NASA engineers tested the RS-25 rocket engine, which will play a crucial role in eventual missions to Mars, on Tuesday.

The test at NASAs Stennis Space Center in Mississippi is the latest in a series of RS-25 firings.

The forthcoming Space Launch System (SLS) rocket will be powered by four R2-25 engines firing simultaneously. The RS-25s will provide 2 million pounds of thrust, according to NASA, and will work in conjunction with a pair of solid rocket boosters, which provide an additional 6.8 million pounds of thrust.

The first unmanned flight of the heavy-lift SLS a trip around the moon was scheduled for 2018, but was recently pushed back to 2019, Space.com reports. A crewed mission was expected to take place in 2021, but it has also been pushed back. NASA said there will be a minimum of 33 months between the unmanned and crewed missions.

NASA plans to harness SLS to achieve its long-term goal of sending a manned mission to Mars by 2035.

Former space shuttle main engines, the RS-25s are modified to meet the demands of SLS with a new controller. The controller is the key modification to the engines, explained NASAin a statement. The component is often cited as the RS-25 brain that allows communication between the engine and the rocket.

Aerojet Rocketdyne is the RS-25 primary contractor, with Honeywell serving as subcontractor.

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NASA tests engine that will eventually take us to Mars - New York Post