Paula Cleggett-Haleim
Headquarters, Washington, D.C.            June 24, 1991
(Phone:  202/453-1549)

Allen Kenitzer
Marshall Space Flight Center, Huntsville, Ala.
(Phone:  205/544-0034)


RELEASE:  91-95

FIRST ADVANCED X-RAY ASTROPHYSICS FACILITY MIRROR 
SHIPPED


   The first mirror for NASA's Advanced X-ray 
Astrophysics Facility (AXAF) space observatory was 
successfully completed at Hughes Danbury Optical System, 
Danbury, Conn., and shipped on June 12 to Eastman Kodak, 
Rochester, N.Y., for assembly.  This mirror will be 
paired with another already in its last polishing cycle 
and shipped by June 30.

   The shipment of these two mirrors will mark the 
culmination of a challenging 2 1/2-year period for the 
AXAF program.  The emphasis during this initial phase of 
the program has been to produce the first set of mirrors 
and then validate the manufacturing process.  The most 
sophisticated aspect of this activity is the highly 
complex measuring (metrology) stations, used to 
characterize the mirrors and guide the polishing 
activity.  The AXAF observatory will be composed of six 
nested pairs of mirrors to obtain high resolution x-ray 
images of the universe.  

   Based on preliminary data, the first mirror pair has 
an angular resolution of 0.37 arc second, better than 
the 0.5 arc second resolution objective.  The expected 
on-orbit accuracy will be significantly better, by a 
factor of 2, due to the weightlessness of space flight.  
The smaller the resolution the more distinguishable are 
the distant x-ray sources.

   During the fabrication of the first two mirrors, 
numerous technical challenges were surmounted including 
the elimination of disturbances as small as 1 millionth 
the force of gravity.  Another challenge was the 
development of several cross checks to validate the 
process.  These include comparative analysis across 
metrology stations, self-consistency checks and end-to-
end x-ray testing.  

   One such cross check detected a minute error of 0.03 
arc seconds in resolution, which was traced to a single 
sign reversal within the more than 200,000 lines of 
computer code used for metrology analysis.  This 
discrepancy already has been removed in the second 
mirror.  

   The AXAF team representing Hughes Danbury Optical 
System; Marshall Space Flight Center, Huntsville, Ala.;  
Smithsonian Astrophysical Observatory, Cambridge, Mass.; 
and TRW, Redondo Beach, Calif., is extremely pleased 
with the excellent quality of this first mirror set and 
the demonstrated capability of the metrology system. 

   AXAF is the x-ray component of NASA's Great 
Observatories program and is tentatively scheduled for 
launch in the late 1990s.

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