A year of firsts in liquid propulsion
By BRANDIE L. RHODES|December 2024
The Liquid Propulsion Technical Committee works to advance reaction propulsion engines employing liquid or gaseous propellants.
Government and commercial entities pushed the boundaries of liquid propulsion this year. SpaceX flew Starship-Super Heavy rockets four times, completing ascent burns on both stages and a soft landing of the Super Heavy booster in June. That flight also marked the first controlled reentry of a Starship, with a flip and burn maneuver before splashdown. In the October test, SpaceX for the first time returned a Super Heavy to the tower, where the 69-meter-tall stage was caught midair by the tower’s “chopstick” arms. Starship is the designated lander for NASA’s Artemis III mission, scheduled for 2026. And in August, SpaceX debuted and test-fired the Raptor 3, a 2.74-meganewton methalox engine capable of 350 seconds of specific impulse — designed for rapid reuse and to eliminate the need for engine heat shields.
In July, Boeing completed the final integrated functional test and delivery of the Space Launch System core stage for NASA’s Artemis II crewed lunar flyby. Boeing engineers, working closely with NASA, rigorously evaluated the propulsion system, avionics and overall performance of the core stage prior to its delivery to NASA’s Kennedy Space Center in Florida.
For the Artemis IV landing and beyond, NASA is developing a more powerful SLS variant, Block 1B, to carry substantially larger payload mass to the moon. In April, Aerojet Rocketdyne, an L3Harris company, completed modernizing and testing the updated RS-25 engines that will propel the core stage. Updates included modern flight computers to withstand the SLS solid rocket motors’ high temperatures. Furthermore, Boeing began production of the SLS Exploration Upper Stage at NASA’s Michoud Assembly Facility in New Orleans. EUS will have four Aerojet Rocketdyne RL10 engines.
In July, Ariane 6 made its inaugural flight from Europe’s Spaceport in French Guiana. The rocket’s solid boosters and the revised main stage motor, Vulcain 2.1, provided a flawless liftoff. The new upper stage allowed the completion of the commercial part of the mission, with two VINCI upper stage engine boosts and a nominal auxiliary power unit operation. In the demonstration phase, the third VINCI deorbit boost could not be performed. Ariane 6 is developed and produced by ArianeGroup on behalf of the European Space Agency.
In August, the German Aerospace Center, DLR, for the first time tested LUMEN, its liquid upper stage demonstrator engine at the European research and technology test bed P8.3 in Lampoldshausen, Germany. With LUMEN, a modular methalox bread-board engine in the 25-kilonewton-thrust class, DLR plans to validate technologies that can only be tested in a complete rocket engine.
In January, United Launch Alliance completed the inaugural flight of a Vulcan Centaur. Vulcan’s first stage is powered by two Blue Origin 2.4 meganewton, oxygen-rich staged combustion BE-4 engines; this was also the inaugural flight of the BE-4. The payload was Astrobotic’s Peregrine lunar lander, the first mission funded under NASA’s Commercial Lunar Payload Services, CLPS, program. While Peregrine never reached the lunar surface due to a leak in its propellant tank, the lander circled the moon and executed a controlled reentry in Earth’s atmosphere.
In February, Intuitive Machines of Texas made history with its lunar lander, Odysseus — also funded under CLPS — as the first commercial company to land on the moon, as well as the first U.S. lunar landing since 1972. Odysseus completed its surface objectives, despite tipping over after touchdown. The lander also demonstrated another substantial milestone: the first ignition of a cryogenic engine in deep space. Its deep-throttling, methalox, VR-900 engine set Odysseus down near the south pole, a region that astronauts are to explore in the Artemis crewed landings.
Contributors: Nathan Andrews, Joel Bridges, Colin Cowles, Christoph Kirchberger, Anne Lekeux, Jason Thrasher and Steve Shark
