NASA will resume efforts to complete a major test to fuel the Space Launch System rocket on Tuesday.
The space agency decided to modify this test, though, due to a problem with a check valve in the upper stage of the rocket leading to a pressurized helium bottle. The valve was discovered to be stuck last week and will need to be replaced.
With the valve in this position, NASA does not feel it would be safe to load the upper stage with cryogenic oxygen and hydrogen during the “wet dress” test as originally planned. Therefore, Thursday’s test will only feed the core stage – the largest and least proven part of the missile – during the tank’s operations. As part of this test, the launch system will be entered into the final countdown before being cut into the T-10 seconds.
NASA plans to collect a range of data from this test, and that information will inform the agency’s plans moving forward, officials said during a conference call with reporters Monday. After about 10 days of testing, NASA will return the SLS rocket to the Vehicle Assembly Building. There, technicians will remove the check valve, which is about 8 cm long, and check the part to understand why it is malfunctioning. They can then be replaced, said John Blevins, chief engineer for the SLS, which should be a relatively simple process.
“We are very comfortable with the path forward,” said Tom Whitmaier, associate deputy director of Joint Exploration Systems Development at NASA Headquarters in Washington. “We think it’s a great way forward.”
Officials on Monday seemed confident they could get a lot of good data from Thursday’s test. For example, during the final countdown from T-10 minutes to T-10 seconds, launch director Charlie Blackwell-Thompson said, there are approximately 25 “critical events” in the missile’s test targets. She said that only two of those are upper-level.
“There’s a great deal of testing, data, and risk that you’re getting in terms of core stage, ground systems, and relative to boosters,” she said.
The upper stage, known as the temporary cryogenic propulsion stage, was manufactured by the United Launch Alliance and delivered to the Kennedy Space Center about four years ago. However, SLS’ chief engineer, John Blevins, said he did not believe the valve problem was due to any shelf life issues. He said the check valve in question is designed to operate for 20 years or more.
“two days” becomes “two weeks”
The wet test was originally supposed to last two days when it began on Friday, April 1. But partly due to a problem with fans in the portable launch tower, the first attempt to refuel the rocket had to be cleaned up on April 4. A second attempt last week saw NASA fill the core stage about halfway with liquid oxygen before the agency discovered that the core stage’s “vent valve,” which is manually adjusted, had been left wrongly in the wrong position. Then NASA discovered the problem with the check valve in the upper stage.
Now, teams of NASA employees and contractors will be called to their stations again Tuesday evening to prepare the vehicles and ground systems for a third fuel loading. Actual refueling of the vehicle is scheduled to begin Thursday morning, with the final countdown reaching 2:40 p.m. ET (18:40 UTC). This exact schedule, of course, assumes no further delay, which seems unlikely for a two-day test that spanned two weeks.
When asked to assess the next steps after this test in terms of preparing the SLS rocket and Orion spacecraft for an uncrewed test flight later this summer, NASA officials did not want to look beyond the conclusion of this primary tank stage. They declined to say whether the missile would undergo a second test of the entire vehicle to ensure the flight-readiness of the upper stage and its ground systems.
“I don’t think we’re ready to really say, one way or another, what we think the next step will look like,” Whitmer said. “I think we really need to do the test on Thursday and then look at the data.”
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