The shuttle main engines were designed in the 1970s, ahead of the first shuttle launch in 1981.
In the 1990s and 2000s, NASA built a new series of upgraded engines with higher thrust and improved reliability, but the engines used much the same architecture as the prior generation.While the RS-25 engines are undeniably old, they remain among the highest-performing and most reliable US rocket engines.
The engines were reusable when they flew on the Space Shuttle.
Now, on the Space Launch System, NASA will discard the engines on each mission.This means NASA must purchase more RS-25 engines from L3Harris'Aerojet Rocketdyne at a staggering cost of $100 million per unit, according to a 2023 report from NASA's inspector general.
The watchdog projected that each SLS rocket flying with brand-new RS-25 engines will cost $2.5 billion.Put simply, these high costs will hamstring any attempt to create an enduring campaign of deep space exploration, the inspector general wrote in 2023.
"Given the enormous costs of the Artemis campaign, failure to achieve substantial savings will significantly hinder the sustainability of NASAs deep space human exploration efforts."NASA placed the first of this new lot of RS-25 engines on a test stand in Mississippi earlier this year in preparation for test-firings to prove it is ready to launch on the fifth Space Launch System rocket.
That assumes it ever flies.The Trump administration is considering canceling the SLS program in favor of less expensive commercial rockets, favoring a pivot toward human missions to Mars.
If the White House does propose cancellation, and Congress agrees, a natural point to terminate the SLS program could be after the Artemis III flight, slated to be NASA's first lunar landing mission since Apollo.This would also end the SLS program before the debut of a larger SLS upper stage.
This alone is estimated to cost $5.7 billion to develop, NASA's inspector general reported.