Continuing
the structure MTM (Mechanical Test Model) assessment conducted this spring,
thermo-vacuum tests were performed on the heat model (TTM: Thermal Test
Model). The photograph shows the condition just before the tectum is closed
within the space chamber. The portion in the upper part of the image is
liquid helium cryostat inside the 70cm aperture telescopic observation
apparatus. The part in the lower half of the image is the bus part, which
includes common equipment for communication, power supply and positional
regulation, etc.
Many ideas are being considered to increase the longevity
of the liquid helium as much as possible with the ASTRO-F. One such idea
is to keep the cryostat’s external wall temperature as low as possible
by radiation cooling. However, this is unknown without confirming the
actual temperature of the cryostat part in space using the thermo-vacuum
test. Therefore, a thermo-vacuum test was performed with liquid helium
inserted into the cryostat while the tank pressure was reduced with a
pump from ouside the space chamber and the liquid helium was made superfluid.
The pipe seen on the right of the body in the photo is the reduced pressure
line.
Moreover, because the cryostat is large and complex,
it takes many days to stabilize the internal temperature distribution.
Therefore, the space chamber operation took 20 days from November 8th
until 27th, a long time compared to usual assessment periods with thermo-vacuum
tests.
Fortunately, the assessment proceeded smoothly, and
two other types of space-imitating assessments were also performed, resulting
in valuable data. This result will reflect on FM (Flight Model) production,
and it is thought that in this way the ASTRO-F will become a more reliable
system.
