RFMG – an innovative sensor from NASA will solve the problem of estimating the remaining fuel
Intuitive Machines' Nova-C lunar lander, which launches on February 14, will be equipped with a new fuel level sensor developed by NASA. This innovative sensor will measure cryogenic fuel using radio waves.
Measuring the amount of liquid in a reservoir on Earth — the task is relatively simple; for this you can use a dipstick or a mechanism with a float and a pressure gauge. In space conditions everything is much more complicated. The gravitational force does not pull the liquid down to the bottom of the tank, so it floats and sticks to the walls of the tank due to surface tension.
Engineers can estimate how much fuel is left in a spacecraft by knowing the initial mass of the cargo and subtracting how much fuel was used. However, cryogenic fuel tends to boil off over time, making estimates “questionable.” This is especially important for interplanetary missions that can last for years.
To solve this problem, NASA has developed a new method called «Radio Frequency Mass Sensor» (RFMG), which helps estimate the amount of cryogenic liquid using an antenna installed in the tank. This antenna measures how the liquid interacts with the natural electromagnetic resonances of the tank walls, then the data is compared with a database, allowing for more accurate fuel level readings with accuracy up to several percent.
Previous tests of the RFMG were carried out on aircraft flying on parabolic trajectories to create short periods of weightlessness, as well as on the ISS. This method will now be tested on the Nova-C lunar module, where NASA engineers will be able to compare its performance with ground-based simulations and previous tests.
«Under conditions of weightlessness, the liquid does not sink to the bottom of the tanks, but rather sticks to the walls and can be anywhere inside», — explains Lauren Amin, deputy project manager for the Cryogenic Fluids Management portfolio at NASA. She also emphasizes that such accurate measurements play a critical role in maximizing mission efficiency or planning the required amount of fuel for launch.