The Space Shuttle's Solid Rocket Boosters (SRBs) ensure simultaneous cutoff to prevent asymmetrical thrust during launch. The cutoff occurs when the chamber pressure of both SRBs is at or below 50 lbf/in² (345 kPa), with thrust profiles designed to provide less than 10% of maximum thrust at separation. The separation sequence involves thrust vector control actuators and transitions the main propulsion system to a second-stage configuration, maintaining orbiter yaw for four seconds. Matched pairs of SRBs, composed of four segments each, are loaded from the same propellant batches to minimize thrust imbalances.
PREREQUISITESAerospace engineers, rocket propulsion specialists, and students studying aerospace dynamics will benefit from this discussion on SRB cutoff and separation mechanisms.
http://en.wikipedia.org/wiki/Space_Shuttle_Solid_Rocket_Booster#PropellantSRB separation is initiated when the three solid rocket motor chamber pressure transducers are processed in the redundancy management middle value select and the head-end chamber pressure of both SRBs is less than or equal to 50 lbf/in² (345 kPa). A backup cue is the time elapsed from booster ignition.
The separation sequence is initiated, commanding the thrust vector control actuators to the null position and putting the main propulsion system into a second-stage configuration (0.8 second from sequence initialization), which ensures the thrust of each SRB is less than 100,000 lbf (445 kN). Orbiter yaw attitude is held for four seconds, and SRB thrust drops to less than 60,000 lbf (267 kN).
http://www.csar.uiuc.edu/F_info/space_shuttle_srb.htmThe SRBs are used as matched pairs and each is made up of four solid rocket motor segments. The pairs are matched by loading each of the four motor segments in pairs from the same batches of propellant ingredients to minimize any thrust imbalance.