Return-path: X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson Received: from beak.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl@andrew.cmu.edu (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests) ID ; Wed, 9 Jan 1991 02:40:07 -0500 (EST) Message-ID: Precedence: junk Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Wed, 9 Jan 1991 02:39:34 -0500 (EST) Subject: SPACE Digest V13 #032 SPACE Digest Volume 13 : Issue 32 Today's Topics: Re: $$/pound of Freedom vs LLNL (was: ELV Support...) I called the Mir 900 number ... Re: Interstellar Light Sails Re: Building a sundial, position of the sun Re: Interstellar Light Sails GUERAP III software Re: Hi girls... (part 2) Re: Interplanetary travel Administrivia: Submissions to the SPACE Digest/sci.space should be mailed to space+@andrew.cmu.edu. Other mail, esp. [un]subscription requests, should be sent to space-request+@andrew.cmu.edu, or, if urgent, to tm2b+@andrew.cmu.edu ---------------------------------------------------------------------- Return-path: X-Andrew-Authenticated-as: 0;andrew.cmu.edu;Network-Mail Date: 3 Jan 91 22:45:05 GMT From: csus.edu!wuarchive!usc!samsung!umich!sharkey!cfctech!teemc!fmeed1!cage@ucdavis.ucdavis.edu (Russ Cage) Organization: Ford Motor Co., Electronics Div., Dearborn, MI Subject: Re: $$/pound of Freedom vs LLNL (was: ELV Support...) References: <2853@polari.UUCP>, <9038@fmeed1.UUCP>, <2919@polari.UUCP> Sender: space-request@andrew.cmu.edu To: space@andrew.cmu.edu In article <2919@polari.UUCP> crad@polari.UUCP (Charles Radley) writes: >I am astonished that you go to so much trouble to mislead the >respected users of this net. There is NOT an OVERALL weight saving, >the entire analysis you presented relates only to the PRESSURIZED >HULL which is a small part of the overall system, and has only second >order effect on the overall weight. Charles, your previous assertion was that artificial gravity required a much greater mass than a non-spinning station. I have refuted this assertion. For you to go and whine that this is suddenly not relevant after making a big deal of it is immature. >In article <9038@fmeed1.UUCP>, russ@m-net.ann-arbor.mi.us (Russ Cage) writes: >+Freedom will be built of aluminum. The strongest alloy >WRONG !! Freedom is made of a variety of materials, mostly >graphite-epoxy composite. That's not what you said in article <2812@polari.UUCP>. On November 29 1990, you posted this: >Also, the shielding capability of LLNL's non-metallic structure is much less than >Freedoms aluminum modules. ^^^^^^^^ So, which is it? Aluminum alloy, or graphite composite? Don't tell me that things other than the pressure hull are the big deal. It is the pressure hull which is the major structural component and the bulkiest part to boot. It is the pressure hull, not any other part, which must be heavier to bear additional stress from artificial gravity. It is the pressure hull of LLNL that you said would be too heavy. I'm getting very tired of watching you play semantic games and never post a number. Getting a single unambiguous FACT out of you seems impossible. Be glad you don't work for me; if you gave me any sort of report with equivocations, half-truths and excuses in it such as I've seen in your postings, I would fire you on the spot, for incompetence. Before you presume to denegrate somebody else's work (such as LLNL's), let's see you first acquire some knowledge about it. Get their proposal and read it. I won't hold my breath. -- Russ Cage Ford Powertrain Engineering Development Department Work: itivax.iti.org!cfctech!fmeed1!cage (CHATTY MAIL NOT ANSWERED HERE) Home: russ@m-net.ann-arbor.mi.us (All non-business mail) Member: HASA, "S" division. ------------------------------ Return-path: X-Andrew-Authenticated-as: 0;andrew.cmu.edu;Network-Mail Date: 5 Jan 91 14:40:00 PST From: "1st Lt. Henry S. Cobb" Subject: I called the Mir 900 number ... To: "space+" [Fair warning: I know some of the people involved in the Mir lottery. I used to live in Houston, and Houston space activists are a surprisingly small group. In particular, I can vouch for Jim Davidson, the director of marketing at Space Travel Services. I can't believe he'd be involved in anything fraudulent. However, I have no connection with the company (other than as a hopeful cosmonaut). Last time I met Jim, he clearly had something up his sleeve, but he wouldn't let me in on the secret.] I called the "Fly to Mir" lottery phone line (1-900-258-2MIR) about 13:30 on 5 Jan 91. My initial impression is that they need a lot more explanation for both prospective and actual callers. Here's what happened: There is an initial message spoken by a very fast-talking woman. As nearly as I can remember, it goes like this: "This is Space Info. You can stay on the line to register for the Mir lottery, or send one hand-written entry per standard business-size envelope to Space Travel Services PO Box 580249 Houston, TX 77258 If you stay on the line, you will be charged $2.99 for this call." After a pause, the same woman delivers about a two-minute spiel on the design and construction of the Mir space station, at the same speed. It seemed accurate at first listen, but you'd have to tape it and repeat it to find out anything you didn't already know. Why is this here? Texas is a populist and somewhat blue-nosed place. I assume there's a law to the effect that 900 numbers must offer "information," not sweepstakes entries (or lascivious dialogue). I remember some controversy when 900 numbers were first introduced there, but I don't specifically recall the law. After the woman finishes, a male Texan voice (talking more slowly, but that's redundant) says something like "You may record your lottery entry now," and you then hear an answering-machine BEEP. At this point, their disorganization becomes clear. What does a lottery entry consist of? They don't describe that at all. You get about thirty seconds to record . It then gets played back to you, and you can re-record by pressing 1 on a touch-tone phone. After the third try, I wound up leaving my name, address, and phone number, with a short comment about clarifying their entry procedure. I have no doubt that Space Travel Services has a signed agreement to fly someone on Mir next year. I don't think they've really figured out how to use it effectively. (And I'm not entirely sure the Soviet Union will be in shape to launch passengers by then.) But it's a great idea, and $3 is relatively painless even if it doesn't pan out. Summary: You apparently don't need to call their 900 number. Instead, you can write to the address above. What does a lottery entry consist of? Your guess is as good as mine. Call the number if you don't mind spending three bucks, but be sure you have a recorder running unless you just want to leave your name and address on the answering machine. ------------------------------ Return-path: X-Andrew-Authenticated-as: 0;andrew.cmu.edu;Network-Mail Date: 6 Jan 91 18:26:05 GMT From: cs.utexas.edu!swrinde!elroy.jpl.nasa.gov!euclid.jpl.nasa.gov!pjs@tut.cis.ohio-state.edu (Peter Scott) Organization: Jet Propulsion Laboratory, NASA/Caltech Subject: Re: Interstellar Light Sails References: <1990Dec30.004107.7363@zoo.toronto.edu>, <20843@crg5.UUCP>, <1991Jan6.020954.11962@zoo.toronto.edu> Sender: space-request@andrew.cmu.edu To: space@andrew.cmu.edu In article <1991Jan6.020954.11962@zoo.toronto.edu>, henry@zoo.toronto.edu (Henry Spencer) writes: > In article <20843@crg5.UUCP> szabo@crg5.UUCP (Nick Szabo) writes: > >>... If you can build the laser system > >>on the necessary colossal scale, laser sails are workable. > > > >What is the spread of a laser over interstellar, or even interplanetary > >distances? Last I heard from the deep-space laser communications people, > >there is large dispersion over even interplanetary distances ... >[...] > This says that at roughly > optical wavelengths (a few hundred nanometers), effectiveness at interstellar > distances (a light year is roughly 1e16 m) requires transmitters and > receivers hundreds of kilometers across. The receiver (sail) is not a big > problem, since its shape is not critical. A diffraction-limited transmitter > lens/mirror/array that size is a challenge, to be sure, but it is not > ridiculous. Exactly what Forward specifies, although I think he even talks in terms of apertures thousands of kilometers across. He has designs, too; I recall a lens formed by a loose mesh enclosing an aerosol, don't remember how he handled diffusion but I assume he did. The man thinks *big*. Best example of someone with their head in the clouds but their feet on the ground that I know of. -- This is news. This is your | Peter Scott, NASA/JPL/Caltech brain on news. Any questions? | (pjs@euclid.jpl.nasa.gov) ------------------------------ Return-path: X-Andrew-Authenticated-as: 0;andrew.cmu.edu;Network-Mail Date: 6 Jan 91 17:33:58 GMT From: isis!ebergman@uunet.uu.net (Eric Bergman-Terrell) Organization: Math/CS, University of Denver Subject: Re: Building a sundial, position of the sun References: <1990Dec28.125421@axion.bt.co.uk>, <1429@mpirbn.mpifr-bonn.mpg.de>, <2087@njitgw.njit.edu> Sender: space-request@andrew.cmu.edu To: space@andrew.cmu.edu There are two books that will give you all the information about sundial design: 1. Albert E. Waugh, "Sundials: Their Theory and Construction", published by Dover Publications 2. R. Newton Mayall and Margaret W. Mayall, "Sundials", published by Sky Publishing Both were published in 1973. Terrell ------------------------------ Return-path: X-Andrew-Authenticated-as: 0;andrew.cmu.edu;Network-Mail Date: 6 Jan 91 02:09:54 GMT From: usc!cs.utexas.edu!news-server.csri.toronto.edu!utzoo!henry@apple.com (Henry Spencer) Organization: U of Toronto Zoology Subject: Re: Interstellar Light Sails References: <1990Dec29.212153.20748@cunixf.cc.columbia.edu>, <1990Dec30.004107.7363@zoo.toronto.edu>, <20843@crg5.UUCP> Sender: space-request@andrew.cmu.edu To: space@andrew.cmu.edu In article <20843@crg5.UUCP> szabo@crg5.UUCP (Nick Szabo) writes: >>... If you can build the laser system >>on the necessary colossal scale, laser sails are workable. > >What is the spread of a laser over interstellar, or even interplanetary >distances? Last I heard from the deep-space laser communications people, >there is large dispersion over even interplanetary distances ... Different assumptions about the optics involved. You cannot do useful power transmission over interstellar distances if you insist on building optics only centimeters, or even meters, across. If I am remembering it correctly (this is not an area I'm intimate with), the basic rule of thumb for diffraction-limited optics is that most of the power of a beam of wavelength lambda from a transmitter of radius Rt will end up in a receiver of radius Rr at distance D if Rt * Rr > D * lambda (it is just possible that those radii should be diameters, but in any case this gives us an order-of-magnitude answer). This says that at roughly optical wavelengths (a few hundred nanometers), effectiveness at interstellar distances (a light year is roughly 1e16 m) requires transmitters and receivers hundreds of kilometers across. The receiver (sail) is not a big problem, since its shape is not critical. A diffraction-limited transmitter lens/mirror/array that size is a challenge, to be sure, but it is not ridiculous. -- "The average pointer, statistically, |Henry Spencer at U of Toronto Zoology points somewhere in X." -Hugh Redelmeier| henry@zoo.toronto.edu utzoo!henry ------------------------------ Return-path: X-Andrew-Authenticated-as: 0;andrew.cmu.edu;Network-Mail Date: 6 Jan 91 02:24:54 GMT From: zaphod.mps.ohio-state.edu!ceres.physics.uiowa.edu!iowasp.physics.uiowa.edu!sigwarth@handies.ucar.edu (John B. Sigwarth) Organization: Department of Physics and Astronomy, University of Iowa Subject: GUERAP III software Sender: space-request@andrew.cmu.edu To: space@andrew.cmu.edu I am looking for sources for the software GUERAP III. This software calculates the stray radiation scattered through an optical system defined by the user. I know of a commercially available source that wants $1500. for their "improved" version. They also told me that the orginal software is in the public domain. Does anybody know where a public domain copy might be available? E-mail to me directly and I will summarize any responses to the NET if there is interest. Thank you for your help. John Sigwarth -- John B. Sigwarth INTERNET: Sigwarth@Iowasp.Physics.UIowa.EDU The University of Iowa NSI: IOWASP::SIGWARTH Department of Physics and Astronomy 403 Van Allen Hall Iowa City, IA 52242-1479 (319) 335-1903 ------------------------------ Date: 4 Jan 91 00:13:18 GMT From: hpda!hpcuhb!hpihoah!jwatts@ucbvax.Berkeley.EDU (Jon Watts) Subject: Re: Hi girls... (part 2) I really shouldn't lower myself to responding to this kind of drivel, but sometimes you just can't resist. From: avery@netcom.UUCP (Avery Colter) >msdos@cs.mcgill.ca (Mark SOKOLOWSKI) writes: > >> - Maximum speed: 750 mph (that's 1250 km/h) (around 2 gallons per >> mile at that speed, after rough calculations) > >And what do you do if you need to put on the brakes? Common wisdom is that >a normal human's reaction time needs a sighting of danger at least 2 seconds >before impact. To decelerate from 750mph in 2 seconds would be more Gs than >the most air-hardened test pilot could handle. About 17g, near the death limit. Not to mention how you achieve it. I don't know where you get the 2 sec. from though, I think human reaction time is around 0.2 sec but that has nothing to do with how fast you slow down. If you do go from 750 mph to 0 in 2 sec. that gives you a stopping distance of ~1100 ft. not counting reaction time, you'd better be far sighted. > >Also, you must be Richie Rich to be able to afford a car which gets a half-mile >per gallon. Not that bad for someone who can afford a $10,000,000 car. > >> - 0-60 in 0.5 sec (aspiration system on the tires to keep it glued..) > >120 miles per second squared. Again, this much acceleration would likely >leave you crushed. > It's really not that bad, about 5.5g - nasty but indurable (with a gee suit and proper training). - Jon Watts ------------------------------ Date: Sun, 6 Jan 91 19:41:40 EST From: John Roberts Disclaimer: Opinions expressed are those of the sender and do not reflect NIST policy or agreement. Subject: Re: Interplanetary travel >From: John Roberts >Subject: Re: Interplanetary travel >>From: cs.utexas.edu!news-server.csri.toronto.edu!utgpu!cunews!cognos!geovision!gd@tut.cis.ohio-state.edu (Gord Deinstadt) >>Fusion engines are just the thing for travelling about in the solar >>system. Since the ideal reaction mass is 4 times the (payload+ > ------------------------------------------------ >>structure) mass, there is no point in having a higher-density fuel. > --------------- >>You just have to carry more reaction mass to compensate for the >>reduction in mass of the fuel. Consequently, for efficient (minimum- >>energy) operation, fusion is just as good as antimatter, provided >>the fusion reactor can be made light enough. >>Gord Deinstadt gdeinstadt@geovision.UUCP >I don't understand why that should be considered an ideal ratio. By the >classic equations, this should allow a total change in velocity of about >1.6 times the exhaust velocity, but why is that a particularly good number? After I posted that, it occurred to me that the concept of an ideal reaction mass ratio might have some significance for a specialized type of problem. Assuming a fixed mass for the rocket (minus reaction mass) and a fixed amount of energy to drive the reaction mass, what amount of reaction mass will result in the greatest total change in velocity for the rocket? I don't believe there's a straightforward answer unless a further constraint is added that the rocket operate with a fixed exhaust velocity. It is also assumed that all the energy used is converted to kinetic energy. Variables: m1 = mass of rocket (not counting reaction mass) E1 = total energy available for rocket drive x = reaction mass r = mass ratio = x / m1 Ve = exhaust velocity dV = total velocity change of rocket Initial formulae: dV = Ve * ln((m1 + x) / m1) (classical rocket equation) E1 = 0.5 * x * Ve^2 (total kinetic energy of exhaust) Derived equations: Ve = sqrt(2 * E1 / x) dV = sqrt(2 * E1 / x) * ln(1 + (x / m1)) = sqrt(1 / x) * ln(1 + (x / m1)) * sqrt (2 * E1) = sqrt(E1 / m1) * sqrt(2 / r) * ln(1 + r) <-- useful form It is possible to solve for r by finding the value that produces the greatest dV, or by differentiating one of these forms and finding the point where the slope equals zero, for example: dV/dx = sqrt(2 * E1) * ((1 / ((m1 + x) * sqrt(x))) - (ln(1 + x / m1) / (2 * x^(3/2)))) (set m1 = 1, dV/dx = 0, solve for x). By either method, I calculate that the ideal mass ratio r is 3.9215536345, which I suppose is pretty close to 4. ----------------- With this ratio, and within the described constraints, you can hope for a total change in velocity of dV = 1.1380775 * sqrt (E1 / m1). ------------------------------ While this math is very interesting, I'm not sure how applicable it is to interplanetary travel. The underlying assumption of this approach seems to be that energy is the most expensive resource in space travel, to the extent that the relative availability of reaction mass is not a factor. I suspect in many cases, the availability and expense of energy will be less of a problem than that of reaction mass. Does anyone know whether the math (and the conclusion) are correct? Note that I did not include relativistic terms, so this applies only to "low" velocities. Good luck to anyone wishing to include relativity. :-) John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ End of SPACE Digest V13 #032 *******************