Reports on Thursday indicated that NASA has settled on a design for the Space Launch System (SLS) heavy-lift booster that would be largely shuttle-derived, but would offer some room for competition. According to Aviation Week and NASASpaceFlight.com, the SLS design will be only slightly different from the reference design released in an interim report to Congress in January, using a core stage based on the shuttle’s external tank and fitted with Space Shuttle Main Engines (SSMEs), later transitioning to the RS-25E expendable variant. The upper stage would use the J-2X engine slated to begin test firings this month at the Stennis Space Center.
That reference design had originally called for the use of five-segment solid rocket boosters. While the reports indicated that SRBs will be used for initial launches, there will be a competition between SRBs and a liquid-propellant booster built by Teledyne Brown and powered by a variant of Aerojet’s AJ-26 engine (itself based on Russian NK-33 engines), at least for the “evolved” beyond Earth orbit SLS version. That approach would at least partially address calls for an open SLS competition made earlier this week by Sen. Richard Shelby (R-AL), which came on the heels of a similar letter by Sens. Barbara Boxer and Dianne Feinstein (D-CA), especially since Teledyne Brown is based in Alabama and Aerojet is headquartered in California.
According to NASASpaceFlight.com, a formal announcement of the SLS plan would come on July 8, the same day as the last shuttle mission is scheduled to launch. That could address some concerns about the lack of details about the follow-on to the shuttle. The NASASpaceFlight.com article cites an “impassioned” speech by shuttle launch director Mike Leinbach after a recent countdown simulation where he was critical of the lack of information regarding what happens after the shuttle. “The end of the shuttle program is a tough thing to swallow and we’re all victims of poor policy out of Washington DC, both at the NASA level and the executive branch of the government,” Leinbach said. “I’m embarrassed that we don’t have better guidance out of Washington DC.”