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NASA's huge rocket needs engine with flight heritage

Posted: February 27, 2012

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NASA must find and purchase a cost-effective, proven cryogenic propulsion system for the first two flights of the agency's heavy-lift Space Launch System because the space agency is slowing development of behemoth rocket's Apollo-era upper stage engine to fit under a flat budget profile.

Artist's concept of the Space Launch System. Credit: NASA
The clock is ticking for the rocket to be ready in time for its first mission in late 2017. And NASA has a tight budget to pay for the upper stage, which is planned to send humans to the moon on a flight in 2021, according to agency managers.

The Space Launch System's initial missions are expected to dispatch Orion space capsules on flights around the moon and back to Earth. The 2021 launching will carry a crew.

Both flights will be powered into space by cryogenic core stage with four space shuttle main engines, known as RS-25D/E engines, and twin five-segment solid rocket boosters. But development of the J-2X upper stage engine, a redesigned version of a powerplant used on the Saturn 5 rocket, is being placed on the backburner to accelerate test flights of the Space Launch System's 70-metric ton configuration.

Instead, NASA is planning to procure an interim upper stage to fly in 2017 and 2021. The space agency released a request for information, or RFI, solicitation in January seeking information on industry concepts for the upper stage, and NASA received three responses, according to Todd May, the Space Launch System program manager at the Marshall Space Flight Center in Huntsville, Ala.

"We got a few interesting inputs back from industry on the cryogenic upper stage," May said in an interview. "We're in the process of taking that data in and then formulating our acquisition strategy as we move forward."

NASA has not decided when it will select an interim Space Launch System upper stage, or how it will procure the rocket system. Based on the number of responses in the RFI and tight funding and schedule requirements, there may be limited interest from contractors.

One possibility is the RL10 engine, which is used on the upper stages of the United Launch Alliance Atlas 5 and Delta 4 rockets. The hydrogen-fueled engine, produced by Pratt & Whitney Rocketdyne, was also used on the Saturn 1 rocket in the 1960s.

The RL10 engine has extensive flight history, high reliability, restart capability, and there are plans to human-rate the version of the engine that powers the Centaur upper stage on the Atlas 5 rocket.

Three of four companies in the running to build a commercial crew spacecraft have picked the Atlas 5 rocket as their launch vehicle. Another, slightly more powerful version of the RL10 engine flies on the second stage of the Delta 4 launcher.

Pratt & Whitney Rocketdyne would not comment on which, if any, companies proposed the RL10 engine in the NASA solicitation. ULA spokesperson Jessica Rye said the Colorado-based firm "did not respond directly" to the RFI.

Boeing Co. also declined comment, and Lockheed Martin Corp. did not respond to questions.

May also would not identify which companies supplied data to NASA on an interim upper stage, citing sensitivity in the ongoing procurement process. He also declined to provide an estimate for the budget NASA is setting aside for the stage, only saying "it's not a lot" in an interview with Spaceflight Now.

NASA's proposed budget for the SLS program calls for nearly $1.4 billion per year through fiscal year 2017, but the numbers can be adjusted by Congress or in future White House budget requests.

"We're in a very constrained budget environment, so it's going to have to come in on mark and show up in time for that first flight," May said. "We're in an environment these days where all of those things are important. We're thinking, in order to come in on budget, you're not going to want to have to do a lot of development to get it there for the first flight. We're really looking for something that is an existing capability with really only minor [changes]."

NASA's requirements state the interim upper stage must be hydrogen-fueled, rated for human launches, and capable of at least three ignitions with power the change the 26.5-ton Orion spacecraft's velocity by more than 6,800 mph.

Agency managers also set mass and length requirements for the rocket stage. The upper stage system must be delivered to the Kennedy Space Center by the end of 2016 to support the first SLS mission.

May said the critical path to support the heavy-lift rocket's 2017 launch date is in the cryogenic core first stage, a 27.5-foot-diameter rocket, the same size of the space shuttle's external fuel tank. Outfitting the core's main propulsion system is the toughest task in the early phase of the program, he said.

"The critical path for the first launch flows through the core of the rocket, specifically through what we call the main propulsion system, which is all the tubes that run through the large tanks and the core engines," May said.

The interim upper stage is just one example of NASA's plans to employ existing technology on the Space Launch System. Shuttle main engines, other orbiter propulsion components, and shuttle-derived solid rocket boosters will also fly on the early flights of the gargantuan launch vehicle.

The first SLS configuration will stand more than 30 stories tall and should haul 70 metric tons, or about 154,000 pounds, to low Earth orbit.

"We're essentially flying out assets we have while we try to evolve to a more afforable and capable booster for the future," May said.

According to May, the Space Launch System program is taking control of 15 existing space shuttle main engines, and there are enough parts in inventory to build one more powerplant, opening up the option to launch four-engine first stages.

Managers expect advanced liquid- or solid-fueled boosters and the J-2X upper stage engine to enter service on the third flight of the Space Launch System. Later flights will require the construction of new first stage engines when the space shuttle's inventory is exhausted.

The SLS will ultimately evolve to haul up to 130 metric tons into low Earth orbit.