NASA took the next big step on its Journey to Mars on Nov. 4 by placing the first RS-25 flight engine, engine No. 2059, on the A-1 Test Stand at Stennis Space Center.

The engine will be tested in the first part of 2016 to certify it for use on NASA's new Space Launch System (SLS). The SLS vehicle is being developed in two versions to return humans to deep space.

The "Block 1" version of the SLS vehicle is set to fly its first uncrewed mission in 2018.

The "Block 2" heavy-lift version will be ready for flight later and will be the largest, most powerful rocket ever built, capable of carrying humans on missions to Mars.

The core stage of both SLS configurations will be powered by four RS-25 engines, all tested at Stennis Space Center.

The core stage for the 2018 SLS flight - Exploration Mission-1 - also will be tested at Stennis.

Testing will involve installing the flight stage on the B-2 Test Stand and firing its four RS-25 engines simultaneously, just as during an actual launch.

The SLS Program has an inventory of 16 RS-25 flight engines, built by Aerojet Rocketdyne of Sacramento, California.

The engines are available for the first four SLS missions, and two development engines are available for ground tests.

These engines are being adapted to SLS performance requirements, including improvements like nozzle insulation and a new electronic controller.