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Date: Sun, 29 Jul 1990 01:53:32 -0400 (EDT)
Subject: SPACE Digest V12 #145

SPACE Digest                                     Volume 12 : Issue 145

Today's Topics:
	   Re: Free Space Station - spacious but needs work
	    Test method for HST primary  (rebroadcast...)
			Re: slowing the earth

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----------------------------------------------------------------------

Date: 28 Jul 90 14:00:17 GMT
From: swrinde!emory!wa4mei!ke4zv!gary@ucsd.edu  (Gary Coffman)
Subject: Re: Free Space Station - spacious but needs work

In article <2609@mindlink.UUCP> a684@mindlink.UUCP (Nick Janow) writes:
>
>I did mention that the framework and equipment would have to allow enough room
>for the fuel volume required for launch.  The mass doesn't matter as much,
>since it would be going up anyways.  Leave the shuttle itself empty if
>necessary; you're saving a lot in very expensive/dangerous labour.  The
>additional mass in the tank might cause problems by being off the center of the
>main engines' thrust, but the idea is worth considering.

Leaving the shuttle empty means you're paying for an entire shuttle
launch just to get the external tank in orbit. This is not cost effective.
If another payload can absorb most of the cost, (the tank already goes
98% of the way to orbit so you only need pay for the remaining 2%), then
the proposal looks much better. If you can keep the additional mass added
to the tank to under 10,000 lbs then we already know that the tank mounts
can handle the stress. This is the amount of mass saved from the original
painted tanks to the current tanks.

Gary

------------------------------

Date: 29 Jul 90 04:35:59 GMT
From: uoft02.utoledo.edu!fax0112@tut.cis.ohio-state.edu
Subject: Test method for HST primary  (rebroadcast...)


This is a sort of repost of my previous message detailing the test
that was performed on the HST primary (not this does not work for
the secondary).

A method widel used is a variation on the Michelson interferomter
called the Twyman-Green inter.  Picture the standard MI, but replace
the movable mirror by the telescope mirror and a null or positive lens.
The lens and mirror are placed so that thier optical axes coincide, with
the focal point of the lens coincident with the center of curvature
of the mirror.  The other change is to replace laser plus beam expander
for a light source, with the pinhole in the beam expander placed at the
foacal point of the input collimator lens.  If the lens-mirror combination
is not perfect (and alignment is) then a pattern similar to that seen
with a knife edge test on a imperfect image is seen.  If there is a tilt
in the alignment distorted fringes will be observed.  Note that this
tests the lens-mirror combo and not the mirror alone.  For further
details see "Optical Shop testing" by Malacara, D. (ed) 1978 or
Astronomical Optics by D Schroeder (1987).

This test was performed on the HST primary.  If the flaw is in the
primary that means that either the test was done incorrectly or that
the null lens was imperfect.  Seems unlikely to me that the lens would
be incorrect to perfectly mask the error in the primary unless they
were generated from the same (incorrect) computer numbers.  SPeculation
seems to be centering around the primary but this is not confirmed yet.
It is my understanding that if the flaw is in the primary this test
should have caught it!  I have heard that PE threw out some test
results that disagreed with other, 'more sophisticated' methods.
Perhaps this is what they were referring to but I do not know.  We
still need more info.

Robert Dempsey
Ritter Observatory

------------------------------

Date: 28 Jul 90 17:41:14 GMT
From: mentor.cc.purdue.edu!mace.cc.purdue.edu!dil@purdue.edu  (Perry G Ramsey)
Subject: Re: slowing the earth

In article <9007272338.AA20105@cmr.ncsl.nist.gov>, roberts@CMR.NCSL.NIST.GOV (John Roberts) writes:
> 
> >From: dil@mace.cc.purdue.edu  (Perry G Ramsey)
> 
> >A big linear accelerator facing west.  Pick up some rocks and shoot them
> >into space.  Chuck enough rocks out fast enough and you could make a dent.
> 
> Good point, but you're going to have a lot of trouble slowing the earth's
> rotation by throwing rocks to the *west* ! :-) :-)
>       John Roberts

John is right.  Throw the rocks to the EAST.

Another person noted that the universe is 1.3e10 years old, not 1e13.  This 
means that, if you want to get in in in under the age of the universe
you need about 10,000 nuke plants.  Now we're never going to get the idea
past the Sierra Club.


-- 
Perry G. Ramsey           Department of Earth and Atmospheric Sciences
perryr@vm.cc.purdue.edu   Purdue University
dil@mace.cc.purdue.edu    We've looked at clouds from ten sides now, 
			  And we REALLY don't know clouds, at all.

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End of SPACE Digest V12 #145
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