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NASA doesn’t need to test SLS anymore, but the Senate mandates it anyway


Photo of SLS core stage hot fire test.
Enlarge / During a second attempt, the SLS core stage fires for a full eight minutes at Stennis Space Center in Mississippi.

Trevor Mahlmann

After spending more than 15 months at the Stennis Space Center in Southern Mississippi, the core stage of NASA’s large Space Launch System rocket departed for Florida in late April. Preparations are now underway for launching this mammoth rocket from Kennedy Space Center, likely sometime in early 2022.

For US Senator Roger Wicker, a Republican from Mississippi, the months with the SLS rocket nestled onto a test stand in his home state kindled memories of NASA’s glory days, when engine and rocket test firings were more common at the space center. “Seeing and hearing all four engines of the SLS core stage fire together for the first time was thrilling,” Wicker said after one of the SLS test firings.

But even as he was celebrating the Stennis hot fire tests, Wicker must have been wondering what his center would do after the SLS rocket was gone. During the 15-month test campaign, officials from NASA and the core stage contractor, Boeing, made it plain that they only needed to perform ground test firings of this vehicle one time. Future SLS rockets would ship straight from the factory in Michoud, Louisiana, to the Florida launch site.

US Senators, however, have some power. And Wicker clearly wanted more high-profile tests for the Mississippi center in order to keep the center’s workforce engaged, so Stennis may well have more tests.

Endless Test Firings Act

The US Senate passed the Endless Frontier Act this week to bolster US research and innovation. It carried a number of amendments, including NASA “authorization” language sponsored by Sen. Maria Cantwell, a Democrat from Washington. Most notably, Cantwell told NASA it must select a second provider to build a Human Landing System for the Artemis Moon Program, alongside SpaceX.

This provision was dubbed the Blue Origin “bailout” by some critics, because it authorized the $10.03 billion that would allow NASA to fund a lander built by Blue Origin. (It does not expressly appropriate the funding, however, leaving NASA with a potential unfunded mandate.) Blue Origin is based in Cantwell’s state of Washington.

But there was more to the NASA amendment. Wicker co-sponsored it and got his own language added to the bill. The Stennis-specific provision says NASA should “initiate development of a main propulsion test article for the integrated core stage propulsion elements of the Space Launch System, consistent with cost and schedule constraints, particularly for long-lead propulsion hardware needed for flight.”

So what exactly is a “main propulsion test article,” and why does NASA need one? According to a Senate staffer, who spoke to Ars on background, this would essentially be an SLS core stage built not to fly, but to undergo numerous tests at Stennis. “Testing on the actual flight hardware is risky from a schedule perspective,” the staffer said. Astronauts would be safer, too, if the SLS vehicle could be subjected to testing under more extreme conditions, he said.

This seems a somewhat curious rationale, as NASA has already said the SLS core stage does not need to be subjected to further ground tests. Rather, the agency is pushing to fly the vehicle as soon as possible, as it is sensitive to criticism that the rocket is years behind schedule, billions of dollars over budget, and viewed by detractors as a jobs program.

After the second “Green Run” test firing of the core stage in March, NASA’s program manager for the SLS rocket, John Honeycutt, said the agency had gotten all of the data it needed. “This longer hot fire test provided the wealth of data we needed to ensure the SLS core stage can power every SLS rocket successfully,” Honeycutt said.

Such a test article is not without precedence. NASA’s shuttle contractor, Rockwell, built a “main propulsion test article” for the space shuttle in the 1970s, and it underwent more than a dozen test firings at Stennis. However, this test campaign ended in January 1981, three months before the first space shuttle launch. In other words, the shuttle test article, with its three main engines, served to uncover any problems before flight.

That will not happen with the SLS test article. NASA is planning the first launch of this rocket, with its core stage, within the next nine months. After this test flight, launching an uncrewed Orion around the Moon, a second flight with astronauts is due to follow in 2023, with potentially a third mission in 2024. The whole point of a test article is to test the system before a high-stakes launch, not afterward.

Delivery, when?

The plan to build a “main propulsion test article” for the SLS rocket becomes even more absurd when we consider how very late in the game it would arrive.

It seems unlikely that Boeing—which presumably would build this test article, as it already is responsible for the core stage—could deliver a vehicle any time soon. The Senate staffer said he could not provide a cost estimate for the test article, nor say when it would be built. However, to make an educated guess, we might consider the timeline for the space shuttle test article. NASA awarded the test vehicle contract to Rockwell in 1972, and the vehicle did not arrive in Stennis until more than five years later, in September 1977. The first test firing took place in April 1978.

The space shuttle external tank for the Main Propulsion Test Article rolls off the assembly line September 9, 1977 at the Michoud Assembly Facility in New Orleans.
Enlarge / The space shuttle external tank for the Main Propulsion Test Article rolls off the assembly line September 9, 1977 at the Michoud Assembly Facility in New Orleans.

NASA

Boeing is already going to be hard-pressed to deliver three flight-worthy SLS core stages within the next five years. The Cantwell-Wicker legislation, which must still be approved by the US House and may well be amended there, is unlikely to become law for several months. And then funds must actually be appropriated for this test article, which almost certainly would not happen until the end of this year. At best, then, the contract for an SLS propulsion test article could be awarded in early 2022. In all likelihood, therefore, this test article would not arrive in Stennis until 2027, and perhaps not be ignited until 2028.

By then, presumably, NASA’s Space Launch System program will either have flown several flights or been canceled because it has been superseded by lower-cost commercial rockets.



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