August 02, 2013
NASA’s heavy-lift Space Launch System (SLS) should be able to reach the high-retrograde lunar orbit where the agency wants to reposition a small asteroid, based on the results of its successful preliminary design review (PDR).
Top SLS managers at Marshall Space Flight Center say the planned 321-ft.-tall, 70-ton-capability block 1 vehicle passed muster with a series of review boards for a first flight in 2017. That unmanned mission is tentatively set to fly 7,000 km (4,350 mi.) behind the Moon, according to SLS Chief Engineer Garry Lyles, provided upcoming wind tunnel tests validate operational solutions to some transonic buffeting engineers believe the big new rocket will experience on ascent.
While the fate of the asteroid relocation mission is the subject of partisan debate on Capitol Hill, Lyles says the lunar orbit targeted for an eventual astronaut/asteroid rendezvous remains the primary design reference mission for the SLS first flight. Placing astronauts in that orbit with an Orion crew vehicle would be the first human mission beyond low Earth orbit since the Apollo era, and is NASA’s goal regardless of the outcome of the relocation debate because of the technologies it would exercise.
“We design to a capability, so that mission happens to be within our capability,” Lyles says. “We have several design reference missions. Those design reference missions we will usually take the [most difficult] of those within the capability of the block one vehicle and design to that.”
Lyles and Todd May, NASA’s SLS program manager, said the PDR was the most significant technical hurdle the heavy-lifter must overcome before it is built and flies. Experts from around the nation, working inside and outside NASA, reviewed some 200 technical documents and 15 terabytes of data to clear the development project on up the chain. Still to come before critical design review is certification by Administrator Charles Bolden to his White House bosses that NASA can build the vehicle as specified, which will follow headquarters-level reviews based on the PDR that are scheduled through the fall.
Among the issues that must be resolved before detailed design can be completed is how to mitigate the aerodynamic buffeting expected between the solid-fuel boosters and the liquid-fueled upper stage. Proposed fixes, which generally involve modifying how the vehicle is flown during ascent, will be validated in upcoming wind tunnel tests scheduled to begin Aug. 19, Lyles says.
“Those tests will run about two months’ time, and will basically demonstrate that we can reduce our air acoustic and aerodynamic loads,” he says. “ … That will basically eliminate a good many of our loads [issues] on the vehicle, so I think we have a good plan.”