Intuitive MachinesThe first lunar landing officially lost power today after spending seven days on the moon. The aircraft made history as the first American hardware to reach the lunar surface since 1972 and the first private spacecraft to land on the Moon. But the landing craft, named Ulysses, will be remembered for another reason: its propulsion system.
This propulsion system, which uses a combination of cryogenic liquid oxygen and liquid methane, could unlock new possibilities in space and de-risk future missions by other commercial carriers.
Prior to Intuitive Machines’ IM-1 mission, no lander had ever used this combination of propellants. If they sound familiar, that’s because they’re used in high-performance rocket engines like SpaceX’s Raptor, Blue Origin’s BE-4, and Relativity Space’s Aeon R.
But ground craft – and most spacecraft today – use “space-stored” or hyperbolic propellants, such as hydrazine or nitrogen tetroxide, which can be passively stored but are extremely toxic. In contrast, “cryogens” are more efficient, higher energy, and significantly less dangerous, but must be actively cooled to very, very low temperatures.
This presents some unique challenges. Because the fuel must be kept so cold, it can only be stored before removal for a very short time. To address this issue, Intuitive Machines and SpaceX began fueling the Nova-C class lander’s VR900 engine (manufactured by IM) just three hours before liftoff, when the rocket was on the launch pad and the spacecraft was already inside the payload fairing. This is anything but typical.
It’s so unusual that SpaceX had to develop entirely new capabilities to power the landing, said Bill Gerstenmaier, SpaceX’s vice president of manufacturing and flight reliability, during a Feb. 13 press conference. second stage of the Falcon 9 rocket and adding an adapter to access the payload fairing when it was already attached to the vehicle.
The two companies conducted two wet dressing trials prior to launch. problems with propellant loading led to the first launch attempt being pushed back by one day, to 15 February. After the successful launch, Intuitive Machines also experienced a brief cooling problem of the liquid oxygen supply line, which took longer than expected. Once the propellant had cooled sufficiently, flight controllers successfully fired the engine into space for the first time the next day.
Because the company used liquid oxygen and liquid methane, which are extremely efficient, they were able to take a more direct trajectory to the moon. The spacecraft only had to cross the Van Allen Belt, a high-radiation belt around Earth, only once, which reduced the spacecraft’s exposure to harmful high-energy particles.
Two VR900 engines will also be used on Intuitive Machines’ much larger ‘Nova-D’ spacecraft to carry 500-750 kg of payload to the moon. (The Nova-C aircraft has a payload capacity of 100 kg.)
The Nova-C and Nova-D spacecraft will be far from the last spacecraft using cryogenic propellants in space. Impulse Space’s high-energy kick stage, Helios, will use cryogenics to deliver payloads directly into geostationary orbit, CEO Tom Mueller explained in an interview from January.
“People have talked about doing big super goal kicking stages in the past, and I just think you’re talking about tons of propellant and the price and the cost of security is just too much,” he said. “So using very low-cost, very high-energy propellants like liquid oxygen and liquid methane is something of a no-brainer.”
One of the six NASA science and research payloads that Ulysses carried to the surface also made direct use of the cryogenic propulsion system. The radio frequency mass meter statement from the agency’s Glenn Research Center uses radio waves and an antenna to measure how much propellant is available in the engine’s tanks. It’s technology that could be crucial to measuring spacecraft fuel levels during long-duration space missions, especially since “slosh” can make measuring liquids in microgravity a challenge.
This issue is of particular importance to NASA because the agency’s Artemis missions to return humans to the lunar surface depend on spacecraft that use cryogenic propellants — notably SpaceX’s Starship Human Landing System and Blue Origins’ Blue Moon. These missions will require the transfer of large quantities of cryogenic fluids from orbital storage to the spacecraft. While these liquids will need to be in orbit for much longer than Ulysses was in transit to the moon, the IM-1 mission is still clearly knocking on the door for cryogenic use in space.
