SpaceX Webcast
At 1:45 a.m. local time on Saturday morning, a Falcon 9 rocket lifted off from the Kennedy Space Center launch site in Florida.
By some standards, this was an exceedingly routine mission: After all, it was SpaceX’s 73rd launch of the calendar year. And like many other Falcon 9 launches this year, the “Starlink 10-9” mission carried 23 of the broadband internet satellites into orbit. After a rare failure earlier this month, however, this particular Falcon 9 rocket made a return to flight for the company, attempting to put the world’s most active booster back into service.
And by all standards it performed. The first stage booster, B-1069, made its 17th flight into orbit before landing on the Just read the instructions drone ship in the Atlantic Ocean. Just over an hour after launch, the rocket’s second stage delivered its payload into orbit, from where the Starlink spacecraft will use its onboard thrusters to reach operational altitudes in the coming weeks.
A tear in the sensory line
The Falcon 9 rocket failed just over 15 days ago, during a Starlink launch from Vandenberg Space Force Base in California, at 7:35 p.m. PDT (02:35 UTC) on July 11. During that mission, just minutes after stage separation, unusual ice formation was observed on the Merlin vacuum engine that powers the vehicle’s second stage.
According to the company, the Merlin vacuum engine successfully completed its first burn after the second stage separated. However, during this time, a liquid oxygen leak occurred near the engine, leading to the icing observed during the webcast.
Engineers and technicians were able to quickly identify the source of the leak, a crack in a “sensor line” for a pressure sensor attached to the vehicle’s liquid oxygen system. “This line ruptured due to fatigue caused by high stress from engine vibration and looseness in the clamp that normally restricts the line,” the company said in an update posted ahead of the launch Saturday morning.
This leak cooled the engine too much and left less ignition fluid available before the Merlin was reignited for the second burn to circularize the rocket’s trajectory before releasing the Starlink satellites. This caused the Merlin engine to have a hard time starting. Ultimately, the satellites were released into a lower orbit, where they burned up in Earth’s atmosphere within days.
The sense line that failed is redundant, SpaceX said. It is not used by the flight safety system and can be covered by alternative sensors already on the engine. In the near term, the sense line will be removed from the second stage engine for Falcon 9 launches.
During a press conference on Thursday, SpaceX CEO Sarah Walker said this sense line was installed based on a customer requirement for another mission. The only difference between this part and other commonly used sense lines is that it has two connections instead of one, she said. This may have made it slightly more sensitive to vibrations, leading to a small crack.
Quickly back
SpaceX identified the cause of the outage within hours of the anomaly and worked with the Federal Aviation Administration to quickly resolve the issue. On Thursday, the launch company was cleared to fly again.
“It was incredible to see how quickly the team was able to identify the cause of the accident and then take the appropriate corrective actions to ensure success,” said Walker.
Before the failure on the evening of July 11, SpaceX had not experienced a single failed mission in the previous 297 Falcon 9 rocket launches, dating back to the explosion on the Amos 6 launch pad in September 2016. The short period between the failure earlier this month and the return to flight on Saturday appears unprecedented in spaceflight history.
The company now plans to launch two more Starlink missions on its Falcon 9 rocket this weekend, one from Cape Canaveral Space Force Station in Florida and Vandenberg Space Force Base in California. It then has three more missions before a crucial astronaut flight for NASA, Crew-9, which could take place as early as Aug. 18.
For this reason, NASA was involved in the investigation into the second stage failure. Steve Stich, manager of NASA's Commercial Crew Program, said SpaceX did an “extraordinary job” of identifying the root cause of the failure and then quickly looking at its Dragon spacecraft and the first stage of the Falcon 9 rocket to make sure there were no other sensors that could be causing similar problems.
