THERMAL STRATIFICATION OF LIQUID-HELIUM IN THE SHOOT DEWARS

The Superfluid Helium On-Orbit Transfer (SHOOT) project was a shuttle payload designed to demonstrate the technology needed to transfer supe rfluid helium between two Dewars in space. It was launched with normal liquid helium which was pumped to superfluid temperatures on-orbit. D uring the 93h prelaunch ground hold, the liquid was thermally stratifi ed, with temperatures of almost-equal-to 4.3 K at the top and rising s lowly from 2.2K at the bottom of each Dewar over time. This stratifica tion was helpful, as it allowed for more efficient removal of the para sitic 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 t he liquid temperature profiles during ground hold and on-orbit pumpdow n, discussing the effects of this stratification and comparing the per formances of the two Dewars. We also discuss the results of a computer model of the isothermal pumpdown of a SHOOT Dewar on-orbit.