Date: Fri, 10 Mar 1989 13:21-EST From: space-tech-request@cs.cmu.edu To: "~/st/lists/stdigest" Subject: Space-tech Digest #28 Contents: Reid Ellis rocket-based laser launching? Henry Spencer Re: rocket-based laser launching? John Lukas laser launching Paul Dietz Re: laser launching Gord Deinstadt Levitated Mirror Larry Klaes (fwd.) The SSI LGAS satellite - a project idea for Space-Tech? Paul Dietz The SSI LGAS satellite - a project idea for Space-Tech? Gord Deinstadt Battery-powered railguns Randall Parker Car batteries in large scale applications Larry Klaes (fwd.) Magazine article on latest plans for magnetic launchers ------------------------------------------------------------ Date: Fri, 3 Mar 89 02:23:04 est From: geaclib!rae@uunet.UU.NET (Reid Ellis) To: space-tech@cs.cmu.edu Subject: rocket-based laser launching? Given that laser launching requires so much power, is it infeasible to mount the laser on the rocket, aimed downward? And then, on the ground [for the first bit] you could have mirrors which reflect the light back at the rocket, which uses it for the initial lift? {<<<<<<<<<<<<<<<<\ ____+__ ^ |>>>>>>>>>>>>>>/ engine| ______|>>>>>>>>>>>>>>\ --- mirrors to reflect primary light + v {<<<<<<<<<<<<<<< Given that laser launching requires so much power, is it > infeasible to mount the laser on the rocket, aimed downward? ... Yes. The whole point of laser launching is to put the power supply on the ground, where it doesn't have to be lifted. The only reason for using a laser in the first place is to get the energy up to the vehicle -- it is used to heat fuel, not for direct photon-pressure thrust (which is negligible). > Is this really possible, even in theory? The idea of a rocket > using light for its exhaust sounds a bit silly, but I don't see > any theoretical grounds against it. It is possible in theory, but getting useful amounts of thrust out of it takes truly staggering power levels, orders and orders of magnitude beyond anything we can do today. Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ From: att!ihlpf!lukas@research.att.com Date: Tue, 7 Mar 89 11:27 CST >From: ihlpf!lukas (John A Lukas +1 312 510 6290) To: space-tech@cs.cmu.edu Subject: laser launching With the discussion about laser launching going on, I had a thought. If we were launching in a vacuum, say from the moon, and we had *good* mirrors and control mechanisms, wouldnt it be possible to launch a vehicle using the laser light alone? My thought is that if we get each pulse to make a large number of round trips between a mirror on the spacecraft and one on the moon (imparting twice its momentum each trip), could we not provide any arbitrary launch thrust? John Lukas att!ihlpf!lukas 312-510-6290 ------------------------------ Date: Tue, 7 Mar 89 16:55:19 EST From: dietz@cs.rochester.edu To: att!ihlpf!lukas@research.att.com Cc: space-tech@cs.cmu.edu Subject: laser launching > If we were launching in a vacuum, say from the moon, and we had *good* > mirrors and control mechanisms, wouldnt it be possible to launch > a vehicle using the laser light alone? My thought is that if we > get each pulse to make a large number of round trips between a mirror > on the spacecraft and one on the moon (imparting twice its momentum > each trip), could we not provide any arbitrary launch thrust? Well, the thrust would not be arbitrary, since the light would be red shifted (twice) every time it reflected off the moving spacecraft. Also, diffraction would limit how many times it could reflect, even assuming the mirror on the spacecraft could be perfectly aligned. A related thought: Unlike around the earth, one can't easily put lunar comsats into synchronous orbit. You can use the Lagrange points, but they are far away. I suggest levitating very lightweight satellites using radiation pressure. This idea has been proposed before for use near earth, at much higher power levels. Consider a 1 gram satellite levitated at a distance of 4 lunar radii (7000 km) above the surface. It experiences (ignoring all but the moon's gravity) a force of 6.6e-5 newtons. If the satellite is a perfect mirror it can be levitated with a 10 kilowatt laser or microwave beam. It is not difficult to use the satellite for broadcasting: modulate the levitation beam, and make the satellite slightly curved so the reflection covers a wide footprint. I'd like to be able to use the satellite to return signals from low power transmitters, however. Perhaps one could exploit nonlinear optical tricks to amplify weak laser beams, or sprinkle the satellite with miniaturized transponders powered by the levitation beam. The round-trip delay routing through a satellite 7000 km away is < .1 seconds. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ From: Date: 9 Mar 89 1:45 -0500 To: cs.cmu.edu!space-tech@cognos.UUCP Subject: Levitated Mirror In message <8903072155.AA03855@kochab.cs.rochester.edu> Paul Dietz writes: >Consider a 1 gram satellite levitated at a distance of 4 lunar radii >(7000 km) above the surface. It experiences (ignoring all but the >moon's gravity) a force of 6.6e-5 newtons. If the satellite is a >perfect mirror it can be levitated with a 10 kilowatt laser or >microwave beam. > >It is not difficult to use the satellite for broadcasting: modulate >the levitation beam, and make the satellite slightly curved so the >reflection covers a wide footprint. I'd like to be able to use the >satellite to return signals from low power transmitters, however. >Perhaps one could exploit nonlinear optical tricks to amplify weak >laser beams, or sprinkle the satellite with miniaturized transponders >powered by the levitation beam. The round-trip delay routing through >a satellite 7000 km away is < .1 seconds. > > Paul F. Dietz > dietz@cs.rochester.edu You could use two different wavelengths, one to levitate the mirror (can it be called a satellite?) and for outbound signals, the other for inbound signals. For example, a convex mesh for microwaves joining at the rim with a concave optical mirror for lasers. I don't think that the use of a simple convex reflector for use in both directions would present any real problems, however. If you're using lasers, you should be able to direct most of the beam's energy onto the mirror. From there, it will be spread to cover the face of the Moon. This does not imply a very high high power in the transmitter - if you're willing to use a parabolic concentrator or just a telescope at the receiver. A watt at the transmitter gives on the order of 1e-13 watts/square_meter at the receiver, which is quite sufficient for kbits/sec. And the latest semiconductor lasers are up to 40% efficient when cooled. How would you keep the reflector stable? Would you use a gradient in the levitating beam, with the greatest power around the edges? Or would you use the intersection of multiple beams, similar to the laser traps people are using to manipulate microscopic objects? How would you keep it from rotating, potentially deforming itself with centrifugal forces? Gord Deinstadt gdeinstadt@geovision.uucp ------------------------------ Date: Tue, 7 Mar 89 07:32:20 PST From: klaes%mtwain.DEC@decwrl.dec.com (CUP/ML, MLO5-2/G1 8A, 223-3283) To: space-tech@cs.cmu.edu Subject: The SSI LGAS satellite - a project idea for Space-Tech? In light of the discussion several months back concerning the possible development by this group of a relatively inexpensive satellite system and space mission, the LGAS sounds like just the thing for this group to work on. The sci.space messages follow: Date: 2 Mar 89 17:17:44 GMT From: hp-pcd!hpcvlx!gvg@hplabs.hp.com (Greg Goebel) Subject: SSI Lunar Probe from: INTERNET: cwo_online@hp-pcd HP DESK: CWO ONLINE / HP3900 / 20 (503) 752-7717 Hewlett-Packard CWO / 1000 NE Circle Boulevard / Corvallis OR 97330 Greg Goebel date: Thu Mar 2 09:12:54 PST 1989 I write a small science-and-technology newsletter for HP and ran the following article on a new Space Studies Institute project: ------------------------------------------------------------------------ * One of the most interesting things I ran across this month was a special report issued by the Space Studies Institute -- a non-profit organization at Princeton that investigates long-term technologies for space exploration. I have been a passive member of SSI for years; I send them a little money every now and then, get their newsletters, read them casually, and file them. But this special report got me excited. SSI has done practical research towards exploitation of lunar resources for years; and one project they have been pursuing is a search for volatile substances on the Moon. The Moon has plenty of oxygen, chemically locked in the materials that make up its crust; but it has no atmosphere and, as far as can be seen, no light, volatile substances like water or methane that contain hydrogen. A lunar source of hydrogen would provide lunar miners both with water and a high-grade rocket propellant; without it, all water in space would have to be exported from the Earth -- which would be prohibitively expensive. However, the axis of the Moon's rotation is virtually at a right angle to the plane of its motion around the Sun (it only is off by 2 degrees) and this orientation has been stable for a long time. Comets contain volatile substances, and are known to collide with the Earth; comet collisions with the Moon in the past could've scattered volatiles all over the surface. Most of the volatiles would have escaped into space over time; but those that fell into craters near the poles -- into crevices where, due to the Moon's axis of rotation, the sun never shines -- might remain frozen, and accumulate. A simple space probe, armed with a gamma-ray spectrophotometer, could orbit the Moon's poles to search for the frozen volatiles (and for ices of the volatiles buried under the surface). SSI has several proposals for a Lunar Polar Probe. By far the most interesting is one that would be launched from the Space Shuttle -- carried into orbit as a "getaway special" (GAS) cargo. The getaway specials are payloads that fit into unused crevices of the Shuttle's cargo bay; they are usually the size of trashcans, and are carried aloft at special rates, which have allowed even high schools to perform experiments in space. SSI's Lunar GAS probe would be extremely rudimentary: it would contain a gamma-ray spectrophotometer on an extensible boom, control and communications electronics, twin solar panels for power, and an ion engine. Ion engines are a speculative technology that has been studied since serious space exploration began; such an engine is basically a electrical accelerator that expels an ionized heavy gas (xenon, in this case) at extremely high velocity. Ion engines have low thrust, but they are very efficient in terms of propellant mass (due to the high exhaust velocity) and can be powered by solar arrays. The LGAS probe would be ejected from the Shuttle; then it would deploy its solar panels and begin a slow spiral away from the Earth that would place it into lunar polar orbit in about two years' time. If LGAS should happen, it would be a landmark in space exploration -- even if it did not reveal deposits of lunar volatiles. Large space projects are difficult to justify in a time of budget deficits, take a long time to implement, and are vulnerable to protracted delays or cancellation. A larger number of smaller projects would be much more practical -- Freeman Dyson refers to this as the "quick is beautiful" approach. If the LGAS was developed through a combination of private funds and government research grants, it would be the first citizen's interplanetary probe -- and would lead the way towards a lower-cost approach to planetary exploration, as well as more sophisticated private space exploration ventures. ------------------------------------------------------------------------------ Does anyone know what the status of this project is? Have any cost estimates been made? Is there any attempt to get funding for it? It would seem that, given the long flight time of the LGAS probe and the need to get input for national space strategies in the near future, SSI must act quickly on this. regards -- gvg ------------------------------ Date: 3 Mar 89 04:02:55 GMT From: thorin!zeta!leech@mcnc.org (Jonathan Leech) Subject: Re: SSI Lunar Probe In article <101270005@hpcvlx.HP.COM> gvg@hpcvlx.HP.COM (Greg Goebel) writes: >Does anyone know what the status of this project is? Have any cost >estimates been made? Is there any attempt to get funding for it? Quoting the SSI Special Report "Lunar Prospector Probe": "First, we are attempting to show NASA and key national leaders the importance of a quick and simple lunar mission which could detect possible water ice at the poles." ... "Secondly... we are working towards a partially or perhaps completely privately funded class of lunar probes." Planned 1989 activities include a lunar prospector workshop preceding the 1989 Princeton Conference on Space Manufacturing and a session on lunar polar science at the 20th Lunar & Planetary Institute Conference. One of the International Space University's summer '89 projects will be the design of lunar orbiting probes. Also, SSI has contracted with ExtraTerrestrial Materials, Inc., to manage a working group to design a probe. >It would seem that, given the long flight time of the LGAS probe and the >need to get input for national space strategies in the near future, SSI must >act quickly on this. The ion drive is only one possibility. Another is to use a surplus Atlas booster. See the special report for photos and lots more info. One more quote from the SSI report: "SSI's extensive work on the lunar polar prospector has been made possible by the contributions of the members and Senior Associates of the Institute." If you want to see this project happen, I suggest sending SSI lots of money ($25/year for a subscription to the newsletter is at least a start). SSI is at: Space Studies Institute PO Box 82 Princeton, NJ 08542 609-921-0377 Send me email if there are more questions. -- Jon Leech (leech@cs.unc.edu) __@/ "Totally bounded: A set that can be patrolled by a finite number of arbitrarily near-sighted policemen." A. Wilonsky, 1978 ------------------------------ Date: Tue, 7 Mar 89 11:37:32 EST From: dietz@cs.rochester.edu To: klaes%mtwain.DEC@decwrl.dec.com Cc: space-tech@cs.cmu.edu Subject: The SSI LGAS satellite - a project idea for Space-Tech? > A lunar source of hydrogen would provide lunar miners both with > water and a high-grade rocket propellant; without it, all water in ^^^^^^^^^^^^ > space would have to be exported from the Earth -- which would be ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > prohibitively expensive. Harrumph. This ignores asteroidal water. Also, I am not convinced that water launched from the moon would be competitive in space with water or other refined hydrogenous substances launched from Earth by some kind of gun-type launcher. I really like the idea of a private lunar probe, though. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ From: Date: 8 Mar 89 10:07 -0500 To: cs.cmu.edu!space-tech@cognos.UUCP Subject: Battery-powered railguns For an Earth-based railgun, where weight doesn't matter, (car batteries + a big inductor) probably does give the cheapest solution. But if weight is a problem (as for Jordin's lunar launcher calculations), even if you want to stick with lead-acid, you can do a lot better than car batteries. Car batteries are designed to deal with currents that would discharge the battery in a few tens of minutes. If you want to discharge the battery in a few seconds, you can replace the rather thick lead plates in the car battery with multiple layers of foil. This multiplies the surface area / volume ratio and therefore the peak power (but not total energy). You can buy these; they are called gel cells and are made by Gates. You can much better with other materials. One of my college teachers once jumpered across the ends of an AA nicad cell with fairly thin wire. (It had just arrived in the mail, and he didn't know it was charged.) It melted the wire! So it must have put out order 50 or 100 amps. Short-circuit current from a far larger car battery is only about 400 amps. Assuming a 1 km railgun, 3.5 km/s and constant acceleration, I get a discharge interval of 570 msec. This may be pushing it a bit, but I think you could design batteries to efficiently discharge in this length of time, obviating the need for an inductor. (Average power during discharge would be 10.7 Gw for a 1000 kg payload!) But - a constant-acceleration profile takes much more power towards the end of the rail than it does at the beginning. Does anybody know what the velocity/time graph for a practical EM launcher would look like? I don't think it would be constant-acceleration, because of the power problem. For use on Earth, the ram accelerator still seems simpler to me. No need to switch gigawatts of electric power. Gord Deinstadt gd@geovision.uucp ------------------------------ Date: Wed, 8 Mar 89 09:05:43 PST From: C43RGP%ENG4.gm@hac2arpa.hac.com To: SPACE_TECH@hac2arpa.hac.com Subject: Car batteries in large scale applications Last year there was an article in Av Leak(Aviation Week) about a facility the Air Force is building that uses a warehouse full of car batteries to power an experiment. I went into a back stack of Av Leaks looking for the article but could not find it. My memory is hazy on the details. Seems like it was at Eglin AFB in Florida and was for lasers or a magnetic gun experiment. An Air Force spokesman said it was cheaper than the alternatives and very practical. Does anyone else remember the article? Randall Parker (805) 967-8051 Delco Electronics - Delco Systems Operations, Goleta CA. c43rgp%eng4.gm@hac2arpa.hac.com My company isn't responsible for these opinions, etc, etc.... ------------------------------ Date: Wed, 8 Mar 89 07:03:31 PST From: klaes%mtwain.DEC@decwrl.dec.com (CUP/ML, MLO5-2/G1 8A, 223-3283) To: space-tech@cs.cmu.edu Subject: Magazine article on latest plans for magnetic launchers. Date: Wed, 1 Mar 89 18:56 CST From: Bill Higgins-- Beam Jockey Subject: Fun with electromagnetic catapults: *IEEE Magnetics* Original_To: SPACE Run to the nearest engineering library, space cadets! The January 1989 issue of *IEEE Transactions on Magnetics* is out. It contains about 660 pages of pure reading pleasure from the Fourth Symposium on Electromagnetic Launch Technology in Austin, Texas last year. A handful of the papers are directly relevant to space launch applications (which, I suppose, means that the idea is moving into the mainstream), and the rest are concerned mostly with the dirty details of EM launchers. Read about compulsators, ultracapacitors, homopolar generators, electrothermal launchers, plasma armatures, explosive foil injection, and ignitron tubes. I don't know what all this stuff means, but it has a certain musical quality when you read it aloud, a little like a *Doctor Who* episode with no picture... Of course, I am already working with an electromagnetic launcher with a high rate of fire (average of 1E13 payloads per minute) and fairly satisfactory muzzle velocity (3,720,000% of orbital velocity). But the payload mass is rather limited-- a real challenge to the lightsat people. And the air resistance is murder. ______meson Bill Higgins _-~ ____________-~______neutrino Fermi National Accelerator Laboratory - - ~-_ / \ ~----- proton Bitnet: HIGGINS@FNALB.BITNET | | \ / NEW! IMPROVED! SPAN/Hepnet/Physnet: 43011::HIGGINS - - Now comes with Free ~ Nobel Prizewinner Inside! Internet: HIGGINS%FNAL.BITNET@UICVM.uic.edu ------------------------------ End of Space-tech Digest #28 *******************