SpaceX’s first West Coast rocket launch in almost a year and a half is back on track after an October 2nd Falcon 9 launch abort triggered several different delays.
Deemed Sentinel-6A Michael Freilich after the late US oceanographer and former NASA Earth Sciences director, Falcon 9 will launch the ~1500 kg (~3300 lb) spacecraft into low Earth orbit, where it will nominally spend a decade or more precisely measuring the height of the ocean surface to track sea level rise, ocean currents, heat distribution, and more.
Minutes after launch, new Falcon 9 booster B1063 will also attempt to land back at Landing Zone 4 (LZ-4), situated barely a thousand feet away from the launch pad. Sentinel-6A will be SpaceX’s first launch from the West Coast since it orbited Canada’s Radarsat Constellation Mission (RCM) satellite trio in June 2019, as well as SpaceX’s third LZ-4 booster recovery ever.
On October 28th, NASA convened a press conference call to provide an update on an investigation SpaceX and the space agency were conducting into October 2nd’s Falcon 9 launch abort. By then, the company had concluded that the abort had been caused by a slip in quality assurance that allowed improperly cleaned vendor parts to slip through the cracks.
“According to SpaceX vice president of build and flight reliability Hans Koenigsmann, in the course of the rapid and complex mechanical and electrical ballet preceding Falcon 9 first stage ignition, the rocket’s autonomous flight computer observed that two of the GPS III SV04 booster’s nine Merlin 1D engines appeared to be running ahead of schedule, so to speak. The computer immediately halted the ignition process to avoid what could have otherwise been a “hard” (i.e. stressful or damaging) start. SpaceX quickly began inspecting the rocket within 24 hours but was unable to detect anything physically or electrically wrong with Falcon 9’s Merlin 1D engines and engine section.
Out of an abundance of caution, SpaceX removed both misbehaving engines and shipped them to its McGregor, Texas development and test facilities where – somewhat miraculously – the same premature startup behavior was replicated on the test stand. After a great deal of increasingly granular inspections, SpaceX finally narrowed the likely cause down to a tiny plumbing line feeding one of the engine’s gas generator relief valves. In a seemingly random subset of relatively new Merlin 1D engines, SpaceX eventually discovered that a supplier-provided relief valve line was sometimes clogged by a protective lacquer Koenigsmann likened to “red nail polish.
When SpaceX uncovered the possible cause and cleaned out the blocked plumbing, each previously affected Merlin 1D engine performed perfectly, all but directly confirming both the cause and the cure for Falcon 9’s October 2nd abort.”
As part of the investigation, SpaceX traced similar bad behavior back to engines on more than just the Falcon 9 booster (B1062) involved in the GPS III SV04 launch abort, ultimately impacting both Falcon 9 booster B1061 – assigned to launch four NASA astronauts to the ISS – and B1063 – assigned to launch Sentinel-6A.
Per Kathy Lueders, NASA’s Associate Administrator of the Human Exploration and Operations Mission Directorate (HEOMD), SpaceX has ultimately decided to replace two of the Sentinel-6A booster’s nine Merlin 1D engines out of an abundance of caution. Formerly scheduled to launch no earlier than (NET) November 10th, the new Falcon 9 rocket is now tracking towards its first Sentinel-6A launch attempt on Saturday, November 21st.
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