The cause of the launch failure of the RS-1 launch of a pair of Varisat-1 communications technology test satellites in January has been revealed. The launch took place at 2327 GMT on 10 January 2023 from Kodiak Island, Alaska, USA. At 10.87s after lift-off the first stage suffered a power cut and due to all valves being deenergised in shut condition all nine E2 engines were simultaneously shut down. Two seconds later the rocket began to fall back onto itself resulting in RS1 impacting the Earth very near to the launch pad (circa 20 m distant) with the resulting explosion extensive damage to the launch facility including the pad and a nearby hangar. Temperature readings during the flight and evidence afterwards appears to indicate a fire on board the stage in an aft cavity a few seconds after lift off.
Before it fell from the sky: RS-1 rocket lifts off. Courtesy: ABL Space Systems
An investigation has found that an aft end fire started early in flight which burned through a set of electrical wires, which cut power and shut off the engines. Specifically, a fire started in the Stage 1 aft end and burned through certain wire harnesses. The loss of power closed our propellant isolation valves. The closed propellant isolation valves shut off the engines. The cause of the fire was the design of the launch mount. The compact Launch Mount and proximity of RS1 to the ground restricted the flow of engine exhaust gas. This caused plume recirculation and drove pressures and temperatures beneath the rocket to exceed the RS1 base heat shield design capability. The hot combustion gases breached the aft heat shield and initiated the engine compartment fire. The launch mount has now been redesigned to increase the height, width and exhaust area.
