Aucbvax.6248 fa.space utcsrgv!utzoo!decvax!ucbvax!space Sun Feb 21 05:24:17 1982 SPACE Digest V2 #111 >From OTA@S1-A Sun Feb 21 03:58:01 1982 SPACE Digest Volume 2 : Issue 111 Today's Topics: SPS tidal stabilization how old Titan II? twisting of orbital platforms ring a ding ding Using Titans L-5 Society "All those lovely Titans going to waste" ---------------------------------------------------------------------- To: SPACE@MIT-MC Reply-To: Space-Enthusiasts at MIT-MC SPACE Digest Volume 2 : Issue 110 Today's Topics: SPS tidal stabilization SPS tidal stabilization Using Titans ---------------------------------------------------------------------- Date: Friday, 19 February 1982 09:29-PST From: KING at KESTREL Subject: SPS tidal stabilization To: space at mit-mc, REM at mit-mc cc: King at KESTREL I'm back on line, at least for the moment. You can send to me and expect replies. This concerns your message about SPS stabilization by masses on the ends of booms. You don't need === - |S| - |P|=================(mass) |S| - === - . This - === - - |S| - (mass1) |P| (mass2) - |S| - - === - will serve. Note the kinship between the design and that of a bicycle wheel. Remember that spokes are tension members of a bicycle wheel. You may need to extend the effective length of the SPS by sticking booms off its ends. - | - - | - - ===== - (mass1) |SPS| (mass2) - ===== - - | - - | - I doubt this will be necessary, but I will try some computations when I get the time. (huh!) Dick ------------------------------ Date: 19 February 1982 15:44-EST From: Robert Elton Maas Subject: SPS tidal stabilization To: KING at KESTREL cc: SPACE at MIT-MC If you extend booms off the sides (to extend the base for the triangular support wires for the weights), they too must be supported, although since they are considerably shorter than the main booms you might get away with triangular-cross-truss aluminum beams instead of explicit support wires in large tringular position. -|X|- ------- |X| ------- ------- |X| ------- W SPS W ------- |X| ------- ------- |X| ------- -|X|- You see, when the SPS drifts out of correct attitude and the tidal force wants to pull the weights clockwise, the force on the upper-right (and lower left) guy wire is increased relative to the upper-left (and lower-right) wire, so the attach-point at top (and bottom) wants to be pulled clockwise, with the same torque as the original weights. The difference is the point of application is closer to center (thus higher thrust over shorter moment-arm) so cross-supported truss might be cost-effective where it wasn't for long distances such as all the way out to the weights. Note, if cross-supported aluminum beams are the standard way of building, using little robots that make the beams continuously at low cost, it may be cheaper to use beams everywhere rather than to use other things that must be tooled up specially. In that case, rather than have a weight or a pair of weights, just stick out a very very long beam and let it be its own weight (the part near the end is most effective, the part near the SPS is mostly wasted, but beam is so cheap we use the word in the singular like we use other bulk cargo on Earth...). Near the place where the beam attaches to the SPS we may need to attach triangular support for extra strength, perhaps we use beams for that too, thus achieving compressive strength needed during rocket firings. ------------------------------ Date: 20 February 1982 09:12-EST From: Robert Elton Maas Subject: Using Titans To: TAW at S1-A cc: SPACE at MIT-MC If we suddenly acquire a gigantic launch capability, put up a space station right away, or lots of parts that will be useful for making one. For example, we could put up tanks of oxygen etc. that are sure to be useful later no matter what our final design will be, and canned food, etc. If the space station is designed and built and waiting to be launched, put it up, otherwise just put up the accessories/supplies that we're pretty sure will be useful later. Maybe buy a space station from the USSR and put it up? ------------------------------ End of SPACE Digest ******************* ------------------------------ Date: 19 February 1982 2015-cst From: Bill Vaughan Subject: how old Titan II? To: space at mc 1t's 1982 unless Multix has got another time warp... so I make those titans to be 20 years old, not 30! (Old Titan II just fine thanx) ------------------------------ Date: 19 February 1982 2018-cst From: Bill Vaughan Subject: twisting of orbital platforms To: space at mc The scheme you are talking about is called "gravity gradient stabilization " and was first tried out on some very early Pioneers in about 1960 give or take a couple. It works. Basically you take a long thin rope with a mass (pendulum, plumb-bob, call it what you will) at one end and the satellite at the other. Some of the early schemes used two long thin ropes attached to top & bottom of satellite with weights at each end, like this: bob | The whole affair aligns its long axis | with the gravity gradient, i.e. normal towards | to the direction of orbit, or pointing the | towards the C.G. of the primary. Earth /-+-\ | | | bird | \-+-/ V | It works just like a plumb bob, or like the | tides, if you prefer. It doesn't need to be | rigid, because the ropes are in tension. In | fact, it is frictional damping in the ropes bob (I think) that makes the system settle down. ------------------------------ Date: 19 February 1982 2036-cst From: Bill Vaughan Subject: ring a ding ding To: space at mc the ring is a neat idea but there may be a problem. If the ring is rigid it is orbitally unstable; Larry Niven discovered this (or more likely somebody pointed it out to him) after RINGWORLD was published & the result was described somewhere (Analog?) but also in THE RINGWORLD ENGINEERS. I don't know whether a flexible ring is stable or not; my gut says it may be (since a discontinuous ring is stable) but man's guts were not made for orbital mechanics as witness the higher/faster/lower/slower discussion of a few days ago. ------------------------------ Date: 20 February 1982 02:50-EST From: Jerry E. Pournelle Subject: Using Titans To: TAW at S1-A cc: SPACE at MIT-MC The second meeting of the Citizens advisory council on National Space policy has one paper n the report that is relevent to this; we have ALWAYS underestimated our requirements for launch capability for both LEO and HEO. Even in terms of just communications, commercial, weather, and USAF payloads, it is likely that we will be feeling a real pinch in not many years. Thus if Titan could be used... It is interesting to develop space plans based on the cost of launches; Gary Hudson has worked out some interesting numbers. His idea of bringing cost down was to relax some reliability requirements, butr make each launch ten times cheaper. Payload costs become important under this sceheme, of course... ------------------------------ Date: 20 February 1982 02:53-EST From: Jerry E. Pournelle Subject: L-5 Society To: SPACE-ENTHUSIASTS at MIT-MC According to our membership figures, about 1/4 of the Society have some kind of professional connection with computers, and many are hackers... ------------------------------ Date: 20 February 1982 02:46-EST From: Jerry E. Pournelle Subject: "All those lovely Titans going to waste" To: Ciccarelli at PARC-MAXC cc: SPACE at MIT-MC, CICCARELLI at MIT-MC Arthur Kantrowitz (current Chmn of Board of L-5 Society) has an interesting story: back when first announcement of going to the Moon was made, the cost of putting a pound in orbit using Titan was about $2000. Figure that a 1,000,000 pound device could go from Earth orbit to Moon landing and back to Earth orbit, and that there was no real learning curve on the cost of a pound in oribt, the whole affair would be $2 billion. But when he asked why, he got very angry responses from White House and PSAC. turns out LBJ wanted some big high-tech factories in the South, and developing Saturn was the way to get that. How true the explanation is I wouldn't say; you can ask Arthur about it at the L-5 Convention if you come... ------------------------------ 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.