Preliminary Results of the IM-1 Lunar Lander RF Mass Gauging Tech Demo

Abstract: A cryogenic propellant mass gauge known as the Radio Frequency Mass Gauge (RFMG) was integrated into the Intuitive Machines (IM) Nova-C lunar lander and provided an estimate of the liquid oxygen and liquid methane mass in the lander propellant tanks throughout the IM-1 mission, including during microgravity coast phases. An antenna sensor was mounted in both the oxygen and methane tanks and provided a way to transmit an RF signal into the tanks. An RFMG electronics controller was used to measure and record the spectrum of the RF signal reflected from each antenna sensor in the frequency range 100 – 1300 MHz. The RF spectrum of each of the tanks is unique and is sensitive to the index of refraction of the propellants and the spatial distribution of the liquid within the tanks. Electromagnetic simulation software was used to simulate the antenna response spectra for a given tank geometry, internal hardware elements, fluid properties, and liquid/vapor configurations within the tank. Over 10,000 antenna response simulations were completed for each propellant tank prior to the IM-1 mission and represented various fill levels, fluid configurations, and thermodynamic states of the fluids. The simulated spectra served as a database against which measured tank spectra were compared. A spectral matching algorithm was used to find the best match between measured and simulated spectra, and the gauged mass is calculated from the most highly correlated fluid mass simulations and reported as an average of the best five or ten matches. RFMG measurements were recorded during tank loading on the launch pad, during trans-lunar coast, lunar orbit injection, low lunar orbit, powered descent to the lunar surface, and post-landing on the moon. This talk describes the RF and fluid simulations, the RFMG measurements and analysis of spectral data, and the gauged results throughout all phases of the IM-1 mission. About the Speaker: Dr. Zimmerli has been at NASA since 1992, where he began working in the Microgravity Sciences Division. Between 1994 and 2003 he participated in microgravity fluids experiments that flew on several Space Shuttle flights. In 2005 he had an idea for a new type of cryogenic propellant gauge called the Radio Frequency Mass Gauge, or RFMG, which is analogous to a fuel gauge for tanks in low-gravity. He received a patent for the RFMG in 2013, and it flew on the International Space Station in 2018 as part of the GSFC Robotic Refueling Mission-3 payload. The RFMG also recently flew on the Intuitive Machines Nova-C lunar lander, and the RFMG results from that mission is the topic of this talk.

Dr. Gregory Zimmerli

6/18/2024 6:00:00 PM