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Active TRL 6 (started at 4, targeting 6)
The purpose of the Non-invasive Detection of Liquid Propellant Location During Microgravity Transfer project is to facilitate the transfer and storage of cryogenic and storable propellants in microgravity. The method utilizes piezoelectric sensors adhered to the outside of a propellant tank while acoustic excitation is applied to the tank and the sensors translate the tank’s vibrations into electric voltages. It is expected that the frequency of these signals can be used to establish total liquid volume and that the amplitudes can be used to reconstruct the instantaneous location and motion of the liquid-free surface.
Problem Statement
The proposed orbit of the Lunar Gateway is unstable and will require occasional station-keeping, and therefore refueling of its power and propulsion element. Visiting spacecraft and lunar ascent modules will also require refueling in order to realize the sustainable human presence required by the Gateway. This challenge requires both microgravity liquid propellant gauging as well as knowledge of equilibrated liquid surface distributions within tanks. Neither technology currently has a sufficient technology readiness level (TRL) for Gateway infusion.
Technology Maturation
Flight tests are expected to help verify sensor operation in a relevant space environment, correlating liquid free surface position and motion with sensor amplitudes. This technology is designed to enable the transfer and storage of cryogenic and storable propellants in microgravity, a key component of the refueling of the power and propulsion element necessary for Lunar Gateway station-keeping. The flight tests aim is to advance this innovation to TRL 6.
Summary of September 18, 2025 Flight Test
The MUD payload experiment seeks to demonstrate the ability to non-invasively determine the location of the liquid-vapor interface in a model propellant tank under microgravity conditions. On the New Shepard P15 flight, the team was able to detect the liquid-vapor interface inside a propellant tank partially filled with propellant simulant.
Summary of March 5, 2024 Flight Test
The Microgravity Ullage Detection experiment is technology demonstration for elements of in-space propellant transfer. Our March parabolic flight campaign provided crucial video data and model calibration data for an upcoming flight test on a suborbital rocket. We also use the parabolic flight program to test procedures, hardware performance in microgravity, and assess our team’s data analysis workflow.
The purpose of the Non-invasive Detection of Liquid Propellant Location During Microgravity Transfer project is to facilitate the transfer and storage of cryogenic and storable propellants in microgravity. The method utilizes piezoelectric sensors adhered to the outside of a propellant tank while acoustic excitation is applied to the tank and the sensors translate the tank’s vibrations into electric voltages. It is expected that the frequency of these signals can be used to establish total liquid volume and that the amplitudes can be used to reconstruct the instantaneous location and motion of the liquid-free surface. This has the potential to benefit NASA missions, the commercial space industry, and other government agencies.
Future Customers
- Commercial satellite providers
- Military satellite providers
- Launch services providers
- Commercial and NASA programs developing on-orbit fuel depots
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This is early/mid-stage (TRL 6) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.
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