Date: Mon, 27 Mar 1989 10:27-EST From: space-tech-request@cs.cmu.edu To: "~/st/lists/stdigest" Subject: Space-tech Digest #29 Contents: Paul Dietz Railguns Paul Dietz gun-launch time criticality Dale Amon Batteries Paul Dietz Beamed Energy Paul Dietz Beamed Energy Don Anderson Would you like to go to Mars in 1992? ------------------------------------------------------------ Date: Sat, 11 Mar 89 13:20:58 EST From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Railguns Gord Deinstadt (gd@geovision) writes: > 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!) The Palmer/Dabiri paper calls for a 600 kg payload, a 250 m railgun and a muzzle velocity of 8 km/s. The average acceleration is 13 kilogees, the discharge interval about 60 milliseconds. The inductor stores 80 gigajoules, so the average discharge power is 1.3 terawatts (railguns are not terribly efficient). Use of an inductor seems unavoidable. They suggest mass-produced one-shot explosive switches, or opening switches based on quenching of high temperature superconductors. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Sat, 11 Mar 89 14:53:34 EST From: dietz@cs.rochester.edu To: szabonj@minke.cs.washington.edu Cc: space-tech@cs.cmu.edu Subject: gun-launch time criticality > How much extra energy is needed by EML or gas-gun launchers given time > constraints? For example, to deliver mail from Pike's Peak to Tokyo, how > much extra energy is required to get it there within 2 hours, instead of > putting it in a highly eliptical orbit? I tried to answer this before, but I think my message bounced. Let's try again... For surface-to-surface mail delivery, one could use suborbital trajectories. This would be much easier than launching to LEO, since lower velocities will work, and because the vehicle need not carry an apogee kick motor. Suborbital trajectories are just like ICBMs ... roughly 30 minutes to target. However, I suspect an SST would be a better bet, since landing and retrieving a ballistic projectile would be challenging. Instead of mail, how about fax? Moving paper is becoming old fashioned. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Sun, 12 Mar 1989 13:23-EST From: Dale.Amon@H.GP.CS.CMU.EDU To: space-tech@cs.cmu.edu Subject: Re: Batteries Keep in mind that another major advantage of lead-acid batteries is their virtually unlimited (relatively speaking) lifetime under continuous charge/discharge cycling. Most of the other battery technologies do not last as many cycles. I would also note that many battery technologies, (possibly even lead acid) have different responses when placed under "deep discharge" that when discharged slowly and not to the death. Deep discharge cuts the cycle life time considerably. There are of course the safety considerations as well, since H2 can be evolved under even normal circumstances and must not be allowed to collect. Measures are taken in battery closets for mainframe UPS's to monitor and remove H2 to prevent explosive buildups. When doing rapid discharge you have the combination of H2 evolution AND heating. For experimental purposes I would imagine lead-acid batteries are quite cost effective. For a commercial operation I would want to see what the lifetimes are like when you are constantly doing rapid deep discharge and fast recharge. I'm curious what the numbers would look like if you think OPERATIONAL rather than EXPERIMENTAL. ------------------------------ Date: Wed, 15 Mar 89 08:22:22 CST From: sedspace@doc.cc.utexas.edu (405986289 abrams) Posted-Date: Wed, 15 Mar 89 08:22:22 CST To: space-tech@cs.cmu.edu Subject: Lunar Polar Probe (Was The SSI LGAS satellite...) I just returned from the Lunar Polar Probe Conference held in Houston last weekend and was getting caught up on my E-Mail when I noticed the discussion of SSI's L-GAS delivery system for a proposed lunar polar probe. Anyway, much work - both on the technical aspects and the publicity/fundraising aspects - was roughed out over the weekend. Approximately half of the c conference's attendees committed to making this Lunar Prospector I fly in the 1991-92 time range. With reference to the L-GAS, it would only be feasible if a NaI gamma ray spectrometer is flown, since the only other major contender (discussed in Houston at least) -- a germanium detector -- is easily damaged by repeated passage through the radiation belts. However, the resolution of the NaI detector (the type flown in later Apollo flights) is so poor, and the deconvolution of the data is so tedious and marginal, that a Ge detector will probably be the detector of choice. Of course, there is the argument that for the first in a series of planned "citizen's initiative" probes to the Moon, we can fly NaI now and Ge later. I think that flying the NaI now will disenfranchise those scientists and developers who are interested in the selenological and seleno- chemical info unobtainable with the NaI detector. For example, the signals that would indicate the presence of aluminum would be swamped by signals from other elements and wouldn't be extractable from the low-resolution data. Now, if there is anyone out there who is interested in getting involved in this project (in any capacity - technical, fundraising, publicity, etc.) or know of any resources that might be committable to this, please let me know. I agreed to coordinate the development of internal network communications between the various design teams, the funding people, the integration people, etc. If you'll send a bio, and some indication of the areas in which you'd like to participate to me, I will present the compiled list to the design team leaders at the SDC in Chicago. The team leaders will be Drs. Canough and Binder for the technical/science teams, Bob Noteboom for the engineering teams, Jim Davidson for the resources team. Individual design teams for each of the payload experiments will be formed for the technical/science teams. Other teams will be formed for propulsion, nav & tracking, control systems and communications, mission planning, andintegration, etc. under Bob. Jim will coordinate the publicity campaigns, fund-raising efforts, etc. As the structure evolves, I'll post the more technically-oriented information to Space-S Space Tech. I wouldlike to consider this discussion group as a possible resource for this venture. Obviously, a separate distribution group is necessary since much of the necessary discussion will not always be technical enough to be appropriate here. To start us off, here's some questions: Does anyone know of any specific advances, either detector-wise or in numerical techniques, since the later Apollo days that might make the deconvolution of NaI detector data easier or might improve the effective resolution? If a Ge detector is flown, it must be cooled. Does anyone know of any options in low-cost, low mass refrigeration options? Obviously, if the probe is three-axis stabilized, it will be easier to keep the detector permanently shaded. However, that's more expensive than spin-stabilization (which, of course exposes every part of the probe to solar thermal radiation). Does anyone have any comments concerning the relative comparisons between a laser-oriented communications system or an RF system? It must be able to handle a large data rate (on the order of 50 kbits/sec at a minimum) and as inexpensive as possible - particularly on the receiving end. Does anyone have any suggestions for maintaining the unstable polar orbit (mean orbital altitude of 100 km) face-on to the Sun and minimizing the mass of the (cold/hot) gas thrusters? Does anyone have any data or references on the reflectance spectrum of thin-film solar cells? Does anyone know anyone at the State University of New York (SUNY) who might be able to help us arrange a guest account on their network hosts for Dr. Gay Canough. Currently, she has to call long distance to use her connection at FermiLab. Any other suggestions? This is a criticality-1 problem in need of immediate solution. Well, that should be enough for now... Ad Luna, Steve Abrams sedspace@doc.cc.utexas.edu ------------------------------ Date: Tue, 21 Mar 89 17:10:18 EST From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Beamed Energy I recommend to everyone this article: Richard W. Ziolkowski Localized Transmission of Electromagnetic Energy Physical Review A, 39(4), pp. 2005-2033, 2/15/89. The paper presents interesting solutions to Maxwell's equations that describe electromagnetic pulse trains which spread out much more slowly than beams satisfying the classical diffraction limit. For example, a folded circular array 1 meter in diameter driven by waveforms with maximum frequency of 15 THz can project a beam out to about 400,000 km, surpassing the diffraction limit by about three orders of magnitude. The applications are clear: SPS power transmission, deep space radar, space weaponry, "Starwisp", light sails, beam-powered ion engine propelled spacecraft. I'm not sure if a rectenna would work efficiently on a broadband signal, though. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Wed, 22 Mar 89 14:18:33 EST From: dietz@cs.rochester.edu To: telesoft!roger@ucsd.edu Cc: space-tech@cs.cmu.edu Subject: Beamed Energy > I find that result hard to credit. I've heard about theoretical > solutions that keep the beam together beyond the diffraction limit, > but they depend on an energy density in the beam that is so high that > the transmission properties of space are altered. The beam becomes > self-focused by the gravitational attraction of the photons in the > beam. The energy densities needed to see this effect are > ridiculous--something on the order of the entire energy output of the > sun, poured into a beam a few centimeters in diameter. No, the result doesn't assume nonlinearity. The results are for the scalar wave equation and for Maxwell's equations. Whether they are interesting is another question. For example, it is not altogether obvious to me that the solutions that preserve the peak amplitude out to large distances have a large amount of energy in the peak. On the subject of nonlinearity: doesn't vacuum polarization become important long before the light beam's self-gravity? Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Wed, 22 Mar 89 16:08:01 PST From: anderson%asuipf.span@VLSI.JPL.NASA.GOV (Don) To: space-tech@cs.cmu.edu Subject: Would you like to go to Mars in 1992? MS/PhD level software designer/programmer wanted for the NASA Mars Observer spaceflight project. Work involves the development of instrument command and data analysis software for an imaging infrared spectrometer. Both a background in physical sciences and mathematics, and strong UNIX/C, DBMS, and graphics experience are desired. Salary commensurate with experience. Send letter of interest, resume, and names of three references/letters of recommendation to: Don Anderson Geology Department Arizona State University Tempe, Arizona 85287-1404. 602-965-6336 uucp: sun!sunburn!tes!anderson ------------------------------ End of Space-tech Digest #29 *******************