The first RS-25 flight engine, engine No. 2059, is lifted onto the A-1 Test Stand at Stennis Space Center on Nov. 4, 2015. The engine was tested in early 2016 to certify it for use on NASA’s new Space Launch System (SLS). The SLS core stage will be powered by four RS-25 engines, all tested at Stennis Space Center. NASA is developing the SLS to carry humans deeper into space than ever before, including on a journey to Mars.