The Wide-field Infrared Survey Explorer (WISE) is a NASA MidEx mission which will survey the entire sky at 3.3, 4.7,
12 and 23 microns. As with most all-sky surveys, WISE results will address many fundamental topics, but the
passbands and sensitivity are particularly well suited to study the distribution and evolutionary history of brown dwarfs
and ultra-luminous IR galaxies. The two long wavelength bands will use 1024x1024 Si:As BIB detectors manufactured
by DRS Sensors & Targeting Systems. NASA ARC has optimized the operating parameters as well as conducted
detailed cryogenic performance and radiation testing of a prototype array. Dark current, noise performance, and radiation
test results will be reported.
Gravity Probe-B (GP-B) is a space mission that was launched in April 2004 that is intended to measure the prediction by General Relativity Theory that a rotating gravitational field, namely the Earth's, "drags" the space-time continuum by a definite amount. GP-B utilizes a telescope with silicon photodiode detectors. Light from a distant reference frame, namely, a star designated as IM Peg, is used to reference the orbital motion of the spacecraft about the Earth and Sun to within 200 milliarcseconds at a frequency of 10 Hz. Fine angular control of the spacecraft orientation uses the signals from the telescope detectors during the 55 minute portion of the orbit during which the star is visible. The performance of the detectors and the control system's resultant pointing are discussed.
The Gravity Probe B Relativity Mission uses a fused-quartz optical star tracking telescope as the sensor for the control system which points the spacecraft towards its guide star. The telescope is cooled to <5 K while the readout which uses photodiodes and JFET preamps operates at 72 K. It is mounted on the front end of the telescope with a thermal standoff. Analysis indicates that the telescope is capable of providing sub-milli-arc- second (marcs)pointing stability information with an angular pointing noise of (formula available in paper) for the guide star IM Pegasi. We describe the design of the telescope and test results under nominal operating conditions. Analysis of the expected performance of the telescope in flight, based on the test results, is also presented.
The spectral noise characteristics of Aerojet GaAs n-JFETs have been investigated down to liquid helium temperatures. Voltage noise characterization was performed with the FET in 1) the floating gate mode, 2) the grounded gate mode to determine the lowest noise readings possible and 3) with an extrinsic silicon photodetector at various detector bias voltages, to determine optimum operating conditions. Current noise characterization was measured at the drain in the temperature range 300 to 77 K. Device design and MBE processing are described. Static I-V characterization is done at 300, 77 and 6 K. The measurements indicate that the Aerojet GaAs n-JFET is a quiet and stable device at liquid helium temperatures. Hence, it can be considered as a readout line driver or infrared detector preamplifier as well as a host of other cryogenic applications. Its noise performance is superior to that of Si MOSFETs operating at liquid helium temperatures, and is equal to the best Si n-JFETs operating at 300 K