order to support the measurements in the MSAM/TopHat program,
we have had to develop some new technology in a number
of areas. The most exciting of these are in cryogenics
and the detector systems. These technologies will be useful
for other measurements in the sub-millimeter wavelength
range, as well as those having demanding cryogenic requirements.
In cryogenics, we have developed an adiabatic
demagnetization refrigerator that can cool the detector
system below 0.1 K. This design was originally developed
for the SIRTF mission, and has been successfully flown
on the MSAM2 flight in June 1997.
In order to cool the detector system during the TopHat
mission, we needed to have a lightweight refrigerator
that will cool to 0.3 K for over two weeks at balloon
altitudes (approximately 120,000 feet). We have developed
a special (long hold-time cryostat)
to fill this need.
The TopHat detectors
are monolithic silicon bolometers that are optimized
for the Antarctic mission. We have also tested perforated
detectors that minimize sensitivity to cosmic ray events
(much lower cross section).
Concurrently, we are also developing an entirely new concept
in monolithic silicon bolometers, the Frequency
Selective Bolometer. This detector design allows a
stack of devices to simultaneously measure a set of predetermined
band passes (up to about 10). The form factor is such
that an array of these devices can be packed together
to form a small imaging array. For a description, download
"Frequency Selective Bolometers'' M. S. Kowitt (