NASA Tests Second Entry of New RS-25 Engine Test Series

NASA performed a second RS-25 single engine hot-fire test on April 6, 2021, as part of a new sequence designed to aid in constructing and manufacturing engines for NASA's Space Launch System (SLS) rocket on possible Moon missions.

The space agency performed a full-duration hot fire lasting more than eight minutes (500 seconds) on the A-1 Test Stand at NASA's Stennis Space Center near Bay St. Louis, SciTechDaily said.

(Photo: NASA/Aerojet Rocketdyne)
Nozzle N6007, seen here at Aerojet Rocketdyne’s Strategic Fabrication Center in Los Angeles, California, is the fifth nozzle from the new production line that uses advanced manufacturing methods. The nozzle just completed hatband welding and will undergo heat treatment in a large furnace (shown in the background). Heat treatments like this strengthen the nozzle and enable it to withstand the extreme environments of SLS flight. Nozzle N6007 is one of four scheduled to fly on Artemis VI. During launch, over 700,000 gallons of liquid propellant will exit the nozzle at temperatures in excess of 6,000 degrees Fahrenheit. The newly designed RS-25 nozzle jacket, the outermost part of the engine that holds the cooling tubes, is welded together using four large cones. The original design required the welding of 37 separate pieces of sheet metal. Aerojet Rocketdyne has upgraded 16 RS-25 engines, that previously flew shuttle missions, with new control systems and has tested them at higher power levels needed for the first four Artemis missions. As with nozzle N6007, the company has begun manufacturing an improved, lower-cost version of the RS-25 for future flights.

It's part of a seven-test series planned to provide Aerojet Rocketdyne, the lead contractor for the SLS engines, useful data as it prepares to start developing new RS-25 engines after the first four SLS flights.

Four RS-25 engines power SLS that fire simultaneously to produce 1.6 million pounds of thrust at launch and 2 million pounds of thrust during ascent. The RS-25 engines for the first four SLS flights have passed certification tests and are modified space shuttle main engines.

What About NASA's RS-25?

Slashgear said that the RS-25 is one of the most common and well-known when it comes to rocket engines. It's the same rocket engine that'll power NASA's Artemis moon missions. Still, the Artemis missions aren't the first time the RS-25 engine has been used. The primary space shuttle engine, the RS-25, has a proven track record of 135 flights over 30 years.

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When the Space Shuttle Program ended in 2011, NASA put 16 RS-25 engines into storage. The space agency used it to help develop the International Space Station and launch the Hubble Space Telescope, among other missions. The RS-25 engines offered a way to save money by not building a new engine when NASA was searching for rocket engines to fuel the Space Launch System (SLS). NASA chose the RS-25 engines because of their ability to use technologies and expertise from the Space Shuttle Program.

The RS-25 is regarded as one of the most reliable, effective, and high-performance engines ever produced, and it was designed, engineered, and performed ahead of its time. Getting the RS-25 engine to work with the new SLS was one of the challenges. To get the venerable engine ready for flight in the more challenging SLS environment, engineers had to make design changes.

NASA and Aerojet Rocketdyne began adapting the engines, with the outdated flight controllers becoming the first to be redesigned. Engine flight controllers effectively monitor engine performance and maintain command and data protocols between the engine and the spacecraft. It was essential to provide a machine capable of running modern SLS algorithms. Four engines sit at the base of the rocket's center stage, directly next to a pair of solid rocket boosters, in the SLS configuration.

RS-25 engine nozzles are due for extreme base heating, especially within the first two minutes of flight. NASA crew added insulation to the nozzles to increase their efficiency. Another enhancement is the liquid oxygen tank's location in relation to the SLS's four RS-25 engines. The tank's position causes high pressure at the RS-25 inlets. The nozzles needed to be qualified to withstand the weight, which they could achieve with only minor modifications. In April 2019, all 16 retired space shuttle main engines passed acceptance inspection.