The Passive Radiative Cooler is a three-stage unit designed
to cool two Focal Plane Assemblies to 83K: the Long-wave and
the Short/Mid-wave. At the same time, the Passive Radiative
Cooler will reject 136mW of power. The Passive Radiative Cooler
weighs 11 kilograms, and is composed of aluminum, Kel-F, magnesium,
Invar, glass-epoxy thermal isolators, and stainless steel.
The Passive Radiative Cooler operates in three stages; cold,
intermediate, and first. In the cold stage, the temperature
can drop as low as 74K under no-load conditions. In the intermediate
stage, the temperature stabilizes at 130 K, and finally, in
the first stage, the temperature reaches 230 K when the three-point
attachment anchors are connected to a room-temperature load.
At the end of the MODIS instrument’s life, the Passive
Radiative Cooler will provide a 3K margin to the 83K operating
temperature for the cold Focal Planes.