Aucbvax.6247
fa.space
utcsrgv!utzoo!decvax!ucbvax!space
Sun Feb 21 05:23:32 1982
SPACE Digest V2 #111
>From OTA@S1-A Sun Feb 21 03:25:19 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
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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 <REM MIT-MC AT>
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 <REM MIT-MC AT>
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 <VAUGHANW AT HI-MULTICS>
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 <VAUGHANW AT HI-MULTICS>
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 <VAUGHANW AT HI-MULTICS>
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 <POURNE MIT-MC AT>
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 <POURNE MIT-MC AT>
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 <POURNE MIT-MC AT>
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
*******************
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