This is the recent hotfire test of Astra's most powerful Rocket 4 first stage engine.The quick green flash comes from a special compound called triethylborane (TEB). It's pyrophoric - meaning it spontaneously ignites the moment it touches air. That super-hot green flame then lights the main propellants: kerosene and liquid oxygen.Once ignited, the engine unleashes a roaring orange plume and huge clouds of smoke. These ground tests prove the engine is ready for flight - checking thrust, stability