LMSC NSSC-1 Target Acquisition Tests; February, 1985

D. Lindler, A.L. Kinney, and H.C. Ford

September, 1985 CAL/FOS-021

For the NSSC-1 binary search target acquisition tests of February,
1985, a star field was simulated by using a platinum lamp, the double
0.l aperture, and the G19OH grating. By processing diodes 270
through 286, this configuration resulted in a pseudo-star field
containing six point sources. These sources are made up of the lines
at 1907.493, 1911.702, and 1916.083 k whicb are imaged once in each
aperture. Using tbe NSSC-1 the test then attempted to flnd one of
these sources and put it on the edge of the diode array.

For the binary search test, three ofthe parameters varied; YNBRT,
NMAX, and NMJN. Each setting of pararneters was testedwith three
different starting values of YBASE. Of the 16 cases run, five failed
due to incorrect YBASES and an additional four failed because there
were not enough y steps to put the target on the edge. These problems
have been corrected; YBASE apparently needed a Ionger waif time when
initially set in a binary searcb sequence, and the maximum number of y
steps has been increased from five to eight. One additional case was
run with NMAX and NMJN set to exclude all sources in the field. This
case failed in the correct way, that is, the correct value of YGIVUP=
10 was returned.

The binary searcb centering accuracy in the y direction is a function
of the maximum count rate and the response of the diode edge to a
point source. We do a linear fit to the data to show that the slope at
half of the peak signal is 3% of the response (see Figure 7). Using
this value, achieving y centering to 1 micron accuracy with ±3o
certainty requires that the sum of the counts per y step exceed 5000.

The target acquisition test showed that in general the software logic
was correct and working. To rectify the problem with YBASEs, changes
have been made in the target acquisition procedure (proc) and to
rectify the problem with y steps changes have been made in the flight
software. The proposed target acquisition test of August 1985 will
check that these changes have been correctly implemented.