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NASA no longer needs to test SLS, but the Senate still gives it a mandate

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

Trevor Mahlmann

After spending more than 15 months at the Stennis Space Center in southern Mississippi, the core phase of NASA̵

7;s large Space Launch System rocket drove to Florida in late April. Preparations are now underway to launch this mammoth rocket from the Kennedy Space Center, probably sometime in early 2022.

For U.S. Senator Roger Wicker, a Republican from Mississippi, lit the months with the SLS rocket at a test booth in his home state reminiscent of NASA’s heyday, when shots of engine and rocket samples were more common in the space center. “It was exciting to see and hear all four engines in the SLS core shoot together for the first time,” Wicker said after one of the SLS test triggers.

But even as he celebrated Stennis’ hot fire test, Wicker must have wondered what his center would do after the SLS rocket was gone. During the 15-month test campaign, NASA officials and main contractor Boeing made it clear that they only needed to perform ground test firings of this vehicle once. Future SLS rockets will be shipped directly from the plant in Michoud, Louisiana, to the launch site in Florida.

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

Endless Test Firings Act

The U.S. Senate passed the Endless Frontier Act this week to bolster U.S. research and innovation. It contained a number of changes, including NASA’s “authorization language” sponsored by Senator Maria Cantwell, a Democrat from Washington. In particular, Cantwell told NASA that it must choose another provider to build a Human Landing System for the Artemis Moon program along with SpaceX.

This provision was called the “rescue” of blue origin by some critics because it approved $ 10.03 billion, which allowed NASA to finance a lander built by Blue Origin. (The funding is not explicitly appropriate, leaving NASA with a potentially unfunded mandate.) Blue Origin is based in Cantwell’s state of Washington.

But there was more to the NASA change. Wicker co-sponsored it and had his own language added to the bill. The Stennis-specific provision states that NASA should “initiate the development of a main propulsion test article for the integrated core propulsion elements of the Space Launch System, in accordance with cost and schedule constraints, particularly for long-range propulsion hardware required for flight.”

So what is a “main propulsion test article”, and why does NASA need one? According to a Senate employee who spoke with Ars in the background, this would be essentially an SLS core phase built not to fly, but to undergo several tests at Stennis. “Testing on the current aircraft hardware is risky from a schedule perspective,” the employee said. Astronauts would also be safer if the SLS vehicle could be tested under more extreme conditions, he said.

This seems a somewhat curious reason, as NASA has already said that SLS core steps do not need to be subjected to further tests on Earth. Rather, the agency is pushing to fly the vehicle as quickly as possible, as it is sensitive to criticism that the rocket is years on schedule, billions of dollars over budget and considered by opponents as a job program.

Following the second “Green Run” test firing of the nuclear phase in March, NASA’s program director for the SLS rocket, John Honeycutt, said the agency had been given all the data it needed. “This longer heat fire test provided the wealth of data we needed to ensure that the SLS core stage could power each 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 shots at Stennis. However, this test campaign ended in January 1981, three months before the first launch of the space shuttle. In other words, the shuttle test article with its three main engines served to uncover any problems Before flight.

This will not happen with the SLS test article. NASA is planning the first launch of this rocket with its core phase within the next nine months. Following this test flight, which launches an unmanned Orion around the moon, another flight with astronauts will 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 afterwards.

Delivery, when?

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

It seems unlikely that Boeing – which would presumably build this test item as it is already in charge of the core phase – could deliver a vehicle soon. The Senate employee said he could not provide a cost estimate for the test item nor say when it would be built. To give a well-educated guess, however, we may consider the timeline of the article on the space shuttle. NASA awarded the test vehicle contract to Rockwell in 1972, and the vehicle first arrived in Stennis more than five years later, in September 1977. The first test firing took place in April 1978.

The space shuttle's external tank for the main propulsion test article rolls out of the assembly line on 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 on September 9, 1977 at the Michoud Assembly Facility in New Orleans.


Boeing will already be under heavy pressure to deliver three airworthy SLS core stages within the next five years. The Cantwell-Wicker legislation, which is yet to be approved by the US House and may well be amended there, is unlikely to be enacted for several months. And then funds actually have to be set aside for this test item, which almost certainly would not happen until the end of this year. At best, the contract for an SLS propulsion test article could be awarded in early 2022. In all likelihood, therefore, this test article would first arrive in Stennis before 2027 and might not ignite before 2028.

By that time, presumably, NASA’s Space Launch System program would have either flown several flights or been canceled because it has been replaced by cheaper commercial rockets.

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