4 Sep 1992 03:50:37 GMT From: Tom Nugent <tjn32113@uxa.cso.uiuc.edu> Subject: SAS Def. Subcom. vote on SDI->Single Stage to Orbit Newsgroups: sci.space The Senate Armed Services Defense Subcommittee will vote September 15th on the SDI (Strategic Defense Initiative) budget, which includes funding for the Single Stage to Orbit (or as it is now called Singe Stage Rocket Technology) program. The one-third scale prototype is due to have its first test flight this coming April. The total one-third scale prototype will cost the government less than $75 million total (over its ~2-3 year lifespan, which this is the last year). Allen Scherzer posted info on this recently; if one of those listed is a Senator of yours, please write and ask for full support for the program. If you are not in one of those states, then please write to the chairman, Senator Daniel Inouye of Hawaii at: SH-722 US Senate Washington, D.C. 20510 Thanks. -- Tom Nugent voice:(217)328-0994 e-mail:tjn32113@uxa.cso.uiuc.edu "To be average scares the hell out of me." -- Anonymous ------------------------------ Date: 4 Sep 92 03:45:09 GMT From: Tom Nugent <tjn32113@uxa.cso.uiuc.edu> Subject: Senate vote on Freedom Newsgroups: sci.space The full Senate will vote Tuesday September 8th on funding for Space Station Freedom. Please call both your Senators _today_ (Friday) (because this is the last working day before the vote) and ask for full funding for Freedom. Thanks. -- Tom Nugent voice:(217)328-0994 e-mail:tjn32113@uxa.cso.uiuc.edu "To be average scares the hell out of me." -- Anonymous ------------------------------ Date: 4 Sep 92 05:02:55 GMT From: Keith Stein <Keith.Stein@f118.n109.z1.fidonet.org> Subject: Shuttle traking progra Newsgroups: sci.space The name of the program for tracking the shuttle or other stellites is called TrakSat or another one is STSORBIT. ------------------------------ Date: 2 Sep 92 16:17:36 GMT From: Dave Benz <benz@calspan.com> Subject: Space Industries International Newsgroups: sci.space Yesterday Arvin Industries (big worldwide manufacturer of automotive parts and related products) announced that they have signed a letter of intenet with Space Industries International (of Houston) to combine Space Industries with Arvin's Calspan - Advanced Technology Division. The new company will retain the Space Industries International Inc. name. I'm looking for some info on Space Industries International. Are you guys on internet? Could some one point me to some info on who Space Industries is and what they do. Articles in trade rags, newspapers, etc. thanks, dave ===== Dave Benz benz@calspan.com Arvin/Calspan Advanced Technology Center P.O. Box 400 Buffalo, NY 14225 Disclaimer: All you've read are my own thoughts, opinions, words, interpretations, misinterpretations, etc. I do not speak for Arvin, I do not speak for Calspan, I do not like green eggs and ham. ------------------------------ Date: 4 Sep 92 02:59:51 GMT From: "Frederick A. Ringwald" <Frederick.A.Ringwald@dartmouth.edu> Subject: Special Relativity Newsgroups: sci.space In article <Bu10or.MKw.1@cs.cmu.edu> 18084TM@msu.edu (Tom) writes: > I bet you can't describe the difference between these interpretations > of the same event, save that they are made by different observers. > One of the standard results of SR is the non-objectiveness of any frame. > (The frame of our near-c trip to M31 becomes inertial when the engines > are turned off, BTW) This is the twin paradox: the resolution is in any decent book on SR. Basically, the twin on Earth ages, because the twin who went to Andromeda, in order to get back to Earth, had to turn around: turn around, did you say? This is an acceleration! So the twin in the rocket was not in an inertial frame, and so is not equivalent to the other. > Wasn't one of the confirmations of SR that unstable particles moving at > near c would decay past their expected places? From our point of view, > their time slowed down. From their point of view, our frame got shorter. > Aren't both interpretations correct? We can easily extrapolate to the > case of an observer at lightspeed, as the original poster (whose name > I've stupidly deleted, and forgotten) has done. This is the barn-and-pole paradox, explained very well in Spacetime Physics, by Taylor & Wheeler. Also, that we can detect cosmic ray muons at all at sea level was an early confirmation of SR: they should all decay in the upper atmosphere, but instead make up the dominant component of cosmic rays, at sea level. Again, see Taylor & Wheeler. > Isn't all math, from calculus on up, based on an understanding > of limits? I think c = infinity, (in the photon's frame) is a pretty > good way to get an intuitive idea of what's going on. After all, c > is a limit, not a speed (for anything with mass). > > Has anyone done any actual math in this vein? See Taylor & Wheeler. c = c, not infinity; a photon has zero rest mass, and any such particle can only travel at c, because of the elementary result E^2 = m^2 c^4 + p^2 c^2, where E = energy, m = rest mass, p = momentum, and you know c. This discussion is very elementary and belongs in sci.physics, anyway: please take it there, after looking at Taylor & Wheeler, Spacetime Physics. ------------------------------ End of Space Digest Volume 15 : Issue 167 ------------------------------