Design Evaluation of Pyro Initiator Circuits for Unmanned and Manned Spacecrafts Using Fault Tree Analysis

A spacecraft pyro chain includes a power source, pyro initiator circuit (PIC), and pyro device. PICs are crucial for isolating the pyro device from the power source until needed and ensuring the correct fire current during operation. MIL-STD-1576 outlines fault tolerance criteria for preventing accidental firings. This paper discusses implementing breaks using Electro-Mechanical Relays (EMR) and Solid-State Relays (SSR) and presents five PIC design options conforming to MIL-STD-1576. It includes a risk analysis of each design and recommends the best circuit for both unmanned and manned spacecraft, ensuring minimal risk of inadvertent operation in all conditions.