Radio Frequency Mass Gauge (RFMG)¶
IM-1 · landed · NASA payload
A propellant gauge for low gravity. An antenna inside each of the lander's liquid oxygen and liquid methane tanks reads the tank's radio-frequency spectrum, and matching it against thousands of simulations gives the propellant mass. It works inside the lander's propulsion system; NASA counts it as one of IM-1's six NASA payloads.
PI: Gregory (Greg) Zimmerli, NASA Glenn
Built by: NASA Glenn Research Center (with support contractors HX5 and USRA); integrated into the tanks by Intuitive Machines (NASA center)
| Technology | low-gravity propellant gauge (cryogenic fluid management) |
| Moon Base need | #1106 (The study's reading. NASA's gap #1106 (cryogenic fluid storage) includes propellant gauging, but #1106 is not among the Users Guide's 19 gaps, so no Moon Base challenge cites it. The link to the Moon Base is through cryogenic cargo landers, the Phase 1 transportation target.) |
| Route onto CLPS | STMD; No NASA payload call in the sources. An STMD Technology Demonstration Missions project, flown through a collaboration with Intuitive Machines under SMD's CLPS program: task order 20C (authority to proceed January 2020) added RFMG integration and cryogenic data delivery to the IM-1 order (TO2-IM). Not on the February 2019 NPLP list or the January 2020 manifest.; 2020-01 |
| Timeline | first funding by 2006-2007 (Glenn RFMG work; Lockheed Martin flight-demonstration study); first flight test 2011-07-19 (FO parabolic flight); selected 2020-01 (authority to proceed for the IM-1 collaboration; CLPS task order 20C); launch 2024-02-15; landing 2024-02-22 |
| On the Moon | operated as planned |
| FO | tested |
Flights before the Moon¶
- FO: Parabolic aircraft, NASA Johnson Reduced Gravity Office, campaigns RGO-01 and RGO-02, 2011-07-19 and 2011-08-30. RFMG gauging in low gravity, which ground tests with liquid hydrogen and oxygen could not give.
"but lacked low-g testing prior to the parabolic flights"
— TechPort project 12177, description"A series of parabolic flights in 2011 supported by Flight Opportunities helped NASA advance this technology"
— nasa.gov: fy24-fo-accomp-report-final-20250422.pdf, FY2024 report p. 9"campaigns RGO-01 (19 Jul 2011) and RGO-02 (30 Aug 2011)"
— earlier finding of this study (not a public source)
- ISS or MISSE: Robotic Refueling Mission 3 (RRM3) payload outside the International Space Station, 2018. RFMG in a small dewar of cryogenic methane on the ISS: feasibility in orbit. The IM-1 avionics design was first developed for RRM3.
"ISS demonstration on Robotic Refueling Mission 3 (RRM3) in 2018"
— NTRS 20220003614, slide 3"proved the feasibility of the technique in a small dewar with cryogenic methane"
— NTRS 20240014338, page 2"While smaller-scale experiments have been conducted on the International Space Station and during"
— NASA Tests New Spacecraft Propellant Gauge on Lunar Lander
Heritage hardware¶
- design heritage (RRM3 avionics): The IM-1 avionics (single-board computer, power and control board, a commercial one-port vector reflectometer and an RF switch) were first developed for the RRM3 ISS payload, to a NASA Class D specification.
"was originally developed for use with the RRM3 ISS payload"
— NTRS 20240014338, page 7
- ground tests: Ground tests that fed the IM-1 work, per Glenn: Cryogenic Propellant Storage and Transfer engineering-unit tests in 2014, and large-tank tests in the SHIIVER program in 2019-2020. Before flight, RFMG also gauged the Nova-C tanks during IM's July 2023 hot-fire test, to about 1% against load cells.
"Scalability to large tanks during eCryo"
— NTRS 20220003614, slide 3"A hot-fire test of the IM Nova-C lander vehicle took place in July 2023."
— NTRS 20240014338, page 11
Funding before the lunar flight¶
- STMD Technology Demonstration Missions, Cryogenic Fluid Management Portfolio Project, and SMD: the project that built and delivered the IM-1 unit (TechPort 105674, 'Radio Frequency Mass Gauging - Intuitive Machines Nova-C Mission', 2020-2025) (STMD TDM (CFM Portfolio Project); SMD; 2020-2025): amount not in public sources
"This work was supported by NASA through the Space Technology Mission Directorate Cryogenic Fluid Management Portfolio Project and the Science Mission Directorate."
— NTRS 20240014338, Acknowledgments"The Radio Frequency Mass Gauge (RFMG) team built, tested and delivered and RFMG System to Intuitive Machines (IM) for integration into their Nova-C lunar lander"
— TechPort project 105674, description
- CLPS task order 20C to Intuitive Machines for RFMG integration and cryogenic data delivery (first award). Linked by the award description. This paid the lander company, not Glenn. (NASA CLPS task order 80JSC020F0285; 2020-07-31 to 2024-11-30): $4,000,000
"CLPS TO 20C, RADIO FREQUENCY MASS GAUGE AND INTEGRATION AND CRYOGENIC DATA DELIVERY"
— USAspending.gov, award 80JSC020F0285, description; amount 4000000.0
- CLPS task order 20C to Intuitive Machines, second award under the same description (NASA CLPS task order 80JSC021F0229; 2021-06-16 to 2024-08-30): $432,000
"CLPS TO 20C, RADIO FREQUENCY MASS GAUGE AND INTEGRATION AND CRYOGENIC DATA DELIVERY"
— USAspending.gov, award 80JSC021F0229, description; amount 432000.0
- RFMG antenna fabrication by HX5 for Glenn, 2021. Linked by the description and the timing (antennas for the IM tanks were due then); the award does not name IM-1. (NASA task order 80GRC021F0098; 2021-06-01 to 2024-03-31): $68,178
"TO-0305 RFMG ANTENNA FABRICATION"
— USAspending.gov, award 80GRC021F0098, description; amount 68177.82
- RRM3-era avionics parts and modeling, before IM-1 (the IM-1 avionics design comes from RRM3): single-board computers (2016), thermal-vacuum test cables (2016-2018), and Purdue modeling for RFMG/RRM3 (2017). Linked by the award descriptions. (NASA purchase orders NNC16QA11P, NNC16VH97P, NNX17ED14P; 2016-2018): amount not in public sources
"SINGLE BOARD COMPUTERS WILL BECOME PART OF THE RADIO FREQUENCY MASS GAUGE (RFMG) INSTRUMENT"
— USAspending.gov, award NNC16QA11P, description; amount 19603.0"RFMG - THERMAL VACUUM TEST CABLES"
— USAspending.gov, award NNC16VH97P, description; amount 22827.62"IGF::OT::IGF RFMG/RRM3 SURFACE EVOLVER MODELING"
— USAspending.gov, award NNX17ED14P, description; amount 22000.0
- Early flight-demonstration study for RFMG by Lockheed Martin, 2006-2007. Linked by the description. (NASA purchase order NNC07QA02P; 2006-11-28 to 2007-09-30): $74,800
"RADIO FREQUENCY MASS GAUGE FLIGHT DEMONSTRATION STUDY"
— USAspending.gov, award NNC07QA02P, description; amount 74800.0
- FO's 2011 parabolic flights supported RFMG work for NASA's Enabling Technology Development and Demonstration Program (NASA Enabling Technology Development and Demonstration Program (per TechPort 12177); 2011): amount not in public sources
"to further the development of the RFMG for the NASA Enabling Technology Development and Demonstration Program"
— TechPort project 12177, benefits
How it got onto CLPS¶
"Collaboration with Intuitive Machines on IM-1 through SMD"
— NTRS 20220003614, slide 3"Task Order 20C included RFMG integration and Cryogenic data delivery"
— NTRS 20220003614, slide 3"Task Order: CLPS TO2-IM (2/20C/OP)"
— TO2-IM Science Payloads - NASA Science, RFMG entry
On the Moon¶
RFMG gauged both tanks through the whole mission: propellant loading, transit coasts in microgravity, lunar orbit insertion, low lunar orbit, powered descent and after landing. It stayed powered on throughout. IM used bookkeeping as its primary gauge and RFMG as a secondary estimate. The team says the in-flight results were about as accurate as the ground hot-fire test, and calls RFMG the first direct-sensing gauge for cryogenic propellant in low gravity.
"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"
— NTRS 20240014338, abstract"produced gauging results that were comparable in accuracy to the ground-based hot-fire test results"
— NTRS 20240014338, page 19, Conclusions"During the 2024 IM-1 mission to the Moon, RFMG helped Intuitive Machines verify the propellant levels in the lander."
— Transitions of Flight Tested Technologies
FO's role¶
Grade: tested. Grade unchanged (tested). FO's 2011 parabolic flights gave RFMG its first low-gravity test: before them the gauge had worked in ground tests with liquid hydrogen and oxygen but 'lacked low-g testing'. FO says the testing helped transfer the technology to Intuitive Machines. RFMG then flew on the ISS (RRM3, 2018), whose avionics design went on to IM-1. FO's follow-on project to gauge a Masten Xaero oxygen tank (91405) shows no flight.
FO flights: 2. Two parabolic campaigns in 2011, shared with other payloads. What FO paid per payload is in FO records, not in public sources.
"Thanks in part to testing with Flight Opportunities, the technology was transferred to Intuitive Machines for integration on the company's CLPS lander vehicle."
— Transitions of Flight Tested Technologies"The technique has been proven to work very well in ground tests using liquid hydrogen and liquid oxygen, but lacked low-g testing prior to the parabolic flights."
— TechPort project 12177, description"Radio Frequency Mass Gauge on Parabolic"
— TechPort project 12177, title (FO, Glenn, 2011-2014)"This technology is an evolution from Technology #7: Radio Frequency Mass Gauge on Parabolic Flights."
— TechPort project 91405, description
Who built it¶
"Developed at NASA Glenn under the agency's Technology Demonstration Missions program, the Radio Frequency Mass Gauge (RFMG) payload"
— NASA Tests New Spacecraft Propellant Gauge on Lunar Lander"Payload PI: Dr. Greg Zimmerli"
— TO2-IM Science Payloads - NASA Science
Moon Base need¶
"propellant gauging will be critical to determine the remaining"
— Moon to Mars knowledge base: ESDMD #1106: Cryogenic Fluid Storage, Description"gauging how much is left in a tank at any time (bin 4, rating 32 of 57)"
— Moon to Mars knowledge base: ESDMD #1106: Cryogenic Fluid Storage, summary"landers with two metric ton cargo delivery capability to the lunar South Pole region"
— Moon to Mars knowledge base: What the architecture says the Moon Base needs, Phase 1 functional gaps, Transportation (cargo)
Open questions¶
- The cost of the IM-1 RFMG unit at Glenn: not in public sources. The CLPS task order 20C awards (USD 4,000,000 and USD 432,000) paid Intuitive Machines for integration and data, not Glenn's hardware.
- TechPort 105674 says IM landed on 'February 26, 2025'; IM-1 landed on 22 February 2024. A TechPort error.
- What FO paid for the 2011 parabolic flights, and whether FO's 91405 (Masten Xaero oxygen-tank gauging) ever flew: FO records.