Ignition SRB ignition can occur only when a manual lock pin from each SRB safe and arm device has been removed. The ground crew removes the pin during prelaunch activities. At T−5:00, the SRB safe and arm device is rotated to the arm position. The solid rocket motor ignition commands are issued when the three
Space Shuttle Main Engines (SSMEs) are at or above 90% of rated thrust, no SSME fail and/or SRB ignition
Pyrotechnic Initiator Controller (PIC) low voltage is indicated and there are no holds from the
Launch Processing System (LPS). The solid rocket motor ignition commands are sent by the orbiter computers through the Master Events Controllers (MECs) to the safe and arm device
NASA standard detonators (NSDs) in each SRB. A PIC single-channel capacitor discharge device controls the firing of each pyrotechnic device. Three signals must be present simultaneously for the PIC to generate the pyro firing output. These signals, arm, fire 1 and fire 2, originate in the
orbiter general-purpose computers (GPCs) and are transmitted to the MECs. The MECs reformat them to 28 volt DC signals for the PICs. The arm signal charges the PIC capacitor to 40 volts DC (minimum of 20 volts DC). The GPC launch sequence also controls certain critical main propulsion system valves and monitors the engine ready indications from the SSMEs. The MPS start commands are issued by the onboard computers at T−6.6 seconds (staggered start engine three, engine two, engine one all approximately within 0.25 of a second), and the sequence monitors the thrust buildup of each engine. All three SSMEs must reach the required 90% thrust within three seconds; otherwise, an orderly shutdown is commanded and safing functions are initiated. Normal thrust buildup to the required 90% thrust level will result in the SSMEs being commanded to the lift off position at T−3 seconds as well as the fire 1 command being issued to arm the SRBs. At T−3 seconds, the vehicle base bending load modes are allowed to initialize (referred to as the "twang", movement of approximately measured at the tip of the external tank, with movement towards the external tank). The fire 2 commands cause the redundant NSDs to fire through a thin barrier seal down a flame tunnel. This ignites a pyro. booster charge, which is retained in the safe and arm device behind a perforated plate. The booster charge ignites the propellant in the igniter initiator; and combustion products of this propellant ignite the solid rocket motor initiator, which fires down the entire vertical length of the solid rocket motor igniting the solid rocket motor propellant along its entire surface area instantaneously. At T−0, the two SRBs are ignited, under command of the four onboard computers; separation of the four
explosive bolts on each SRB is initiated; the two T-0 umbilicals (one on each side of the spacecraft) are retracted; the onboard master timing unit, event timer and mission event timers are started; the three SSMEs are at 100%; and the ground launch sequence is terminated.
Lift-off and ascent Timing sequence referencing in ignition is critical for a successful liftoff and ascent flight. The explosive hold-down bolts relieve (through the launch support pedestals and pad structure) the asymmetric vehicle dynamic loads caused by the SSME ignition and thrust buildup, and applied thrust bearing loads. Without the hold-down bolts the SSMEs would violently tip the flight stack (orbiter, external tank, SRBs) over onto the external tank. That rotating moment is initially countered by the hold-bolts. Prior to release of the vehicle stack for liftoff, the SRBs must simultaneously ignite and pressurize their combustion chambers and exhaust nozzles to produce a thrust-derived, net counter-rotating moment exactly equal to the SSME's rotating moment. With the SRBs reaching full thrust, the hold-down bolts are blown, releasing the vehicle stack, the net rotating moment is zero, and the net vehicle thrust (opposing gravity) is positive, lifting the orbiter stack vertically from the launch pedestal, controllable through the coordinated
gimbal movements of the SSMEs and the SRB exhaust nozzles. During ascent, multiple all-axis accelerometers detect and report the vehicle's flight and orientation (referencing the flight deck aboard the orbiter), as the flight reference computers translate navigation commands (steering to a particular waypoint in space, and at a particular time) into engine and motor nozzle gimbal commands, which orient the vehicle about its center of mass. As the forces on the vehicle change due to propellant consumption, increasing speed, changes in aerodynamic drag, and other factors, the vehicle automatically adjusts its orientation in response to its dynamic control command inputs.
Separation The SRBs are jettisoned from the space shuttle at an altitude of about . SRB 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 . 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 seconds from sequence initialization), which ensures the thrust of each SRB is less than . Orbiter yaw attitude is held for four seconds, and SRB thrust drops to less than . The SRBs separate from the external tank within 30 milliseconds of the ordnance firing command. The forward attachment point consists of a ball (SRB) and socket (External Tank; ET) held together by one bolt. The bolt contains one NSD pressure cartridge at each end. The forward attachment point also carries the range safety system cross-strap wiring connecting each SRB Range Safety System (RSS) and the ET RSS with each other. The aft attachment points consist of three separate struts: upper, diagonal and lower. Each strut contains one bolt with an NSD pressure cartridge at each end. The upper strut also carries the umbilical interface between its SRB and the external tank and on to the orbiter. There are four
booster separation motors (BSMs) on each end of each SRB. The BSMs separate the SRBs from the external tank. The solid rocket motors in each cluster of four are ignited by firing redundant NSD pressure cartridges into redundant confined detonating fuse manifolds. The separation commands issued from the orbiter by the SRB separation sequence initiate the redundant NSD pressure cartridge in each bolt and ignite the BSMs to effect a clean separation.
Range safety system A
range safety system (RSS) provides for destruction of a rocket or part of it with on-board explosives by remote command if the rocket is out of control, in order to limit the danger to people on the ground from crashing pieces, explosions, fire, poisonous substances, etc. The RSS was only activated once – during the
Space Shuttle Challenger disaster (37 seconds after the breakup of the vehicle, when the SRBs were in uncontrolled flight). The shuttle vehicle had two RSS, one in each SRB. Both were capable of receiving two command messages (arm and fire) transmitted from the ground station. The RSS was used only when the shuttle vehicle violates a launch trajectory red line. An RSS consists of two antenna couplers, command receivers/decoders, a dual distributor, a safe and arm device with two
NASA standard detonators (NSD), two confined detonating fuse manifolds (CDF), seven CDF assemblies and one linear-shaped charge (LSC). The antenna couplers provide the proper impedance for radio frequency and ground support equipment commands. The command receivers are tuned to RSS command frequencies and provide the input signal to the distributors when an RSS command is sent. The command decoders use a code plug to prevent any command signal other than the proper command signal from getting into the distributors. The distributors contain the logic to supply valid destruct commands to the RSS pyrotechnics. The NSDs provide the spark to ignite the CDF, which in turn ignites the LSC for booster destruction. The safe and arm device provides mechanical isolation between the NSDs and the CDF before launch and during the SRB separation sequence. The first message, called arm, allows the onboard logic to enable a destruct and illuminates a light on the flight deck display and control panel at the commander and pilot station. The second message transmitted is the fire command. The SRB distributors in the SRBs are cross-strapped together. Thus, if one SRB received an arm or destruct signal, the signal would also be sent to the other SRB. Electrical power from the RSS battery in each SRB is routed to RSS system A. The recovery battery in each SRB is used to power RSS system B as well as the recovery system in the SRB. The SRB RSS is powered down during the separation sequence, and the SRB recovery system is powered up.
Descent and recovery . The SRBs are jettisoned from the shuttle system at 2 minutes and an altitude of about . After continuing to rise to about , the SRBs begin to fall back to earth and once back in the denser atmosphere are slowed by a parachute system to prevent damage on ocean impact. A command is sent from the orbiter to the SRB just before separation to apply battery power to the recovery logic network. A second, simultaneous command arms the three nose cap thrusters (for deploying the pilot and
drogue parachute), the
frustum ring detonator (for main parachute deployment), and the main parachute disconnect ordnance. The recovery sequence begins with the operation of the high-altitude
baroswitch, which triggers the pyrotechnic nose cap thrusters. This ejects the nose cap, which deploys the
pilot parachute. Nose cap separation occurs at a nominal altitude of , about 218 seconds after SRB separation. The diameter conical ribbon pilot parachute provides the force to pull lanyards attached to cut knives, which cut the loop securing the
drogue retention straps. This allows the pilot chute to pull the drogue pack from the SRB, causing the drogue suspension lines to deploy from their stored position. At full extension of the twelve suspension lines, the drogue deployment bag is stripped away from the canopy, and the diameter conical ribbon drogue parachute inflates to its initial reefed condition. The drogue disreefs twice after specified time delays (using redundant 7- and 12-second reefing line cutters), and it reorients/stabilizes the SRB for main chute deployment. The drogue parachute has a design load of approximately and weighs approximately . following the launch of
STS-116, floating in the Atlantic Ocean about 150 miles northeast of
Cape Canaveral. On this occasion, the boosters landed several miles apart, but overnight winds and currents drifted them to the same location After the drogue chute has stabilized the SRB in a tail-first attitude, the frustum is separated from the forward skirt by a pyrotechnic charge triggered by the low-altitude baroswitch at a nominal altitude of about 243 seconds after SRB separation. The frustum is then pulled away from the SRB by the drogue chute. The main chute suspension lines are pulled out from deployment bags that remain in the frustum. At full extension of the lines, which are long, the three main chutes are pulled from their deployment bags and inflate to their first reefed condition. The frustum and drogue parachute continue on a separate trajectory to splashdown. After specified time delays (using redundant 10- and 17-second reefing line cutters), the main chute reefing lines are cut and the chutes inflate to their second reefed and full open configurations. The main chute cluster decelerates the SRB to terminal conditions. Each of the diameter, 20° conical ribbon parachutes have a design load of approximately and each weighs approximately . These parachutes are the largest that have ever been used, in both deployed size and load weight. The RSRM nozzle extension is severed by a pyrotechnic charge about 20 seconds after frustum separation. Water impact occurs about 279 seconds after SRB separation at a nominal velocity of . The water impact range is approximately off the eastern coast of
Florida. Because the parachutes provide for a nozzle-first impact, air is trapped in the empty (burned out) motor casing, causing the booster to float with the forward end approximately out of the water. mission being recovered and transported to Cape Canaveral by the . Formerly, the main chutes were released from the SRB at impact using a parachute release nut ordnance system (residual loads in the main chutes would deploy the parachute attach fittings with floats tethered to each fitting). The current design keeps the main chutes attached during water impact (initial impact and slapdown). Salt Water Activated Release (SWAR) devices are now incorporated into the main chute riser lines to simplify recovery efforts and reduce damage to the SRB. The drogue deployment bag/pilot parachutes, drogue parachutes and frustums, each main chute, and the SRBs are buoyant and are recovered. Specially fitted
NASA recovery ships, the and the , recover the SRBs and descent/recovery hardware. Once the boosters are located, the Diver Operated Plug (DOP) is maneuvered by divers into place to plug the SRB nozzle and drain the water from the motor case. Pumping air into and water out of the SRB causes the SRB to change from a nose-up floating position to a horizontal attitude more suitable for towing. The retrieval vessels then tow the boosters and other objects recovered back to
Kennedy Space Center. ==
Challenger disaster==