Transferring Superfluid Helium in Space

A preliminary concept of a system for resupplying superfluid helium in space has been developed at NASA Ames Research Center. Such a system would greatly enhance several planned scientific missions. These include the Space Infrared Telescope Facility (SIRTF), Large Deployable Reflector (LDR), Gravity Probe-B (GP-B), Hubble Space Telescope (HST), and Advanced X-ray Astrophysics Facility (AXAF). Resupplying helium in orbit would extend the lifetime for each of these missions without the difficulties, delays, and costs associated with retrieving the system, resupplying on the ground, and relaunching. This is especially true of systems such as the LDR that are assembled in space. A simple thermodynamic model of a transfer system is presented and discussed. The different thermodynamic regimes that can be expected in the transfer line are also discussed. The relations between these regimes are used to evaluate the relative efficiencies of different transfer techniques that could be used with the transfer system. The efficient transfer of liquid helium requires a low heat leak into the transfer line, particularly at point sources such as the coupling. It is also shown that the proper selection of supply tank temperature is critical during helium resupply.