Struggling to stay within a flat budget for the heavy-lift Space Launch System (SLS), NASA plans to halt development of the J-2X rocket engine that will power its upper stage after the ongoing development-test series.

Once the pacing item for the defunct Ares I crew launch vehicle, the Saturn-heritage J-2X may not fly until well into the 2020s. With the SLS program office expecting an annual development budget of $1.2 billion, near-term engine-development money is deemed better spent on a throwaway version of the RS-25D space shuttle main engine (SSME) that will power the SLS main stage. That engine—designated RS-25E—will use advanced manufacturing and design changes to lower the cost of the reusable SSME.

“Because we don't know exactly what SLS will need from a certification standpoint now, we've taken the certification segment and said we'll push that out a little bit,” says Mike Kynard, who manages liquid-propulsion engine development for the SLS program. “That allows us to get the yearly budget profile down to the point that we can focus on -25D and E and get those guys up and going.”

The first full-duration 500-sec. burn, which Kynard says “ran great” on the basis of first-look analysis, sets up a minimum two-year test series with five J-2X development engines and other test articles. The series will lead to a milestone the engine program calls basic development complete. After that, J-2X development essentially will be put on hold until 2017-18 while rocket-engineering experts at NASA and Pratt & Whitney Rocketdyne (PWR) shift over to the RS-25E.

The J-2X program will resume with two certification engines before delivery of the first flight engine. Ron Ramos, PWR vice president for exploration and missile defense, says it will take six months to a year after certification testing before the first operational J-2X is ready to fly.

The first flight of the SLS—a lunar flyaround planned for 2017—will use some of the RS-25D engines left over from the shuttle program. NASA has 15 of the state-of-the-art liquid oxygen/liquid hydrogen engines that it plans to use for SLS development flights while it prepares the follow-on throwaway.

Using the heritage engine hardware instead of developing new systems follows an approach adopted across the SLS program in an effort to move ahead under flat spending.

“When you develop a large complex vehicle, you typically want a development curve [where] you peak out at critical design and then you come down,” says Todd May, NASA's SLS program manager. “Under a flat budget, you have to do some fairly innovative things to avoid that large hump. One of the things you can do is use things that have already been through that hump.”

The SLS program office at Marshall Space Flight Center has been able to keep some momentum going with residual Ares funding while Congress and the White House wrangled over whether there would be a government-owned heavy-lifter and what it would look like. Ultimately, spending-profile considerations shaped the SLS configuration as much as performance requirements for deep-space exploration.

“Our challenge is not so much technological,” May says. “It's how to field the biggest and most affordable rocket ever in an affordable way, and not just affordable but sustainable—'affordable' meaning we live within our means; 'sustainable' meaning we create a production and operations wedge so we can build the other things for the architecture to be able to explore in earnest.”

May says the engine choices also were driven by a top-level policy decision to go with U.S. strengths in that arena, instead of shifting to the liquid oxygen (LOX)/refined petroleum (RP) cycle that was under consideration. “Perhaps the biggest trade in getting to the configuration decision was whether to start out with core engines that have LOX/RP or LOX/hydrogen,” he says. “The SSMEs are the most advanced liquid-hydrogen engines in the world, [so] did we want to maintain that leadership or did we want to take the risk of starving that while we spent our precious few dollars on recreating a [very large] LOX/RP capability that, frankly, we abandoned, and make that the critical path to launch?”

The 15 remaining RS-25Ds will be stored at Stennis Space Center, Miss., until they are needed for the SLS. Kynard, who gained responsibility for RS-25 development along with J-2X upon selection of the SLS configuration, says the shuttle engines can be used essentially as they are, although NASA may decide to upgrade them with the controller developed for the J-2X.

“The controller avionics that we have now are much more inexpensive than the old shuttle controller,” he says. “Obviously, modern electronics are cheap. Even though it's space-rated, it's inexpensive, and now we can get economies of scale by having it do two engines.”

The shift to a common controller would take place while Kynard's liquid-propulsion team is completing development tests on the J-2X, running through the test series with the first engine—No. 10001—before moving on in January to detailed testing with a powerpack article consisting of the gas generator and turbomachinery. After that work, which will push the powerpack to “the corners of the envelope,” Kynard says, the program will move on to testing with the remaining development engines.

Completing development tests should take about two years, Kynard says. The RS-25E development should be well under way when the first SLS flight with the surplus RS-25Ds occurs at the end of 2017. The follow-on engine's design will change as little as possible so the development cost does not begin to consume more than the SLS program's expected $250 million annual engine development budget.

“We want to make changes to make it less expensive, but we do not want to lose the heritage of the more than 1 million seconds that we have,” Kynard says.

Changes include adopting the hot isostatic pressing technique PRW uses to bond the combustion chamber to its structural jacket on the RS-68 and J-2X to the RS-25D, and using modern manufacturing techniques for engine flex joints. The program also hopes to gain cost savings from supply-chain changes.

“One of the things we were very intentional about with J-2X was using RS-68 suppliers,” Kynard says. “That way Rocketdyne, when they went to a supplier, could use the buying power of both engines to get a better deal. We want to add RS-25 to that mix.”

NASA expects to spend $3 billion a year to develop the SLS, the Orion-based multipurpose crew vehicle (MPCV) and the ground infrastructure needed to send humans beyond low Earth orbit. The MPCV and SLS each will get $1.2 billion of that for development, on a schedule that would use a first-generation SLS by the end of 2017 to send an unmanned Orion capsule around the Moon. That shot will generate enough velocity to validate the capsule's thermal protection system for a 20,000-mph atmospheric reentry from deep space. A manned lunar flyaround would follow in 2021.

Just as those early flights will use existing SSMEs in the core stage, they will also use five-segment solid-fuel boosters developed for the Ares I first stage and perhaps a Delta IV upper stage. After that, the program will “evolve” the SLS from a 70-metric-ton capability to the 130-ton capability ordered by Congress.

Among plans for gaining that increase are adding engines to both stages, with as many as five RS-25Ds powering the main stage and two J-2Xs on the upper stage, and holding a competition for more capable solid- or liquid-fueled strap-on boosters (AW&ST Oct. 24/31, p. 40). Also in the wings are advanced developments like out-of-autoclave cryogenic propellant tanks that could save 30% in weight and 25% in cost over traditional aluminum tankage (see p. 24).

Meanwhile, NASA has just added an unmanned test flight of the MPCV in 2014 in an effort to reduce risk in developing the capsule, which can carry four astronauts beyond low Earth orbit and serve as a backup route to the International Space Station in case plans to use commercial carriers do not work out.

NASA will modify its contract with Orion prime Lockheed Martin to include the new test. The $372 million cost will come out of existing Orion funding but should not affect the schedule of the projected first flight in 2017, according to a NASA spokesman. The current value of Lockheed's Orion contract is $6.3 billion, of which $5 billion has been spent, according to company managers.

Known as Exploration Flight Test 1 (EFT-1), the mission will launch from Cape Canaveral. The launch vehicle has not yet been chosen, according to NASA, although Lockheed has considered a Delta IV Heavy for the job. In the test, the Orion-based vehicle will fly two Earth orbits before reentering the atmosphere at 84% of the speed of the reentry from a lunar mission. The capsule will splash down for an ocean recovery.