Trevor Mahlmann
NASA will resume its efforts on Tuesday to complete a major fuel test of the Space Launch System rocket.
However, the space agency has decided to modify this test due to a problem with a check valve on the top stage of the rocket that leads to a pressurized helium cylinder. The valve turned out to be stuck last week and will have to be replaced.
With the valve in this position, NASA does not consider it safe to charge the upper stage with cryogenic oxygen and hydrogen during the “wet dress” test as originally planned. That’s why Thursday’s test will only feed the nuclear phase — the missile’s largest and least proven component — during tank operations. As part of this test, the launch system is put into a terminal countdown before aborting at T-10 seconds.
NASA plans to collect a wealth of data from this test, and this information will inform the agency’s plans going forward, officials said during a media conference call with reporters on Monday. About 10 days after the test, NASA will roll the SLS rocket back into the Vehicle Assembly Building. There, technicians will remove the check valve, which is about 8 cm long, and inspect the part to understand why it is defective. It can then be replaced, which should be a relatively simple operation, said John Blevins, SLS’ chief engineer.
A path forward
“We’re very comfortable with the path forward,” said Tom Whitmeyer, deputy associate administrator for common exploration systems development at NASA headquarters in Washington. “We think it’s a great way forward.”
Officials on Monday’s conference call seemed confident they could extract a lot of good data from Thursday’s test. For example, said launch director Charlie Blackwell-Thompson, during the terminal’s countdown from T-10 minutes to T-10 seconds, there are nearly 25 “critical events” in the missile’s test targets. Only two of them are specific to the upper phase, she said.
“There’s a significant amount of testing and data and risk redemption that you get against the core stage, the ground systems and against the boosters,” she said.
The upper stage, known as the Interim Cryogenic Propulsion Stage, was manufactured by United Launch Alliance and delivered to Kennedy Space Center about four years ago. However, SLS’ chief engineer, John Blevins, said he doesn’t believe the valve problem was due to shelf-life issues. The check valve in question, he said, has been rated to function for 20 years or more.
“Two days” becomes “two weeks”
The wet dress test was originally scheduled to last two days when it began on Friday, April 1. But partly due to a problem with the fans on the Mobile Launch Tower, the first attempt to fuel the rocket had to be scrubbed on April 4. A second attempt last week saw NASA fill the core stage about halfway with liquid oxygen before discovering that a core stage “vent valve,” which is manually adjusted, had been accidentally left in the wrong position. Then NASA discovered the problem with the check valve on the top stage.
Now Tuesday evening, teams of NASA employees and contractors are being called back to their stations to prepare the vehicle and ground systems for the third time for propellant loading. Actual refueling of the vehicle is scheduled for Thursday morning, with the terminal’s countdown at 2:40 PM ET (6:40 PM UTC). That precise timeline, of course, assumes no further delays, which seems unlikely for a two-day test extended to two weeks.
Asked to assess the next steps after this test in terms of getting the SLS rocket and Orion spacecraft ready for an unmanned demonstration flight later this summer, NASA officials didn’t want to look too far beyond the conclusion of this tanking in the core phase. They declined to say whether the missile could be subjected to a second full-vehicle wet dress test to ensure the flight readiness of the upper stage and its ground systems.
“I don’t think we’re ready to somehow really say what we think the next step will look like,” Whitmeyer said. “I think we should really do the test on Thursday and then look at the data.”
