Space Shuttle Solid Rocket Booster

Space Shuttle SRB

Two Space Shuttle SRBs on the crawler-transporter in preparation for the launch of STS-134
Manufacturer	Thiokol, later ATK United Space Boosters Inc., Pratt & Whitney
Country of origin	United States
Used on	Space Shuttle
General characteristics
Height	149.16 ft (45.46 m)
Diameter	12.17 ft (3.71 m)
Gross mass	1,300,000 lb (590 t)
Propellant mass	1,100,000 lb (500 t)
Empty mass	200,000 lb (91 t)
4-segment SRB
Powered by	1
Maximum thrust	3,300,000 lbf (15,000 kN) sea level
Specific impulse	242 seconds (2.37 km/s)
Burn time	123 s
Propellant	PBAN-APCP

The Space Shuttle Solid Rocket Booster (SRB) was the first solid-propellant rocket to be used for primary propulsion on a vehicle used for human spaceflight.^[1] A pair of them provided 85% of the Space Shuttle's thrust at liftoff and for the first two minutes of ascent. After burnout, they were jettisoned, and parachuted into the Atlantic Ocean, where they were recovered, examined, refurbished, and reused.

The Space Shuttle SRBs were the most powerful solid rocket motors to ever launch humans.^[2] The Space Launch System (SLS) SRBs, adapted from the shuttle, surpassed it as the most powerful solid rocket motors ever flown, after the launch of the Artemis 1 mission in 2022.^[3][4] Each Space Shuttle SRB provided a maximum 14.7 MN (3,300,000 lbf) thrust,^[5] roughly double the most powerful single-combustion chamber liquid-propellant rocket engine ever flown, the Rocketdyne F-1. With a combined mass of about 1,180 t (1,160 long tons; 1,300 short tons), they comprised over half the mass of the Shuttle stack at liftoff.

The motor segments of the SRBs were manufactured by Thiokol of Brigham City, Utah, which was later purchased by ATK. The prime contractor for most other components of the SRBs, as well as for the integration of all the components and retrieval of the spent SRBs, was USBI, a subsidiary of Pratt & Whitney. The contract was subsequently transitioned to United Space Alliance, a joint venture of Boeing and Lockheed Martin.

Out of 270 SRBs launched over the Shuttle program, all but four were recovered – those from STS-4 (due to a parachute malfunction) and STS-51-L (terminated by the range during the Challenger disaster).^[6] Over 5,000 parts were refurbished for reuse after each flight. The final set of SRBs that launched STS-135 included parts that had flown on 59 previous missions, including STS-1.^[7] Recovery also allowed post-flight examination of the boosters,^[8] identification of anomalies, and incremental design improvements.^[9]