Propellant Gauging During On-Orbit Refueling and Transfer Operations

In-space propellant transfer and refueling is a critical-path technology for sustained human presence in space. Researchers at Carthage College are advancing Propellant Gauging During On-Orbit Refueling and Transfer Operations with Modal Propellant Gauging(MPG),which is a technique that translates measured modal frequencies and mode shapes for precise estimates of propellant quantity. Parabolic and suborbital flights will test the ability of MPG to gauge equilibrated liquids in microgravity during continuous transfer. This will represent the first microgravity testing of a method capable of identifying the volume, location and distribution of the liquid surface during propellant transfer. 

Problem Statement 
In-space propellant transfer and refueling is a critical-path technology for a sustained human presence in space. Lunar and planetary, orbiting stations, including Lunar Gateway will require the ability to refuel spacecraft and transfer propellant between vehicles. In-space propellant transfer relies on accurate microgravity liquid mass gauging technologies, which at present are either non-existent or low-TRL. 

Modal Propellant Gauging (MPG) is designed to reduce risk for critical Gateway elements and enable extended human presenceon the lunar surface. MPG is the only low-gravity liquid gauge with significant flight heritage as well as the only approach that is propellant agnostic, non-invasive (i.e., no tank penetrations), and sufficiently advanced to have a radiation-hardened development path for deep-space use. 

Technology Maturation
Flight testing is expected to raise the TRL for (1) measurement of the liquid phase volume and surface distribution in the upper dome of spherical transfer tank during propellant transfer in microgravity, (2) determination of gauge resolution during draining/transfer from spherical tank in microgravity, (3) demonstration of autonomous gauging algorithms in flight-path hardware.

Summary of Flight Testing

2025-09-18: The Carthage College PROTO experiment conducted a successful microgravity test of propellant mass gauging during dynamic transfer of propellant simulant between two tanks. The gauging technology under test is non-invasive, operates in real-time, and can achieve sub-1% gauging resolution during propellant refueling operations in space.

2023-12-19: The Carthage College PROTO experiment conducted a successful microgravity test of a propellant gauging and refueling experiment, transferring 1 liter of liquid propellant simulant during microgravity between two tanks. The gauging technology under test is non-invasive, operates in real-time, and can achieve sub-1% gauging resolution during propellant refueling operations in space.

2022-05-09: The MPG-PROTO parabolic flight campaign was a great “shakeout” test for the experiment’s upcoming suborbital flight on New Shepard. Every time we fly in microgravity we learn new things about the behavior of the hardware. These early insights are critical to a successful suborbital mission as they teach us how to anticipate and mitigate the myriad complexities of the space environment.

2021-11-16: The Zero-G campaign was crucial to the Propellant Refueling and On-orbit Transfer Operations (PROTO) experiment develop because it gave us real-time data on the performance of our hardware in microgravity, allowing us to tweak voltages and other parameters during simulated propellant transfers in microgravity. These data are critical to preparing for our upcoming New Shepard flight. This week’s flights were an essential step in our effort to demonstrate transfer of liquid propellant simulant between two tanks in microgravity.

In-space propellant transfer and refueling is a critical-path technology for sustained human presence in space. Researchers at Carthage College are advancing Propellant Gauging During On-Orbit Refueling and Transfer Operations with Modal Propellant Gauging (MPG), a technique that translates measured modal frequencies and mode shapes to precise estimates of propellant. Flights will test the ability of MPG to gauge equilibrated liquids in microgravity during continuous transfer, establishing the first microgravity tests of a method to identify the location and distribution of the liquid surface during propellant transfer. This would benefit NASA missions, the commercial space industry, other government agencies, and the nation.

Future Customers
•NASA’s Orion spacecraft and Space Launch System
•Commercialand military satellite providers
•NASA’s Human Research Program
•NASA’s Lunar Gateway
•Commercial launch services providers
•Commercial and NASA programs developing in-orbit fuel depots

This is a mature technology (TRL 7) — the realistic path in is usually NASA's Technology Transfer Program: licensing an existing NASA patent, or a Space Act Agreement to use NASA facilities/expertise directly. NASA also runs a startup licensing program with no upfront fee for companies formed to commercialize a specific NASA technology.

None of these are guaranteed paths for this specific project — TechPort itself doesn't have an "apply" button. Reaching out to the contact(s) above with a specific question is usually the fastest way to find out what's actually open.