NASA Goddard Cryogenics Group

Thermal Stratification of Liquid Helium in the SHOOT Dewars

J. G. Tuttle
Hughes STX, Inc.

M. J. DiPirro and P. J. Shirron
Code 713, NASA/Goddard Space Flight Center
Greenbelt, MD 20771

The Superfluid Helium On Orbit Transfer (SHOOT) project was a Shuttle payload designed to demonstrate the technology needed to transfer superfluid helium between two Dewars in space. It was launched with normal liquid helium which was pumped to superfluid temperatures on orbit. During the 93 hour pre-launch ground hold, the liquid was thermally stratified, with temperatures of about 4.3 K at the top and rising slowly from 2.2 K at the bottom of each Dewar over time. This stratification was helpful, as it allowed for more efficient removal of the parasitic heat inputs. There were also temperature gradients in the dewars during the on-orbit pumpdown, with a much higher degree of beneficial stratification in the port Dewar than in the starboard. We describe the liquid temperature profiles during ground hold and on orbit pumpdown, discussing the effects of this stratification and comparing the performances of the two Dewars. We also discuss the results of a computer model of the isothermal pumpdown of a SHOOT Dewar on orbit.

Cryogenics.34(1994) 369.

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