Like most modern boosters, the Falcon 9 has monitors and telemetry for everything on board that an engineer could imagine wanting to know about, and all of those signals have go/no-go limits assigned. The vehicle takes over the countdown on its own at the T-60 second mark in the countdown.
This is mainly done to allow the vehicle to simultaneously analyze thousands of channels of telemetry far faster and more reliably than humans ever could. During today’s launch attempt, that meant that Falcon 9 saw something it didn’t like just milliseconds before it was scheduled to command the release of the pad’s hold-down clamps and lift off.
Per one of SpaceX’s on-console engineers, the specific issue Falcon 9’s computer flagged was an “engine high power” alert. Soon after, SpaceX provided an update on Twitter, stating that the abort was “triggered due to out-of-family data during [an] engine power check” – putting the blame more on the sensors and software used to determine engine thrust than the engine hardware itself. An actual hardware or software failure that caused one or several booster engines to exceed their design limits could have potentially damaged B1048’s Merlin 1Ds, likely requiring weeks of repairs or a full swap with a different booster.
The last time a Falcon booster did this sort of abort was in February 2016, just over four years ago. Considering that they've only been launching the Block 5 F9 since May of 2018, that was either a Block 4 or 3, which means it was a different launch vehicle in many details.
This is a noteworthy launch because it will be the fifth use of booster B1048, and the first launch with a complete fairing made of two recovered halves from previous flights. The Block 5 Falcon9 was designed with the idea of flying 10 times with minimal reprocessing between launches; none has flown more than four so far. If a booster can fly 10 times, that opens the door to replacing progressively more parts on it, or perhaps a major refurbishment every 10 launches. Could we see tens of launches by the same booster? 100 launches on an F9? It's an intriguing thought.
Now, according to Next Spaceflight, pathfinder Falcon 9 booster B1048 is scheduled to launch for the fifth time in support of Starlink L6 – a bit less than four months after it became the first SpaceX rocket to cross the fourth-flight milestone. Just days ago, SpaceX President and COO Gwynne Shotwell revealed that Falcon boosters might never need to fly more than ten times. Given that Falcon 9 Block 5 boosters were first and foremost designed to launch no less than ten times each, B1048 is now on the brink of reaching the halfway point of one SpaceX’s most ambitious Block 5 design goals.If you're interested in watching the retry, https://www.spacex.com/webcast goes active around 10 to 15 minutes before launch and they always have some commentary by SpaceX managers during the mission.
If B1048 (and B1049 shortly after that) can prove that Falcon boosters can successfully launch five times, it’s hard to imagine any technical showstoppers that could prevent SpaceX from achieving its self-imposed ten-flight milestone. With SpaceX likely to attempt anywhere from 10-20 more Starlink launches this year, there will be no shortage of opportunities for Falcon 9 to continue pushing the envelope of reusability.