Date: Sun, 9 Aug 92 05:00:03 From: Space Digest maintainer Reply-To: Space-request@isu.isunet.edu Subject: Space Digest V15 #087 To: Space Digest Readers Precedence: bulk Space Digest Sun, 9 Aug 92 Volume 15 : Issue 087 Today's Topics: A 12 mile tether that generates 5000v? Atlas and Soyuz Clinton Space Position Comments, Misc Energiya's role in Space Station assem Hubble used for spying? Looking for information on OSC/Pegasus Physics of shuttle & tether (LONG) (was: Re: Two questions about ...) rising and setting of the Moon ROCKET trajectory program Russian Comment on Soyuz vs Shuttle Tether Tether Applications (was Re: A 12 mile tether that generates 5000v?) tether circuit closure 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: Wed, 5 Aug 1992 20:38:37 GMT From: Andreas Windemuth Subject: A 12 mile tether that generates 5000v? Newsgroups: sci.space Greetings to all tether fans, What has been thought or done about rotating tethers? They would still be able to interconvert angular momentum and electrical power using the electrodynamic effects discussed here so far. They could also be used to slingshot payloads between low and high elliptical orbits, acting as angular momentum banks to trade angular momentum between spacebound and earthbound payloads. Reaction mass could be made almost obsolete. A payload in a low elliptical orbit would match velocities with the lower end of a heavy, rotating tether (the lower end would lag, i.e. be slower than the orbital velocity of the tether as a whole), dock to it, travel half a tether revolution to the upper end and cut lose for a high elliptical orbit (the upper end of the tether is faster than the tether orbital velocity) The angular momentum gained by the payload is taken from the tether, of course, but it can be regained either by slinging another payload back to the lower orbit or, alternatively, by using solar energy and the electrodynamic effect. You can even imagine tethers long enough to reach a planetary surface and act as elevators. Rotation speed would have to be such that the tether "walks" the surface of a planet. It's lower ends would match velocity with the planets surface and effectively dip into the athmosphere almost vertically, leaving enough time to just hang some payload onto a hook, to be dragged out into space as the tether rotates. I believe that existing materials are not strong enough to support this scheme on earth, but on the moon it might well be feasible today. Anybody have any ideas or knowledge on this? --- Andreas Windemuth +-------------------------------------------------------------------- |Theoretical Biophysics windemut@lisboa.ks.uiuc.edu |University of Illinois Tel: (217)-244-1612 |3121 Beckman Institute Fax: (217)-244-8371 |405 N Mathews, Urbana, IL61801 NeXTmail Ok +-------------------------------------------------------------------- ------------------------------ Date: 07 Aug 92 23:31:54 From: Wales.Larrison@ofa123.fidonet.org Subject: Atlas and Soyuz Newsgroups: sci.space Hi David! >Several points on the issue of using Atlas as a launch vehicle for >Soyuz: > The nominal SSF orbit is somewhat higher than the nominal Atlas >orbit cited (220 nmi). However, the Centaur upper stage is very >good at creating Delta V; it is not so good at lifting realtively large payloads, such as a oyuz.Soiyuz Yes, the "nominal" SSF orbit is somewhat higher than 220 nmi I used. But the planned SSF rendezvous altitude for resupply is 220 nmi. SSF's altitude will vary (for a variety of reasons - including atmospheric drag, which will decay the orbit over a period of several months), with orbits from 290 nmi to about 200 nmi. However, I looked up the planned altitudes for shuttle rendezvous, and found it was consistently planned at 220 nmi. The plan is to let the SSF's altitude decay to 220 nmi or so, then rendezvous with the logistics resupply craft (Shuttle), and then reboost after resupply. This altitude was derived from a trade study that tried to maximize launch performance and minimize reboost propellant needed. Since I was trying to compare "apples to apples", I used the same rendezvous altitude. To compare, I pulled the Atlas IIAS performance data off a performance curve from the Atlas II Users Handbook and used it. Since I'm reading off a poorly reproduced curve, my performance numbers may easily be +/- 100 kg. Also, I agree that a Centaur is probably not the best designed for lifting large payloads due to its pressure stabilzed structure. But Centaurs have been designed for up to 6000 Kg payloads (the Centaur G' planned and built for the shuttle was to carry over 13000 lbs into GEO), and the Centaur does lift payloads of approximately 3500 Kg into Geotransfer orbit (burning the Centaur dry inserting the payload into GTO rather than circularizing the payload in GEO). I figured for the ROM estimate I was making here that a Centaur probably could handle the additional mass with a bit of care and a hint of redesign. As I stated in my previous message - I THINK when everything gets added up, a Soyuz is too heavy for a Atlas IIAS. I haven't had the time to dig through them in more detail as a preliminary design study to get a more precise answer. But the numbers are close enough the possibility of launch of a Soyuz on a Atlas IIAS is very interesting. ---------------------------------------------------------------- Wales Larrison Space Technology Investor --- Maximus 2.00 ------------------------------ Date: 8 Aug 92 09:24:49 GMT From: "Frederick A. Ringwald" Subject: Clinton Space Position Newsgroups: sci.space In article strider@acm.rpi.edu (Greg Moore) writes: > (Now, the question is, does Henry have Bono's voice? :-) Let's just hope he doesn't have his funny looks! ------------------------------ Date: 07 Aug 92 21:57:22 From: Wales.Larrison@ofa123.fidonet.org Subject: Comments, Misc Newsgroups: sci.space Allen, this is the text of the email I have been trying to send My apologies to the net, but my mail server (or my comm program) has been acting up. Hi Allen! Could you please stick my name and address on the space activists mailing list, please. I hope this email makes it through - the net connection at this end has been pretty flaky, and my machine has been down at home, as well. Been following the flame fest on sci.space regarding use of a Soyuz. Here's a random comment or two for you which I didn't deem appropriate for the net. >>No problem, if that's all you need. Are you willing to expend the >>logistics modules that would be brought up and down with a crew >>rotation? > I don't think we need to. We can stick some Shuttle tiles on it, >put a parachute on top, and teather it down (which saves fuel and >reduces station keeping fuel needs). It will land just like a >capsule. ... Whoosh! You're kidding, I hope. Controlled reentry is a tricky business, unless you're willing to take the Soviet "hypersonic cannonball" approach by using a sphere and accepting a dispersion (2 sigma) of about +/- 30 miles. To get a reasonable reentry (no fine guidance, just enough control to maintain attitude and control to avoid tumbling or excessive entry heating), you'll need a RCS plus some type of aerodynamic control to maintain attitude after separating from that tether. [Note: nominal reentry interface is about 400,000 feet -- about 75 miles altitude. The tether has to be 175 miles long, or else you'll need some attitude control after letting go.] Mercury/Gemini didn't use aerocontrol and had an dispersion of about +/- 20 nautical miles (2 sigma). Apollo used active aerocontrols. Furthermore, a logistics module is rather unsuited for reentry - the c.g. is way off from the c.p., which either means a ferocious control system (huge fins or one mother of a RCS) or you'll have to redesign to redistribute the mass. Not cheap. "Sticking on shuttle tiles" probably won't work either. There's enough protrubrences that you'll probably have to cover large sections with ACC or RCC, not just shuttle "tiles". Not cheap. The structure also isn't strong enough to take a parachute landing impact. The logistics module is designed to couple with the orbiter structure, so landing it with a 30 ft/sec impact would probably buckle the structure - at least. You'd have to add deployable airbags (and hope you don't have cross wind - air bags are notorious for collapsing in a cross wind as we've found out on the F-111 ejection capsule), or use a Russian-style retro rocket system. Both of these add complexity and cost and weight. >>Again, no problem on the surface. Although Soyuz has never had to >>land in water, it has missed it's target area by hundreds of miles >>on more than one occasion. > The question here is why. It could be that Russian position >location isn't good enough ... From what I've heard, the problem is timing of reentry burn and attitude. The Soviets didn't care about fine guidance in reentry since they had all of Kazakahastan (sp?) to land in. A typical entry was +/- 30 km, if all went well. The worst case was driven by failure of the automatic reentry sequence. The on-board system was recycled, failed again, and then overridden manually and fired some seconds late. At orbital velocity, timing errors can really throw the system off. A one minute error translates into about 277 miles. >>Your point about the single point failure is well taken, however, >>four crewmembers simply cannot fit inside a Soyuz return module. > They can for the short time needed to get to the other one. Errr.... beg to differ here. I've been inside an early-model Soyuz (circa 1978) and have examined the interior of a Soyuz TM at close range (couldn't get into that one - had a plexiglas cover over the hatch area). The three people inside have to be very good friends, as the inside of a Soyuz is about the size of a large phone booth. If I remember correctly on Soyuz 11, they launched 3 crew without suits becuase they couldn't fit three suited cosmonauts into the interior volume. After the deaths on Soyuz 11, the Soviets launched 2 man Soyuzes with suited crews. Only after the Soyuz TM did they return to 3 man crews (in suits) - achieving the additional internal volume through repacking upgraded avionics. You MIGHT get 4 persons in (very doubtful), but I doubt you could get the hatch shut (and there is only one hatch). And if you could the 4th person couldn't get turned around and would have to shimmy out the way he got in. >We use some of the savings to fund the hard suit (which they should >have done in the first place). Pre-breath won't be needed. This >gives us two ways to get the crew to the vehicle. Difficult to don a hard suit in a Soyuz. You need at least 3 times the volume of a person. 1 for the person, 1 for the suit, and 1 for maneuvering the suit and the person around to don it. That type of delta volume in just not available in a Soyuz. And what happens when you open the hatch? Where are the other 3 suits stored? >We use the Russian automatic docking system to dock the two Soyuz's >together. The automatic docking system is currently running about 50% reliability - the past 2 Progress missions have failed on at least 1 attempt each (although they succeeded on subsequent trys with a lot of ground intervention), and the latest Soyuz mission had to abort its automatic dock and come in on manual. Not really a trustworthy system if it's the only way to get to your ride home... Cheers! - Wales - --- Maximus 2.00 ------------------------------ Date: 6 Aug 92 23:15:59 GMT From: Charles Frank Radley <3001crad@ucsbuxa.ucsb.edu> Subject: Energiya's role in Space Station assem Newsgroups: sci.space SSF is in 28.5 deg orbit because congress limited the number of Shuttle flights, and NASA wants to squeeze as much mass as it can into each Shuttle. Launching into 55 deg orbit is a mass payload penalty of about 15 % ------------------------------ Date: 8 Aug 92 16:12:28 GMT From: John Roberts Subject: Hubble used for spying? Newsgroups: sci.space -From: hoyt@isus.UUCP (Hoyt A. Stearns jr.) -Subject: Re: Hubble used for spying? -Date: 5 Aug 92 00:56:16 GMT -Organization: International Society of Unified Science -A PBS broadcast on spying a couple of years ago described the KH11 and KH12 -spy satellites. They seemed remarkably similar in size and shape to the -Hubble telescope. Are you sure they're not related? :-) The *mirrors* are related. Hughes Danbury also makes spy satellite mirrors, and the HST primary mirror was made at the spy telescope mirror facility, though to different specifications than the spy telescope mirrors. This was a contributing factor to the mirror aberration - DoD essentially told NASA to keep their noses out of the fabrication process, because they were uncomfortable about having civilians knowing about the classified portions of the process. As a result, NASA didn't have enough supervisory presence to catch the errors Hughes Danbury made. There's no reason to believe there's any close relation between the *instruments* of the two systems. FOC, for instance, was made by ESA, which probably doesn't make US spy satellite instruments. :-) I'm not sure, but when HST is pointed at the Earth for half of each orbit, I think the door in front of the telescope aperture is kept closed until Earth is out of the way. There must be a reaction wheel routine programmed to compensate for the opening and closing of this door. John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ Date: Sat, 8 Aug 1992 16:40:31 GMT From: Brian Reynolds Subject: Looking for information on OSC/Pegasus Newsgroups: sci.space,rec.models.rockets I would like to build a model of the OSC/Pegasus, but I have no scale information. The sci.space FAQ doesn't really provide much information. Can anyone give me the address or phone number for OSC so that I can request some information? Does anyone know of a model of the Pegasus? I recall that Monogram re-released their B-52 carrier aircraft / X-15 model substituting a Pegasus for the X-15, but I really don't want to build the B-52. Did Monogram ever release the Pegasus as a separate kit the way they issued the desktop version of the X-15? Thanks in advance. -- Brian Reynolds reynolds@panix.com NAR# 54438 IPMS# 30162 ------------------------------ Date: 7 Aug 92 16:40:29 From: Craig Powderkeg DeForest Subject: Physics of shuttle & tether (LONG) (was: Re: Two questions about ...) Newsgroups: sci.space,sci.space.shuttle kilian@cray.com (Alan Kilian) writes: 1) The shuttle is at one end of a conductive wire. The satellite is at the other. If the wire moves through a magnetic field you can generate an electric potential. Now how do you measure the potential? They were hoping for 5000 Volts on a 12 Mile tether but got 40 Volts on a 750 Feet tether. The potential is an emf around a conductive loop. More explanation under (3), below. 2) Why does the ball (It's easier than satellite) keep moving away from the shuttle as you unwind the tehter? This is a pretty cool effect, and it can be explained in two equivalent ways. First, one can say that the ball, being at a different altitude than the shuttle, `wants' to orbit with a different period, so will pull `ahead' (if, as on this flight, it's lower than the shuttle), or `behind' of the shuttle. The tether pulls it back against this tendency, so is kept taut. Alternatively (and perhaps better), the space around the shuttle is subjected to a gravitational gradient. That is to say, the gravitational field (due to the Earth) in the vicinity of the shuttle, changes with altitude above the Earth. The ball, being closer (farther) to (from) the earth than is the shuttle, is pulled more strongly (weakly) by the earth than is the shuttle. The result is that things in orbit about one another, tend to want to stretch along the axis between the things. This is the effect that creates tides on the Earth (and Moon too!), aligns the LDEF experiment, and (in an extreme and hypothetical case) would hold up the Space Elevator[1]. 3) (I know I said two but what the heck) How can you use the potential from the one wire tether? This is a really cool effect, and uses the plasma around the earth. You can make an electromotive force around a loop of wire by cutting magnetic field lines with the wire, by the Maxwell equation relating curl of V to dB/dt. In fact, the emf exists around any closed loop of space, whose flux linkage is changing, regardless of whether there's a wire there or not. The tether experiment uses the conductive properties of the plasma around the earth, to make a *really* *large* loop of conductor using just the tether. The (very tenuous) atmosphere at Shuttle orbital height is a plasma, ie a gas that is mostly ionized, and thus conducts electricity. (You have probably seen electrically conductive plasmas -- you need only look as far as the nearest neon light -- but that's a different story.) The shuttle used the plasma surrounding it as the return wire for the tether experiment. There's one more effect we need to describe. That's the reason why the conductive loop was *really* *large*, instead of just (more-or-less) shuttle-sized. When a charged particle moves at right angles to a magnetic field, it `feels' a force at right angles to the motion and to the field. The result is that its motion (if there's no electric field) is circular. But *any* motion can be resolved into a component at right angles to the field, and one along the field. So any charged particle travelling through a magnetic field (in the absence of collisions and electric field) will spiral around the field lines themselves. If you stand far back and squint (ie you care only about really long distances), this means that electrons travel *only* along magnetic field lines. The only ways to conduct across the field lines involve a high electric field, or collisions between charge carriers. So it's really easy to conduct electricity along magnetic field lines and hard to conduct it across them. The magnetic field lines act almost like wires! The conductive loop in the tether experiment consists of (a) the tether between the shuttle and the ball; (b) the (REALLY LONG!) field line extending from the shuttle to the nearest magnetic pole of the Earth; (c) some small resistive elements between nearby field lines (which get really close as you get closer to the poles); and (d) the field line extending back to the ball from the magnetic pole. The ball is, well, a conductive ball, so it has a lot of surface area to collect electrons from the surrounding space. The shuttle has an electron gun mounted on it (in the nose? the bay? I forget.) to expell electrons out into the surrounding plasma. If there were enough emf, a simple (lightning-rod type) needle point would do the trick, concentrating the electric field enough to rip electrons out of the metal. There's one catch: In order for the separation of field lines to work, the two magnetic field lines that you use have to be much farther apart than the diameter of the spiral made by each electron around its `home' field line. When the field lines get that close, then a single collision can cause an electron to skip from one to the other, so there isn't much electrical isolation between the field lines. The gyroradius (as it's called) increases linearly with the velocity of the electron, and decreases as the magnetic field strength increases. I can't remember offhand a `typical' gyroradius for electrons at that height, but I imagine it's on the order of 100m -- which would mean that electrons can easily `hop' about 100m across the magnetic field. So the shuttle-and-ball system wasn't very effective at all, as a dynamo -- if the tether had unreeled more than a few hundred feet, there would've been much better electrical isolation between the ball and the shuttle, and the conductive loop for the experiment would've been vastly, mind-bogglingly more huge. Considering that most of the electrons probably stayed in the near vicinity of the shuttle/tether system, rather than wandering out on the magnetic field, it's amazing it worked at all! [1] as described in _The_Fountains_of_Paradise_, another one of Arthur Clarke's self-important novels. -- Craig DeForest: zowie@banneker.stanford.edu *or* craig@reed.bitnet "So, if you guys make a living looking at the SUN, why do you spend so much time at the SYNCHROTRON, working UNDERGROUND at NIGHT?" ------------------------------ Date: Sat, 8 Aug 1992 9:31:17 -0500 (CDT) From: REIFF@spacvax.rice.edu (Patricia Reiff (713)527-4634) Subject: rising and setting of the Moon To the person interested in times of moonrise and moonset: A great piece of software is "Voyager" for the Mac - it can give altitudes, azimuths, etc, for stars and planets, any day, any location - in fact, you have to be careful - if you put in the year as "92" you get the result for 1900 years ago! Similar software exists for pc's, and shareware versions are probably available. Many people aren't aware of the basics of moonrise and moonset - that it's linked to the phase of the moon. A first quarter moon rises at noon and sets at midnight, a full moon rises at sunset, etc. (draw a simple diagram of the sun- earth - moon from above the ecliptic plane (look down from the north), and recall that the earth spins, and the moon orbits, counter- clockwise). Another lkf (little-known fact): a full moon in summer is low in the sky (like a winter sun, and for the same reasons), and high in the sky in winter. That, plus the deviation of +/- 5 degrees from the eclipic, can make a full moon in summer not last very long in the sky. There is a fascinating legal case that Abe Lincoln won that concerns the rising and setting of the full moon. ------ From the First Space Science Department in the World: : _^ ^_ ____ Patricia H. Reiff : / O O \ |GO \ Department of Space Physics and Astronomy : \ V / |OWLS\ Rice University, Houston, TX 77251-1892 : / ""R"" \__/ internet: reiff@spacvax.rice.edu (128.42.10.3) \ ""U"" / SPAN: RICE::REIFF : _/|\ /|\_ "Why does man want to go to the Moon? ... Why does Rice play Texas?" ....JFK, Rice Stadium, 1962 ------------------------------ Date: 6 Aug 92 23:13:32 GMT From: Charles Frank Radley <3001crad@ucsbuxa.ucsb.edu> Subject: ROCKET trajectory program Newsgroups: sci.space Has anybody heard of an old public domain NASA trajectory analysis program called (I think) ROCKET or something like that ? Would appreciate it if anybody has heard of it, or preferably knows where I can get a copy. Please e-mail to my other address which is :- Thanks ------------------------------ Date: 07 Aug 92 21:45:44 From: Wales.Larrison@ofa123.fidonet.org Subject: Russian Comment on Soyuz vs Shuttle Newsgroups: sci.space Just thought I'd add this to the discussion going on about Soyuz and shuttle for space station operations.... According to the trade press, cosmonaut Anatoly Artsebarsky stated at a press conference in Chicago last Tuesday, regarding the Buran: "We need it (Buran) to bring back (to Earth) materials and experiments from the station... When using the Soyuz spaceship, we have to abandon some experiments and materials due to its limited (return) capability." Artsebarsky is on a visit to Chicago to promote a Russian space exhibition. Since the Russians have some years of space station operating experience, and their space station configuration is somewhat smaller than the planned SSF configuration, and Artsebarsky has recently returned from a Soyuz/Mir mission, I thought this was an interesting comment, re the current continuing discussion |-). ------------------------------------------------------------------ Wales Larrison Space Technology Investor --- Maximus 2.00 ------------------------------ Date: 8 Aug 92 16:44:31 GMT From: John Roberts Subject: Tether Newsgroups: sci.space -From: andy@osea.demon.co.uk (Andrew Haveland-Robinson) -Date: 6 Aug 92 20:32:01 GMT -Organization: Haveland-Robinson Associates -In article <1992Aug4.100338.1502@uni2a.unige.ch> pfennige@uni2a.unige.ch writes: ->On the contrary, if energy is extracted from an orbiting body, its kinetic ->energy *increases* by this exact amount. All this additional energy is ->provided by the gravitational binding energy. A very useful use of a tethered ->loop could be not to extract electric energy at the expense of gravitational ->energy, but the contrary: electric energy, coming from solar cells for ->instance, can then be used in the opposite way to lift up the satellite orbit. -> -> Daniel Pfenniger -You make some interesting though to my mind, rather curious assertions. -How does it gain kinetic energy if you take energy out of it? Drawing power from the tether takes away from the kinetic energy of the Shuttle. This in turn causes it to drop to a lower orbit. The drop in orbit causes some of the gravitational potential energy of the Shuttle to be converted into Shuttle kinetic energy. Thus the net effect is that the change in gravitational potential energy goes partly into the power drawn from the tether, and partly into increased kinetic energy for the Shuttle. Whether the two amounts are equal takes a little more math. -As I understand it, if you take energy out of an orbiting body, it moves -into a higher orbit at a slower velocity. If you take more out then it -ceases to orbit and starts falling to earth. If there is still an angular -moment then it will stabilise in an orbit (if the Earth doesn't get in -the way of the trajectory!). That's backwards. Centripetal force on the Shuttle from its orbit equals v^2 / r, where v is the orbital velocity of the Shuttle, and r is the distance from the Shuttle to the center of the Earth. The gravitational attraction between the Shuttle and the Earth is essentially GmM / r^2, where G is the gravitational constant, M is the mass of the Earth, and m is the mass of the Shuttle. (Note that if the tether is very long, and if the mass of the satellite is nearly the mass of the Shuttle, then the calculation of r is a little more complicated.) Kinetic energy equals 0.5 * m * v^2. So a high circular orbit has less kinetic energy but more gravitational potential energy than a low circular orbit. The high orbit has greater (kinetic plus gravitational potential) energy than the low orbit. -I suppose the current will alternate during the orbit too, depending on which -orbit was chosen (I guess a polar one would be most productive). If the plane of the orbit is exactly perpendicular to the axis of the magnetic poles (not sustainable because this axis wobbles with the rotation of the Earth), then you would get DC out. For a Shuttle orbit, you get DC with a slight AC ripple superimposed. If you move parallel to the lines of magnetic force, you don't get any voltage out. John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ Date: Sat, 8 Aug 1992 18:02:00 GMT From: seds%cspara.decnet@Fedex.Msfc.Nasa.Gov Subject: Tether Applications (was Re: A 12 mile tether that generates 5000v?) Newsgroups: sci.space In article , windemut@lisboa.ks.uiuc.edu (Andreas Windemuth) writes... > >Greetings to all tether fans, > >What has been thought or done about rotating tethers? >You can even imagine tethers long enough to reach a planetary surface >and act as elevators. Rotation speed would have to be such that the >tether "walks" the surface of a planet. It's lower ends would match >velocity with the planets surface and effectively dip into the >athmosphere almost vertically, leaving enough time to just hang some >payload onto a hook, to be dragged out into space as the tether rotates. >I believe that existing materials are not strong enough to support this >scheme on earth, but on the moon it might well be feasible today. > >Anybody have any ideas or knowledge of this? Great set of questions there. The formost person that I know working on tethers right now is Dr. Robert Forward. He is the guy who was working with the U.S. Air Force on antimatter research. He has guggested that a lunar transportation system could be set up with tether of a length of about 1000 km. The center would be in a stable lunar orbit at 500 km and would rotate. The lower end of this rotation would be at the lunar surface and of course the higher end would be in a pretty high lunar orbit. The only problem with a rotating tether transportation system is that the mass that you pick up and or leave either on the moon or in orbit about the earth must be balanced with picking up or dropping an equivalent weight on the other end. If you are very good with your transportation logistics this would work but scheduling would be a major pain. Also a non rotating tether transportation system has been proposed for Martian operations, I beleive by Paul Penzo of JPL. His system would have payloads in LMO catch the bottom end of a Phobos anchored tether where a simple elevator would move the payload up to phobos, then upwards on another tether where it would be released. The length of this upper tether would be such that the orbital altitude gained would place it in a position that would allow it to be caught by a tether on the low side of Deimos. Again by a simple elevator the payload would be moved up to Deimos then outward from Deimos to a point to where the delta V from the tether gravity gradient would propel the payload into an interplanetary trajectory. Neat huh! The only problem with electrodynamic power generation in LEO is that you do not get something for nothing. If you take power from the Earth's magnetic field you lose orbital momentum. If you have extra power and put it into the tether you gain orbital momentum, which increases your orbital altitude. Someone on here posted that if you decrease orbital energy you gain altitude, this is wrong. The applications of tethers are so rich that it should be one of the two or three critical technologies to pursue in truly opening up the solar system to development. That is the underlying reasons that we are doing our satellite deployment via a tether. If our scenario works out it will help all of our scenarios, even Allen's to become faster cheaper and better. Dennis, University of Alabama in Huntsville. ------------------------------ Date: Sat, 8 Aug 1992 9:05:35 -0500 (CDT) From: REIFF@spacvax.rice.edu (Patricia Reiff (713)527-4634) Subject: tether circuit closure re closure of tether circuit: This closure is, as has been mentioned, effected by collection of charge on the shuttle surface. Since the surface is covered mostly by non-conducting tiles, this is rather poor and the effective collecting area is small. Thus, when the shuttle "Atlas" program a few months ago flew an artificial aurora experiment, putting out a ~kV electron beam with ~0.5 amps merely just makes the shuttle charge up to ~kV with respect to the local plasma, shutting the beam off. To get a full current circuit, they turned on a plasma gun (yes, ions and electrons). The ions would then escape to close the circuit and the electrons return to the shuttle, effectively replacing the electrons emitted (it's a bit more complicated than that, but you get the idea). The video is really impressive - only when the *plasma* gun is on can you see the effects of the *electron* gun, because only then is the circuit closed effectively. The aurora experiment was a tremendous success, and posed new questions (as every really good experiment does) - the beam spread was larger than expected, etc. Because it was such a success, it didn't get the press it deserved, and despite pleas, is probably not going to be reflown. Note that the PIs for the artificial aurora experiment are very close colleagues with the TSS PIs (lots of overlapping Co-I's, very similar instrumentation and plasma gun, etc.), and, had the tether itself not failed, the odds of tether science success would have been nearly unity. Another fact possibly not generally known is that this is the second tether reel system. The first was recognized to be bad, and was replaced by the Italians, and this one had been the cause of a great deal of worry by the scientists as well. One would hope that both the artificial aurora AND the tether systems can be reflown, but with the shuttle politics, it is probably unlikely that they will be. It is this kind of thing that makes the "small" scientist really get fed up with the manned program, that absorbs such a great fraction of the dollars for such a relatively small science payoff, and why so many space scientists fear Fred. (No flames, please, just stating the facts - we don't need another several megabytes of discussion there). These kinds of delays and frustrations have really plagued the scientific community for the last decade or two, and make our graduate students wonder whether it's worth all the effort to get a degree. My reply is, yes, it's not the field for everyone - if you want safety in funding and assurance of results, it's better to go into high energy physics, fusion research, or work at a federally funded lab ;) ! But when things *do* work, and you learn something that noone has ever seen before, or prove something that people had always suspected, then it seems more worthwhile. It's just sad to have to put in 10 days of paper-pushing for 1 day of research! As Charles Darwin said: "A naturalist's life would be a happy one if he had only to observe and never to write". ------ From the First Space Science Department in the World: : _^ ^_ ____ Patricia H. Reiff : / O O \ |GO \ Department of Space Physics and Astronomy : \ V / |OWLS\ Rice University, Houston, TX 77251-1892 : / ""R"" \__/ internet: reiff@spacvax.rice.edu (128.42.10.3) \ ""U"" / SPAN: RICE::REIFF : _/|\ /|\_ "Why does man want to go to the Moon? ... Why does Rice play Texas?" ....JFK, Rice Stadium, 1962 ------------------------------ End of Space Digest Volume 15 : Issue 087 ------------------------------