Space
Shuttle Basics
Solid
Rocket Boosters
The solid rocket
boosters (SRB) operate in parallel with the main engines for the
first two minutes of flight to provide the additional thrust needed
for the orbiter to escape the gravitational pull of the Earth. At
an altitude of approximately 45 km (24 nautical miles), the boosters
separate from the orbiter/external tank, descend on parachutes,
and land in the Atlantic Ocean. They are recovered by ships, returned
to land, and refurbished for reuse. The boosters also assist in
guiding the entire vehicle during initial ascent. Thrust of both
boosters is equal to 5,300,000 lb.
 In
addition to the solid rocket motor, the booster contains the structural,
thrust vector control, separation, recovery, and electrical and
instrumentation subsystems.
The solid rocket
motor is the largest solid propellant motor ever developed for space
flight and the first built to be used on a manned craft. The huge
motor is composed of a segmented motor case loaded with solid propellants,
an ignition system, a movable nozzle and the necessary instrumentation
and integration hardware.
 | | The
SRBs separate from Columbia about two minutes after the first
launch of the Shuttle Program. |
Each solid
rocket motor contains more than 450,000 kg (1,000,000 lb.) of propellant,
which requires an extensive mixing and casting operation at a plant
in Utah. The propellant is mixed in 600 gallon bowls located in
three different mixer buildings. The propellant is then taken to
special casting buildings and poured into the casting segments.
Cured propellant
looks and feels like a hard rubber typewriter eraser. The combined
polymer and its curing agent is a synthetic rubber. Flexibility
of the propellant is controlled by the ratio of binder to curing
agent and the solid ingredients, namely oxidizer and aluminum. The
solid fuel is actually powdered aluminum—a form similar to the foil
wraps in your kitchen—mixed with oxygen provided by a chemical called
ammonium perchlorate. | 
