From: roberts@cmr.ncsl.nist.gov (John Roberts)
Newsgroups: sci.space
Subject: Re: COSTAR
Date: 15 Nov 92 22:15:43 GMT
Article-I.D.: cs.Bxs381.M9v.1
Distribution: sci
Organization: National Institute of Standards and Technology formerly National Bureau of Standards
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-From: roberts@cmr.ncsl.nist.gov (John Roberts)
-Newsgroups: sci.space
-Subject: COSTAR
-Date: 14 Nov 92 03:04:57 GMT

--From: prb@access.digex.com (Pat)
--it's essentially three little mirrors on a sliding arm on a giant optical
--bench (phone booth sized).  each of the little mirrors is calibrated
--to adjust each of the intruments.

-There was a replica of COSTAR on display at the World Space Congress.
-I couldn't make head or tail of it. (An explanatory video would have
-been useful, but I didn't notice one.)

NASA Select showed a video yesterday. Essentially, four of the instruments
are in "phone booth size" packages mounted at the end opposite the aperture,
apparently installed from the back. These instruments have small holes in the
front for the (off-axis) input from the secondary mirror to enter. One of these
instruments is the High Speed Photometer, which is replaced by COSTAR.

Once installed, COSTAR extends a triangular truss toward the front of the
telescope. This truss holds three small pairs of mirrors, one of each pair
facing the front of the telescope, and the other facing the back.

Once the truss is extended, it pivots about the leg closest to the 
"centerwards" corner of the COSTAR box, apparently about 180 degrees,
swinging it more nearly in front of the other instruments. (The long axis
of the truss remains aligned with the long axis of the telescope.)

Once the truss is in place, the three pairs of mirrors swing out from the
truss to carefully assigned positions. Light from the secondary mirror
bounces off the front-facing mirror of each pair (situated toward the back
of the truss), then off the front mirror of each pair (located toward the
front of the truss), then into the original aperture of each instrument.
This therefore adds two reflections to the optical path of each instrument.
The angle and curvature chosen for the COSTAR mirrors presumably adds the
correction to compensate for the error in the primary, plus a correction
for the longer optical path, plus (I assume) a correction for the fact 
that the front-facing mirrors have to be offset from the original aperture
openings, so the "off-axis angle" is different from what it originally was.

It's also necessary to block the original light path into the apertures.
This appears to be done by the rear-facing mirrors at the front of COSTAR,
which are rather large, and presumably painted black on the back.

That's just my interpretation of the video - corrections or amplifications
would be welcomed.

Also, I'm not sure where WF/PC is located relative to the other instruments.

Another video shows the making of the 1/3 scale MSU mockup of NASP.
It's hollow, and opens in the back - the wings stow inside for shipping.
Some of the techniques developed for the building of the model may have
further aerospace application. It's 50 feet long, and weighs 5000 pounds.

John Roberts
roberts@cmr.ncsl.nist.gov
Newsgroups: sci.space