Flown and retrieved shuttle Solid Rocket Booster Separation Motor (BSM) from the forward section of a Shuttle SRB. The BSM is the rocket motor that separates the reusable solid rocket boosters (SRB) from the main tank before the orbiter leaves the atmosphere. The BSM weighs 177 pounds when loaded with propellant and is 31 inches long.
About 2+ minutes into a space shuttle flight, 16 of these small, but powerful, motors are fired simultaneously for 1.2 seconds. This provides the precise thrust angled away to safely separate the spent boosters from the space shuttle’s ET and Orbiter. Altogether, there are 8 such BSMs attached to each of the twin reusable SRBs, four on the forward skirt and 4 on the aft skirt. The BSMs in each cluster are ignited while traveling through the atmosphere at more than 3,000 mph with an altitude of about 24 nautical miles.
The BSMs are produced by ATK Launch Systems Group, part of Alliant Techsystems (ATK) Inc., at their production plant in Brigham City, Utah. Top is stamped X33012 and the nozzle enclosure B12007-01-01 MMA7075
Other side 
Top 
With Initiator wires still in place 
Nozzle enclosure part stamp
Diagram
and firing up top 
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