Date: Mon, 23 Jan 1989 20:49-EST From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU To: "~/st/lists/stdigest" Subject: Space-tech Digest #23 Contents: Paul Dietz Asteroid searching Marc Ringuette Navstar for spacecraft? Randall Parker Space Industry Lucius Chiaraviglio Hybrid air-breathing/solid fuel engine? Roger Arnold Re: Hybrid air-breathing/solid fuel engine? Paul Dietz Re: Hybrid air-breathing/solid fuel engine? ------------------------------------------------------------ Date: Wed, 18 Jan 89 16:28:13 EST From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: asteroid searching I looked up some more on CCD asteroid searches. There is already one in progress, the Spacewatch project: PI: Tom Gehrels, U. of AZ Location: Steward Observatory Scope: f/5 91 cm newtonian scope, modified to f/3.85 by a relay lens CCD: 512x320 pixel RCA SID 53612 (30 micron pixels), cooled to -60 C in a vacuum housing pixel size: 1.73 arcsec readout noise +-200 electron/hole pairs (rms, I think) dark current 50 ehp/pixel/s Exposure time: 60 seconds Limiting magnitude: 19.6 (six sigma) The CCD is operated in a "drift scan" mode: charge is clocked along the rows to compensate for movement of the image due to the earth's rotation (rows are 512 pixels). A typical 30 minute scan covers a strip of 30 minutes of right ascension x .156 degrees. A set of three 30 minute scans near the opposition point is claimed to net about five main belt asteroids, although I don't know if this rate has been achieved. As described, it has a problem with nearby asteroids at, say, 10^7 km: at a relative speed of 15 km/s, the asteroid would move up to 10 pixels in 60 seconds, increasing the magnitude of a 100 meter C class asteroid from ~ 18.5 to 21. Maybe searching for dim streaks would let you recover some of these asteroids. Algorithm question: is there a fast technique for recovering small line segments in very noisy images? According to a recent report in Bull. AAS, in 242 nights of observing, from 4/27/84 to 2/26/87, it spotted 69 new asteroids and determined preliminary orbits for 16 of them. It also helped recover 72 asteroids. This same camera has recently been used by Clayne Yeates (JPL) to try to spot Frank's minicomets (see Science, 10 June 1988), putative small objects that fill the inner solar system in great numbers. Some streaks were found, but I have not heard that they were confirmed. I also saw a report on a converted surplus Baker-Nunn satellite tracking camera: Location: U. of New South Wales Scope: 0.5 m, f/1 super-Schmidt, donated by SAO CCD: 385x576 pixels Field of view: 1.4 x 0.9 degrees (9 arcsec/pixel) Operating modes (at snr = 10) mag 10 in .02 sec (video rate) mag 15 in 1 sec (autoguiding) mag 19 in 300 sec (deep sky search) This scope was hoped to be in operation by mid-1986; I do not know if this is the case. The scope is controlled by an Apple IIe (!), and data is collected by a NEC APC III. (Reference: Instrumentation and Research Programs for Small Telescopes, IAU Symposium No. 118, 2-6 Dec 1985.) Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Mon, 23 Jan 1989 01:31-EST From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU To: space-tech@cs.cmu.edu Subject: Navstar for spacecraft? From Henry Spencer's 'space news from Dec 5 AW&ST': > DARPA is exploring use of small Navstar receivers on spacecraft for > automatic orbit control, reducing workload on ground stations. Does anybody know what capabilities a Navstar receiver needs to have? Is Navstar currently compatible with use from orbit? [ I just saw this on Ted Anderson's "space-magazine" mailing list. If you aren't reading sci.space, you should at least read this list, which has fewer, more "article-like" posts. However, if you read sci.space, you will see this material anyway. To join it, send mail to space-mag-request@andrew.cmu.edu. ] ---------------------------------------------------------------------------- | Marc Ringuette | mnr@cs.cmu.edu | "Where's the beef?" | | CMU Computer Science | 412-268-3728(w) | -- watch this space for other | | Pittsburgh, PA 15213 | 412-681-5408(h) | quotes from great literature | ---------------------------------------------------------------------------- ------------------------------ [ This was very long and wandered into discussion of space policy. I've abridged it where you see the dots. -- Marc ] Date: Mon, 23 Jan 89 08:44:47 PST From: C43RGP%ENG4.gm@hac2arpa.hac.com To: SPACE_TECH@hac2arpa.hac.com Subject: Space Industry and Policy I'd like a discussion of what scientific and technological advances would be helpful in the creation of new space industries. To my knowledge there are currently only two uses of space that are providing an economic return thru their pursuit: 1) communications and 2) remote sensing. ... likely candidates: 3) Low Mass Materials Processing (biochemicals, small alloy parts, possibly electronic parts) 4) High Mass Materials Processing with non-Earth sourced materials (asteroid or moon mining for LEO processing centers) Space-based low mass materials processing will be characterized by the production of very low bulk products which have high economic value. ... Questions: ========== 1) What ... policies would accelerate the development of new space industries? 2) Are there key areas of scientific research or technological development whose advance would contribute most to space development? 3) Is the proposed space station a cost-effective way to fund microgravity experiments? 4) Can the volume and quality of microgravity experiments be cost-effectively enhanced by a continual human presence in space? My intuition tells me yes because of the nature of scientific experimentation. 5) What kinds of long-term research projects should be pursued to lower launch costs? -- Randall Parker ------------------------------ Date: Fri, 20 Jan 89 03:09:54 EST From: Lucius Chiaraviglio To: space-tech@cs.cmu.edu Subject: Hybrid air-breathing/solid fuel engine -- could this work? A couple of days ago I came up with an idea formed from seeing relatively recent sci.space articles on hybrid rockets and air-breathing engines. So far everything I have read has been about an engine that is either one or the other of these. It finally occurred to me: why not combine the two ideas and get the advantages of both? This may be totally insane (since I don't have any training in rocket engineering), but why not have a scramjet intake sending air into a solid-fuel (as opposed to solid-oxidizer) rocket engine? Of course, this would require something else to get the rocket up to speed. Speeds considerably above the supersonic would be required to generate enough heat by air friction within the engine for the air flow to sustain the combustion rather than blow it out. Also, the fuel would need to be something that easily sustains a reaction in air (speculation: magnesium carbide grains in a matrix of whatever substance is conventionally used to bond solid rocket fuels? -- I originally thought of carbon, but that doesn't burn well enough, and therefore the flame would go out too easily). Another potentially serious problem is due to one of the features (or bugs?) of scramjets, which is that not only the intake geometry but the geometry of the rest of the engine must be very carefully designed or it simply won't work. Obviously this is going to produce complications due to the fact that the interior geometry of the engine will change as fuel burns away. It will probably be necessary to have part of the intake and nozzle for the engine be made out of fuel whose consistency and composition will be graded so that burning rates will be such as to change the shape in the right way. Some actively variable geometry may also be needed. Note that the varying geometry will have to take into account not only the change in interior conditions due to fuel consumption but also the change in conditions caused by increasing speed and decreasing air density. It might be possible to design the engine so that these changes in conditions compensate for each other, but I can't be sure of this. Also, this might result in its being unusually sensitive to variations payload weight and drag (you don't want to have to adjust the design of the engine for each mission, unless this can be done very easily, which I doubt is possible). The advantages of such an engine would be that it will be almost as simple and cheap as a solid-fueled engine (once the initial design problems are worked out), as safe as a hybrid engine (it can catch fire but it can't explode, and if it does catch fire it can be extinguished -- also, no accidental blastoff from the pad), and has much higher performance-to-weight ratio than a conventional solid or non-air-breathing hybrid engine because it doesn't have to carry its own oxidizer (also, it uses the air it takes in as reaction mass). In other words, it has much of the advantages of each of air-breathing, hybrid liquid-oxidizer/solid-fuel, and conventional solid-fueled engines. How about it, people? | Lucius Chiaraviglio | ARPA: chiaravi@silver.bacs.indiana.edu BITNET: chiaravi@IUBACS.BITNET (IUBACS hoses From: fields; INCLUDE RET ADDR) ARPA-gatewayed BITNET: chiaravi%IUBACS.BITNET@vm.cc.purdue.edu Alt ARPA-gatewayed BITNET: chiaravi%IUBACS.BITNET@cunyvm.cuny.edu ------------------------------ Date: Fri, 20 Jan 89 10:52:34 PST From: telesoft!roger@ucsd.edu (Roger Arnold @prodigal) To: chiaravi@silver.bacs.indiana.edu Cc: space-tech@cs.cmu.edu Subject: Re: Hybrid air-breathing/solid fuel engine -- could this work? Sorry, won't work. Oh, the solid fuel may burn, if the speed is high enough that friction sustatins the reaction temperature, but it won't be able to produce useful thrust. The combustion products will be mostly confined to a relatively thin boundary layer, simply by virtue of not having enough time to diffuse and mix with the main body of the air flow. If solid fuels could work in a SCRAM jet, so could liquid fuels other than hydrogen. Hydrogen works because it diffuses so rapidly into the air stream. Also, I believe that because of its low molecular weight, it doesn't generate combustion temperatures immediately on mixing with the air stream. Instead, combustion temperatures are generated when the air stream is compressed. That makes for much more efficient conversion of chemical energy to reaction impulse. How well do you think a car engine would work if the fuel were burned *before* the fuel/air mixture were compressed? - Roger Arnold ..ucsd!telesoft!roger ------------------------------ Date: Mon, 23 Jan 89 11:36:45 EST From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Hybrid air-breathing/solid fuel engine -- could this work? It's not clear to me that a solid fuel ramjet at scramjet speeds is impractical. Consider: one is not as worried about wall heating -- you *want* the wall (fuel) to ablate. So, you maybe can afford to compress the incoming air much more fiercely than in a hydrogen scramjet. I imagine a solid fueled ram(not scram)jet operating at near orbital speeds. Incoming air is compressed and heated to dissociation. The fuel is phenolic plastic or graphite. It's too hot in the first part of the engine for combustion to occur; the air and carbon vapor burn farther downstream, in the nozzle, say, after some expansion. Since combustion isn't strictly necessary for a ramjet to generate thrust, I wonder if solid fueled ramjets could be used in the atmospheres of Venus or Jupiter? Paul F. Dietz dietz@cs.rochester.edu ------------------------------ End of Space-tech Digest #23 *******************