WASHINGTON — As NASA studies ways to accelerate development of the Space Launch System, an independent safety panel called on the agency to retain a major upcoming test of the vehicle.

NASA had been contemplating eliminating the so-called “green run” of the SLS core stage as a way to cut several months of schedule. In that test, the completed core stage would be brought to the Stennis Space Center and placed on a test stand, where its four RS-25 engines would be fired for eight minutes, simulating the actual flight of the vehicle.

In testimony before a House appropriations subcommittee in March, NASA Administrator Jim Bridenstine said the agency was studying doing away with the green run test. Instead, NASA would ship the completed core stage directly to the Kennedy Space Center, where its engines would be briefly fired on the pad at Launch Complex 39B.

Bridenstine suggested in his testimony that alternative testing of the RS-25 engines could eliminate the need for the green run. “Could we test each engine individually at very high off-nominal kinds of conditions to get certainty, or at least eliminate as much risk, or almost as much risk, as we would if we ran the green run?” he said. Doing so, he said then, could cut six months from the vehicle’s development schedule as NASA sought ways to keep the first SLS launch scheduled for 2020.

However, at an April 25 meeting of the Aerospace Safety Advisory Panel (ASAP) at the Marshall Space Flight Center, members recommended that NASA carry out the green run test as one of several milestones to ensure the vehicle is safe to carry crewed spacecraft.

“There is no other test approach that will gather the critical full-scale integrated propulsion system operational data required to ensure safe operations,” Patricia Sanders, chair of the panel, said of the green run test. “Shorter-duration engine firings at the launch pad will not achieve an understanding of the operational margins, and could result in severe consequences.”

“I cannot emphasize more strongly that we advise NASA to retain this test,” she added.

NASA has not provided an update on efforts to accelerate SLS development since Bridenstine, speaking at the National Space Council meeting March 26 in Huntsville, Alabama, concluded that it was not feasible to shift Exploration Mission (EM) 1 from the SLS to commercial vehicles. However, there is growing belief in the space industry that NASA will keep the green run test even if it jeopardizes the ability to launch the SLS in 2020.

Sanders said at the meeting that the committee was aware NASA was trying to launch EM-1 as soon as possible, and that effort could find ways to streamline the process. “But as NASA evaluates different paths to potentially accelerate the EM-1 flight, it cannot lose sight that the ultimate objective of that flight is to mitigate risk and provide a clear understanding of the risk posture prior to the first crew flight,” she said.

She noted there are two approaches NASA can take to test flights like EM-1: either waiting to launch until all flight components have been qualified, or launching earlier and incorporating data into the qualification process. Each approach as its own strengths and weaknesses, she said. “Determining the proper timing of an integrated flight test requires a deliberate, detailed and important dialogue on the risk tradeoffs for the overall program,” he said.

Aging spacesuits

In a separate discussion at the meeting, panel members raised concerns about aging extravehicular mobility units (EMUs): spacesuits worn by astronauts who perform spacewalks, or extravehicular activities (EVAs), outside the International Space Station. Those units are decades old and, the panel believes, represent a growing safety risk.

“The EMUs used for ISS are now about 40 years old and aging out,” said Susan Helms, a panel member and former astronaut. NASA seeks to extend the life of those suits to 2028, but she argued that is insufficient.

“The view of this panel is that, in spite of their heroic efforts, the current suit is now outside its design life and we are growing increasingly concerned about the risk posture that NASA has adopted with the current suit,” she said. “We recommend that NASA begin an immediate transition to a next-generation EVA suit system before the risk becomes unmanageable.”

Another committee member and former astronaut, Sandra Magnus, agreed, saying that NASA is too focused on the day-to-day issues of maintaining the current spacesuits to see the overall issue with the risk the suits pose. “I would like to invite the NASA management to really take themselves out of the system for a moment and look at this particular issue objectively, because it’s really important,” she said.

“We have reached a point with the EMUs where it’s time to retire the current suit and move on to a next-generation suit,” Helms said.