Aerojet Rocketdyne on Thursday test-fired four Valley-made rocket engines on the Space Launch System, the new heavy-lift rocket NASA has under development to power future manned missions to the moon and possibly to Mars.

The engines ran for 499 seconds during the test at NASA Stennis Space Center in Mississippi. It was the second time the four engines had been fired in unison on the core stage of the Space Launch System rocket, or SLS. The test simulated the profile of an actual SLS flight, including throttling sequences.

Aerojet Rocketdyne makes the RS-25 engines at its Chatsworth campus. It is a modified version of the engines used on the space shuttle.

Aerojet Rocketdyne Chief Executive Eileen Drake called the test firing a huge milestone for the rocket as it marks the most challenging test before all the SLS hardware is assembled at NASA’s Kennedy Space Center.

“SLS has been designed specifically for exploration and is key to returning American astronauts to the Moon and eventually sending humans to Mars,” Drake said in a statement.

After post-test inspections, the vehicle’s 212-foot core stage will travel by barge to Kennedy Space Center in preparation for the first flight. During its inaugural mission, known as Artemis I, the SLS rocket will launch NASA’s Orion exploration vehicle on an uncrewed mission around the Moon and back to Earth, the company said.

The Chatsworth facility is ramping up to manufacture more of the engines, which fit on the bottom of the core stage of the rocket. The company will use the latest in manufacturing methods, including 3-D printing, in making the engines.