Compact High-Pressure Compressor for Efficient Gas Transfer in Space

Future space exploration missions will call for extended, complex operations in space or on lunar and planetary surfaces, including many that require the efficient transfer and compression of gaseous propellant, pressurant, expendables, or products. Storage pressures may be extremely high, and gases of interest range from helium (He) to xenon (Xe). We have developed an innovative, compact compressor that will enable emptying essentially all the gas from a supply vessel while pressurizing to extremely high pressures (up to 6,000 psia) in a receiver vessel. Our innovative compression and drive technology enables isothermal compression of any gas using high-reliability components that provide high rates of transfer, maintain ultrahigh gas purity, provide accurate measurement of the transfer rate, and simplify integration with spacecraft systems. We have built a prototype compressor and demonstrated operation of the critical components, including prototypical, positive displacement compression heads, an all-welded structure for pressure containment, miniature high performance check valves, extremely low dead volumes that enable very high pressure and density ratios, and isothermal gas compression. Results of these tests show that all gases can be transferred from a supply to receiver vessel with extremely high efficiencies. Final density ratios (receiver/supply) have been measured in the range of 20:1 to 350:1, depending on whether the compressor is operated in a single- or two-stage configuration. We have demonstrated operation with helium, nitrogen, carbon dioxide, krypton, and xenon. Key components have been tested beyond 750,000 cycles with no sign of performance degradation. Gas transfer data agree extremely well with analysis models for isothermal compression, demonstrating that all gases can be compressed to extremely high pressure ratios without significant increases in temperature. Isothermal compression ensures maximum gas transfer per cycle, maximizes the overall flow rate, and enables simple calculation of the gas flow rate during transfer. System demonstrations to date have coupled the compressor heads with a laboratory drive system. We have developed conceptual designs for a flight configuration with a compact, self-contained drive system. These designs show the potential for a compact flight unit with inlet volumetric flow capacity up to 5 L/min.