Description of COBE Cooling System Schematic

This diagram represents the cooling system used by COBE. The diagram shows the helium coolant in its tank at a temperature of 1.5 Kelvin. Helium vapor evaporates from the liquid in the tank, then flows through the tubing, eventually being vented to space at a temperature of 150 Kelvin. The outer shell of the cooling system, called the Main Shell, is at a temperature of 150 Kelvin. The tube through which the helium vapor flows does not go directly from the helium tank to the outside. The tube connects to 3 sheet metal shields between the helium tank and the main shell. These shields block the path of thermal radiation from the relatively warm surface of the main shell. These shields are cooled by the helium vapor flowing in the vent tube. The inner shield is at 10 Kelvin, the middle shield at 40 Kelvin, and the outer shield at 70 Kelvin. Between each pair of shields is a ablanket of multi-layer insulation. There is also multi-layer insulation between the inner shield and the helium tank, as well as between the outer shield and the outer shell. The insulation reduces the amount of heat conducted in to the helium tank. There is also some heat conducted to the helium tank along the support straps, which hold the helium tank in place. There are 12 support straps.