SLS on pad
The first SLS on the pad at Launch Complex 39B for a countdown test scheduled for April 3. If that schedule holds it would delay a Crew Dragon launch to the ISS by at least a day. Credit: SpaceNews/Jeff Foust

WASHINGTON — A practice countdown for NASA’s Space Launch System could cause a delay in the launch of a commercial mission to the International Space Station, a move with potential ripple effects for other missions to the station.

Officials with NASA, Axiom Space and SpaceX said March 25 that they successfully completed a flight readiness review for the Ax-1 mission to the ISS. A Falcon 9 is scheduled to launch the Crew Dragon spacecraft on that mission April 3 from Launch Complex 39A at the Kennedy Space Center.

However, NASA is also planning to conduct a wet dress rehearsal (WDR) of the first Space Launch System from neighboring Launch Complex 39B that day. During that test, the rocket will be loaded with liquid oxygen and liquid hydrogen propellants and go through a practice countdown that stops at around T-10 seconds, just before the core stage’s RS-25 engines would ignite.

NASA said at a briefing after the Ax-1 flight readiness review that the Artemis 1 WDR would have priority, assuming both remain on their current schedules. “Right now, Artemis 1 wet dress has the range. Our plan is to get that done as early as possible,” said Kathy Lueders, NASA associate administrator for space operations. “We’ve still got 8 to 10 days of processing on both sides to get there.”

She said there have been daily meetings among the NASA and SpaceX teams working on their respective missions, with another “check point” on March 28. “From a planning perspective, it made a lot of sense for us to just get the wet dress mission done,” she said, “and then letting us have the time for successive launch attempts.”

If the Artemis 1 WDR does take place as planned, the earliest Ax-1 could launch is April 4 at 12:50 p.m. Eastern. Lueders said one of the factors that drives separation between the two missions is commodities like nitrogen gas needed at both launch sites. At one point, she said that might require a two-day separation between the missions, but that teams worked to shorten that to a day. “Potentially, if we get wet dress off on the 3rd, maybe we could launch on the 4th.”

Like other Crew Dragon missions to the ISS, Ax-1 has an instantaneous launch window once per day. A complicating factor is the next NASA crew rotation mission to the ISS, Crew-4, which will launch on another Crew Dragon no earlier than April 19.

“We’ve got a little bit of buffer” in the schedule, said Dana Weigel, NASA ISS deputy program manager. NASA wants two days between the Ax-1 splashdown and Crew-4 launch, so Ax-1 could launch on its 10-day mission as late as April 7 without affecting the Crew-4 launch date, she said.

A complicating factor, though, is weather at the splashdown site, which could delay the return of Ax-1. “I think the real key for us is getting off as early as we can. We’ll want to take those early opportunities, assuming we have good launch weather, because we don’t know what we’ll get on the back end for undocking,” Weigel said.

Any delays in the return of Ax-1 after April 17 would cause a day-for-day slip in Crew-4. NASA wants to have the Crew-3 Crew Dragon spacecraft currently at the station to return with its four astronauts by May 10, about six months after its launch and after a five-day handover between Crew-3 and Crew-4.

The schedule conflict, though, is the only major issue with Ax-1 mission. That mission, the first in a series by Axiom Space as precursors to adding a commercial module to the ISS, will carry a former NASA astronaut, Michael López-Alegría, and three customers: Larry Connor, Mark Pathy and Eytan Stibbe. All have completed training and are in pre-launch quarantine, said Michael Suffredini, company president and chief executive.

The Ax-1 mission will be the first for a Dragon spacecraft since a cargo Dragon spacecraft splashed down Jan. 24 after one of its four main parachutes was slow in opening. A similar “lagging” parachute was observed on the Crew-2 splashdown in November.

Bill Gerstenmaier, vice president of build and flight reliability at SpaceX, said the company investigated the lagging parachutes but could not find a root cause for the issue, adding that it did not affect the safety of either splashdown.

“We could not find anything that stood out as a contributing cause,” he said. “We spent a lot of time looking at that to figure out if there was anything we were missing. We can’t find anything. It’s almost a feature of this design.” He added SpaceX would dedicate more bandwidth to cameras on the spacecraft during reentry to get better imagery of the parachute deployment.

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...