initiator

This term is defined in ECSS-E-ST-33-11C as
first explosive element in an explosive train that, upon receipt of the proper mechanical, optical or electrical impulse, produces a deflagrating or detonating action

This term is defined in ECSS-E-ST-35C Rev. 1 as
first element in an explosive chain that, upon receipt of the proper impulse, produces a deflagrating or detonating action

This term is defined in ECSS-E-ST-50-51C as
SpaceWire node that starts a transaction by sending a command to a SpaceWire node