Subject: Space-tech Digest #92 Contents: Aliza Panitz "In The Shade" John Roberts Re: "In The Shade" Dani Eder Spacewatch Camera Project/Near Earth Asteroids Jonathan Leech Re: Spacewatch Camera Project/Near Earth Asteroids Paul Dietz Re: Spacewatch Camera Project/Near Earth Asteroids Karl Dishaw Re: Getting stuff off the moon Nick Szabo Re: Getting stuff off the moon Paul Dietz Re: Getting stuff off the moon Phil Fraering Re: Getting stuff off the moon Tom Neff Circularizing Catapulted Ore John Roberts Re: Circularizing Catapulted Ore Joe Beaufait MARS MISSION ------------------------------------------------------------ Date: Fri, 13 Dec 1991 8:32:41 EST From: PANITZ@CAYMAN.GSFC.NASA.GOV (Aliza R. Panitz - The Bug Lady) Subject: "In The Shade" To: space-tech%cs.cmu.edu@uunet.uu.net [Discussion of ways to shade an orbiting object, or increase emissivity, deleted.] !! !! From: John Roberts !! An object in Earth orbit has the additional problem of heat radiating !! from the Earth. COBE needed both a sun-synchronous orbit and an !! onboard cryogenic source. I don't believe that heat from the Earth was a critical factor here. COBE has the additional wrinkle of being concerned not merely with temperature, but with light emitted from the Earth (and Sun) shining into the instruments. So COBE hangs out along the terminator, keeping its working (shaded) end pointed away from both the Sun and the Earth, but using Sun and Earth sensors mounted on the electronics box for first-cut attitude determination. The shaded Dewar, even a year post-cryogen, has reached equilibrium (?) at a temperature much lower than that of the exposed portions, of course. (If I can find publicly released numbers I'll post them.) During cryogenic operations, the DIRBE instrument (one of the two cryogenic instruments onboard COBE) operated at temperatures "below 2K", which is certainly far below what any simple radiatively cooled object could hope to attain. - Aliza R. Panitz COBE/Hughes STX Disclaimer: I speak only for myself, not for the COBE Project or NASA's Goddard Space Flight Center. ------------------------------ Date: Sat, 14 Dec 91 12:50:37 EST 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: "In The Shade" Aliza - Thanks for the more detailed explanation. I expect that if the light from Earth could get to the instruments, then the infrared thermal radiation could too. And while this might not prevent the instruments from working, it could cause the cryogenic material to be consumed faster. (By the way, I recall that a payload launched sometime in the last few years used frozen argon as a coolant. Was that COBE?) >The shaded Dewar, even a year post-cryogen, has reached equilibrium (?) at >a temperature much lower than that of the exposed portions, of course. >During cryogenic >operations, the DIRBE instrument (one of the two cryogenic instruments >onboard COBE) operated at temperatures "below 2K", which is certainly far >below what any simple radiatively cooled object could hope to attain. That stands to reason - the sensor should be colder than the blackbody radiation that it's trying to detect. > - Aliza R. Panitz > COBE/Hughes STX John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ Date: Thu, 12 Dec 91 11:59:46 CST From: eder@hsvaic.boeing.com (Dani Eder) To: space-tech@cs.cmu.edu Subject: Spacewatch Camera Project/Near Earth Asteroids As most of you probably know, a small object passed by the Earth very recently, whether it was natural or manmade is in debate, although natural origin is the leading hypothesis right now. I talked today (12/12) to Dr. Tom Gehrels, the principal investigator for the Spacewatch camera, the instrument that found that object. He needs our help to increase the discovery rate for Near Earth Asteroids from about 25 per year (with the current 36 inch telescope) to about 200 per year (with the next generation 72 inch telescope). We are all aware, I hope, of the value of Near Earth Asteroids for space development, and we need to find large numbers of them to find the easy to get to ones. The Spacewatch Camera is a telescope with a CCD attached, and software to automatically detect asteroids in real-time by their motion relative to the background stars. The next generation instrument is at a critical point in it's development where a small amount of money can shave years off the date when we start finding asteroids. They already have the mirror, the dome, the drive, and CCD detectors in hand or funded. What is needed is $1.8 million over the next few years to pay for design and construction of the telescope frame (the steel parts, mainly), and to put the whole package together. For 1992, they need the first $200,000 to cover the design work. They requested funding from NASA for this work, but were turned down (for some spurious reasons, as it turns out). The $1.6 million balance will be needed in the following 2-3 years for the actual construction. What I need from my fellow space-tech readers is (1) If you can spare some bucks, send them Tom's way. His address is: Dr. Tom Gehrels Lunar Laboratory, University of Arizona Tucson, AZ 85721 If it is under $100, you may send it to me and I'll collect it into a big check to send to him. This is efficient because it costs the University admainistration to process gifts, and for small amounts they are not set up well to handle it. I'm going to send him $100 myself. My address is Asteroid Search Support Fund c/o Dani Eder Route 1, Box 188-2 Athens, AL 35611 (205)232-7467(h) (205)461-2697(w) (2) Write your congresscritter and tell them about why looking for asteroids is important. In addition to the space development reasons, you can talk about why it is not a good thing for the Earth to be hit by an asteroid, and how we ought to find these things before they come knocking, and maybe then we can do something with them before they hit, but at least we should characterize the risk by knowing how many there are and what their orbits and size distribution is. It helps if you live in AZ, where the money will be spent (3) Contact other space activists, environmentalists, etc. to recreuit fellow travellers. (4) Contact a random NASA person and tell them why you think asteroids are important. There are 8,000 engineers and scientists at NASA, and educating them all about asteroids is a serious task. I hope I haven't over-stepped the bounds of the mailing list, but here's where a relatively small effort can make literally years of difference to when we get things done in space. Dani Eder ------------------------------ Date: Thu, 12 Dec 91 13:33:28 -0500 From: Jonathan Leech To: space-tech@cs.cmu.edu Subject: Re: Spacewatch Camera Project/Near Earth Asteroids Dani Eder: >you can talk about why it is not a good thing for the Earth to be hit by >an asteroid, and how we ought to find these things before they come knocking, It's not clear to me that this is a good strategy. Regardless of the truth of such assertions, I suspect the average congressional staffer reading about them will lump the writer in with UFO cultists and other bogons. Spacewatch can be justified in scientific terms, without recourse to global diaster scenarios. Are we supposed to make checks out to you personally, or to the "Asteroid Search Support Fund"? Jon (leech@cs.unc.edu) __@/ ------------------------------ Date: Thu, 12 Dec 91 14:42:54 EST From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Re: Spacewatch Camera... I've thought for some years that the Spacewatch Camera project is quite an excellent idea. Glad to see they're closer to really getting it going. On the subject of asteroids... I was just reading a book discussing the minerology of meteorites. The section on irons caught my attention. Apparently, these were formed in substantial globs of molten nickel-iron in protoasteroids that have subsequently been broken up by collisions. As nickel-iron cools, metals solidfy out in a particular pattern. The first metals to come out are iron-rich, the last are nickel-rich. The interesting kicker is that trace elements, like iridium, are even more strongly fractionated. Iridium (and, I presure, the other PGEs) preferentially go into the initial iron-rich part. Iridium concentrations can vary by 4 or more orders of magnitude in this process, with concentrations up to hundreds of ppm. This is very rich for a platinum ore. The upshot is that a program to mine asteroids for PGEs should look for asteroids that are fragments of a central, iron-rich part of a well fractionated proto-asteroid. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Fri, 13 Dec 91 05:43 GMT From: Karl Dishaw <0004244402@mcimail.com> To: Dani Eder To: Bill Trost To: space-tech Subject: Re: Getting stuff off the moon Dani Eder: >Summary: You don't need to use a rocket to get stuff off the Moon, >mechanical catapults will suffice! Bill Trost: >Ah yes, the Wile E. Coyote launch system.... :-) Electromagnetic or mechanical catapults can boost stuff off the Moon, but you're still going to need a rocket attached to each load, or a helluva catcher's mitt. Say your catapult boosts an ore barge to 1.2 Vc (circular orbit around the Moon), ejecting it horizontally from the top of a mountain. The barge will go into an elliptical orbit, passing just above the lunar surface on each revolution until it runs into another mountain.... A rocket engine to circularize the orbit would really help. A payload boosted at greater than escape velocity will go into an orbit around the Earth that intersects the Moon's orbit. Making that ore barge rendezvous with any specific target will probably require two or three maneuvers, including mid-course steering corrections. The initial orbit will depend on the location of the catapult and the direction it launches in. If the lunar mine will have only one major customer (ex. L-5) the catapult might be set up specifically to launch to there, minimizing the number of maneuvers and reducing the size of the rocket and its fuel. Some of the mechanical catapult designs can launch in different directions. This lets it reach a number of different targets, but a large burn will still be needed to insert the payload into the customer's orbit. If the customer is low in the gravity well, the payload could be launched directly against the Moon's motion to put it in a transfer orbit. Circularizing to GEO would take a delta-V of more than 1.1 km/sec, LEO orbit more than 3.1 km/sec. Either way a good chunk of your payload is going to go for reaction mass. Staying at the top of the gravity well would be lots cheaper. Catapults can do most of the work of getting off the Moon, but you'll still need a rocket on your payload if you're fussy about where it ends up. Karl PS. I've completed a program that does several types of orbital mechanics calculations on a Macintosh. If you'd like to take a look at it, please email me your address and I'll mail you a floppy. ------------------------------ From: sequent!techbook.com!szabo@uunet.UU.NET (Nick Szabo) Subject: Re: Getting stuff off the moon To: uunet!mcimail.com!0004244402@uunet.UU.NET (Karl Dishaw) Date: Sat, 14 Dec 91 2:30:55 PST Cc: space-tech@cs.cmu.edu > A payload boosted at greater than escape velocity will go into an orbit > around the Earth that intersects the Moon's orbit. Making that ore barge > rendezvous with any specific target will probably require two or three > maneuvers, including mid-course steering corrections. The initial orbit > will depend on the location of the catapult and the direction it launches in. > If the customer > is low in the gravity well, the payload could be launched directly against > the Moon's motion to put it in a transfer orbit. Circularizing to GEO would > take a delta-V of more than 1.1 km/sec, LEO orbit more than 3.1 km/sec. > Either way a good chunk of your payload is going to go for reaction mass. This is an important problem, since all current major markets are in GEO or below. Objects captured from heliocentric orbit will also enter a highly eccentric orbit around the Earth (HEEO), so the same general problem exists for asteroid and comet resources as well as lunar. Warning: the following is from hand-drawing (hand-waving? :-) not math. Related to Tom Neff's suggested, we might grab a HEEO payload at perigee with a tether in LEO. The tether can simultaneously grab a payload being launched from Earth in a suborbital trajectory, with the momentums balanced. Tight launch windows, though. The tether can redistribute the mass and place it in LEO and/or GTO. Unfortuneately, tether solutions require high start-up mass. Another way to get to LEO or GTO is aerobraking. The HEEO can barely intercept Earth's atmosphere for a stretch of 10^5 m during which a decelleration of 0.4 m/s^2 (~1/25 g) will provide a delta-v of 200 m/s. 16 such passes (c. 4 months) will circularize the orbit into LEO, a lesser number to get to GTO (but then further boost is needed to get to GEO). Crude but sufficient aerobrakes can be made by microwave sintering regolith or dust. For any Earth flyby or HEEO trajectory, but especially those using aerobraking, payload should be partioned and packaged so that there is no chance of environmental "impact" in Earth's lower atmosphere or surface from a misguided payload. Loosely packed regolith or ice, along with explosive charges sufficient for dispersing the payload in an emergency, should be safe for even kiloton packages. > Staying at the top of the gravity well would be lots cheaper. The major paying customers (spysats, satcoms, SDI, SPS, etc.) have specific orbital needs and require the end product in GEO or lower. The largest market for native fuels is in LEO's. The issue of how much processing takes place in-situ, how much in HEEO, and how much at market is a complex issue that depends on the details of the processes themselves. szabo@techbook.COM ...!{tektronix!nosun,uunet}techbook!szabo Public Access UNIX at (503) 644-8135 (1200/2400) Voice: +1 503 646-8257 Public Access User --- Not affiliated with TECHbooks ------------------------------ Date: Sat, 14 Dec 91 12:10:55 EST From: dietz@cs.rochester.edu To: sequent!techbook.com!szabo@uunet.UU.NET Subject: Re: Getting stuff off the moon Cc: space-tech@cs.cmu.edu Nick Szabo suggested that ET materials be sent to GEO by: (1) Aerocapture into HEEO, (2) Aerobraking to GTO, (3) Raise perigee to GEO. I believe less non-aero delta-V is required if, instead, the following is done: (1) Aerocapture into HEEO (2) Adjust this orbit for a very large apogee, (3) At apogee, raise the perigee to GEO altitude and plane-change to equatorial orbit (this may require more than one burn), (4) Circularize to GEO. The idea is that GTO --> GEO requires more delta-V than step (4) of the second maneuver sequence. For very eccentric orbits, the outer part of the orbit will be strongly influenced by the sun and/or moon, perhaps in useful ways. The velocity changes at apogee could also be done over long periods using low thrust rockets. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Sat, 14 Dec 1991 16:01:14 -0600 From: Fraering Philip G To: dietz@cs.rochester.edu, szabo@techbook.com Subject: Re: Getting stuff off the moon Cc: space-tech@cs.cmu.edu I have seen analyses done for lifting from lower orbits to higher ones where if r2/r1>~14, it is less costly to raise the (the starting and ending orbits are both circular, I just remembered to add) apogee to past r2 (I don't have the number handy; I think this case is in Orb. Mech. by Roy) and from that apogee to raise the perigee to r2, and then to lower the apogee to r2... Phil ------------------------------ From: tneff@bfmny0.BFM.COM (Tom Neff) Date: Fri, 13 Dec 1991 11:05:29 EST X-Mailer: Mail User's Shell (7.1.1 5/02/90) To: SPACE-TECH Mailing List Subject: Circularizing Catapulted Ore Could you circularize without a rocket by tethering away part of the load after launch? ------------------------------ Date: Sat, 14 Dec 91 12:28:17 EST 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: Circularizing Catapulted Ore >Could you circularize without a rocket by tethering away part of the load >after launch? Intuitively, I'd say yes you could to some extent - whether it would be enough would have to be calculated for each case. Of course, you'd end up dumping some of the payload on the surface, and if that's not precisely controlled, it could end up being a nuisance (i.e. landing on the launcher). There are all sorts of possible maneuvers that probably don't count as proper tethering, in which the components are actively slung around, and mechanical energy expended reeling in a tether against a spin is used in lieu of rocket thrust to build up velocity. (Or reeled out to reduce velocity, which doesn't take any additional energy source.) That might be useful well away from a planet, to send two probes in opposite directions: - Launch two spacecraft, connected by a long tether. - Use a small amount on rocket thrust to set the assembly spinning. - Use solar power or other energy source to drive motors that gradually reel in the tether, greatly increasing the velocity of the two spacecraft. - At a precisely calculated instant, release the tether. The two spacecraft fly off in opposite directions, on the way to separate missions. There would of course be some interesting engineering problems to solve. :-) John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ Date: Mon, 16 Dec 91 13:12 EDT From: BEAUFAIT%CEBAFVAX.BITNET@BITNET.CC.CMU.EDU Subject: MARS MISSION To: space-tech@DAISY.LEARNING.CS.CMU.EDU Hi. I'm new to space-tech. I ran across this paper that relates to a propulsion design for the mars mission (dates 1983). Its from a DOE sorce so I thought the powers that be may not be aware of it. The paper is titled "A LASER-FUSION ROCKET FOR INTERPLANETARY PROPULSION". Author is Roderick A. Hyde Lawrence Livermore national Labs, call no# ucrl-88857, dated sept 1983. It deals with the development of an interplanetary vehicile mass 486 ton without reaction mass. Acceleration .1g continuos. Trip times to mars from 9 to 22 days depending on cargo. The paper contains ruf calculations a refrence to certain modeling software developed and in general (I feel) is fairly comprehensive in it s approch to the problem. With the development of high tc superconductors and FEL efficiancies in exsess of 90% this proposal seems even more doable than it must have in 1983. I hope you'll look it up and pass the information on to the groupe doing the NTR studies. * one more positive atribute * the system uses a much more politicaly acceptab- le fuel. No launching that dirty u word or p word. Less political hassel more chance of getting things done. Joe "I'll get ther if I have to walk" Beaufait ::: Beaufait@cebaf2.cebaf.gov ------------------------------ End of Space-tech Digest #92 *******************