Tweaked Space Shuttle Main Engine gets ready for final testing

NASA will run out of RS-25s to drop into the ocean unless the production line restarts

A test run of the engines powering NASA's Moon rocket is due to kick off this week, an essential milestone since the Space Shuttle cast-offs will need to be replaced – beginning with Artemis V.

NASA's Artemis uses parts left over from the Space Shuttle program. It is notable for having managed to turn the Space Shuttle Main Engines from marvels of reusability into disposable units to be dumped into the ocean during launch, along with the rest of the core stage.

However, only a finite number of engines are available, and NASA has contracted Aerojet Rocketdyne to restart production of the RS-25 engine.

The new engines differ from the Space Shuttle originals. Reusability is no longer required, but extra power is. The engines must also be cheaper to produce so a new design is needed. This design must also be certified, hence the testing.

The first Artemis mission launched in 2022. The next three will also use modified engines from the Space Shuttle program, tweaked to go to 109 percent of their rated level. The new RS-25 engines will go to 111 percent and be tested to 113 percent to gain a margin of operational safety.

The October 5 test will take the development engine E0525 to 111 percent and run it for 550 seconds. The longest test will be 650 seconds, and crews will also perform a gimbal test to ensure the engine can pivot correctly. Overall, 6,350 seconds of firing is planned for the test series, and should all go well, the green light will be given to produce 24 new RS-25 engines using the new design.

The tests at the Fred Haise Test Stand at NASA's Stennis Space Center are critical if the Artemis program is to progress beyond the fourth flight in its current form. However, the RS-25 is hardly the only Space Shuttle component that will become scarce should NASA keep launching the SLS.

The Solid Rocket Boosters (SRBs) used in the launch are derived from Space Shuttle parts and expended where the Space Shuttle program would recover and reuse them. NASA has enough parts to get through to Artemis 8 but will need to produce new ones for Artemis 9.

Similarly, the European Service Module (ESM) currently uses a Space Shuttle Orbital Maneuvering System engine for its primary method of propulsion. From ESM-7, it will require something new.

However, it is the RS-25 engine that is most urgent. Assuming, of course, the SLS is still flying in its current form by the time Artemis V eventually rolls around. ®

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