Weight Reduction Approaches for Helium Flight Dewars

Abstract

The dry weight of conventional helium flight dewars has been 3.4 to 7.2 times the weight of the contained liquid helium; the larger the dewar, the lower the weight ratio. For long life systems, the dewar weight can be the major weight subsystem of the satellite. To keep launch costs down, it is often necessary to reduce the satellite weight in order to launch on a smaller and lower cost launch vehicle. The cost of reducing the dewar weight is normally substantially less than the cost of upgrading to higher lift launch vehicles. The approaches described in this paper include going to lower density, higher modulus aluminum-lithium alloys, using advanced construction (waffle, ring stiffening) for the compression critical vacuum shell and helium tank, and changing to perforated aluminum honeycomb vapor cooled shields from monocoque shields. Weight savings as high as 22% of the dry weight are possible, using the Gravity Probe-B (GP-B) dewar as an example.

Work supported through Stanford University, via subcontract PR 4660 and NASA contract NAS 8-36125 with the Marshall Space Flight Center