Valves are a regular concern at SpaceX, just like every other space company

SpaceX is launching a mission about once every four days, and most of those flights are going to space to deploy Internet satellites for the company's own Starlink broadband network. But this week is different. Aside from two more missions carrying Starlink satellites, SpaceX is preparing to send a four-person crew to the International Space Station early Friday.

The crew launch from the Kennedy Space Center in Florida will deliver NASA commander Jasmin Moghbeli, European Space Agency astronaut Andreas Mogensen, Japanese astronaut Satoshi Furukawa, and Russian cosmonaut Konstantin Borisov to the space station for a half-year stay. This mission, known as Crew-7, will be SpaceX's 11th astronaut flight and the company's seventh operational crew rotation mission for NASA using a Crew Dragon spacecraft.

Bill Gerstenmaier, SpaceX's vice president of build and flight reliability, says these crew missions are special. SpaceX and NASA managers met Monday for a flight readiness review, a customary milestone before every crew launch, to deliberate on any problems that could affect the upcoming mission.

“It’s nice to get a chance to step back and look at all the issues, problems, and things that are going right with the vehicles," Gerstenmaier said. "We get a chance to take a look at the Falcon vehicle maybe in a little more in-depth way for crew flights than we do for other flights. We know the importance of flying crew, and the trust that the crew puts in us in delivering."

SpaceX has launched its Falcon 9 and Falcon Heavy rockets 81 times over the last year (that number could climb to 83 by the end of the week). Since the start of 2023, the company has launched its Falcon rockets 57 times, on pace for roughly 90 missions by the end of the year. For an orbital-class rocket, this is an unmatched launch rate in the entire history of spaceflight.

“We have separate teams that are monitoring all these activities," Gerstenmaier said. "In fact, we can support launches from three pads simultaneously with our support teams the way we are. So we’re not overstressed, we’re not overworking the workforce."

According to BryceTech, SpaceX launched more than 447 metric tons of payload mass in the first half of this year, nearly 10 times more than all Chinese rockets.

"From the outside, it may look like we’re flying a lot of flights, and they’re all trouble-free," Gerstenmaier said. "They are not all trouble-free. They are not easy. Every time we fly, we learn something. We spend the time to go analyze it."

Cleared for flight

NASA and SpaceX officials gave the green light Monday to proceed with preparations to launch the Crew-7 mission Friday, but only after formally signing off on several technical issues. One of those involved a drogue parachute that took longer than anticipated to fully inflate on a Dragon crew capsule returning from the space station earlier this year.

That issue was cleared for the launch of the Crew-7 mission during the flight readiness review.

“The parachute system is something that we monitor very carefully," said Steve Stich, manager of NASA's commercial crew program. "We have imagery of the chutes every landing, and SpaceX has done a great job of recovering those chutes from every single landing.”

Stich said the other "special topic" discussed Monday was a valve failure on a Dragon cargo capsule in June. During that mission, an isolation valve in the Dragon's propulsion system became stuck. There was no effect on the Dragon resupply mission because the valve in question is only used if there's a problem elsewhere in the propulsion system, when it would close or isolate a leaky thruster to avoid losing propellant.

SpaceX engineers removed the stuck valve from the Dragon cargo capsule after it splashed down at the end of its mission in June. They found signs of corrosion.

"The corrosion is caused by oxidizer vapors mixing with a little bit of moisture," Stich said. "The materials are corrosion resistant, but if you get enough vapor from the oxidizer along with water, you can form a little bit of acid and get some corrosion."

That may sound familiar for Ars readers. A test flight of Boeing's delay-stricken Starliner crew capsule, which still hasn't flown with astronauts, was grounded in 2021 after engineers discovered stuck valves in the spacecraft's propulsion system just hours before launch. Inspections revealed corrosion in the valves caused by moisture mixing with vapors of nitrogen tetroxide, the oxidizer used for maneuvering thrusters on both Starliner and Crew Dragon.

Stich said the process that led to the corrosion is "somewhat similar" to the issue facing the Starliner and Dragon spacecraft. "We have, on the valves, an environmental seal that leaks a little bit of vapor across into the dry side of the valve, which is the electrical part that actuates the valve, and then forms corrosion on the components inside, combined with a little bit of moisture," he said.

There were numerous stuck valves inside Boeing's Starliner spacecraft, delaying its unpiloted test flight by more than nine months. Over the last couple of months, SpaceX was able to remove valves on the Crew Dragon Endurance spacecraft slated to fly the Crew-7 mission, replace some parts in the valves, then reassemble them and test them on the capsule. "We know all of those valves are functioning just fine," Stich said.

"We’re very agile in the fact that we can get into tests (of hardware)," Gerstenmaier said. "We have a lot of vertical integration. We can do things ... to tear valves apart and dissect things. We use the NASA team where appropriate. We shift some of the work to them to go take a look. I think that’s a strength between us both to make sure we’re ready to fly.”

The valves on SpaceX's Crew Dragon Endeavour spacecraft currently docked at the space station are also functioning as designed. Ground teams will likely remove and inspect those valves after the capsule returns to Earth next month, following the launch of the Crew-7 mission.

"I would say we learned quite a bit from the investigation we did on Starliner, and it probably helped us get to the root cause a little bit faster on the Dragon valve issue," Stich said. "The materials inside the valves are a little different, so the kind of corrosion is a little different between the Dragon valve and the Starliner valves, but it’s a similar mechanism."

Stich said SpaceX and NASA would consider adding purge air to the propulsion system to keep vapors from building up and leading to corrosion. That's similar to something Boeing did to mitigate the problem with Starliner's corroded valves.

"I think we’re learning a little bit about capsules and valves between the two different vehicles—Starliner and Dragon—and we have a little bit more work ... to remediate the corrosion for the long term because we really want to re-fly each one of these (Dragon) vehicles up to five times," Stich said.

Those pesky valves

Gerstenmaier said SpaceX's blistering launch cadence presents an opportunity for engineers to discover and resolve problems before they pop up on an astronaut mission.

"We’re humbled every time we learn something," he said. "We learn some small things, and then we go investigate those things, and then we learn more, and then hopefully we’re then preventing some bigger problem from coming in the future. There’s an advantage of flying a lot, and the fact that we get to see these vehicles operate a lot, we get to see the hardware tested in various environments."

SpaceX also gets its Falcon 9 boosters and Dragon spacecraft back after every flight. Engineers can inspect the hardware and swap out components showing signs of wear and tear, such as valves, engines, or landing legs.

“My words are, 'stay hungry,'" Gerstenmaier said Monday. "I’d say the company’s words are, 'stay paranoid.' I like hungry better than paranoid. But the idea is that you’ve just got to keep looking, and when you find some small problem, you’ve got to really understand what it’s trying to tell you because later, when the big problem happens, you’ll see the breadcrumbs that lead all the way back to that little problem at the beginning."

Gerstenmaier led NASA's human spaceflight programs before joining SpaceX in 2020. NASA officials have long identified valves as a leading concern for the US space industry. These devices are used in propulsion, hydraulic, pneumatic, and other systems.

A faulty valve led to the explosion of a Crew Dragon capsule during a ground test in 2019, and valves were a point of concern throughout NASA's Artemis I launch campaign last year, requiring troubleshooting before the Space Launch System rocket could take off on its inaugural test flight.

Gerstenmaier mentioned a couple of other valve issues that SpaceX has recently encountered. On a recent Falcon Heavy launch, a valve stuck open and led to a liquid oxygen leak.

"We were able to go in and inspect and see some corrosion in that valve, so we were able to then go inspect this vehicle (the Falcon 9 for Crew-7), and we did an inspection to make sure it was fine and OK to go fly," Gerstenmaier said. "That’s an example of another valve, not one of these nitrogen tetroxide valves, but another valve in the oxygen system that had some salt water in it that ended up with corrosion we were able to go find and remediate.”

SpaceX also found a valve leak during Falcon 9 ground testing, and an investigation revealed it was caused by a missed step in a procedure to prepare the hardware. The company is performing more checks to ensure all similar valves that went through the same procedure are OK to fly, Gerstenmaier said.

It's not just valves. SpaceX runs the Falcon 9 rocket's kerosene-fueled engines at higher throttle settings on Starlink missions, allowing those flights to haul more Internet satellites into orbit on a single shot.

"When we fly Starlink missions, we’ll typically fly a higher thrust profile and actually run pumps at higher turbine speeds," Gerstenmaier said. "That actually lets us see how the engines really perform. Then we go fly a crew mission, and we fly that crew mission at reduced levels with more margin available for the hardware.

"I think that gives us another benefit of getting a chance to see this hardware operate in a more stressful environment, and then we need the higher reliability, we back off to more typical kind of values for crew missions."