SLS on pad with Moon
NASA says it’s ready for the fourth Space Launch System practice countdown at Launch Complex 39B, scheduled for June 20. Credit: NASA/Ben Smegelsky

PASADENA, Calif. — NASA is gearing up for a fourth attempt to perform a fueling test and practice countdown of its Space Launch System ahead of a launch now no earlier than the latter half of August.

During a June 15 call with reporters, agency officials said they were ready to proceed with a wet dress rehearsal (WDR) of the SLS at Launch Complex 39B. The test will begin with a “call to stations” for personnel at 5 p.m. Eastern June 18. Loading of liquid oxygen and liquid oxygen into the rocket’s core stage and upper stage will begin at 7 a.m. Eastern June 20, with the countdown ticking down to a T-0 at 2:40 p.m. Eastern that day.

The overall approach of the WDR will be similar to three attempts to complete the test in April. That includes counting down to T-33 seconds, recycling and then counting down to about T-10 seconds, stopping just before the core stage’s engines would ignite.

The three earlier attempts never reached the terminal stage of the countdown, running into a series of technical problems. NASA rolled the SLS back to the Vehicle Assembly Building (VAB) to perform repairs that included replacing a helium check valve in the rocket’s upper stage and fixing a hydrogen leak in ground equipment.

NASA also refined procedures for loading propellants into the core stage after running into issues with both liquid oxygen (LOX) and liquid hydrogen. “We saw some things with LOX when we loaded, and hydrogen,” said Jim Free, NASA associate administrator for exploration systems development. “Our team was able to go back in, in that time we had back in the VAB, to automate those procedures, which we know will help us,”

The changes are intended to prevent pressure fluctuations seen during loading in previous attempts, said Charlie Blackwell-Thompson, Artemis launch director. “Some of it was demonstrated last time as well but we were able to automate some of it, and then we’re also able to look at some other ways in which we might be able to do that,” she said.

NASA also promised to provide more real-time information for the upcoming WDR. During the three attempts in April, the agency provided only occasional blog posts and tweets, saying it could not provide more detailed technical information because of export control concerns, even though the agency provided such information during the shuttle program.

For the upcoming test there will be commentary during the fueling and countdown, Free said, along with “fantastic” graphics, although the agency will still not release the same level of detail as during the shuttle program. “We are trying to be more transparent,” he said.

Even if the upcoming WDR goes as planned, which was not the case the first three attempts, Free said a launch in the next available window, which opens July 26 and closes Aug. 10, is unlikely. “That late July/early August launch period is very difficult for us to hit,” he said, given the work needed after the WDR to return the vehicle to the VAB, make final preparations, and return to the pad. “I think we’re probably looking at the latter part of August.” That window opens Aug. 23 and closes Sept. 6, although there are no launch opportunities on Aug. 30, 31 and Sept. 1.

That schedule also assumes there are no major issues during the upcoming test. “This is the first time that we’re flying this vehicle, and I think we need to understand everything we can before we commit to launch,” he said when asked if NASA would proceed with a launch even if it did not complete every part of the WDR. “We’re going to understand what every situation is and run it to ground before we would press to commit to launch.”

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...