Subject: Space-tech Digest #70 Contents: Nick Szabo Re: Is an asteroid capture possible/feasible? Henry Spencer Re: Is an asteroid capture possible/feasible? Joe Pistritto Re: Is an asteroid capture possible/feasible? Phil Fraering Asteroid movement/retrieval Keith Henson Re: Asteroid movement/retrieval Rich Schroeppel Asteroid relocation Nick Szabo Re: Asteroid relocation Paul Dietz Re: Asteroid relocation Nick Szabo Re: Asteroid relocation John Roberts Re: Asteroid relocation Keith Henson Re: Asteroid relocation/mining Nick Szabo Re: Asteroid relocation/mining Nick Szabo Re: Asteroid relocation Ted Anderson JBIS Interstellar Studies Ted Anderson Alternative Mass Drivers Ted Anderson Light Gas Gun for launching to LEO ------------------------------------------------------------ Date: Thu, 19 Jul 90 14:54:13 -0700 From: "Nicholas J. Szabo" To: uunet!cs.cmu.edu!space-tech@uunet.UU.NET Subject: Re: Is an asteroid capture possible/feasible? (This is from a discussion in sci.space but may interest folks here too). In article dlbres10@pc.usl.edu (Fraering Phi lip) writes: >But you don't have to use nuclear charges to move asteroids. You could >use a giant mass driver to push some of the smaller ones using rock >mined from the surface as reaction mass. > We may need large advances in technology before this becomes practical. An extensive suite of mining and processing equipment is needed to convert the asteroidal material into armatures that won't foul up the mass driver. An imbalance at 10 km/s is not pretty. Energy is also a problem. This table crudely illustrates the economics. I assume 50 W/kg each for the mass driver, generator, and mining equipment. Underestimating launch cost at the GEO price of $20,000/kg, we get $1,200 per installed watt. Power is that needed to provide delta-v of 500 m/s per year to an asteroid of density 4 g/cm^3 and the stated diameter. An M-type asteroid's platinum-group contents value shown for comparison. asteroid dia,mass power(W) launch cost value of asteroid ----------------- -------- ----------- ----------------- 10 m, 2.09e6 kg 8.3e3 $61e6* $1.7e6 100 m, 2.09e9 kg 8.3e6 $3.3e9 $1.7e9 1,000 m, 2.09e12 kg 8.3e9 $3.3e12 $49e9** * lowest cost for any launcher with upper stage ** market limit for Pt-group metals (NPV of $20e9/yr cash flow at 20% interest rate, delayed 4 years) Practically speaking, R&D, manufacturing, and the Pt-group mining costs will also be large, as well as the time cost of money when moving asteroids so slowly, so that launch costs for asteroid transfer equipment should probably be < 1/10 the value of the asteroid to be economical. If we want to move the asteroid faster, launch costs increase as the square of delta-v per year in this scenario. Other ways to move an asteroid are cheaper but less predictable: (1) nuclear explosives (already discussed) (2) collision with another asteroid or the moon (3) aerobraking in Mars or Venus atmosphere (not the earth's!) (4) Mars or Venus gravity assists I suspect that supercomputer simulations of fracture mechanics, nuclear explosions, and aerodynamics of the surface of the asteroid will become practical as supercomputer prices come down. Supercomputers may also search the space of trajectories, including gravity assists and aerobraking, among hundreds of thousands of asteroids to find the quickest and lowest-energy opportunities. Sensors and computer time are cheap compared to launching engines and equipment. Combinations of (1)-(4) may then yield satisfactory results. I envision an industrial park located at an Earth-Sun trojan point into which several comets and asteroids have been moved in the above manner. This park would export platinum-group metals and ureilite diamonds (if they exist) to earth, while providing volatiles, metals, and ceramics for various uses in space. This would also become a center for microgravity and vacuum manufacturing. The earth exports would be loaded into Shuttle- sized cones of foamed iron and tungsten, and carefully shoved off by solar- or nuclear-thermal powered tugs into a collision course with the Indian Ocean off of Australia. (This will boost the local economy a bit more than Skylab :-) The largest problem remains, developing the technology for space mining, which does not exist. Nick Szabo uunet!ibmsupt!szabonj These opinions do not reflect those of any organization I am affiliated with. ------------------------------ From: henry@zoo.toronto.edu Date: Fri, 20 Jul 90 01:37:35 EDT To: uunet.UU.NET!ibmsupt!ibmpa!szabonj@zoo.toronto.edu Cc: cs.cmu.edu!space-tech@zoo.toronto.edu Subject: Re: Is an asteroid capture possible/feasible? > An extensive suite of mining and processing equipment is needed > to convert the asteroidal material into armatures that won't foul up > the mass driver. An imbalance at 10 km/s is not pretty. ??? A mass driver does not need to have the asteroidal material formed into armatures. "Mass driver" is **NOT** a generic term for "electromagnetic catapult"; it refers to a specific device, invented by Gerard K. O'Neill in 1974. O'Neill's key innovation -- it seems obvious in retrospect, but he really does seem to have been the first to think of it -- was to use recirculating payload-carrying "buckets". The problem of electromagnetic catapults is that really good ones need magnet coils on the projectile, and those are too expensive to throw away. So, said O'Neill, *don't* throw them away: separate the payload, which goes its own way, and decelerate and re-use the coil assembly. That way, the payload (reaction mass, in the case of the mass-driver rocket) can be anything that is easy to handle. Modulo possible problems with static electricity and abrasion, rock dust will do. Slugs of solid rock would also work, but dust is less antisocial downrange. If you're willing to do more chemical processing, liquid oxygen would be ideal: oxygen is common in most any rock, and it vaporizes after expulsion, eliminating the downrange problem entirely. The material-preparation problem remains non-trivial, but it's a lot simpler with a mass driver than with (say) a railgun. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ Subject: Re: Is an asteroid capture possible/feasible? To: henry@zoo.toronto.edu Date: Fri, 20 Jul 90 9:07:14 MESZ From: Joseph C Pistritto Cc: uunet.UU.NET!ibmsupt!ibmpa!szabonj@zoo.toronto.edu, cs.cmu.edu!space-tech@zoo.toronto.edu Mailer: Elm [revision: 64.9] A problem with a 'mass driver' solution would also be size. You're going to want high exit velocities, and although you don't really care about the material you're exhausting, the faster you want to go, the smaller pulse-width you need to apply to the electromagnets. Electromagnets that respond very dynamically at high currents are *EXPENSIVE*, and they get very hot in operation. Superconducting coils help, but there are very real limits to the flux density of a superconducting medium (ask one of the folks from the accelerator labs about this). We're going to need a 'fine adjustment' motor of some kind for our rock, and this might very well be it, but for major corrections, go with the nukes. Cheap at 10 times the price. Also, theres a lot of experience exploding nukes in contact with rock, so I bet we know a lot more about this application than you might think. The best chance would be with Earth crossing asteroids, as has been noted before. By making each charge a fraction of the total delta-v required (this probably won't be optional), we can guard against accidentally smashing the earth by keeping a few spares. Remember the earth is a tiny thing. Not hitting it is easy, comets have been doing it for millinea... -jcp- -- Joseph C. Pistritto (bpistr@ciba-geigy.ch, jcp@brl.mil) Ciba Geigy AG, R1241.1.01, Postfach CH4002, Basel, Switzerland Tel: +41 61 697 6155 (work) +41 61 692 1728 (home) GMT+2hrs! ------------------------------ Date: Fri, 20 Jul 90 09:55:40 -0500 From: Fraering Philip To: space-tech@CS.CMU.EDU Subject: Asteroid movement/retrieval Comments on Nick Szabo's posting: 1. As Henry Spencer has pointed out, armatures can be reused. This means that the mining equipment can be a lot less complex. 2. The price of launching material to orbit can be lower than you say. Mainly, A. The launch cost to GEO is about the same as to escape velocity. B. The cost of launching material may fall in the near future (and I have some land in the Atchafalya basin - real cheap :-). Seriously, though, I think the Soviets charge less for that now (although I am leery of doing business with them right now - let's not get into this in the technical mailing list), besides that Proton is better optomized to launch to escape velocity than to geosynchronous orbit. Also, some- one here might develop something cheap, but that's another posting altogether. 3. Lunar resources could be used to help build the power equipment and structural mass of the mass driver/mining equipment. 4. Since rock is being used as reaction mass, you can make the Isp as low as you can and not still be throwing away the Platinum and the water (or whatever you're moving the asteroid to get). I do agree, however, that we will need new technologies. However, we must 1. Work to develop them. 2. Work to make sure the price of launching a Kg into orbit doesn't remain astronomical. Phil Fraering dlbres10@pc.usl.edu P.S. : I'm not sure this discussion belongs in the space-tech mailing list. Pretty soon I'll have to start doing some serious math, and at the USL library they don't have half the things I need to look up to do the calculations (info on lunar materials, etc...), which is why I'm on this list to begin with. ------------------------------ From: portal!cup.portal.com!hkhenson@Sun.COM To: space-tech@CS.CMU.EDU Subject: Re: Asteroid movement/retrieval Date: Fri, 20 Jul 90 10:58:44 PDT X-Origin: The Portal System (TM) X-Possible-Reply-Path: hkhenson@cup.portal.com X-Possible-Reply-Path: sun!portal!cup.portal.com!hkhenson Re this topic, metal asteriods can be processed by the carbonal process, where warm CO forms volitile compounds, heat makes the gas stream drop the metal, and you recycle the CO. Works on Ni, Fe, and Co. What's left may be worth shiping without further refining. Mass wise, a plant would be expected to process its own mass every eight hours, or something in the range of 1000 times its mass in a year. Keith Henson ------------------------------ Date: Sat, 21 Jul 90 19:10:22 PDT From: Richard Schroeppel To: space-tech@CS.CMU.EDU Subject: Asteroid relocation A problem with using nukes for the job: trash. If each nuke sends a lot of little rock fragments into orbits near our asteroid, the environment around the processing plant could be unhealthy. Also we might make dangerous the region around the Earth's orbit, which might otherwise become a useful resource. An alternative: how about a high speed turntable or centrifuge, that throws rock dust in the designated direction? Design goal is 1kg of dust per second, thrown at 1km/second. (Multiple turntables would probably be used.) Note that an acceleration of 500m/sec/year is not a necessity, if we are willing to search for good near-Earth asteroids, and take our time for the capture. JBIS had an article discussing the use of the moon (for gravity assist) to help capture an asteroid into high earth orbit. Multiple passes (one/year) are required. But the deltaV isn't too bad, if you steer carefully. The main problem is setting up the initial pass, which requires altering the asteroid's position rather than its velocity. Perhaps we could go after Toro, which is already in an orbit between Venus and Earth. Rich Schroeppel rcs@la.tis.com ------------------------------ Date: Mon, 23 Jul 90 11:22:20 -0700 From: "Nicholas J. Szabo" To: uunet!cs.cmu.edu!space-tech@uunet.UU.NET Subject: Re: Asteroid relocation Thanks for the correction on armatures. What is the status of SSI's mass driver studies? Last I heard they had driven small, gram-sized payloads to a few klicks per second. I do not know if they used and slowed buckets. Joseph C Pistritto points out the expense of electromagnets. How expensive? What is their mass? My analysis assumed a coil gun could operate at a continuously averaged rate of 50W per kg of driver. One heck of a WAG. :-) It would be good to compare to solar- and nuclear-thermal power/mass ratios, since the latter can also use asteroid-derived volatiles for reaction mass. For launch cost, I used the cost to GEO for Ariane, which as Phil Fraering points out is near enough to cost for escape velocity. However, there are also costs for getting from earth's orbit to the asteroid's. I would very much like to see launch costs come down, but we should also try to find a solution at current launch costs. Using lunar resources to build the mining equipment is more difficult than using the asteroid itself. We would be down half the time during the lunar night, lack essential volatiles, and need to launch the equipment out of the 3.1 km/s gravity well. Either way, it is horrendously difficult: we are talking about translating millions on tons of earth-bound industrial equipment needed make further equipment. The bootstrapping problem. No one has figured out how to solve this. Fragments from an explosion or collision will reaccrete or disperse into different orbits. The problem should be several orders of magnitude smaller than the current LEO problem. Stony asteroids will fragment quite a bit; metallics should stay together. Comets and carbonaceous chondrites may also fragment badly. In the long run, Orion plates can be manufactured from metallic asteroids and used to minimize shock. Nick Szabo uunet!ibmsupt!szabonj These opinions do not reflect those of any organization I am affiliated with. ------------------------------ To: "Nicholas J. Szabo" Cc: space-tech@CS.CMU.EDU, dietz@cs.rochester.edu Subject: Re: Asteroid relocation Date: Tue, 24 Jul 90 10:59:50 -0400 From: dietz@cs.rochester.edu Some important points about asteroid mining: It is usually the case in mining that "beneficiation" of the raw ore should be done before it is transported. For asteroids, this means some kind of crude separation should be done at the asteroid so that much of its mass need not be returned to earth orbit. The kind of beneficiation depends on the kind of ore being processed. Chondrites (not carbonaceous) have maybe 1% metal grains. These grains can be concentrated by pulverizing the debris, then magnetically sorting. Metal grains, if they have variable composition, can be separated by techniques that depend on density differences. Another very important asteroidal resource is water (and other volatiles). It likely makes sense to extract these from carbonaceous chondrites on-site. Not only would this require less mass be moved, but these asteroids are thought to be very fragile, breaking under pressures of only a few psi. Fortunately, extracting the water simply requires a source of heat, a condenser and a radiator. Near state-of-the-art space-rated nuclear reactors can produce ~1 MW of heat in a very small volume (SP-100), and continue doing so for years. Once extracted, water can be used directly as reaction mass in nuclear-thermal rockets -- not to move the entire asteroid, but to return beneficiated material to Earth. Braking at the end should be by aerocapture (probably not directly into LEO). The mass payback of the system would depend on the mass of the aerobrake. I have read that an aerobrake can return six times its mass to earth orbit; however, I wonder if an aerobrake that uses asteroidal water for transpiration cooling might do better. You could also do better if the aerobrake can be reused, or if you can make aerobrakes in space from ET materials, perhaps by deposition of metal vapor on a form. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Tue, 24 Jul 90 09:33:51 -0700 From: "Nicholas J. Szabo" To: uunet!cs.cmu.edu!space-tech@uunet.UU.NET Subject: Re: Asteroid relocation Kevin comments on mining equipment needed to produce LOX: > Requirements: enough mining ability to grind up rubble (bulldozer or >drill), either baking it in a solar furnace for O2 or using it directly. >Handling equipment to load the reaction mass (gravel or O2) into >buckets, which fling the mass for propulsion. Solar or nuclear power >supply for running mass driver and engine feed. A really big baggie to >wrap up the asteroid if your acceleration is larger than the asteroid >gravity. No complicated mining/refining equipment. The amount of reaction mass m that must be mined per year is given by m = MV^2/v^2, where V is delta-v for the asteroid, v is the exhaust velocity, and M is the mass of the asteroid. This assumes V << v. Using V=500 m/s per year, v=7,000 m/s, and M=2.09e9 kg, we get m=10.7e6 kg per year, or 1,211 kg per hour average. 7,000 m/s is the exhaust velocity proposed both for nuclear-thermal rockets and the Sandia coil gun. I don't have figures for oxygen composition handy but if it is 10%, we need to mine 12,110 kg of rock per hour. (This is average; actual capacity must account for down time, queuing, etc.). On an M-type asteroid we can melt and mold the iron instead so we get 100% minus inefficiency. On the other hand, metal is harder to mine. Doubling exhaust velocity cuts reaction mass by a factor of 4. The turntable suggestion at 1 km/s requires 49 times as much mass to be mined. Bulldozers don't work in microgravity. A shovel on a long crane well-anchored to the asteroid might work. It must reanchor to new locations each time it runs out of local regolith. It needs a powerful electric motor designed for vacuum (Boeing developed a much less powerful one for the Lunar Rover). This adds to our power requirements; possibly a significant fraction of the 8.3 megawatts our mass driver needs. When we run out of regolith altogether, we need to fracture the rock or metal into bite-sized pieces. This must also be done in preparing metal for the carbonyl process to extract the platinum group. One possibility is ultrasound. Another is heating the surface with mirrors and spraying it with LOX. We may use diamond drills, which also require powerful motors. Feeding the rock from the drill to the furnace requires a conveyor belt with fully enclosed boxes, and several scoops to insert the material into the proper part of the furnace. Remember we can't rely on gravity to hold things down or drop them. Another possibility is containerless processing; use electromagnets to move magnetized or ionized materials. Most of these schemes suffer from too many moving parts, and wear and tear from rock, which is *hard*. All must be redesigned for microgravity, vacuum, and minimal launch mass. The mining equipment will indeed be complicated. I heartily agree that much research needs to be done; IMHO the mining equipment technology is the critical path. Nick Szabo uunet!ibmsupt!szabonj These opinions do not reflect those of any organization I am affiliated with. ------------------------------ Date: Tue, 24 Jul 90 17:36:49 EDT From: John Roberts Disclaimer: Opinions expressed are those of the sender and do not reflect NIST policy or agreement. To: space-tech@CS.CMU.EDU Subject: Re: Re: Asteroid relocation >Date: Tue, 24 Jul 90 09:33:51 -0700 >From: "Nicholas J. Szabo" >Message-Id: <9007241633.AA10033@ibmpa.paloalto.ibm.com> >To: uunet!cs.cmu.edu!space-tech@uunet.uu.net >Subject: Re: Asteroid relocation >The amount of reaction mass m that must be mined per year is given by > m = MV^2/v^2, >where V is delta-v for the asteroid, v is the exhaust velocity, and M >is the mass of the asteroid. This assumes V << v. Using V=500 m/s per >year, v=7,000 m/s, and M=2.09e9 kg, we get m=10.7e6 kg per year, or 1,211 >kg per hour average. 7,000 m/s is the exhaust velocity proposed both for >nuclear-thermal rockets and the Sandia coil gun. >Doubling exhaust velocity cuts reaction mass by a factor of 4. The >turntable suggestion at 1 km/s requires 49 times as much mass to be >mined. I haven't really looked at the numbers, but I don't think you should be squaring those velocities, since what you want to equalize is momentum, not kinetic energy. If that's right, then doubling exhaust velocity only cuts reaction mass by a factor of 2, while increasing propulsive energy required by a factor of 4. Using m = M * V / v and your asteroid example, I get m = 1.49E8 kg per year, or 17030 kg per hour average. It would also require an average of 116 MW to launch the reaction mass (assuming 100% efficiency). John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ From: cup.portal.com!hkhenson@uunet.UU.NET To: space-tech%uunet.uu.net@CS.CMU.EDU Subject: Re: Asteroid relocation/mining Date: Tue, 24 Jul 90 13:37:59 PDT Nick Szabo in a recent posting: >Most of these schemes suffer from too many moving parts, and wear and tear >from rock, which is *hard*. All must be redesigned for microgravity, vacuum, >and minimal launch mass. The mining equipment will indeed be complicated. Well, maybe not so bad. Repair of worn metal parts can be done by simple vapor deposition of native metal (Ni/Fe). At least for extracting the reduced Fe/Ni/Co, the carbonal process needs nothing more complex than vapor moving pipes/heaters/radiators. Radiators, pipes, and a large fraction of other stuff can be vapor deposited on thin plastic forms, perhaps inflatable ones. Sunlight powered metal boilers built out of graphite can process 1000 times their mass in a year. Rock dust and a little gas makes a fine heat transfer fluid to move low grade heat to radiator surfaces. Much of this is in the Space Manufactuing Conf proceedings at Princeton from 1977 and 1979. Keith Henson ------------------------------ Date: Wed, 25 Jul 90 11:54:29 -0700 From: "Nicholas J. Szabo" To: uunet!cs.cmu.edu!space-tech@uunet.UU.NET Subject: Re: Asteroid relocation/mining Jim Roberts corrects my bogus freshman-physics error. Thanks. This makes the problem even worse than I thought -- to drive a 2.09e9 kg asteroid to 500 m/s, we must extract 1.49e8 kg. To drive LOX (a payload that can be packed well-balanced for high velocities) we need to mine c. 1.49e9 kg, 71% of the asteroid, the amount of rock taken from a 60 meter train tunnel. Tunnel drilling equipment is *not* simple, nor is it light enough to be launched. It also must be redesigned for microgravity and vacuum. Keith Henson writes: >Repair of worn metal parts can be done by simple vapor deposition of >native metal (Ni/Fe). Ni/Fe alloy melts too low to cut through rock (not to mention Ni/Fe itself). For rock, a Fe/Co|W alloy is often used. These elements can be also be obtained through the carbonyl process; but I do not know the if the tough alloys can be deposited in the way you describe. For grinding native metal, we will need industrial diamond bits. Wear will occur at the grinding surfaces, joints, cogs, and motors. Seizure of moving parts in space has already occurred (on Voyager). Many surfaces will accumulate dust and deposits from vapor-depositing processes. Repair will be scarce; we will need lots of lubrication, generous tolerances, and generous redundancy. This all adds to the launch mass. >Radiators, pipes, and a large >fraction of other stuff can be vapor deposited on thin plastic forms, >perhaps inflatable ones. This is a great idea! To make space mining and manufacturing work we must use the new environment our best advantage. Nick Szabo uunet!ibmsupt!szabonj "Let the solar system do the work for us." These opinions do not reflect those of any organization I am affiliated with. ------------------------------ Date: Wed, 25 Jul 90 18:42:10 -0700 From: "Nicholas J. Szabo" To: uunet!cs.cmu.edu!space-tech@uunet.UU.NET Subject: Re: Asteroid relocation Collision and aerobraking are two methods for letting the solar system place asteroids into a desired orbit. Of these, collision is often too destructive for the object being moved, and aerobraking is restricted to asteroids that nearly intercept Venus or Mars. However, we can combine the two ideas by creating temporary atmospheres with comets. We locate a desirable asteroid near intercept course with a comet. We steer into direct intercept course. Moments before impact, the comet is vaporized. We want to maximize the number of molecules the asteroid hits, so our atmosphere may look like two cones expanding directly towards and away from the approaching asteroid. Ideally the peripheral (maximum) diameter of each cone should be less than the diameter of the asteroid, so that the asteroid hits all the molecules, and the length of the cones should be large enough to avoid densities that shock the asteroid. Practically the diameter and length of the cones depend on our ability to place the nuclear charges in a good configuration. The momentum transfer of comet molecules to asteroid (ignoring heat loss) is (Casey goes to bat again :-) given by mv = hMV where M and V and are the mass and velocity of the comet wrt the asteroid, v is the desired delta-v, m the asteroid mass, and h the percentage of molecule mass hit. (The cone velocities wrt to the comet cancel). Aerodynamics will provide a more accurate equation. For example, if our asteroid masses 2.09e9 kg, our comet masses 5.23e9 kg, they collide at 2 km/s (the faster the better!), and 10% the the comet mass is hit, we will impart a delta-v of of 500 m/s on the asteroid. Required technology is the ability to: * Discover and track many small asteroids and comets, and determine optimal intercept trajectories * Seismically map the comet * Predict the vaporization and expansion of the comet to a reasonable degree with computer simulation over the seismographic map in various explosive configurations * Predict the aerodynamics of the asteroid through the atmosphere to a reasonable degree * Move the asteroid and/or comet into collision course * Place the nuclear explosives in precise locations on or near the comet Since we only need to launch sensors and a small amount (perhaps as little as 100 MT) of nuclear explosives, our launch costs are significantly lower than directly using nuclear explosives to move the asteroid. Also, there is little danger of fragmenting the asteroid. It may be possible to move an asteroid to L5 for launch costs of just $1.8e8 (3 Ariane launches; 1 for pre-aerobrake steering, 1 for analyzing and vaporizing the comet, and 1 for post-steering). A 2.09e9 kg type-M asteroid would contain $1.7e9 worth of platinum-group metals alone. Cometary aerobraking requires a large search space, since not only must the comet and asteroid intercept, they must intercept in an orientation that will impart the delta-v in the proper direction. We may be able to play some aerodynamic games with the direction. Optimal trajectories will minimize steering energy and the time needed to complete the operation. Two increase the search space, we may: * Significantly change the direction and velocity of the gas wrt the asteroid. We have a range from straight cometary aerobraking to direct nuclear relocation, with more explosive energy required the closer we get to direct nuclear. * Use combinations of one or more cometary aerobrakings, gravity assists, and Mars or Venus aerobrakings. * Start looking. We've discovered less than 1/10 of 1% of what's out there. Nick Szabo uunet!ibmsupt!szabonj "Let the solar system do the work for us." These opinions are not related to those of any organization I am affiliated with. ------------------------------ Date: Wed, 25 Jul 1990 08:58:36 -0400 (EDT) From: Ted_Anderson@transarc.com To: space-tech@CS.CMU.EDU Subject: JBIS Interstellar Studies Cc: Dietz@cs.rochester.edu A few months ago I got into an argument about whether Bussard Ramjets had any possible basis in fact (perhaps it was in the space list). I don't remember being exactly convinced by the ensuing arguments. Among the problems were that fusing protons is ridiculously difficult (even compared to fusing deuterium), and the implementation of the scoop. The easy answer to the first problem is not to bother with fusion but to bring along antimatter and use the interstellar medium for reaction mass. But I've never seen a plausible design for a scoop. However, the June issue of Journal of the British Interplanetary Society, entitled "Interstellar Studies", contains an article by G.D. Nordley, "Application of Antimatter - Electric Power to Interstellar Propulsion". His main thesis was that instead of building a magnetic combusion chamber to exhaust the matter-antimatter reaction products directly you instead use an MHD generator to make electricity to run an ion drive. I apparently missed the argument about why this was an improvement, however. You'd think the extra stages of conversion would just add to the mass and reduce the overall efficency. Anyway, at the end he talks about building a ramscoop to collect protons for reacting with the antimatter. His basic design for the scoop was to use a very powerful laser (at about the Lyman alpha frequency) directed forward at a levitating mirror which directed the annular beam towards the axis of the scoop. The photon pressure pushes the protons towards the center. In practice there are many problems with this, but it's the first more-or-less plausible design I've seen. He also does several mission profile scenarios. Even with what seemed like incredibly optimistic assumptions he was getting one-way trip times of 85 years. The net result (in my opinion, not his conclusion) is that even antimatter is not up to the task. The only reasonable approach seems to be keeping the power supply at home, such as Forward's laser powered light sail. This entire issue is worth checking out for those interested in extra solar system activities. By the way this issue is edited by (you guessed it) Robert Forward. Ted Anderson ------------------------------ Date: Wed, 25 Jul 1990 09:24:57 -0400 (EDT) From: Ted_Anderson@transarc.com To: space-tech@CS.CMU.EDU Subject: Alternative Mass Drivers This recent discussion of mass drivers reminds me of a proposal I saw quite a while ago to push material around at very high speeds. The original purpose was to get bulk material like aluminum to LEO (or maybe just off the Moon). The basic idea was to use a very high pressure gear pump to squirt a liquid at speeds up to 10 km/s or so. If you make the pump out of tungstun and the orifice of saphire this would handle something as messy as molten aluminum. If this is possible and you can find or produce something liquid (at a temperature you can handle) on your asteroid this might be a create deal simpler than building and running a mass driver. I don't know what the efficiency of a gear pump is but electric motors can be made to run in the 90'ies as I recall. Has anyone else heard this idea or know anything about pressure limits for gear pumps or candidates for astroidal material that melts below 750C? Ted Anderson ------------------------------ Date: Wed, 25 Jul 1990 09:10:35 -0400 (EDT) From: Ted_Anderson@transarc.com To: space-tech@CS.CMU.EDU Subject: Light Gas Gun for launching to LEO Cc: Dietz@cs.rochester.edu The most recent issue of Aviation Week & Space Technology (July 23, 1990) contains a fairly detailed article about a project at LLNL to build a light gas gun to launch small, G-tolerant payloads to LEO. This project is headed by John Hunter and is apparently actually building a small prototype in Livermore, CA to accellerate 1.5 Kg payloads to 6 km/s later this year. The plan for next year is to build a vertical version to study atmosphere transit problems. The article claims it is a $1 billion project but I suspect they mean $1 million. Bottom line, Hunter claims that a system to orbit 340 Kg payloads for about $500/Kg could be built for about $3B by 1997. Ted Anderson ------------------------------ End of Space-tech Digest #70 *******************