Date: Mon, 31 Aug 92 04:59:57 From: Space Digest maintainer Reply-To: Space-request@isu.isunet.edu Subject: Space Digest V15 #152 To: Space Digest Readers Precedence: bulk Space Digest Mon, 31 Aug 92 Volume 15 : Issue 152 Today's Topics: 2 stage to orbit question LDO shuttle and pilot readiness What is the speed of light measured from? (4 msgs) Welcome to the Space Digest!! Please send your messages to "space@isu.isunet.edu", and (un)subscription requests of the form "Subscribe Space " 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: 31 Aug 92 04:22:25 GMT From: Douglas R Fils Subject: 2 stage to orbit question Newsgroups: sci.space sci.space The August 24th, 1992 issue of Aviation Week (page 23) has an article on an XB-70 style aircraft. Part of the speculation about this aircraft concerns its possible use as the first stage of a two stage to orbit craft. If a Pegasus (sp) style rocket could be released from 100,000 feet at Mach 6-8, what could one expect as a payload to LEO (say 200 Km). just curious Doug fils@iastate.edu -- ------------------------------ Date: 30 Aug 92 20:32:29 GMT From: "Michael V. Kent" Subject: LDO shuttle and pilot readiness Newsgroups: sci.space In article <1992Aug29.162920.24117@ucsu.Colorado.EDU> grasso@tramp.Colorado.EDU (GRASSO CHRISTOPHER A) writes: >After being on orbit for 2 months, how realistic is it for a shuttle pilot > to be capable of performing a reentry and landing? Seating in the > shuttle is upright, airliner-style, while seating in a capsule is > reclined to horizontal. I believe this is being looked at by NASA. The re-entry part should not be too different than normal, but the landing part is a concern. NASA has devel- oped an "Autoland" capability for the flight control system (?) that will take over the trickier aspects of the landing operations. I don't know much about` the particulars, but it is scheduled for testing on STS-53 this November. > If the extended stay in microgravity damages the shuttle pilots' > ability to bring the spacecraft back for a landing, doesn't this > mandate a separate ACRV if shuttle is to be used for resupply and > crew rotation? It would only mandate a different approach be taken. It may very well be possible (and cost effective) to adapt the current approach to the new require- ments than to develop a second one. Mike -- Michael Kent kentm@rpi.edu McDonnell Douglas Rensselaer Polytechnic Institute All facts in this post are based on publicly available information. All opinions expressed are solely those of the author. Apple II Forever !! ------------------------------ Date: Sun, 30 Aug 1992 18:53:00 GMT From: "BRUTON, WILLIAM DANIEL" Subject: What is the speed of light measured from? Newsgroups: sci.space In article <1992Aug30.130555.7676@spuddy.uucp>, spark@spuddy.uucp (Steve) writes... > > >OK. Someone can perhaps clear this little nagging thought in my head. > >I haven't done any relativity, or any complicated physics, so please >keep it simple. > >Even though I'm sitting down, I'm still travelling at about (say) 300m/s, >as the Earth is rotating. Furthermore, the Earth orbits the Sun, so, I'm >travelling at, say 20km/s (or whatever, + my 300m/s) > >Now, of course, the Solar System is orbiting around the centre of the Milky, >Way, so add another 150km/s. > >So, really to answer the question 'how fast am I travelling', I have to >specify - relative to what. > > >But here's the bit that's troubling me. > >The speed of light is said to be the fastest anything can go, but no-one >ever mentions in which direction. As I am travelling already at anything up >to 150km/s, if I turn on a torch, pointed in the direction I am travelling, >will the light from it travel at a different speed than if I pointed it >backwards? > That's the crazy thing about light.....no matter what reference frame you're in or what direction you point a light beam, the speed of light measured in any reference frame is c=2.997925 x 10^8 m/s. You can check me out on this by looking at a "Modern Physics" text in the special relativty section. It seems conterintuitive......but see text and compare Galilean transformations to Lorentz transformations. > >Where is the speed of light measured relative to? > Any frame yields the same result....strange eh? >If I travel at near the speed of light, and look behind me, at something on the >other side of the universe, which is also travelling at near the speed of light, >but in the other direction, it will look as if it is going twice as fast as >the speed of light. > I don't think so. I think the Lorentz transformations will tell you that that something is moving even "nearer" to the speed of light when compared to it's velocity in the "rest" frame. It has to do with the gamma factor = (1-((v/c)^2))^-(1/2) >Do designers of particle accellerators have to take the rotation of the earth >etc. into account when they are measuring the speed their particles have >reached? > The speed of light is invariant with respect to different reference frames, but the speed of slower object is governed by the Lorentz transformations (from special relativity). I don't think that the designers of particle accelerators have to consider the rotation of the Earth in the manner in which you are speaking. They use a reference frame either fixed with respect to the accerator or fixed with respect to one group of particles that is gonna smash another group of particles...... The results from the two frames are different but I think one uses the later frame as a standard way of describing the efficiently of an accelerator. > >Steve > >-- > > ---- Steve Parkinson (spark%spuddy.uucp@uknet.ac.uk) ---- > ----- Call Spuddy for Free UK USENET on 0203 638780 ----- Thanks for the questions, helps me prepare for exams. Dan "You can go faster than the speed of light, you can't, can't, can't....and it's invariant." -- Patton Priene ------------------------------ Date: 30 Aug 92 19:27:48 GMT From: "Frederick A. Ringwald" Subject: What is the speed of light measured from? Newsgroups: sci.space In article <1992Aug30.130555.7676@spuddy.uucp> spark@spuddy.uucp (Steve) writes: > Where is the speed of light measured relative to? > That is EXACTLY the punchline: The speed of light is CONSTANT in ALL inertial reference frames. This is REGARDLESS of direction. Sounds crazy, doesn't it? Well, that's how the Universe works. The speed of light does not add and subtract to other velocities, like relative velocities of anything else. ALL observers will measure it to be the SAME. This was first found by Michelson and Morley, who couldn't believe it, either. They redid their famous experiment over and over, with fancier and costlier embellishments, and the result was still the same. Some time later, a young man named Einstein provided an explanation, which is rather surprising, in itself. This discussion really belongs in sci.physics, and it is somewhat elementary: this astonishing result will be discussed at length in any book on special relativity. Two are Spacetime Physics, by Taylor and Wheeler, and Inside Relativity, by Mook and Vargish. Fred Ringwald Department of Physics & Astronomy Dartmouth College Hanover, NH 03755-3528 U.S.A. ------------------------------ Date: 30 Aug 92 22:56:29 GMT From: "Frederick A. Ringwald" Subject: What is the speed of light measured from? Newsgroups: sci.space In article <1992Aug30.130555.7676@spuddy.uucp> spark@spuddy.uucp (Steve) writes: > Where is the speed of light measured relative to? > That is EXACTLY the punchline: The speed of light is CONSTANT in ALL inertial reference frames. This is REGARDLESS of direction. (In a vacuum, that is.) Sounds crazy, doesn't it? Well, that's how the Universe works. The speed of light does not add and subtract to other velocities, like relative velocities of anything else. ALL observers will measure it to be the SAME. This was first found by Michelson and Morley, who couldn't believe it, either. They redid their famous experiment over and over, with fancier and costlier embellishments, and the result was still the same. Some time later, a young man named Einstein provided an explanation, which is rather surprising, in itself. This discussion really belongs in sci.physics, and it is somewhat elementary: this astonishing result will be discussed at length in any book on special relativity. Two are Spacetime Physics, by Taylor and Wheeler, and Inside Relativity, by Mook and Vargish. Fred Ringwald Department of Physics & Astronomy Dartmouth College Hanover, NH 03755-3528 U.S.A. ------------------------------ Date: 30 Aug 92 23:54:20 GMT From: "Alan M. Carroll" Subject: What is the speed of light measured from? Newsgroups: sci.space In article <1992Aug30.192748.23240@dartvax.dartmouth.edu>, Frederick.A.Ringwald@dartmouth.edu (Frederick A. Ringwald) writes: > spark@spuddy.uucp (Steve) writes: > > Where is the speed of light measured relative to? > That is EXACTLY the punchline: > > The speed of light is CONSTANT in ALL inertial reference frames. This > is REGARDLESS of direction. I think it's important to point out that the basic formulas of Special Relativity follow from this fact. For instance, the time dilation formula can be worked out by considering a clock that "ticks" by firing a light beam off a mirror, and considering the path from another intertial reference frame. -- Alan M. Carroll "Weren't there yams involved, too?" - J. Ockerbloom Epoch Development Team Urbana Il. "I hate shopping with the reality-impaired" - Susan ------------------------------ End of Space Digest Volume 15 : Issue 152 ------------------------------