Subject: Space-tech Digest #123 Contents: Fuzzy Boundaries and Ballistic Capture (1 msg) SSI activities (1 msg) ISU attendee (1 msg) UTASROC(student rocket project) (1 msg) SSTO materials (1 msg) questions on lunar tethers, lumpy gravity (5 msgs) ------------------------------------------------------------ Date: Sun, 14 Jun 92 03:25:26 PDT From: David.Michelson@mtsg.ubc.ca To: space-tech@cs.cmu.edu Subject: Fuzzy Boundaries and Ballistic Capture Ref: Edward Belbruno, "Through the Fuzzy Boundary: A New Route to the Moon." The Planetrary Report, May/June 1992, pp. 8-10. The Planetary Report would be a lot more satisfying if the authors would include a list of further reading for those interested in a more "in-depth" treatment of a particular topic. Like the folks at Scientific American do. For example, Belbruno's article looks rather neat but I want more details. Can someone refer me to the appropriate journal articles or other publications? Any comments on "ballistic capture" and "fuzzy boundaries" on the net? I for one was intrigued at the thought of reaching the moon with a small payload using only a Pegasus booster. Dave Michelson "davem@ee.ubc.ca" ------------------------------ From: sequent!techbook.com!szabo@uunet.UU.NET (Nick Szabo) Subject: Re: Should I renew my SSI membership? To: rcs@cs.arizona.edu (Richard Schroeppel) Date: Thu, 18 Jun 92 2:08:07 PDT Cc: space-tech@cs.cmu.edu X-Mailer: ELM [version 2.4dev PL32] > Much has happened since 1980: > O'Neill is dead, Drexler has moved on to new things, L5 is dead, > and Keith Henson has signed up with ALCOR (Cryonics) as the only > likely way to ever get to space. "Conquering space is the work of generations" -- possibly mangled Goddard. Too much of the O'Neil/L-5 movement had the "we want all it now" spirit, but that is not the pioneering spirit. Nanotech was inspired by Drexler's work in space manufacturing: his realization that manufacturing tech is the key to space colonization. He's not on to new things so much as on to a high-payoff way to accomplish the same long-term goals. > The military has made great > progress with railguns (oops, I mean mass-drivers). Even more important, in the shorter term, is the sensing, communications, and computing tech coming out of SDI. Applying this tech to prospecting (a la Clementine) is an exciting prospect. > We've seen no progress on remote manipulators, and a little bit on > autonomous robots. There is significant progress being made in the military (remote land-mine removers) and in offshore-oil drilling (Troll Oseberg deep-sea drilling project: no divers). There is rapid progress being made on the user interface end (interactive 3D graphics, glove input, etc.). Even better news: most useful automation is not anthropomorphic. CAM milling and 3D printing are more important than robots for manufacturing, for example. > We have pictures of Gaspra (as well as Phobos & Deimos). Gaspra is a boring S-type asteroid, and the moons are two C-type asteroids smothered in their own re-accreted regolith. We have yet to see up close the three most useful varities: ammoniated C-type, hydrated C-type and M-type (metallic). We have only seen one comet semi-close-up, and no P or D type asteroids. Most of our work is ahead of us. We must be smarter about target selection and how it relates to the material needs of space industry. > The Biosphere group is trying to understand what's required for an > isolated colony. The closed ecology problem is easy (B2's tribulations notwithstanding). Drexler et. al. are working on the much tougher and important problem, a self-sufficient industrial base. > Satellites have achieved a small economic niche in observation & > communications, which may survive the introduction of fiber-optics. The world space market is around $40 billion a year (military, commerce, civilian total). The comsat industry continues to grow at 10% per year. It is building new niches (remote, mobile, broadcasting) far faster than fiber is replacing it for bulk fixed communications. The comsat market at over $4 billion per year worldwide is already larger than, for example, global platinum group metal mining ($3 billion per year). The prejudice that dismisses communications as an important industry must end. The rapid growth has been accomplished by increasing value/lb., not decreasing cost/lb. The latter would multiply the effect. > It looks to me like we > are spinning our collective wheels: much noise & burning rubber, > but not even a quarter-milestone passed. You may be looking for the wrong milestones. Many are pursuing a path that is far superior to the brute-force method envisioned by the previous generation. The brute-force method failed to provide affordable launches. It failed to find anything compelling on the Moon. It failed to create industry. On the other hand, the smart approach has given us several military applications and a commercial industry, and has increased the value of payloads per pound by orders of magnitude. Our milestones should be how much we know about space, and how many useful things we can do there, not how much we have launched or where we have planted flags. The smart approach, not the brute force approach, will also give us the stars. ------------------------------ Date: Thu, 18 Jun 92 23:08:16 -0700 From: George William Herbert To: space-tech@cs.cmu.edu Subject: ISU Well, I'm here at ISU in Kitakyushu in Japan... so far so good. If anyone on the list is interested in periodic updates on what International Space University is like, I can do so. 8-) -george [ A couple of people did express interest. --MNR ] ------------------------------ From: phinds@pieman.compserv.utas.edu.au (Phillip Hinds) Subject: UTASROC(student rocket project) To: space-tech@cs.cmu.edu (Space Tech Mailing List) Date: Mon, 6 Jul 92 14:26:57 EST Cc: phinds@pieman.compserv.utas.edu.au To All Interested Parties, After a major effort here over the last couple of weeks, the UTASROC design team have come up with a few preliminary design parameters : Max Burnout Mass : 30 kg Max Fueled Mass : 40 kg Nominal SL Thrust: 2000 N Burn Duration : 10 sec Fuel / Oxidiser : jet fuel, LOX Estimated Isp. : 235 sec Burnout Velocity : ~ 515 m/s (Mach 1.5) Burnout Altitude : ~ 5000 m Payload : ~ 3 kg Pressurant : Helium Tank Pressure : 2 MPa Combustion Press.: 1.5 MPa The vehicle will be about 2m in length and about 115 mm diameter, pressure fed with a helium supply at 5 MPa, regulated to 2 Mpa. We plan using solenoid/pilot valves for the main propellant valves, as well as for the parachute/nose cone ejection(ie vent tank pressure to the back of a piston to push out chute etc), ignition will be by spark plug. Any comments or questions about the project are welcomed, as we aren't very experienced and any help will be greatly appreciated. Hope to hear from you soon, Phill -- **************************************************************** * Phillip R. Hinds Email address : * 276 Vermont Road, phinds@pieman.compserv.utas.edu.au * Launceston, Tasmania, * Australia, 7250 . * Phone : (003) 262040 **************************************************************** P.S. Can anyone think of a better name for the project ? ------------------------------ Date: Sat, 25 Jul 92 21:55:00 -0700 From: George William Herbert To: space-tech@cs.cmu.edu Subject: SSTO materials Posit that there are more than one unsolved materials problems with the full scale McD-D SSTO program. Presume that those problems are not in the following areas: Forebody/fuel tank materials; aft body (thermal shielding etc). Part of the problem is in engine materials (a push to develop ablative engine linings); what else is potentially going on? -george william herbert ------------------------------ gwh@soda.berkeley.edu Date: Wed, 29 Jul 1992 12:03:19 MST From: "Richard Schroeppel" To: space-tech@cs.cmu.edu Subject: questions on lunar tethers, lumpy gravity What's been done on Lunar beanstalks & rotating tethers? From a simple energy perspective, lifting a kg of green cheese from the moon and dropping it toward the earth is energeticly favored. The raw strength requirements on the tether are much less, perhaps even achievable with current materials. It's been claimed that there are no stable orbits around the moon because of the mascons, which perturb any orbit to intersect the surface. What's the truth? Since gravity is time-reversible, "half" of all orbits should exhibit an increase in perilune, rather than a decrease. Perturbations generally have little influence on the semi- major axis, so the orbit should have a stable size. An orbit far from the surface shouldn't be influenced much at all by mascons; maybe just a bit of jitter. Has somebody done believable simulations? I've seen papers claiming that the L5 position is unstable because of solar perturbations, but I doubted the numerical accuracy of the results. Finally, has anyone examined the stability of orbits in the banana-shaped region connecting L4 & L5? Rich Schroeppel rcs@cs.arizona.edu ------------------------------ Date: Wed, 29 Jul 92 15:52:28 CDT From: ssi!lfa@uunet.UU.NET (Louis F. Adornato) To: uunet!cs.cmu.edu!space-tech@uunet.UU.NET Subject: questions on lunar tethers, lumpy gravity Rich Schroeppel (rcs@cs.arizona.edu) writes: > What's been done on Lunar beanstalks & rotating tethers? > >From a simple energy perspective, lifting a kg of green cheese > from the moon and dropping it toward the earth is energeticly favored. > The raw strength requirements on the tether are much less, perhaps > even achievable with current materials. > > It's been claimed that there are no stable orbits around the moon > because of the mascons, which perturb any orbit to intersect the > surface. What's the truth? I think you're confusing a stable orbit and a geostationary (or lunastaionary) orbit. A stationary orbit (which would be needed for a beanstalk) wouldn't be effected by passing over masscons - since it remains over the same peice of real estate, there's a uniform gravitational force. However, you have to keep in mind the long rotational period of the moon (28 days), and the relative size of the gravitational field (1/6 of the Earth). I once did some back of the envelope calculations, and as I recall, the orbital altitude needed for a stationary lunar orbit exceeded the Earth-Moon distance. I don't have my books with me right now to reproduce the calculations, but intuitively, a geostationary orbit is about 1/10th the Earth-Moon distance (22,000 mi vs 225,000 mi), and that the orbital period at the same distance from the center varies in proportion to the mass of the primary, so an orbit 28 times longer around a primary 1/6th as dense would probably come out at least 10 times larger. Lou Adornato | "Eat cheese or die!" Supercomputer Systems, Inc | Wisconsin state motto Eau Claire, WI | The secretary (and the rest of the company) uunet!ssi!lfa or lfa@ssi.com | have disavowed any knowledge of my actions. ------------------------------ From: henry@zoo.toronto.edu Date: Wed, 29 Jul 92 16:16:58 EDT To: space-tech@cs.cmu.edu Subject: Re: questions on lunar tethers, lumpy gravity >What's been done on Lunar beanstalks & rotating tethers? A classical beanstalk isn't possible because there is no selenostationary orbit; at the very least it would have to go all the way to one of the Lagrange points. My impression is that it isn't considered practical. Rotating tethers should work fine, with quite ordinary materials, provided you can keep them in orbit. >It's been claimed that there are no stable orbits around the moon >because of the mascons, which perturb any orbit to intersect the >surface. What's the truth? Since gravity is time-reversible, "half" >of all orbits should exhibit an increase in perilune, rather than a >decrease. Perturbations generally have little influence on the semi- >major axis, so the orbit should have a stable size. I'm not sure you can make such a strong statement about anything as messy as lunar orbits. In any case, even if you can, the result is a stable semimajor axis with constantly changing eccentricity, and sooner or later the eccentricity will rise far enough to bring the perilune into the surface. Time-reversing that orbit will get you back to the original and then off into another set of wanderings ending in a "thump". Lunar orbits intersect the surface at both ends, so to speak. Actually, a more precise claim is that we don't know of any stable lunar orbits. Our gravity data for the Moon is pretty poor, partly because we have no tracking data over the farside and partly because what data we have is twenty years old and pretty crude. There might be some orbits that are stable or nearly so. >An orbit far >from the surface shouldn't be influenced much at all by mascons... An orbit far from the surface is a trajectory in the Earth-Moon system with perturbations from the Sun, and almost certainly isn't centered on the Moon for very long. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: Wed, 29 Jul 92 17:47:05 EDT From: Hans Moravec To: space-tech@cs.cmu.edu Subject: questions on lunar tethers, lumpy gravity Reply-To: moravec@cs.cmu.edu >> about stationary lunar beanstalks << Because of the Earths's major influence, a simple synchronous orbit around the moon doesn't make much sense (altenatively, note that the earth is in synchronous lunar orbit!). There are two stable positions for stationary lunar beanstalks, though: through the L1 and L2 points (pointing directly towards, and directly away, from earth, and about 50,000 (km?) from the lunar surface). Because of the shallow gravity well, L1 and L2 lunar stalks can be built comfortably with existing materials. Jerome Pearson analysed them extensively in AIAA papers around 1979. -- Hans Moravec ------------------------------ Date: Wed, 29 Jul 92 15:52:28 CDT From: ssi!lfa@uunet.UU.NET (Louis F. Adornato) To: uunet!cs.cmu.edu!space-tech@uunet.UU.NET Subject: questions on lunar tethers, lumpy gravity Rich Schroeppel (rcs@cs.arizona.edu) writes: > What's been done on Lunar beanstalks & rotating tethers? > >From a simple energy perspective, lifting a kg of green cheese > from the moon and dropping it toward the earth is energeticly favored. > The raw strength requirements on the tether are much less, perhaps > even achievable with current materials. > > It's been claimed that there are no stable orbits around the moon > because of the mascons, which perturb any orbit to intersect the > surface. What's the truth? I think you're confusing a stable orbit and a geostationary (or lunastaionary) orbit. A stationary orbit (which would be needed for a beanstalk) wouldn't be effected by passing over masscons - since it remains over the same peice of real estate, there's a uniform gravitational force. However, you have to keep in mind the long rotational period of the moon (28 days), and the relative size of the gravitational field (1/6 of the Earth). I once did some back of the envelope calculations, and as I recall, the orbital altitude needed for a stationary lunar orbit exceeded the Earth-Moon distance. I don't have my books with me right now to reproduce the calculations, but intuitively, a geostationary orbit is about 1/10th the Earth-Moon distance (22,000 mi vs 225,000 mi), and that the orbital period at the same distance from the center varies in proportion to the mass of the primary, so an orbit 28 times longer around a primary 1/6th as dense would probably come out at least 10 times larger. Lou Adornato | "Eat cheese or die!" Supercomputer Systems, Inc | Wisconsin state motto Eau Claire, WI | The secretary (and the rest of the company) uunet!ssi!lfa or lfa@ssi.com | have disavowed any knowledge of my actions. ------------------------------ End of Space-tech Digest #123 *******************