RS-25

The RS-25, formerly the Space Shuttle main engine, burns liquid hydrogen and liquid oxygen. Three were mounted at the back of each Shuttle orbiter, and the engine powered the Shuttle for more than three decades and 135 missions. NASA calls it one of the most tested large rocket engines in history, with more than 3,000 starts and more than 1 million seconds of ground-test and flight firing time.

Four RS-25s power the core stage of NASA’s Space Launch System, producing more than 2 million pounds of thrust. The SLS program began with 16 flight engines transferred from the Shuttle program—enough for the first four flights—and fitted them with new controllers and added insulation to run at 109 percent of their original rated thrust. On SLS the engines are not recovered; they are lost with the core stage after each launch.

Aerojet Rocketdyne, now part of L3Harris Technologies, is building 24 new RS-25s with a simplified design and new manufacturing methods such as 3D printing, aiming to cut cost by 30 percent compared with the Shuttle engine. NASA finished certification testing of the new-production engine in April 2024 and has said the first new engines will fly on Artemis V.

Read more about RS-25

• The Moon rocket Congress ordered from Shuttle parts in 2010Congress wrote SLS into law in 2010, with Shuttle engines and boosters and a 2016 goal. It first flew in 2022, at an estimated $4.1 billion a launch with Orion, and in 2026 NASA stopped upgrading it.
• Artemis II: the first crewed flight around the Moon since 1972From April 1 to 10, 2026, four astronauts flew Orion around the far side of the Moon and farther from Earth than anyone before them. What the flight tested, day by day, and what NASA found afterward.
• Artemis: how NASA’s plan to land on the Moon was built and rebuiltA rocket, a capsule, two commercial landers, new suits and propellant refilled in orbit: who builds each piece, what it costs, and how a 2024 landing became Artemis IV in 2028.
• Promised as routine transport, the Shuttle flew 135 times in 30 yearsNixon approved a $5.5 billion reusable spaceplane in 1972 to make spaceflight routine and cheap. It repaired Hubble and built a space station, lost two crews, and never flew more than nine times in a year.