The new year is off to a hot start for NASA’s Space Launch System (SLS). The engine that will drive America’s next great rocket to deep space blazed through its first successful test Jan. 9 at the agency’s Stennis Space Center near Bay St. Louis, Mississippi.
The RS-25, formerly the space shuttle main engine, fired up for 500 seconds on the A-1 test stand at Stennis, providing NASA engineers critical data on the engine controller unit and inlet pressure conditions. This is the first hot fire of an RS-25 engine since the end of space shuttle main engine testing in 2009. Four RS-25 engines will power SLS on future missions, including to an asteroid and Mars.
“We’ve made modifications to the RS-25 to meet SLS specifications and will analyze and test a variety of conditions during the hot fire series,” said Steve Wofford, manager of the SLS Liquid Engines Office at NASA’s Marshall Space Flight Center in Huntsville, Alabama, where the SLS Program is managed. “The engines for SLS will encounter colder liquid oxygen temperatures than shuttle; greater inlet pressure due to the taller core stage liquid oxygen tank and higher vehicle acceleration; and more nozzle heating due to the four-engine configuration and their position in-plane with the SLS booster exhaust nozzles.”
The engine controller unit, the “brain” of the engine, allows communication between the vehicle and the engine, relaying commands to the engine and transmitting data back to the vehicle. The controller also provides closed-loop management of the engine by regulating the thrust and fuel mixture ratio while monitoring the engine’s health and status. The new controller will use updated hardware and software configured to operate with the new SLS avionics architecture.
“This first hot-fire test of the RS-25 engine represents a significant effort on behalf of Stennis Space Center’s A-1 test team,” said Ronald Rigney, RS-25 project manager at Stennis. “Our technicians and engineers have been working diligently to design, modify and activate an extremely complex and capable facility in support of RS-25 engine testing.”
Testing will resume in April after upgrades are completed on the high pressure industrial water system, which provides cool water for the test facility during a hot fire test. Eight tests, totaling 3,500 seconds, are planned for the current development engine. Another development engine later will undergo 10 tests, totaling 4,500 seconds. The second test series includes the first test of new flight controllers, known as green running.
The agency’s new rocket will build on the success of the RS-25 space shuttle main engine, the shuttle’s solid rocket booster and the 27.5-foot-diameter external tank manufacturing infrastructure. The result will be the most powerful launch vehicle in the world, with more than twice the payload mass of the shuttle.
The first flight test of the SLS will feature a configuration for a 70-metric-ton (77-ton) lift capacity and carry an uncrewed Orion spacecraft beyond low-Earth orbit to test the performance of the integrated system. As the SLS is upgraded, it will provide an unprecedented lift capability of 130 metric tons (143 tons) to enable missions even farther into our solar system.
The SLS core stage is designed around four RS-25s. NASA has 16 flight engines currently in its fleet, as well as two of development engines for ground testing. Engineers have performed extensive analysis to understand how the engines will work for SLS, but will continue to study the integrated design with detailed analysis and, ultimately, by firing the engine on its test stand at NASA’s Stennis Space Center near Bay St. Louis, Mississippi.
“The RS-25 is the most efficient engine of its type in the world,” said Steve Wofford, manager of the SLS Liquid Engines Office at NASA’s Marshall Space Flight Center, in Huntsville, Alabama, where the SLS Program is managed. “It’s got a remarkable history of success and a great experience base that make it a great choice for NASA’s next era of exploration.”
Under an existing contract with Aerojet Rocketdyne, prime contractor for the RS-25, engineers at Stennis are preparing for engine testing to begin the process of adapting the engine to meet SLS performance requirements and environments from the launch pad to space.
On the shuttle, the RS-25 routinely operated at 491,000 pounds of thrust. On SLS, it will operate at 512,000 pounds of thrust for the first four flights. Before launch, the four engines in the SLS core stage will encounter colder liquid oxygen propellant temperatures and a colder engine compartment in the SLS core stage.
Beginning at engine and booster ignition, the engines will encounter higher propellant inlet pressure and greater exhaust nozzle heating due to differences in the SLS design. The higher thrust and greater cooling, heating and pressure will be part of the upcoming test series and later core stage testing. The upcoming tests will also include the new engine controller design that replaces the RS-25’s original three-decade-old engine computer.
NASA plans to restart RS-25 production to provide engines for future flights by working with Aerojet Rocketdyne to further adapt and modify the engine design to be more affordable, while increasing the planned thrust to 521,700 pounds.
“We had identified significant cost and time saving ideas for the RS-25 before the shuttle program ended,” Wofford said. “We see many opportunities for process and manufacturing savings with the change to an expendable engine and the maturation of technologies, such as 3D printing and structured light scanning.”
Initial production will be for six new engines and more beyond that once NASA gains experience with the design and manufacturing changes. With that, the RS-25 is expected to be exploring space for many more decades and building on its space shuttle legacy.
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