PRE-TEST OPERATIONS
On July 19th, 2024, ABL conducted RS1 vehicle operations with the objective of a 13-second static fire of all 11 first stage engines. Our launch team commanded RS1 and GS0 through a smooth, flight-like countdown. After polling “GO,” we entered Terminal Count at 8:20PM, handing over control to RS1 for the final ten minutes of the countdown.
STATIC FIRE + INITIAL FIREFIGHTING
RS1 entered Stage 1 startup at T- 7.76 seconds. All 11 engines ignited and successfully bootstrapped, entering main-stage combustion for approximately 0.5 seconds. RS1 auto-aborted out of the test due to a low pressure reading on Engine 10 caused by a faulty pressure sensor.
Immediately after shutdown, a fire developed external to RS1’s base, fed by fuel leaks from Engines 5 and 8. Water- and inert gas-based fire suppression systems were able to contain the fire, but were not able to extinguish it. Fuel offload began at T+ 04:20, with LOx offload following at T+ 09:20.
DEPLETION + LOSS OF VEHICLE
Due to the launch pad having no direct water supply, ABL relies on mobile water tanks for fire suppression. While the water system was active, vehicle temperatures were maintained within design limits. Water stores were depleted at T+ 11:30, which resulted in loss of fire containment and a progressive loss of pad systems. LOx and fuel offload capability were lost at T+ 14:28 and T+ 15:30 respectively, and all Stage 1 telemetry was lost at T+ 20:43.
At T+ 23:24, the fire exceeded the thermal capability of the structure and RS1 buckled to the pad. While a majority of plumbing and electrical connections to the Launch Mount were damaged, the structures of the Launch Mount, the Flame Deflector, and all GS0 equipment behind pad berms were unharmed.
RESPONSE + PATH FORWARD
ABL immediately initiated its mishap plan and an investigation, with oversight from the FAA. Post-anomaly data review indicates Engines 5 and 8 experienced a 4.5 kHz combustion instability during startup, in alignment with the expected first tangential mode of the E2 thrust chamber. Inspections revealed significant erosion of the E5 and E8 propellant injectors and liners in a pattern consistent with instability-induced failure.
Our current leading theory is that differences in the Block 2 Stage 1 propellant feed system led to a higher energy startup than on the test stand, triggering an instability in 2 of 11 engines. In 300+ prior E2 engine tests, we observed this phenomenon only once, and attributed it to a separate timing anomaly with that particular test. While our static fire sequence was within our experience, on-vehicle conditions were in a corner of the start box where we have a relatively low number and limited duration of tests. We are conducting a test campaign at our Mojave Air and Space Port test site to iteratively replicate the as-measured stage conditions and assess our theory. The investigation will also evaluate other contributing factors and potential root causes of the anomaly.
GS0 will return to our Port of Long Beach facility for refurbishment. RS1 Block 2 SN02 is well into production. Pending the results of the investigation, we’ll be ready to share more about the expected actions and timeline for these efforts.
This is not the outcome we wanted, and it eclipsed the incredible endurance and execution of our team that got Flight 2 just short of the finish line. While the campaign ended in anomaly, many key elements of RS1 and GS0 were validated in the process. We look forward to concluding our investigation and incorporating these learnings into the RS1 program.