Spaceflight Insider

Starliner’s propulsion system engines complete qualification tests

Boeing CST-100 Starliner

Boeing CST-100 Starliner. Image Credit: Boeing

Boeing’s CST-100 Starliner space capsule got a further boost toward completion when the engines being built for its reactive propulsion system by Aerojet Rocketdyne passed their qualification tests.

Twelve of the monopropellant MR-104J engines, fueled by hydrazine, will be used for reaction control during the re-entry phase of each mission. The system is designed to keep the spacecraft on the correct trajectory and orientation for a safe re-entry and landing.

Aerojet Rocketdyne’s MR-104J Hydrazine Monopropellant Engine. Photo Credit: Aerojet Rocketdyne

The qualification tests involved hot-fire testing of the engines to not only prove their functionality and reliability but also to demonstrate their reusability. The MR-104J engines have been built to withstand multiple firings to allow them to be used on more than one mission.

The Starliner has been designed to fly up to 10 missions while keeping maintenance on the spacecraft to a minimum between flights.

“Our engineers have incorporated a unique design that will allow the MR-104 engine to be used on multiple missions, providing the reliability, cost-efficiency and reusability our customer needs to be competitive in the current commercial space environment,” said Aerojet Rocketdyne CEO and President Eileen Drake.

Aerojet Rocketdyne is also building other important parts for the Starliner vehicle including the Orbital Maneuvering and Attitude Control thrusters, the Service Module Reaction Control System thrusters, as well as the Launch Abort engines. All are being built under the Commercial Crew Transportation Capability (CCtCap) subcontract to Boeing.

Aerojet Rocketdyne propulsion systems have been flown on manned and unmanned missions for NASA since the beginning of the U.S. Space Program, and are used by Boeing, Lockheed Martin, and Raytheon on their spacecraft.

While the Starliner is capable of carrying seven astronauts into orbit, it will, for NASA crew rotation missions, carry just four astronauts along with scientific experiments and equipment to the International Space Station. The Starliner, which is designed to make a ground landing, will return crew members, time critical scientific experiments, and other equipment to Earth.

Starliner’s first flight, a demonstration mission, is currently scheduled for mid-2018 with crewed flights to follow, but those dates are expected to slip until at least late 2018.



Lloyd Campbell’s first interest in space began when he was a very young boy in the 1960s with NASA’s Gemini and Apollo programs. That passion continued in the early 1970s with our continued exploration of our Moon, and was renewed by the Shuttle Program. Having attended the launch of Space Shuttle Discovery on its final two missions, STS-131, and STS-133, he began to do more social networking on space and that developed into writing more in-depth articles. Since then he’s attended the launch of the Mars Science Laboratory Curiosity rover, the agency’s new crew-rated Orion spacecraft on Exploration Flight Test 1, and multiple other uncrewed launches. In addition to writing, Lloyd has also been doing more photography of launches and aviation. He enjoys all aspects of space exploration, both human, and robotic, but his primary passions lie with human exploration and the vehicles, rockets, and other technologies that allow humanity to explore space.

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