The test was carried out on Earth: the engine was simply cooled down greatly.
SpaceX has tested the Raptor engine designed to operate on the Moon. Engines of this type will be used during NASA’s lunar missions as part of the Artemis program.
The Raptor engine has been modified to handle vacuum and low temperature conditions. The tests were carried out on Earth, but under conditionally “lunar” conditions.
Before the test began, the engine was cooled to a very low temperature, corresponding to that observed on the Moon. The modified Raptor launched successfully, here’s what it looked like.
Testing of the lunar version of the Raptor engine has been ongoing since at least 2021. The engines will be used both for landing on the Moon – they will provide braking before touching the satellite – and for take-off and subsequent return to Earth.
NASA is expected to send humans to the Moon again in 2025 or 2026 with the Artemis 3 mission. Before this, the agency will conduct a manned mission, Artemis 2: a crew of astronauts will fly around the Moon, but will not land on the satellite.
The launch of the Artemis 2 mission is tentatively scheduled for the end of 2024.
This is interesting