Trevor Mahleman
NASA will continue efforts to complete major tests of its Space Launch System rocket fuel on Tuesday.
The space agency decided to modify this test, due to a problem with a check valve on the top of the rocket leading to a pressurized helium bottle. The valve was found stuck last week and needs to be replaced.
With the valve in this position, NASA did not feel it was safe to load the top stage with cryogenic oxygen and hydrogen during the “wet shirt” test as originally planned. Therefore, Thursday’s test will only feed the core stage – the largest and least proven part of the missile – during tank operations. As part of this test, the launch system will be put into a final countdown before being cut to T-10 seconds.
NASA plans to collect a variety of data from these tests, and that information will inform the agency’s plans for 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, the technician will remove the check valve, which is about 8 cm long, and inspect the section to understand why it is not working. They can then be replaced, said John Blevins, chief engineer for the SLS, which should be a relatively simple process.
way forward
“We are very comfortable with the way forward,” said Tom Whitmaier, associate director of Joint Exploration Systems Development at NASA Headquarters in Washington. “We think that’s a great way forward.”
Officials on Monday looked confident they could get a lot of good data out of Thursday’s test. For example, during the final countdown from T-10 minutes to T-10 seconds, launch director Charlie Blackwell-Thompson said, there were about 25 “significant events” at the missile test target. He said that only two of them were top level.
“There’s a lot of testing, data, and risk you get in terms of the core stage, the ground system, and relative to the booster,” he 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 a shelf life issue. He said the check valve in question was designed to operate for 20 years or more.
“two days” becomes “two weeks”
The wet test was supposed to last two days when it started on Friday, April 1. But in part due to problems with the fan in the portable launch tower, the first attempt to refuel the rocket had to be cleared 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 manually adjusted core stage “vent valve” had been left incorrectly in the wrong position. Then NASA discovered a 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 ground vehicles and systems for a third fuel load. Actual vehicle refueling is scheduled to begin Thursday morning, with the final countdown hitting 2:40 p.m. ET (18:40 UTC). This exact schedule, of course, does not assume any further delay, which seems unlikely for a two-day test lasting two weeks.
When asked to assess the next steps after this test in terms of preparing the SLS rocket and Orion spacecraft for unmanned test flights later this summer, NASA officials did not want to look beyond the conclusions of this primary tank stage. They declined to say whether the missile would undergo a second full-vehicle test to ensure flight readiness of its top-stage and ground systems.
“I don’t think we’re ready to actually say, in one way or another, what our next move will be,” Whitmer said. “I think we really need to do a test on Thursday and then look at the data.”
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