[summary]The Federal Aviation Administration has ruled that SpaceX can resume
Falcon 9 rocket launches while the investigation into a failed July 11
mission continues, and the next liftoff could take place as early as
tonight. The FAA’s go-ahead came after SpaceX reported that the failure
was caused by a crack in a sense line for …

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Universe Today: (Alan Boyle)

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The Federal Aviation Administration has ruled that SpaceX can resume Falcon 9 rocket launches while the investigation into a failed July 11 mission continues, and the next liftoff could take place as early as tonight.

The FAA’s go-ahead came after SpaceX reported that the failure was caused by a crack in a sense line for a pressure sensor attached to the upper stage’s liquid-oxygen system. That resulted in an oxygen leak that degraded the performance of the upper-stage engine. As a near-term fix, SpaceX is removing the sense line and the sensors for upcoming Falcon 9 launches.

SpaceX scheduled a Falcon 9 launch from NASA’s Kennedy Space Center in Florida for no earlier than 12:21 a.m. ET (04:21 GMT) July 27. Like the July 11 mission, this one is aimed at sending a batch of SpaceX’s Starlink satellites to low Earth orbit.

FAA investigations of launch anomalies typically take months to wrap up, but in this case, the agency said it “determined no public safety issues were involved in the anomaly” on July 11. “The 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,” the FAA said.

SpaceX said it worked under FAA oversight to identify the most probable cause of the anomaly as well as corrective actions, and submitted its mishap report to the agency, clearing the way for the public safety determination.

The company said the upper stage’s liquid-oxygen sense line cracked “due to fatigue caused by high loading from engine vibration and looseness in the clamp that normally constrains the line.”

Despite the oxygen leak, the upper-stage engine successfully executed its first burn and shut itself down for a planned coast phase. But during that phase, the leak led to excessive cooling of engine components — and when the engine was restarted, it experienced a hard start rather than a controlled burn, SpaceX said. That damaged the engine hardware and caused the upper stage to lose altitude.

The upper stage was still able to deploy its Starlink satellites, but at a lower altitude than planned. SpaceX couldn’t raise the satellites’ orbits fast enough to overcome the effect of atmospheric drag, and as a result, all 20 satellites re-entered the atmosphere and burned up harmlessly. It was the first failure of a Falcon 9 mission in eight years.

SpaceX said it worked out a strategy for removing the suspect sense lines and clamps from the upper stages slated for near-term Falcon 9 launches. “The sensor is not used by the flight safety system and can be covered by alternate sensors already present on the engine,” SpaceX said.

The return to flight raises hopes that upcoming Falcon 9 launches will go forward without lengthy delays. One high-profile crewed flight, the privately funded Polaris Dawn mission, had been scheduled to launch as early as July 31. The mission’s commander, billionaire entrepreneur Jared Isaacman, suggested in a posting to the X social-media platform that the crew would need some extra time for training.

“There are training currency requirements,” Isaacman said. “We will likely have a few days of sim and EVA refreshers before launch. Most importantly, we have complete confidence in SpaceX and they have managed the 2nd stage anomaly and resolution. We will launch when ready and it won’t be long.”

Sarah Walker, director of Dragon mission management, said today that SpaceX is “still holding a late-summer slot” for the Polaris Dawn launch. That mission will feature the first private-sector spacewalk.

Another high-profile Falcon 9 mission involves the delivery of a U.S.-Russian quartet of astronauts to the International Space Station in a SpaceX Dragon capsule. NASA said today that the Crew-9 mission is currently set for launch no earlier than Aug. 18. “We’ve been following along, step by step with that investigation that the FAA has been doing,” said Steve Stich, the manager of NASA’s Commercial Crew Program manager. “SpaceX has been very transparent.”

An uncrewed Dragon cargo capsule is due for launch to the ISS no earlier than September.

Meanwhile, SpaceX is proceeding with plans for the fifth test flight of its Starship / Super Heavy launch system. A static-fire engine test was conducted successfully at SpaceX’s Starbase launch complex in Texas on July 15, and the Starship team is awaiting the FAA’s go-ahead for liftoff.

The upcoming test flight is thought to involve having the Super Heavy booster fly itself back to Starbase and make a touchdown back on its launch pad with the aid of two giant arms known as “chopsticks.” For the four previous test missions, SpaceX’s flight plan called for the booster to splash down in the Gulf of Mexico. Modifying the flight profile may require a re-evaluation of SpaceX’s FAA license for Starship test flights.

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