Allan J. McDonald

“The primary element of the SRBs was the solid rocket motor provided by Morton Thiokol. USBI supplied the forward and aft aluminum skirts, the external tank attach ring for attaching the SRBs to the ET, the explosive bolts for holding the SRBs on the mobile launch platform, the pyrotechnics and electronics for the SRB separation and recovery system, the hydrazine-powered hydraulic thrust vector actuation system for moving the solid rocket motor nozzles for steering the vehicle, the booster separation motors (four each on top and bottom of each solid rocket booster to separate the SRBs from the ET after motor burnout), and the nose cap, frustum, parachutes, and recovery system for the SRBs. To”
― Allan J. McDonald, Truth, Lies, and O-Rings: Inside the Space Shuttle Challenger Disaster