Falcon 9 Returned to Flight

As reported on Tuesday and updated Thursday, SpaceX had applied for permission to restart flying Falcon 9 missions, which was granted Thursday evening.

The launch was this morning, later than originally scheduled, 1:41 AM EDT launch as opposed to its originally scheduled 12:21 AM EDT launch time. This was the 17th flight for first stage booster B-1069, briefly orbital altitudes before returning and landing on Just Read the Instructions (JRTI) drone ship in the Atlantic Ocean about 8:15 later. A little more than an hour after liftoff, the rocket's second stage released its payload into a good orbit, confirmed by SpaceX on X, from which the Starlink spacecraft use their on-board thrusters to reach operational altitudes in the coming weeks. The second stage's second burn was the cause of the failure of the previous Starlink mission that caused the launch pause. 

Video of the launch through booster landing here.  

In Tuesday's post, I somewhat facetiously suggested that compared to "old space" instead of taking months to figure out what went wrong and how to fix it, that SpaceX would take, "How about twenty minutes? A half hour?" The official report is that "within hours of the anomaly" the issue and fix were announced and decided upon.

Engineers and technicians were quickly able to pinpoint the cause of the leak, a crack in a "sense line" for a pressure sensor attached to the vehicle’s liquid oxygen system. "This line cracked due to fatigue caused by high loading from engine vibration and looseness in the clamp that normally constrains the line," the company said in an update published prior to Saturday morning's launch. [Note: the update is dated July 25, second one down at that link. SiG]

This leak excessively cooled the engine, and caused a lower amount of igniter fluid to be available prior to re-lighting the Merlin for its second burn to circularize the rocket's orbit before releasing the Starlink satellites. This caused a hard start of the Merlin engine. Ultimately the satellites were released into a lower orbit, where they burnt 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 alternate sensors already present on the engine. In the near term, the sense line will be removed from the second stage engine for Falcon 9 launches.

During a news briefing Thursday, SpaceX director Sarah Walker said this sense line was installed based on a customer requirement for another mission. The only difference between this component and other commonly flown sense lines is that it has two connections rather than one, she said. This may have made it a bit more susceptible to vibration, leading to a small crack.

While I feel somewhat chagrined at saying it might take SpaceX as much as a half hour to understand what went wrong and how to fix it, I wouldn't be surprised if saying it took "hours" might be an overstatement. It's easy to focus on the simple contrast between Falcon 9 and Starliner. SpaceX went into their period of launches being forbidden on July 11, when Starliner had been docked to the ISS for five days (July 11). Two weeks later, Falcon 9 is flying while Starliner is in exactly the same place. I think a slightly different way of looking at that is the overall numbers. That was SpaceX's 73rd launch of this calendar year. Just the familiarity of seeing everything a Falcon 9 does during a mission given the shear number of launches they do gives SpaceX an incredible advantage in spotting unusual things.

Before the failure on the night of July 11th, SpaceX had not experienced a mission failure in the previous 297 launches of the Falcon 9 rocket, dating back to the Amos-6 launch pad explosion in September 2016. The short interval between the failure earlier this month, and Saturday's return to flight, appears to be unprecedented in spaceflight history.

Screen capture from this morning's launch on SpaceX's launches page. Image credit: SpaceX 

To borrow a phrase, the weekend is young and SpaceX intends to do two more Falcon 9 launches tonight through tomorrow morning. The first will be at 12:17 AM EDT Sunday morning from SLC-40 at Cape Canaveral SFS. The second will be just over three hours later, at 3:24 AM EDT Sunday from SLC-4E, at Vandenberg SFB, California. Note that SFS is an abbreviation for Space Force Station while SFB is for Space Force Base. To grossly simplify, "Bases" have more facilities and resources than "Stations" have.