Description: The most promising propellant subcooling systems for LH2 require compression systems that involve development of significant head. The inlet pressure for these systems is typically on the order of 1.4 psia with a discharge pressure requirement above atmospheric pressure. In the past this has required multiple stages of compression by machines operating at high speeds on ball bearings. The bearing life in these machines was at most a few hundred hours. While this is feasible to use for a proof of concept test system, it is not acceptable for the H2 compressors in application at the launch pad. It is desired to replace these grease-packed ball bearings with foil bearings to greatly increase compressor life. Additionally higher speed can eliminate several stages thus reducing complexity and cost of the system. If this technology proves feasible it could finally make densified LH2 propellant a reality for future launch and space applications.

Benefits: The potential applications for this technology at NASA are widespread. In addition to propellant densification for use in liquid rocket engines at launch, there are also applications that involve long term in-space storage of the propellants to be used on vehicles over months or years. By subcooling the propellant it drastically reduces boil-off of the cryogens over time and thus improves storage life. The applications include on-vehicle propellant storage for long range mission and propellant depots that are planned for space. Liquid cryogenic injection at the foil bearing also makes sense for rocket engine turboumps. This bearing innovation for LOX and LH2 turbopumps could greatly increase life over the ball bearings currently used which will be especially appealing for the long range missions planned for the future.

There are also numerous applications outside of NASA. Numerous private companies are currently designing and building rockets that use turbopumps. Many of these applications are seeking longer bearing life and would greatly benefit from this technology. Grease-packed ball bearing cryogenic H2 circulators are currently in use for neutron sources and flux reactors at facilities around the world. In each of these applications longer bearing life along with the possibility of attaining even higher speeds are needed. There are also numerous other applications involving cryogenic He expanders and compressors in superconducting magnet cooling and refrigeration that could greatly benefit from this technology.