When it comes to rocket engines, one of the most prolific and famous is the RS-25. It’s the same rocket engine that would be used for the NASA Artemis moon missions, but the Artemis missions certainly aren’t the first time RS-25 engines have been used. The RS-25 engine was the main space shuttle engine and has a proven record of 135 missions over 30 years.
When the Space Shuttle Program was retired in 2011, 16 RS-25 engines that NASA used to help build the ISS and deploy the Hubble Space Telescope, among other missions, were placed into storage. When NASA began looking for rocket engines to power the Space Launch System (SLS), the RS-25 engines were a chance for NASA to save money on developing a new engine. NASA chose the RS-25 engines because of the ability to leverage the capabilities of the technology and experience from the Space Shuttle Program.
The RS-25 is described as one of the most reliable, efficient, high-performance engines ever built and is considered to have been ahead of its time in design, engineering, and performance. One of the challenges was getting the RS-25 engine to work with the new SLS. Engineers had to make design improvements to get the venerable engine ready for flight in the more demanding SLS environment.
NASA and contractor and Aerojet Rocketdyne began adapting the engines, with the first parts to be redesigned being the obsolete flight controllers. Flight controllers are critical components that actively control engine operation and manage command and data protocols between the engine and spacecraft. A computer able to handle modern SLS algorithms was required. With the SLS design, four engines sit at the base of the rocket’s core stage directly next to a pair of solid rocket boosters.
That means the RS-25 engine nozzles will be subject to extreme base heating, especially during the first two minutes of flight. The nozzles were improved by adding insulation. Another improvement has to do with where the liquid oxygen tank sits in relation to the four RS-25 engines on the SLS. The location of that tank results in high pressure at the RS-25 inlets. The nozzles had to be certified to withstand that pressure and were able to do so with minimal upgrades. All 16 former space shuttle main engines completed acceptance testing in April 2019.