|COBE Engineering Information
from the Cryogenics & Fluids Branch
Goddard Space Flight Center.
Michael S. Rhee, Gary Agranat
The sensitivity of the FIRAS and DIRBE detectors is highly dependent on their operating temperature. The temperature is set primarily by the flow conductance of the dewar vent. An analysis of the flow, incorporating helium thermodynamic properties was completed and, as a result, the "E-Fitting" on the vent was changed. The dramatically reduced flow impedance resulted in excellent detector sensitivity. The vent analysis correlated well with on-orbit conditions, confirming other dewar temperature data and lifetime predictions. The analysis was performed by Code 713 (now Code 552).