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Length: 149 feet, 2 inches

Diameter: 12 feet, 2 inches

The vast majority of thrust needed to launch the Space Shuttle is provided by two Solid Rocket Boosters (SRB). SRB's are manufactured by the Wasatch Division of Morton Thiokol Corporation, located in Brigham City, Utah.

In addition to providing the bulk of Space Shuttle liftoff thrust, the SRB's support the entire weight of the Orbiter and External Tank (ET) prior to launch. The Space Shuttle SRB's are the largest solid-fueled motors ever built, and the first designed to be reused.

Each SRB weighs about 1,300,000 pounds at launch. The solid fuel contained in the SRB weighs about 1,100,000 pounds while the inert weight of each SRB is about 200,000 pounds.

The primary elements of each SRB are the motor, structure, separation system, operational flight instrumentation, recovery system, pyrotechnics, deceleration system and range safety destruct system.

Each SRB is attached to the ET at the SRB's aft frame by two lateral sway braces and a diagonal attachment. The forward end of each SRB is attached to the ET at the forward end of the SRB's forward skirt.

On the launch pad, Each SRB is fastened to the Mobile Launcher Platform (MLP) at the SRB aft skirt by four large bolts and nuts that are severed by small explosive charges at liftoff.

The propellant mixture in each SRB is made up of 69.6% ammonium perchlorate oxidizer, 16% aluminum fuel, 0.4% iron oxide catalyst, 12.04% polymer binder and 1.96% epoxy curing agent.

The propellant is contained within the SRB beginning with an 11-point star-shaped perforation in the forward segment to a double-truncated cone perforation in both of the aft segments and the aft closure segment.

These varying shapes allow the SRB thrust to be reduced by about 33% at launch plus 50 seconds. This reduction in thrust is intended to alleviate stress to the Space Shuttle as it enters its area of maximum dynamic pressure during ascent.

The SRB's employed during each Space Shuttle mission are matched pairs, each made up of four solid rocket motor segments. To minimize any thrust imbalance, the SRB pairs are matched by loading each of the four SRB segments in pairs using the same batches of solid fuel.

The segmented solid rocket motor design assures maximum flexibility during manufacturing operations, and also ease of transportation. The SRB's are transported to the launch site using heavy-duty rail cars equipped with special SRB covers.

The cone-shaped aft skirt of each SRB provides one of the most vital supports for the Space Shuttle prior to launch, since it can react to loads that may shift between the SRB's and the MLP during pre-launch operations.

Four SRB separation motors are also mounted on the aft skirt of each SRB. The aft section of each SRB contains avionics and a thrust vector control system that consists of two auxiliary power units, hydraulic pumps, hydraulics systems and a nozzle extension jettison system.

The forward section of each SRB contains avionics, a sequencer, four forward separation motors, a nose cone separation system, drogue and main parachutes, recovery beacon, recovery light, range safety system and, in certain flights, a parachute camera system.

Each SRB has two integrated electronic assemblies, one at the forward and one at the aft. These assemblies provide the electronic command connections to initiate and control various functions of SRB components during flight.

The SRB's are ignited by electronic command from the Orbiter at Launch Minus Zero, provided that the Space Shuttle Main Engines (SSME) have built up enough thrust to support a launch.

The SSME's are ignited first, since the SRB's cannot be shut down once they are ignited. The results would be catastrophic if the SRB's were ignited after an SSME failure on the launch pad.

Also at Launch Minus Zero, the four bolts which hold each SRB to the MLP are blown by explosive charges. Each bolt measures 28 inches long by 3.5 inches in diameter.

Each SRB can produce a thrust of about 3,300,000 pounds of thrust at liftoff. The combined thrust of the SRB's accounts for just over 70% of the total thrust needed to carry the Space Shuttle into space. Each SRB exhaust nozzle may be gimbaled up to eight degrees to help steer the Space Shuttle during ascent.

About 125 seconds after launch and at an altitude of about 150,000 feet, the SRB's burn out and are jettisoned from the ET. The jettison command originates from the Orbiter, and jettison occurs when the forward and aft attach points between the SRB's and ET are blown by explosive charges.

Milliseconds after SRB separation, 16 solid-fueled separation motors, four in the forward section of each SRB and four in the aft skirt of each SRB, are fired for just over one second to help carry the SRB's away from the rest of the Space Shuttle. Each of the separation motors can produce a thrust of about 22,000 pounds.

The SRB's continue to ascend in a slow, tumbling motion for about 75 seconds after SRB separation, to a maximum altitude of about 220,000 feet. The SRB's then begin to quickly fall toward the Atlantic Ocean.

About 225 seconds after SRB separation and at an altitude of about 15,700 feet the nose cap of each SRB is ejected, which results in deployment of a pilot parachute. The pilot parachute has a diameter of 11.5 feet, and provides the force necessary to activate mechanisms which pull the drogue parachute from its stored position.

The drogue parachute has a diameter of 54 feet, and is used to orient and stabilize the descent of each SRB to a tail-first attitude in preparation for the deployment of the main parachutes. About 248 seconds after SRB separation and at an altitude of about 6,000 feet, deployment of the main parachutes begins.

Three main parachutes are deployed on each SRB. Each main parachute has a diameter of 136 feet. The main parachutes accompany each SRB to water impact, which occurs about 295 seconds after SRB separation at a speed of about 81 feet per second.

The SRB's impact the Atlantic Ocean about 140 miles from the launch site. Since each SRB impacts the water nozzle-first, air trapped within the SRB casings causes each SRB to float with its forward end extending about 30 feet out of the water.

Crews aboard specialized SRB retrieval ships quickly set about locating each SRB by homing in on radio beacon signals transmitted from each SRB. Crews may also be aided in locating the SRB's by flashing lights activated on each SRB.

Once located, the crews begin recovering each SRB, plus the drogue parachutes and main parachutes. The SRB nozzles are then plugged, the solid rocket motors dewatered and the SRB's towed back horizontally to a receiving and processing site on Cape Canaveral Air Station.

There, each SRB is removed from the water. After a set of thorough inspections, the SRB components are disassembled and washed with fresh and deionized water to limit saltwater corrosion. Refurbishing of each SRB then begins, with some components sent back to the manufacturer and some components remaining at the launch site.

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