Aucbvax.6156 fa.space utcsrgv!utzoo!decvax!ucbvax!space Thu Feb 11 16:03:46 1982 SPACE Digest V2 #104 >From OTA@S1-A Thu Feb 11 15:31:16 1982 SPACE Digest Volume 2 : Issue 104 Today's Topics: shadows on power satellites. . . Re: watmath.1678: Mooning Around Solar power satellite not usually eclipsed by earth Lunar SPS (Solar Power Station, not satellite) Shuttle Progress Space News ---------------------------------------------------------------------- Date: 10 Feb 1982 11:32:33-EST From: csin!cjh at CCA-UNIX To: space at mit-mc Subject: shadows on power satellites. . . It looks like we have a lot of people who weren't here the last time this went around. . . . The Earth's shadow for any low orbit is effectively a cylinder with r .= 4000 miles (farther out you have to imagine a cone with this as base); this means that a powersat in GEO is in shadow for (at a rough average) 4/(26.2 * pi) or around 1/20 of its orbit. There are all sorts of variations in this (because it should travel in equatorial plane rather than ecliptic, it might not be shadowed at all during the solstices). ------------------------------ Date: Wed Feb 10 09:28:38 1982 To: Space at MIT-MC From: ucbvax!decvax!duke!phs!dennis at Berkeley Subject: Re: watmath.1678: Mooning Around Source-Info: From (or Sender) name not authenticated. A synchronous powersat would NOT be in earth's shadow half the time; it's much less than that. The shadow goes directly away from the sun, not outwards at the terminator. Planar platforms wouldn't tend to tumble; they would tend to align the long axis toward the planet; some sort of stabilizing thruster would be needed. A better thing than putting two power stations on the Moon is putting three at 120 degree intervals. That way somebody always has a good angle on the sunlight. If the moon were exactly in the ecliptic, there would be a lunar eclipse every full moon. It's pretty far off, but my books are far, far away and I can't give the right number. ------------------------------ Date: 10 Feb 1982 13:36:12-PST From: A.exp at Berkeley Subject: Solar power satellite not usually eclipsed by earth The difference in orbital plane of the solar power satellites around the earth and the earth around the sun prevents eclipse all but about 98% of the time (or more, but I can't be sure). ------------------------------ Date: 10 Feb 1982 14:19:15-PST From: jef at LBL-UNIX (Jef Poskanzer [rtsg]) To: space at mit-mc Subject: Lunar SPS (Solar Power Station, not satellite) The antenna size and feedback loop problems both go up only linearly with increased distance of transmitter. The moon is ten times as far as GEO. Thus the transmitting and recieving antennas must be sqrt(10) times as big (their PRODUCT must be 10 times as big), and the earthside reference transmitter must lead the recieving array by kilometers instead of 100's of meters. (For those of you who haven't come across the rule-of-thumb for minimum antenna sizes before, it's: d d = l lambda 1 2 where d1 and d2 are the antenna sizes, l is the distance between them, and lambda is the wavelength you want to transmit.) So, the extra distance of a lunar SPS is a disadvantage, but not a big one. As was mentioned before, there are obvious advantages: the materials are available locally, we don't have to cope with the unknowns of zero-G engineering. The day/night problem remains, though. One suggested solution was two SPS's on opposite sides of the moon. I think you would want three, but either way, this either requires relay antennas in orbit (in which case, why not build the SPS there in the first place??!?), or a power transmission grid on the moon's surface. Since the grid would have to cover many thousands of km, it had better be superconducting. So here's my question: what about superconducting cables on the moon? Would simply shielding them with a mirror keep them cool enough, or is refrigeration necessary? --- Jef ------------------------------ Date: Wed Feb 10 20:58:19 1982 To: Space at MIT-MC From: ucbvax!ihnss!vax135!harpo!npois!rabbit!sjb at Berkeley Subject: Shuttle Progress Source-Info: From (or Sender) name not authenticated. Testing of Columbia inside the VAB has been rescheduled due to a leak of hydraulic fluid and a problem with the SRB's. However, in spite of these, officials now hope to get the shuttle rolled out to pad 39A on 16 February, a day earlier than the last early date, and the launch was still scheduled for 22 March. Workers will repair the leak and replace a ``nozzle actuator,'' which steers the nozzle of the SRB in flight, while astronaut crews take part in simulated tests of the upcoming mission. The sims will takes place one day early each, thus saving (hopefully) a day. These will start at 1000 EST Thursday. Roll-out is now scheduled to begin at 0500 EST Tuesday (the 16th), with preparations finished by Sunday or Monday. ------------------------------ Date: Wed Feb 10 20:54:40 1982 To: Space at MIT-MC From: ucbvax!ihnss!vax135!harpo!npois!rabbit!sjb at Berkeley Subject: Space News Source-Info: From (or Sender) name not authenticated. NASA officials today asked Congress to approve money for a fifth space shuttle, citing that the fleet of four will not be enough to meet demands of those who want to launch cargo into Earth orbit. Last year, NASA signed up 41 customers who will pay to have their satellites launched with either the shuttle (upon operational readiness) or expendable boosters, (to be phased out slowly). A launch schedule was released, containing plans for 70 flights up to September, 1987, with most of them being multi-payload. These contain (in order of most to least) communications satellite, DoD cargo (usually secret), scientific instruments, and the European Spacelab. NASA plans 24 shuttle launches per year by 1988. Major General James Abrahamson, head of the shuttle project, said that when one of the shuttles needs to be taken out of action, be it for repairs or to fix a major accident, a fifth would smooth out launch schedule disruptions. The Columbia is scheduled to launch on its third test flight on 22 March, with STS-4 on 7 July and then it's first operational flight (with two communications satellites) is to come on 11 November. Challenger is scheduled to be delivered in June, with its maiden flight in January, 1983. Discovery is to be delivered in September, 1983 with Atlantis to follow in December, 1984. STS-4 will land at Edwards, in contrast to earlier hopes of landing on the runway at Cape Canaveral, to gain further descent and landing data. On the November, 1982, launch, the first shuttle spacewalk, utilizing a new jack backpack, may be made. New, lighter heat-protective tiles will be installed on Discovery, thus lightening it by 3500 pounds. Lighter external tanks and SRB's are also being developed. ------------------------------ End of SPACE Digest ******************* ----------------------------------------------------------------- gopher://quux.org/ conversion by John Goerzen of http://communication.ucsd.edu/A-News/ This Usenet Oldnews Archive article may be copied and distributed freely, provided: 1. There is no money collected for the text(s) of the articles. 2. The following notice remains appended to each copy: The Usenet Oldnews Archive: Compilation Copyright (C) 1981, 1996 Bruce Jones, Henry Spencer, David Wiseman.