[summary]The rocket launched more than 340 times successively and successfully
before it encountered an issue with its upper stage on July 11. Liftoff of
the Starlink 10-9 mission is set for 12:21 a.m. EDT (0421 UTC).

A notable amount of ice builds up around the Merlin Vacuum engine on the Falcon 9’s upper stage during the Starlink 9-3 mission. Image: SpaceX

A two-week launch hiatus for SpaceX is set to come to a close shortly after midnight on Saturday. The launch company scheduled Starlink 10-9 as its return to flight mission following a mishap with a Falcon 9 upper stage on July 11.

The Falcon 9 rocket will launch from Launch Complex 39A at NASA’s Kennedy Space Center at 12:21 a.m. EDT (0421 UTC). The mission also marks the 50th dedicated Starlink launch in 2024.

Spaceflight Now will have live coverage beginning about an hour prior to liftoff.

The Federal Aviation Administration, the agency that oversees commercial space activities in the U.S., gave SpaceX permission to resume launches of its Falcon 9 rocket before the formal mishap investigation is completed.

The FAA signed off on SpaceX’s requested public safety determination, one of two routes that a launch provider who suffers a mishap during a mission can use to return to launching its rockets.

“After a comprehensive review, the FAA determined no public safety issues were involved in the anomaly that occurred during the SpaceX Starlink Group 9-3 launch on July 11,” the FAA said in a statement on Thursday. “This public safety determination means the Falcon 9 vehicle may return to flight operations while the overall investigation remains open, provided all other license requirements are met.”

SpaceX’s Falcon 9 rocket, the most flown vehicle today, encountered a liquid oxygen leak on its upper stage during the Starlink 9-3 mission, which launched from Vandenberg Space Force Base in California on July 11. During its initial burn, viewers of the launch broadcast could see copious amounts of ice building up around the engine section of the rocket.

“The cause of the leak was identified as a crack in a sense line for a pressure sensor attached to the vehicle’s oxygen system,” SpaceX wrote in a blog post on Thursday. “This line cracked due to fatigue caused by high loading from engine vibration and looseness in the clamp that normally constrains the line.

“Despite the leak, the second stage engine continued to operate through the duration of its first burn, and completed its engine shutdown, where it entered the coast phase of the mission in the intended elliptical parking orbit.”

During a briefing on Friday at NASA’s Johnson Space Center regarding the upcoming Crew-9 astronaut launch, Sarah Walker, the director of Dragon Mission Management for SpaceX, said that the FAA gave them clearance to return to flight. She added that NASA was involved throughout the process.

“In all of the data briefings and digging through the data that we did together with the FAA, NASA officially had a seat at the table to participate in, all of that,” Walker said. “We had a Q&A period where we exchanged more data and [the FAA] gave us the final determination yesterday that they agreed with our conclusions and we are ready to return to flight.”

She said that the freezing around the engine section caused by the liquid oxygen leak, made the Merlin Vacuum engine perform a “hard start” due a slow delivery of ignition fluid into the chamber.

“That damaged the engine hardware and it caused the upper stage to lose steering capability,” Walker said.

Steve Stich, manager of NASA’s Commercial Crew Program, said they viewed video of that hard start along with SpaceX and it was instrumental in their investigation of the mishap.

SpaceX said in its Thursday blog post that neither the upper stage nor the Starlink satellites posed a danger to the public. Moreover, them emphasized that the first stage booster, tail number B1063, operated without issue, landing safely on the droneship, ‘Of Course I Still Love You,’ a little more than eight minutes after liftoff.

The remedy involves removing the problematic sensor, which was left in that configuration from a previous customer mission. Stich said this is a teachable moment on “the attention to detail that’s required in spaceflight.”

“Small changes matter. And we had looked at the change and we didn’t see any problem on the NASA side as well,” Stich said. “So SpaceX has done a great job of going back to look at this area and any other areas on the vehicle that could’ve had the same problem where you did a qualification by a little bit of similarity with what you had before, but maybe without having quite the thorough testing you should have.

“And so, I think it was a great lesson learned for all of us.”

In order to prevent a similar issue in the future, the problem sensor, which Walker described as being redundant with other sensors on the engine, SpaceX decided to remove it. It tested the update at its facilities in McGregor, Texas.

The Falcon 9 upper stage that will support the Crew-9 mission is undergoing testing there soon.

“It’s going to undergo a second stage hot fire around the 30th of July and that’s really to check out some of the new modifications that that vehicle will have as a result of the anomaly,” Stich said.

The crew of NASA’s SpaceX Crew-9 mission to the International Space Station poses for a photo during their Crew Equipment Interface Test at NASA’s Kennedy Space Center in Florida. Image: SpaceX

Back to launching

The determination from the FAA paves the way for the company to resume launching its workhorse rocket. Beginning last weekend, SpaceX deployed multiple marine assets that would support launch operations. Both of its Florida-based droneships were deployed along with recovery vessels to scoop up the payload fairings.

Two more launches could follow the return to flight mission, with the Starlink 10-4 mission lined up for Space Launch Complex 40 (SLC-40) as well as the Starlink 9-4 mission from Vandenberg.

The resumption of launches is critical not only for SpaceX’s Starlink constellation, but for customers like NASA and the Polaris program. NASA is waiting to launch a Northrop Grumman Cygnus spacecraft on the NG-21 cargo resupply mission to the International Space Station, followed by the Crew-9 astronaut flight to the orbiting outpost.

Jared Isaacman and three other private astronauts are also awaiting their turn to launch onboard the Crew Dragon Resilience for the roughly five-day Polaris Dawn mission. That will be highlighted by the first commercial spacewalk in history.

On Friday, NASA announced that the mission is set to launch from LC-39A no earlier than Aug. 18 with a window of opportunity that extends to early September. Stich said that timing is driven by the time needed to convert that pad from a Falcon 9 to a Falcon Heavy configuration and allow its Europa Clipper to launch on time in October.

SpaceX has multiple marquee missions lined up for the back half of 2024, including the launch of the CRS-31 Cargo Dragon mission to the ISS around the September timeframe.