Space Shuttle Solid Rocket Booster

Space Shuttle Solid Rocket Booster:
The Space Shuttle Solid Rocket Boosters (SRBs) are the pair of large solid rockets used by the space shuttle during the first two minutes of powered flight. Together they provide about 83% of liftoff thrust for the Space Shuttle. They are located on either side of the orange external propellant tank. Each SRB produces 80% more liftoff thrust than one F-1 engine, the most powerful single-chamber liquid-fueled rocket engine ever flown — 5 of which powered the Saturn V "moon rocket's" first stage. The SRBs are the largest solid-fuel rocket motors ever flown, and the first to be used for primary propulsion on human spaceflight missions.The spent SRBs are recovered from the ocean, refurbished, reloaded with propellant, and reused for several missions. The prime contractor for the SRBs and the manufacturer of the vital solid fuel rocket segments is the Thiokol Corporation of Brigham City, Utah. SRBs are reused many times, for example a SRB from STS-1 flew 48 times into space over 30 years, and in 2009 was used as an Ares I test engine.
The two reusable SRBs provide the main thrust to lift the shuttle off the launch pad and up to an altitude of about 150,000 ft (28 mi; 46 km). While on the pad, the two SRBs carry the entire weight of the external tank and orbiter and transmit the weight load through their structure to the mobile launch platform. Each booster has a liftoff thrust of approximately 2,800,000 pounds-force (12.5 MN) at sea level, increasing shortly after liftoff to about 3,100,000 lbf (13.8 MN). They are ignited after the three space shuttle main engines' thrust level is verified. Seventy five seconds after SRB separation, SRB apogee occurs at an altitude of approximately 220,000 ft (67 km); parachutes are then deployed and impact occurs in the ocean approximately 122 nautical miles (226 km) downrange, after which the two SRBs are recovered. The SRBs are the largest solid-propellant motors ever flown and the first of such large rockets designed for reuse. Each is 149.16 ft (45.46 m) long and 12.17 ft (3.71 m) in diameter. Each SRB weighs approximately 1,300,000 lb (590,000 kg) at launch. The two SRBs constitute about 60% of the total lift-off mass. The propellant for each solid rocket motor weighs approximately 1,100,000 lb (500,000 kg). The inert weight of each SRB is approximately 200,000 lb (91,000 kg).
COMPONENTS:
Hold-down posts Each solid rocket booster has four hold-down posts that fit into corresponding support posts on the mobile launcher platform. Hold-down bolts hold the SRB and launcher platform posts together. Each bolt has a nut at each end, the top one being a frangible nut. The top nut contains two NASA standard detonators (NSDs), which are ignited at solid rocket motor ignition commands. When the two NSDs are ignited at each hold down, the hold-down bolt travels downward because of the release of tension in the bolt (pretensioned before launch), NSD gas pressure and gravity. The bolt is stopped by the stud deceleration stand, which contains sand. The SRB bolt is 28 in (710 mm) long and is 3.5 in (89 mm) in diameter. The frangible nut is captured in a blast container. In the event of a hold down failure the thrust from SRB ignition is enough to break the bolts, freeing the vehicle. The solid rocket motor ignition commands are issued by the orbiter's computers through the master events controllers to the hold-down pyrotechnic initiator controllers (PICs) on the mobile launcher platform. They provide the ignition to the hold-down NSDs. The launch processing system monitors the SRB hold- down PICs for low voltage during the last 16 seconds before launch. PIC low voltage will initiate a launch hold. Electrical power distribution Electrical power distribution in each SRB consists of orbiter supplied main DC bus power to each SRB via SRB buses labeled A, B and C. orbiter main DC buses A, B and C supply main DC bus power to corresponding SRB buses A, B and C. In addition, orbiter main DC bus C supplies backup power to SRB buses A and B, and orbiter bus B supplies backup power to SRB bus C. This electrical power distribution arrangement allows all SRB buses to remain powered in the event one orbiter main bus fails. The nominal operating voltage is 28±4 volts DC
HYDRAULIC POWER UNITS:
There are two self-contained, independent Hydraulic Power Units (HPUs) on each SRB. Each HPU consists of an auxiliary power unit (APU), fuel supply module, hydraulic pump, hydraulic reservoir and hydraulic fluid manifold assembly. The APUs are fueled by hydrazine and generate mechanical shaft power to drive a hydraulic pump that produces hydraulic pressure for the SRB hydraulic system. The two separate HPUs and two hydraulic systems are located on the aft end of each SRB between the SRB nozzle and aft skirt. The HPU components are mounted on the aft skirt between the rock and tilt actuators. The two systems operate from T minus 28 seconds until SRB separation from the orbiter and external tank. The two independent hydraulic systems are connected to the rock and tilt servoactuators. The HPU controller electronics are located in the SRB aft integrated electronic assemblies on the aft external tank attach rings. The HPUs and their fuel systems are isolated from each other. Each fuel supply module (tank) contains 22 lb (10.0 kg) of hydrazine. The fuel tank is pressurized with gaseous nitrogen at 400 psi (2.8 MPa), which provides the force to expel (positive expulsion) the fuel from the tank to the fuel distribution line, maintaining a positive fuel supply to the APU throughout its operation. In the APU, a fuel pump boosts the hydrazine pressure and feeds it to a gas generator. The gas generator catalytically decomposes the hydrazine into hot, high-pressure gas; a two-stage turbine converts this into mechanical power, driving a gearbox. The waste gas, now cooler and at low pressure, is passed back over the gas generator housing to cool it before being dumped overboard. The gearbox drives the fuel pump, its own lubrication pump, and the HPU hydraulic pump. As described so far, the system could not self-start, since the fuel pump is driven by the turbine it supplies fuel to. Accordingly, a bypass line goes around the pump and feeds the gas generator using the nitrogen tank pressure until the APU speed is such that the fuel pump outlet pressure exceeds that of the bypass line, at which point all the fuel is supplied to the fuel pump.
THRUST VECTORING:
Each SRB has two hydraulic gimbal servoactuators: one for roll and one for tilt. The servoactuators provide the force and control to gimbal the nozzle for thrust vector control. The space shuttle ascent thrust vector control portion of the flight control system directs the thrust of the three shuttle main engines and the two SRB nozzles to control shuttle attitude and trajectory during lift- off and ascent. Commands from the guidance system are transmitted to the ATVC (Ascent Thrust Vector Control) drivers, which transmit signals proportional to the commands to each servoactuator of the main engines and SRBs. Four independent flight control system channels and four ATVC channels control six main engine and four SRB ATVC drivers, with each driver controlling one hydraulic port on each main and SRB servoactuator. Each SRB servoactuator consists of four independent, two- stage servovalves that receive signals from the drivers. Each servovalve controls one power spool in each actuator, which positions an actuator ram and the nozzle to control the direction of thrust. The four servovalves in each actuator provide a force summed majority voting arrangement to position the power spool. With four identical commands to the four servovalves, the actuator force-sum action prevents a single erroneous command from affecting power ram motion. If the erroneous command persists for more than a predetermined time, differential pressure sensing activates a selector valve to isolate and remove the defective servovalve hydraulic pressure, permitting the remaining channels and servovalves to control the actuator ram spool. Failure monitors are provided for each channel to indicate which channel has been bypassed. An isolation valve on each channel provides the capability of resetting a failed or bypassed channel.
Rate gyro assemblies Each SRB contains two Rate gyro assemblies (RGAs), with each RGA containing one pitch and one yaw gyro. These provide an output proportional to angular rates about the pitch and yaw axes to the orbiter computers and guidance, navigation and control system during first-stage ascent flight in conjunction with the orbiter roll rate gyros until SRB separation. At SRB separation, a switchover is made from the SRB RGAs to the orbiter RGAs. The SRB RGA rates pass through the orbiter flight aft multiplexers/demultiplexers to the orbiter GPCs. The RGA rates are then mid-value-selected in redundancy management to provide SRB pitch and yaw rates to the user software. The RGAs are designed for 20 missions. Propellant The propellant mixture in each SRB motor consists of ammonium perchlorate (oxidizer, 69.6% by weight), aluminum (fuel, 16%), iron oxide (a catalyst, 0.4%), a polymer (such as PBAN or HTPB, serving as a binder that holds the mixture together and acting as secondary fuel, 12.04%), and an epoxy curing agent (1.96%). This propellant is commonly referred to as Ammonium Perchlorate Composite Propellant, or simply APCP. This mixture develops a specific impulse of 242 seconds at sea level or 268 seconds in a vacuum. The main fuel, aluminum is used because it has a reasonable specific energy density of about 31.0MJ/kg, but having a high volumetric energy density, as well as being difficult to accidentally ignite. The propellant is an 11-point star-shaped perforation in the forward motor segment and a double-truncated-cone perforation in each of the aft segments and aft closure. This configuration provides high thrust at ignition and then reduces the thrust by approximately a third 50 seconds after lift-off to avoid overstressing the vehicle during maximum dynamic pressure