Date: Thu, 10 Nov 1988 16:26-EST From: space-tech-request@cs.cmu.edu To: "~/st/lists/stdigest" Subject: Space-tech Digest #14 Contents: Bill Newman Re: Colloidal Electrostatic Engines Paul Dietz Re: Colloidal Electrostatic Engines Ted Anderson Re: Colloidal Electrostatic Engines Paul Dietz Orbital mechanics routine Paul Dietz Orbital mechanics routine Jim Meritt Re: Orbital mechanics routines Steve Abrams RE: Solar Dynamic Power Paul Dietz RE: Solar Dynamic Power Doug Reeder Returning from asteroids Paul Dietz Returning from asteroids ------------------------------------------------------------ Date: Mon, 7 Nov 88 12:18:09 EST From: newman@tcgould.tn.cornell.edu (Bill Newman) To: dietz@cs.rochester.edu, space-tech@cs.cmu.edu Subject: Re: Colloidal Electrostatic Engines What is the principle of phase stability, and how would it "fix" small errors in particle size? Bill Newman newman@batcomputer.tn.cornell.edu ------------------------------ Date: Mon, 7 Nov 88 13:34:16 EST From: dietz@cs.rochester.edu To: newman@tcgould.tn.cornell.edu Cc: space-tech@cs.cmu.edu, dietz@cs.rochester.edu Subject: Colloidal Electrostatic Engines Phase stability is the principle that makes a synchrotron work. Suppose we are driving a series of accelerating cavities with sinusoidal voltages. During the time the particles are passing through the cavity, the voltage is rising. Therefore, particles that arrive late (are going too slowly) experience a greater potential than those that arrive early (are going too fast). Particles perform "phase oscillations" around an equilibrium phase angle. In the case of the colloidal accelerator, the hope is that particles of higher m/e oscillate around a phase point where the potential is high; those with low m/e where the potential is lower. The "bunch" of particles gets spread longitudinally according to m/e. Perhaps we can play with the waveform (for example, use a sawtooth, or some other waveform) to make this fly. See Segre's "Nuclei and Particles", section 4-5 (page 143). Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Tue, 8 Nov 88 09:33:41 -0500 (EST) From: Ted Anderson To: dietz@cs.rochester.edu, newman@tcgould.tn.cornell.edu Subject: Re: Colloidal Electrostatic Engines Cc: space-tech@cs.cmu.edu An interesting application of this process would depend on the ability to make these tiny particles out of most any solid. If you are planning on asteroid retrieval that is like to be necessary anyway. My suggestion is to practice by building a small version, powered by solar cells that collects NEA (Near Earth Accumulations (of orbital garbage)) and chops them up for reaction mass to get to the next chunk of space debris. This seems like an excellent testbed for this idea which has the added advantage that there is some political consensus (and hence money) that the orbital debris problem is getting serious. If someone is really spending money on ASPOD they must be fairly desparate. This idea seems much more attractive. For a more advanced design you could make this machine self-replicating and probably clean up LEO in no time. -ota ------------------------------ Date: Sun, 6 Nov 88 14:04:18 EST From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Orbital mechanics routine I wrote a set of C routines for solving the Kepler problem: given the position and velocity of an orbiting body at time t0, find its position and velocity at time t1. The routine makes use of the universal variable formulation, so it should work for all eccentricities. It seems to be fast and accurate, although not guaranteed to be bug free. If anyone wants a copy, mail me a note. Anyone have a routine for the Gauss problem (given two positions and times, find the orbit(s) connecting them)? Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Tue, 8 Nov 88 16:04:31 EST From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Orbital Mechanics Routines I've now implemented and completed preliminary tests on the following routines: "predict", which, when given a position and velocity vector for an orbiting body, finds its position and velocity at time t, and "gauss", a routine that, given two positions separated by time t, finds an orbit connecting them. The results from the second have been checked against the first; they are consistent. The routines assume only the central body has nonnegligible gravity. The next step is to integrate these two with a function minimizer to search for simple (no intermediate burns) interplanetary trajectories subject to delta-v and time constraints. Some people who asked me for copies haven't received them, due to mail problems (some due to recent network immunological excitement). I'll post a shar file to space-tech when the trajectory searcher is done. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Tue, 8 Nov 88 16:49:38 EST From: jwm@stdc.jhuapl.edu (Jim Meritt) To: dietz@cs.rochester.edu, space-tech@cs.cmu.edu Subject: Re: Orbital Mechanics Routines I see real use for this! Jim ------------------------------ Date: Tue, 8 Nov 88 12:30:12 CST From: sedspace@doc.cc.utexas.edu (405986289 abrams) Posted-Date: Tue, 8 Nov 88 12:30:12 CST To: space-tech@cs.cmu.edu Subject: RE: Solar Dynamic Power By discussing SDP, has Solar Thermal Propulsion been ruled out. If, instead of converting thermal irradiance to electrical power - - and enduring the efficiency losses -- we simply heat a propellant up to umpteen-kazillion (I'll hafta' look up how many zeroes that is in my CRC someday) degrees and squirt it "out thataway." After all, the efficiency losses go into waste heat anyway (and heat is deucedly difficult to get rid of), so why not use it. The following succinct argument comes from "Space Resources" -- I can look up the author if anyone wants it: " The main factor limiting the performance of electrical propulsion systems is the large mass of the electrical equipment, and the main factor limiting chemical propulsion is the large mass of propellant necessary to provide the needed thrust. It sounds at first as if there is no way to win. Fortunately, it is possible to devise a scheme that uses solar power (and therefore need not carry a heavy reactor); it uses the solar energy directly, without conversion to electricity (and therefore does not need acres of solar cells and bulky power- conditioning equipment, nor does it suffer from the 20% efficiency of conversion of sunlight into electricity). This scheme uses a large inflatable or deployable reflector, made of very thin, metal film, to focus sunlight directly onto a blackened thrust chamber made of a material such as rhenium metal, which is extremely resistant to melting and evaporation: it is a refractory metal. Hydrogen is fed into the thrust chamber, where it is heated to temperatures of thousands of degrees by the absorbed solar energy. The jet of very hot hydrogen can have a specific impulse in the range of 1000 to 1200 seconds. Furthermore, sunlight provides more than 1000 watts of usable power per square meter. This means that it is easy to deliver megawatts of power to the thrust chamber with only a few kilograms of reflecting film. The thrust level may be quite high, and accelerations of 0.01 to 0.1 Earth gravities could be achieved. This "hot rod" delivers the specific impulse of a nuclear rocket, and it does so with clean solar power and without the enormous dead weight of a shielded nuclear reactor. Maintaining the acceleration of 0.0l gravities permits interplanetary trips of 50 million kilometers to be carried out in less than two weeks. At 0.1 Earth gravities, interplanetary trip times would be a few days." Solar Thermal Propulsion (STP) also has some slight possibility of future enhancement should SDI screw up and actually produce gigawatt lasers and adequate targeting systems. The primary objections to STP to date have been limits imposed by a low solar constant past the orbit of Mars. This has some possibility of being rectified without "laser cannon." What I envisage is a large solar sail/phase-reversal zone plate (or series of them) in a station-keeping orbit between Mercury and Venus. Alternate zones are coated with a layer of, say, the aforementioned rhenium - it has an index of refraction of 4.04 and, so can induce a phase change of pi/2 with a thinner layer which will increase the transmittance. With the size I'm talking about, the PRZP could have hundreds of thousands of zones yielding a very high energy flux density at the Airy disk of the primary focus. [A few years ago, I originally considered this as a "farce" weapon for SDI ala Bloom County - a few hundred million dollars for development and deployment and BAM! a weapon that can firestorm -- by delivery of megajoules of energy to the atmosphere -- an enemy nation in 10 km east-to-west swathes as the Earth rotated under it; by oscillating the PRZP north-to-south a few fractions of a degree, greater coverage can be achieved. Detection could avoided by tilting the sail edge-on until needed. I stopped considering it because I was afraid it might actually work) Guidance would be somewhat of a problem, as would solar flares. Radiation pressure can be used to keep the PRZP orbiting with the same heliocentric angular velocity as the targeted STP-craft -- that which we call a solar sail by any other name... -- the focal point will obviously librate about the target, but a high, net energy delivery can be realized. I also considered how to handle the presumably increasing radial separation between the PRZP and target craft. This can be done by adjusting the thicknesses of each zone -- means we need some super-duper 'puters -- since, over the distances we're considering, radial differences of a few meters should matter too much. I estimated a maximum, net variance due to [1) PRZP radial deviations; 2) normal solar irradiance variation; and 3) hitting the target off-center] as 20%. Remember, these things are far apart and work slowly -- lots of time for prediction/correction. I certain that the above concept can be refined. I know that a friend of mine at JPL was reviewing progress in this area some months ago. Any suggestions? Steve Abrams ------------------------------ Date: Tue, 8 Nov 88 15:26:02 EST From: dietz@cs.rochester.edu To: sedspace@doc.cc.utexas.edu Cc: space-tech@cs.cmu.edu Subject: Solar Dynamic Power > Maintaining the > acceleration of 0.0l gravities permits interplanetary trips of 50 > million kilometers to be carried out in less than two weeks. At 0.1 > Earth gravities, interplanetary trip times would be a few days." Steve should have continued to quote from the book (Space Resources, John S. and Ruth A. Lewis, Columbia U. Press, 1987): " Such fantastic performances, however, would consume vast amounts of propellant. Sending a 1000-ton payload to Mars by this means, at an acceleration of .01 gravities, would reach a maximum speed of 70 kilometers per second at the halfway point, and would use up 160 million tons of hydrogen. Surely solar thermal propulsion would be better used to replace chemical propulsion on shorter, lower-velocity trips. " Solar thermal is limited because it cannot heat propellant hotter than the surface of the sun (doing so would violate the Second Law). However, using solar thermal with asteroidal water is surely a better idea than laboriously electrolysing the water for use in a chemical rocket, assuming you don't need high peak thrust. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Wed, 9 Nov 88 00:41:29 PST From: reeder%REED.BITNET@VMA.CC.CMU.EDU To: space-tech@cs.cmu.EDU Subject: Returning from asteroids Is there any reason why a mass catcher could not be used instead of aerobraking to slow down incoming material to orbital velocity? If the incoming material is ice, how about a catcher made out of ice? When it gets large enough, its kicker motor just kicks it over to where it is needed and you detach the kicker motor. Doug Reeder USENET: ...!tektronix!reed!reeder 971 Lathan Devers Av. BITNET: reeder@reed.BITNET Terminus City from ARPA: tektronix!reed!reeder@berkeley.EDU Terminus,The Foundation Box 971 Reed College,Portland,OR 97202 ------------------------------ Date: Wed, 9 Nov 88 15:49:55 EST From: dietz@cs.rochester.edu To: reeder%REED.BITNET@VMA.CC.CMU.EDU Cc: space-tech@cs.cmu.EDU Subject: Returning from asteroids > Is there any reason why a mass catcher could not be used instead of > aerobraking to slow down incoming material to orbital velocity? If > the incoming material is ice, how about a catcher made out of ice? > When it gets large enough, its kicker motor just kicks it over to > where it is needed and you detach the kicker motor. I don't think mass catchers are feasible at these velocities. Consider the engineering problems. Going from 12 km/sec to 10.5 km/sec dissipates 16 MJ/kg, the equivalent of 4 kilograms of TNT. This will vaporize a lot of ice. Recall that lunar mass catchers operating with mass drivers would operate with payloads moving at perhaps 100 m/sec -- 300 times less energy for the same mass. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ End of Space-tech Digest #14 *******************