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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
------------------------------