Reduced Gravity Cryogenic Storage and Transfer
The storage and handling of cryogenic fluids will be needed to support missions beyond low Earth orbit. Technology to effectively store, manage, and transfer propellants over long periods in space would improve mission feasibility and affordability.
Flight experiments are needed to test and validate key capabilities and technologies required for the storage and transfer of cryogenic propellants to and from advanced propulsion stages and propellant depots. The ISS could play an important role in validating long-term storage and handling of cryogenic propellants. Technologies to be demonstrated include:
• Cryogenic fluid instrumentation and sensors
• Passive thermal control
• Active thermal control
Instrumentation and sensors are needed to ascertain and monitor fluid mass and location in reduced gravity tanks. Cryogenic systems include passive techniques (such as multilayer insulation and vapor-cooled shields), as well as active thermal control techniques (such as cryocoolers) to manage remaining heat leaks after passive techniques are applied. In addition to supporting cryogenic propellant storage and transfer, active thermal control technology can enable long-term storage of consumables such as LOX for human missions and support scientific instruments that require cryogenic conditions. The 2011 NRC decadal survey Recapturing a Future for Space Exploration: Life and Physical Sciences Research for a New Era recommended near-term research and technology development in zero-boil-off propellant storage (both passive and active techniques) and cryogenic handling and gauging (NRC, 2011a). These technologies are approaching a high level of technical maturity but remain to be tested and demonstrated in a reduced-gravity environment.
Recommendation. Cryogenic Storage and Handling. Reduced-gravity cryogenic storage and handling technology is close to a “tipping point,” and NASA should perform on-orbit flight testing and flight demonstrations to establish technology readiness.
Relevance of High-Priority Technologies to National and Commercial Space Needs
When pursuing the 16 technologies recommended by the steering committee as high-priority efforts in the next 5 years, it is useful to simultaneously consider the value of those technologies to the interests of others outside NASA, specifically those that address broader national needs as well as the needs of the commercial space industry. Alignment with national and commercial needs outside NASA (both aerospace needs and non-aerospace needs) was a scoring category used by the panels as they made their initial assessments of all the level 3 technologies, although the weighting factor given to this category was not high relative to other categories such as benefit and risk. The steering committee identified those technologies that would either be essential or could make a significant contribution to national and commercial space interests outside NASA (shown in Table 3.13). In the case of national needs— for example, dual-use technology of interest to the Department of Defense— this information shows those technologies that offer the best chance to partner with other government institutions through sharing of information and resources.
The technologies shown in Table 3.13 were selected based on NASA’s most critical needs and highest priorities. NASA is the first and primary user, although there is relevance to other national interests. The strong importance of commercial space activities to NASA was recognized by the steering committee, and this relationship is discussed further in Chapter 4.