Intuitive Machines’ first lunar lander officially lost power today after spending seven days on the moon. The lander made history for being the first American hardware to reach the lunar surface since 1972 and the first privately built spacecraft to land on the moon, but its name, Odysseus, will be forever remembered for its groundbreaking propulsion system.
This presents some unique challenges. Because the fuels must be kept so cold, they can only be stored prior to lift-off for a very short amount of time.
The propulsion system, powered by a combination of cryogenic liquid oxygen and liquid methane, opens up exciting possibilities for space exploration and reduces risk for future commercial missions.
Before Intuitive Machines’ IM-1 mission, no lander had ever utilized this combination of propellants. If they sound familiar, it’s because they’re commonly used in high-performance rocket engines like SpaceX’s Raptor, Blue Origin’s BE-4, and Relativity Space’s Aeon R.
However, unlike traditional “space storable” or hypergolic propellants, which can be passively stored but are highly toxic, “cryogens” are more efficient, higher energy, and considerably less dangerous. However, they must be actively cooled to very low temperatures, presenting a unique set of challenges for spacecraft technology.
To overcome this hurdle, Intuitive Machines and SpaceX had to implement a fueling process for the Nova-C class lander’s VR900 engine, which was built by IM, just three hours before lift-off while the rocket was on the launch pad and the spacecraft was already inside the payload fairing. This was an unconventional approach and required significant modifications, as SpaceX’s VP of Build and Flight Reliability, Bill Gerstenmaier, explained during a press conference on Feb. 13. These modifications included adjusting the launch pad, the second stage of the Falcon 9 rocket, and adding an adapter to access the payload fairing after it was mated to the vehicle.
The two companies conducted two wet dress rehearsals before the actual launch, but issues with propellant loading resulted in a one-day delay, pushing the launch to Feb. 15. Thankfully, the launch was successful, and after a brief delay due to an issue with chilling the liquid oxygen feed line, the VR900 engine was successfully fired for the first time in space the following day.
Thanks to the use of liquid oxygen and liquid methane, which are highly efficient, Intuitive Machines’ spacecraft was able to take a more direct trajectory to the moon. This approach allowed the spacecraft to transit the Van Allen belt, a high-radiation zone around the Earth, only once, reducing the exposure to damaging high-energy particles.
The company’s larger “Nova-D” spacecraft, which will have a payload capacity of 500-750 kilograms, will also use two VR900 engines. In comparison, the Nova-C lander has a payload capacity of 100 kilograms.
And Intuitive Machines and SpaceX are not the only companies looking to use cryogenic propellants in space. Impulse Space’s high-energy kick stage, Helios, will use cryogens to deliver payloads directly to geostationary orbit, as CEO Tom Mueller previously explained in an interview from January.
“People have talked about doing big kick stages with hypergols before, and I just think, you’re talking tons of propellant and the price and the cost of safety are just exorbitant,” he said. “So using very low-cost, very high-energy propellants like liquid oxygen and liquid methane is kind of like a no-brainer.”
One of the six NASA science and research payloads that Odysseus carried to the surface also directly leveraged the cryogenic propulsion system. The Radio Frequency Mass Gauge statement from the agency’s Glenn Research Center uses radio waves and an antenna to measure the amount of propellant in the engine’s tanks. This technology could be critical for measuring spacecraft fuel levels during long-duration space missions, especially considering the challenges of accurately measuring liquids in microgravity due to “slosh.”
This is of particular significance to NASA because the success of their Artemis missions, which aim to return humans to the lunar surface, will depend on spacecraft that use cryogenic propellants. These missions will require transferring large amounts of cryogenic fluids from on-orbit depots to the spacecraft, and while these fluids will need to remain in orbit for much longer than Odysseus, the IM-1 mission has firmly paved the way for the use of cryogenics in space.
