The Reason Behind Starship SN8’s Failed Landing

By Minjoon Choi

Northwood High School

On December 9th, SpaceX’s 160-foot tall Starship Prototype SN8 lifted off of South Texas at 4:45PM local time. The rocket was planned to soar above the clouds, skydive back down at terminal velocity, and finally land on the launchpad. However, one of the engines started to emit bright green flames and dark smoke during the landing maneuver, leading to the destruction of SN8. So what was the cause of this failed landing attempt?

We have always seen green flashes upon the engine startup of other rockets, such as SpaceX’s Falcon 9. This is because the Falcon 9’s Merlin engines use a special substance called TEA-TEB to initiate combustion. This boron-rich liquid emits the familiar green flames upon its spontaneous combustion when it meets the rocket’s onboard oxygen.

The Raptor engines found in all Starship prototypes however, use torch igniters to start the combustion cycle. Torch igniters create a spark that ignites the fuel and oxygen mixture, similar to spark plugs inside car engines. Since torch igniters and TEA-TEB serve the same job, raptor engines do not need any TEA-TEB, so the green flash could not have been caused by this substance.

It was later discovered that the flash of green was in fact the engine’s metallic internals being melted and ejected out of the engine nozzle. During the landing sequence, the header tanks, smaller fuel tanks only used during landing, did not achieve adequate pressure. As a result, one of the engines received too much oxygen in relation to fuel. Not only did this reduce combustion efficiency, extremely hot residual oxygen was able to travel down the combustion chamber, destroying the engine in the process. As one of the two engines that were planned to be used in the landing sequence went offline, the rocket couldn’t slow down fast enough for a gentle landing.

Even though Starship SN8’s landing ended up being a failure, the mission itself was far from it. SN8 was able to withstand far greater pressure, altitude, and speeds than any of its predecessors. Most importantly, SN8 collected plenty of data that would prove its worth in helping future prototypes. Starship prototypes have come a long way with SpaceX continuously pushing the boundaries of reality, and although Starship SN8 has met its end, it has opened the gate for SpaceX’s dreams to become a reality.