ABL Space Systems rocket destroyed by fire caused by leaking engines

WASHINGTON — ABL Space Systems said it lost its second RS1 rocket after a static fire test when a fire broke out beneath the vehicle, fed by leaking fuel, that could not be extinguished by pad systems.

The company on Aug. 26 released details of the July 19 incident that resulted in the loss of the vehicle during one of its final tests before its second launch at the Pacific Space Complex – Alaska on Kodiak Island.

In a statement, ABL Space Systems said that the company fired the E2 engines in the first stage of the RS1 rocket as part of the test, but aborted the test after just half a second because the pressure in one engine was too low. The company said the reason for this was a faulty pressure sensor.

The engines shut down, but then a fire broke out under the floor of the vehicle, fueled by fuel leaking from two engines. The fire was contained, but could not be extinguished with water or inert gas systems. The company began unloading kerosene and liquid oxygen from the vehicle.

The launch pad the company uses in Kodiak does not have its own water supply. Instead, the company uses mobile tanks that ran out of water 11.5 minutes after ignition. This led to the spread of the fire “and a progressive failure of the launch pad's systems,” the company explained. This included the inability to further drain the rocket and eventually obtain telemetry data from the rocket.

“At T+ 23:24, the fire exceeded the thermal capacity of the structure and RS1 collapsed on the launch pad,” the company said, damaging a “majority” of the launch pad's electrical and plumbing connections, although the launch pad structure itself and other ground equipment survived.

An examination of the two engines that experienced fuel leaks that fueled the fire found “significant erosion” of the fuel injectors and liners, which the company said is a sign of failure due to combustion instability. “Our current leading theory is that differences in the fuel delivery system of Unit 2, Stage 1, resulted in a higher energy start than on the test bench, triggering instability in two of 11 engines,” it said.

ABL added that it had only observed this phenomenon once in more than 300 tests of the E2 engine and attributed it to another problem. However, the company added that it had little experience with this particular configuration and was launching a series of tests at its Mojave Air and Space Port test site in California to verify this explanation and to look for other possible causes.

The company did not provide a timetable for completion of this work or a new launch attempt. ABL said that the ground equipment would be sent back to Long Beach, California, for repairs, while production of the next RS1 rocket was already “well advanced.”

The launch pad fire occurred just over 18 months after ABL's first RS1 launch. The vehicle lost power 10 seconds after liftoff and crashed on the launch pad. The company later concluded that the launch pad design contributed to a fire in the rocket's engine compartment that led to the loss of power, and redesigned the mount.

The vehicle destroyed by fire in July was a redesigned Block 2 version of the RS1. It has 20% more thrust and 20% more fuel, as well as two additional engines in addition to the original nine-engine first stage.

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