Return-path: X-Andrew-Authenticated-as: 0;andrew.cmu.edu;Network-Mail Received: from po5.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr1/ota/space/space.dl@andrew.cmu.edu (->+dist+/afs/andrew.cmu.edu/usr1/ota/space/space.dl) (->ota+space.digests) ID ; Wed, 10 Aug 88 04:10:05 -0400 (EDT) Received: from andrew.cmu.edu via qmail ID ; Wed, 10 Aug 88 04:05:39 -0400 (EDT) Received: by andrew.cmu.edu (5.54/3.15) id for +dist+/afs/andrew.cmu.edu/usr1/ota/space/space.dl; Wed, 10 Aug 88 04:04:57 EDT Received: by angband.s1.gov id AA04207; Wed, 10 Aug 88 01:04:39 PDT id AA04207; Wed, 10 Aug 88 01:04:39 PDT Date: Wed, 10 Aug 88 01:04:39 PDT From: Ted Anderson Message-Id: <8808100804.AA04207@angband.s1.gov> To: Space@angband.s1.gov Reply-To: Space@angband.s1.gov Subject: SPACE Digest V8 #320 SPACE Digest Volume 8 : Issue 320 Today's Topics: Re: Solar Sails Re: Libertarian space policy Solar flares 20-year anniversary Satellites Re: Lithium cells Re: Space Station Name chosen -- Fred Re: E stamp RE: Solar Sails Re: Libertarian space policy Re: 20-year anniversary ---------------------------------------------------------------------- Date: 2 Aug 88 09:47:50 GMT From: polya!crew@labrea.stanford.edu (Roger Crew) Subject: Re: Solar Sails In <8807311909.AA21830@doc.cc.utexas.edu> sedspace (Steve Abrams) writes: > In V8 #306, Eric "TheBoo" Bazan (eric@shorty.cs.wisc.edu) writes: >> My question is this: just how does the sun 'push' against the sail? >> Is it the solar wind of charged particles (protons and electrons), >> or the actual photonic flux, or both? > > Since the wave and particle paradigms for electromagnetic radiation are > equivalent, you can certainly think of "material" photons bouncing off a sail > film and, thereby, transferring momentum to the sail. However, I assume you > want to view it from the wave perspective. > > [...stuff about photons ...] Look, if you want to view it from the wave perspective, you're supposed to forget you ever heard the word ``photon.'' An electromagnetic wave in a vacuum consists of an electric field and a magnetic field oscillating perpendicularly to one another, both perpendicular to the direction of motion. So consider what happens if you have a single charged particle sitting off in the middle of nowhere when an EM wave hits it: Let's just put a positron (+ charge so that we don't get too messed up by sign changes) in the middle of your terminal screen and have the wave be moving into the screen. Just to keep things simple let's have the wave be polarized so that the electric field (E) is oscillating up and down. By itself, the electric field causes the positron to vibrate up and down. As with any simple harmonic oscillator the force will be 180 degrees out of phase with the displacement; the positron reaches its lowest point just when the electric field is at its strongest pointing upward (thus pushing the particle back up...) and vice versa. Note that the velocity of the particle is 90 degrees ahead of the dislacement. No problem so far, but now we've also got a magnetic field (B) as well which will be oscillating left to right. Recall that the magnetic field is generated by the changing electric field (Maxwell's version of Ampere's Law) [B ~ dE/dt] --- and vice versa (Faraday's Law E ~ -dB/dt), after all, this is how we get an electromagnetic wave in the first place --- and will thus be 90 degrees ahead of the electric field. After lots of exercises with your right thumb and index finger, you'll get that whenever the positron is moving upwards (electric field changing downwards), the magnetic field points to the right, and whenever the positron is moving downwards, the magnetic field is to the left. Thus, at all times, the magnetic force on the particle q(v x B) is pointed into the screen. If the particle were an electron, the magnetic force would be reversed, but we also have that it would be vibrating in the opposite direction --- still ends up being pushed into the screen. To first order, this is what's happening. But it's not the whole story. Whenever a charged particle accelerates, it radiates a wave of its own. Part of this wave heads into the screen, cancelling out a part of the original wave headed in that direction. The other part heads out of the screen back towards your face. Thus, energy has been taken out of the original wave; some of it goes to the particle, the rest gets reflected back. If you consider the waves to have momentum inversely proportional to the wavelength, it turns out that momentum is conserved as well. Note that this is a completely classical explanation; at no point have we drawn on anything from quantum mechanics. -- Roger Crew ``Beam Wesley into the sun!'' Usenet: {arpa gateways, decwrl, uunet, rutgers}!polya.stanford.edu!crew Internet: crew@polya.Stanford.EDU ------------------------------ Date: 2 Aug 88 04:51:39 GMT From: clyde!watmath!utgpu!utzoo!henry@bellcore.com (Henry Spencer) Subject: Re: Libertarian space policy In article <978@bucket.UUCP> leonard@bucket.UUCP (Leonard Erickson) writes: >Note that Argentina has *already* started claiming *soveriegnty >over it's portion of Antartica... Claims of sovereignty over parts of Antarctica are nothing new; I don't believe it has *ever* been the case that *all* interested parties were willing to renounce them completely. Just because the superpowers have renounced them does not mean everybody has. (In fact, this is the sort of assumption that really irritates citizens of non-superpower nations.) However, the big powers *have* played a key role in keeping those claims in the realm of unimportant legal fiction. When the US and the USSR ignore your claims and violate them regularly, nobody else is likely to take them seriously either. -- MSDOS is not dead, it just | Henry Spencer at U of Toronto Zoology smells that way. | uunet!mnetor!utzoo!henry henry@zoo.toronto.edu ------------------------------ Date: Wed, 3 Aug 88 02:17:17 EDT From: "Keith F. Lynch" Subject: Solar flares To: eos%spacvax.rice.edu@rice.edu Cc: KFL@ai.ai.mit.edu, Space@angband.s1.gov > From: "Pat Reiff" > ... the great flare of August 2, 1982 ... the Apollo program was > still going on at that time ... Are you sure you don't mean 1972? ...Keith ------------------------------ Date: 3 Aug 88 01:10:02 GMT From: tektronix!teklds!mrloog!dant@ucbvax.berkeley.edu (Dan Tilque;1893;92-101;) Subject: 20-year anniversary Next year will be the 20th anniversary of Apollo 11 and I'm sure that everyone would like to celebrate it. It never hurts to be prepared in advance, so lets start to kick ideas around. My idea is that they launch Discovery on or before July 20, 1989, even if its faucets do leak. Any others? --- Dan Tilque -- dant@twaddl.LA.TEK.COM ------------------------------ Date: 2 Aug 88 22:45:37 GMT From: unccvax!nrk@mcnc.org (Nitin R Kulkarni) Subject: Satellites Hello, fellow-netters. I am a newcomer to this group. Can anybody in net-world give me the following information : 1. How many satellites has the US and the USSR launched into deep space ? 2. Their probable location in our solar system as of today. 3. The dates when they were launched. Thanks in advance. Nitin. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ UUCP : nrk@unccvax.UUCP ARPA : nrk%unccvax@mcnc.org ****** Is it clean in other dimensions ? ****** ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ------------------------------ Date: 3 Aug 88 02:14:51 GMT From: killer!tness7!tness1!nuchat!splut!jay@ames.arc.nasa.gov (Jay "you ignorant splut!" Maynard) Subject: Re: Lithium cells In article <880729-124705-5997@Xerox> "chaz_heritage.WGC1RX"@XEROX.COM writes: >Some reported explosions of lithium cells are due not to short-circuiting but to >application of AC. >[...] >Since in the astronautics application no high-voltage AC will be present in the >circuit, there appears to be no risk of such violent explosions. Assessment of >the outgas hazard is clearly in the hands of experts. Uhm...not quite. Main power on the space station is specified as 220 VAC at 20 kHz. This, of course, makes power supplies efficient (since, in essence, they're giving you the front half of a switching power supply), but can indeed generate AC across a lithium battery in the manner described. -- Jay Maynard, EMT-P, K5ZC...>splut!< | Never ascribe to malice that which can uucp: uunet!nuchat! | adequately be explained by stupidity. hoptoad!academ!uhnix1!splut!jay +---------------------------------------- {killer,bellcore}!tness1! | Birthright Party '88: let's get spaced! ------------------------------ Date: 2 Aug 88 08:33:11 GMT From: mcvax!enea!liuida!yngla@uunet.uu.net (Yngve Larsson) Subject: Re: Space Station Name chosen -- Fred In article <605@ecrcvax.UUCP> johng@ecrcvax.UUCP (John Gregor) writes: >>space station "Freedom". > ^^^ ^ Well, coincindence of coincidences; The strange fact is that "Fred" is the Swedish word for "Peace". How nice of you to (sort of) honor Mir in this way.. :-) > >John Gregor johng%ecrcvax.UUCP@pyramid.COM -- Yngve Larsson UUCP: ...mcvax!enea!liuida!yla Dept of CIS Internet: yla@ida.liu.se Linkoping University, Sweden Phone: +46-13-281949 ------------------------------ Date: 1 Aug 88 19:15:32 GMT From: trwrb!aero!venera.isi.edu!rogers@ucbvax.berkeley.edu (Craig Milo Rogers; FAST) Subject: Re: E stamp Since the center of illumination lies over Siberia, and the orange bands in the background might have the correct elevation for orbital platforms, perhaps the E stamp depicts SDI deployment. What a subtle method to subliminally influence the US voting public! This, too, would explain why the stamp is limited to "domestic" use; wouldn't want too many Soviets or Europeans getting the wrong ideas through repeated exposure to these stamps. Craig Milo Rogers ------------------------------ Date: Wed, 3 Aug 88 12:20:22 CDT From: sedspace@doc.cc.utexas.edu (Steve Abrams) Posted-Date: Wed, 3 Aug 88 12:20:22 CDT Subject: RE: Solar Sails In V8 #312, Alan Bostick replies to a simple question (FLAME ON) in his ubiquitously obnoxious and condescending manner intended, not so much to answer the question or enlighten the questioner, as to impress us with his virtuosity in physics. However, as a former professor of mine used to say, "If you can't answer a physics question in words, *without resorting to formulae*, then you don't understand the topic well enough. (FLAME OFF) Now, the original poster asked and Alan responded: >In article <10922@oberon.USC.EDU> robiner@ganelon.usc.edu (Steve) writes: >>If the light bounces off the sail, how does it impart momentum. What >>energy of the photon is now reduced? I think the photons must be >>ABSORBED by the sail for this to work. > >Well, you're wrong. However, Alan (in his response) implicitly agreed that the momentum trasnfer *does* occur when the photon *is* absorbed by the sail film... >The photon bounces off of the mirror and is reflected in >accordance with the laws of reflection. Well, Alan, you kinda' glossed over the mechanism of momentum transfer by the "in accordance with the laws of reflection" phrase. Let's look at exactly what happens when the photon is "reflected." In an "ideal" reflective surface, the incident photon is *temporarily* absorbed by the electrons (at some equilibrium energy level dictated by thermal effects and its "nearest neighbor" electrons) in the surface of the sail (look up "classical skin depth" and "anomalous skin effects"). An electron absorbing a photon increases its energy level. The photon's momentum is transmitted, via interaction with the electron's potential "barrier," to the metallic lattice of atoms of the sail film. In addition, the electron with the higher energy level is unstable and perturbations induced by the "re-bound" of the potential barrier cause it to decay to its original energy level thereby emitting a photon with the original energy *but* in a direction of "least opposition" (i.e. back towards the surface and not further into the film; this new photon's polarization is also reversed from the original's) thereby imparting more momentum because of the change in direction; of course, in a *real* reflective surface, the electron decays to a higher energy level and the re-emitted photon has less energy than the original. Occasionally, some "higher energy" electrons are more stable in their new configuration and survive the "re-bound." These photons are the ones we call "absorbed." Also, since skin depths for most metals are for the same order of magnitude as the thicknesses of sail films and thin films are close (within a couple of orders of magnitude) in thickness to the wavelengths of the radiation incident, some photons make it all the way through and are "transmitted." BOTTOM LINE: For the ideal sail films you were discussing, *all* incident photons *are* absorbed, transmit a "unit" of momentum, and are re-emitted (transmitting another "unit" of momentum). FLAME RE-IGNITED: See, Alan, it can be explained without the tedium of working through ASCII equations and in a manner that conveys the *physics* of the topic and not just the math. So, >Next time, think for a minute before shooting off your mouth... FLAME RE-DOUSED I've been wondering if anyone has looked into the possibility of using thin, conducting polymer films rather than metallic films for sail films. I know that polymers were once used for backing for a metallic film and dropped to improve the thrust to mass ratio. Can thin films be polymerized to appropriate thicknesses? If so, the doping to make them electrically conducting (and reflective) can be done rather easily. The electrical conduction mechanisms are different in these polymers from metals so, presumably, are the reflections mechanisms. With metals, you must consider specular, diffuse, and back reflectances. Anyone know if all of these apply to the reflection mechanism of conducting polymers? Are there any different ones? Ad Astra, Steve Abrams \ / --"You have twenty seconds to put down your slide rule...19...18...17..."-- / \ -- RoboDweeb 2721 Hemphill Park, Apt. C ARPANET: sedspace@doc.cc.utexas.edu Austin, TX 78705 CompuServe: [70376,1025] (512)480-0895 OR c/o Students for the Exploration and Development of Space P.O. Box 7338, 358 Texas Union, University of Texas at Austin Austin, TX 78713-7883 (512)471-7097 ------------------------------ Sender: "James J. Lippard" Date: Wed, 3 Aug 88 10:49 MST From: "James J. Lippard" Subject: Re: Libertarian space policy Reply-To: Lippard@bco-multics.arpa To: WALL%BRANDEIS.BITNET@mitvma.mit.edu Cc: Space@angband.s1.gov >Date: Mon, 25 Jul 88 15:05 EDT >From: (Matt) > I can hardly wait to see the outer space equivalent of Love Canal and > Manville asbestos. Ah yes, Love Canal--where the government used its power of eminent domain to take a Hooker Chemical dump site and build a school on it despite Hooker's warnings against it. Jim Lippard Lippard at BCO-MULTICS.ARPA ------------------------------ Date: 3 Aug 88 21:58:52 GMT From: jec@iuvax.cs.indiana.edu (James E. Conley) Subject: Re: 20-year anniversary In article <2087@silver.bacs.indiana.edu> konath@silver.UUCP (kannan) writes: >In article <3763@teklds.TEK.COM> dant@mrloog.LA.TEK.COM (Dan Tilque) writes: > >