In support of NASA’s Constellation Program, all NASA centers have organized their skills and resources to plan future missions to the moon, Mars and beyond. NASA’s Cryogenic Fluid Management (CFM) Project is performing experimental and analytical evaluation of several areas of propellant management systems to enable safe and cost effective exploration missions.

CFM is led by NASA’s Glenn Research Center who has partnered with Marshall Space Flight Center, Johnson Space Center, Ames Research Center, Kennedy Space Center and Goddard Space Flight Center. CFM is sponsored by the Exploration Technology and Development Program Office.

By performing testing and analysis, the CFM Project team must prove that cryogenic propulsion is a viable propellant alternative. Non-toxic propellants are being tested for their performance and ability to reduce overall system mass. The CFM team is investigating the storage and distribution of non-toxic propellants. If the project’s goals are realized, non-toxic, cryogenic propellants could be used by the lunar lander and become the NASA standard for future exploration vehicles.

Cryogenic propellants have been favored for their high-energy, high-efficiency performance and are commonly used to lift off of the surface of the Earth. However, cryogenic propellants have not been used in extended duration space missions since they are difficult to store for long time periods in space and on the moon at temperatures low enough to maintain them in a highly dense, liquid form. Performance requirements for the Earth Departure Stage (EDS) and the lunar lander descent and ascent stages point toward the use of cryogenic engines and propellants for missions of up to 210 days on the surface of the moon.
  

Cryogenic propellant storage and distribution concept for the lunar lander.

Cryogenic propellants include liquid hydrogen and liquid methane (fuels) and liquid oxygen (oxidizer). The fuel is combined with oxygen to provide thrust. Hydrogen appears ideal as a propellant for the EDS and lunar lander descent stage when the most energy is needed to launch the spacecraft toward the moon, insert it into lunar orbit, and descend to the surface of the moon. Methane, a denser fuel with a higher normal boiling point than hydrogen, is a prime candidate for propelling the lunar lander ascent stage off of the surface of the moon after up to a 210-day stay.

CFM focuses on the storage, fluid distribution, liquid acquisition, and mass gauging of cold propellants. The overall objective of these tasks is to reduce the development risk and increase the technology readiness of advanced CFM subsystems to store and distribute cryogenic propellants required for long-term exploration missions. CFM utilizes the development of prototype CFM hardware, the creation and use of analytical models to predict subsystem performance, and the execution of ground-based tests using liquid oxygen, liquid hydrogen, and methane to demonstrate the performance, applicability, and reliability of CFM subsystems.

Feed system for Cryogenic Liquid Reaction Control System during build up.

Storage: Cryogenic propellants must be stored in liquid form at temperatures below or near their boiling point in a manner that is both safe and efficient in space and on the moon, with minimal propellant loss. The project will develop prototype subsystem hardware for tank thermal and pressure control and perform ground-based tests to demonstrate applicability and reliability using liquid oxygen, liquid hydrogen, and methane. It will also address the efficient on-orbit and surface storage of these cryogens.

Distribution: When the fuel is needed for thrust, it must travel through a series of insulated feed lines that lead to the engine. Some of these lines are very small and difficult to keep cold. The project will develop and test feed-system concepts that effectively distribute propellants. This task is critical to the reliable distribution of cryogenic propellants to an Orbital Maneuvering Systems (OMS)/Reaction Control Systems (RCS) propulsion system.

Top left: Conceptual design of screened Sump for lunar lander ascent module liquid acquisition. Top right: View of Liquid Acquisition Devices test screen through window during bubble point tests. Bottom middle: Channel outflow test article.

Low g propellant management: This effort is critical to the successful liquid propellant delivery to the OMS/RCS propulsion system and the allowance of smaller propellant tank residuals to assure mission success.

• Liquid acquisition ensures that liquid is successfully delivered under reduced gravity conditions to the OMS/RCS system without any vapor. These devices prevent gas and vapor from leaving the tank and entering critical systems that require liquid only feed. They account for liquid positioning within the tank in a microgravity environment and from any residual accelerations imparted on the fluid by firing either the main or steering thrusters.

• To ensure mission safety, mass gauging is vital to effectively measure how much propellant is currently in a storage tank. Mass gauging technologies must accurately measure propellant quantities in zero-gravity where liquid settling cannot be assumed. (Liquid settling occurs when the liquid propellant is temporarily forced to one side by the force of the firing engines.) Several promising techniques are currently under development including the pressure-volume-temperature (PVT) method and the optical mass gauge (OMG), which senses the fluid quantity by measuring absorption of light in a tank. A third option is the Radio Frequency (RF) mass gauge that emits a radio frequency signal and measures the electromagnetic resonances of the tank to infer the quantity of propellant.

Integrated Testing: To test how all the parts of the system work together, the CFM team plans to perform an integrated cryogenic fluid management feed-system test. This test will use prototype hardware that is representative of the actual components used for thermal and pressure control in the tank, propellant distribution, liquid acquisition and mass gauging.

LO2 test tank being installed.

The feed-system test will use either methane or liquid oxygen as the test fluids to characterize the relationships between the CFM components and subsystems while observing their overall integrated performance under nominal lunar lander mission operational conditions. This task will evaluate the effect of significant variations (during a nominal lunar lander mission) in the tank fluid state properties, thermal environments, and fluid dynamics (mixing, outflow, and level) on the CFM subsystems within a liquid methane filled tank. The above factors could degrade individual CFM component and/or subsystem performance.

The efforts of the CFM subproject team to develop better methods to store, distribute and manage cryogenic propellant should result in higher performance lunar missions. By efficiently storing the propellant, the size of the propellant tanks can be reduced, leading to a reduction in the overall mass of the spacecraft and a reduction in cost. The reduced mass could also allow the inclusion of larger payloads for exploration research.

 

Contact at NASA Glenn Research Center
Chief,  Advanced Capabilities Project Office: Ann P. Over
Space Flight Systems  Directorate / Advanced Flight Projects Office
216-433-6535