The SGD will detect “soft” gamma-rays with energies in the range 60-600 keV. To do this, the SGD sensors must be operated at a temperature of -20 degrees. But the SGD will be mounted on the outside panel of the Astro-H satellite, where it will be exposed to radiant heat from both the sun and the earth. Further, the spacecraft panels, the LSI and amplifiers will also serve as sources of heat input. All of this will tend to raise the temperature of the SGD and so to combat this the heat will be conducted away via a heat pipe to a radiator. Also the MLI will be surrounded by multiple layers of aluminum foil which will serve to block the input of heat to the SGD.
Another concern is electrical discharges in the vacuum environment of the spacecraft. This is a concern because the semi-conductor devices will be operated at high voltages ranging from 200-1000 volts. Tests must therefore be carried out to assess this danger as well. To this end, last week thermal and electrical tests were begun in the 8 meter long thermal vacuum chamber at the Tsukuba Space Center. In the picture, the SGD-2 has been installed in the center of the 8-meter vacuum chamber. The SGD is surrounded by heating units which will control the temperature. Around the periphery, liquid nitrogen is circulated to maintain the required low temperature, simulating the space environment. Because the SGD will be directly exposed to this space environment these ambitious tests are very important.
In the next picture, commands are sent to the SGD using the same kind of system that will be used with the satellite. Signals are sent to turn on the power and apply the high voltage to the SGD, and data acquisition begins. The next picture is taken deep in the night as the data are still being monitored. These ambitious experiments are run around the clock and so of course different staff members are on duty during the day and at night. This particular experiment is expected to run for 10 days continuously, and the graduate and under-graduate students from around Japan took part.
The SGD-1 thermal vacuum tests were finished last December and no problems were found.