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103-490: The three Space Shuttle main engines (SSMEs) were ignited roughly 6.6 seconds before liftoff, and computers monitored their performance as they increased thrust. If an anomaly was detected, the engines would be shut down automatically and the countdown terminated before ignition of the solid rocket boosters (SRBs) at T = 0 seconds. This was called a "redundant set launch sequencer (RSLS) abort", and occurred five times: STS-41-D , STS-51-F , STS-55 , STS-51 , and STS-68 . Once

206-579: A Bachelor of Science degree in military engineering from the United States Military Academy in 1967 and was awarded a Master of Science degree in aeronautical engineering from the U.S. Air Force Institute of Technology in 1975. Mullane, an air force colonel, graduated from West Point in 1967. He completed 134 combat missions as an RF-4C weapon systems officer while stationed at Tan Son Nhut Air Base , Vietnam , from January to November 1969. He subsequently served

309-715: A 4-year tour of duty, in England. In July 1976, upon completing the USAF Flight Test Engineer Course at Edwards Air Force Base , California , he was assigned as a flight test weapon systems officer to the 3246th Test Wing at Eglin Air Force Base , Florida . Selected by NASA in January 1978, Mullane became an astronaut in August 1979. He flew on three Space Shuttle missions, serving as

412-531: A TAL abort would have been declared between roughly T+2:30 (two minutes 30 seconds after liftoff) and about T+5:00 (five minutes after liftoff), after which the abort mode changed to Abort Once Around (AOA) followed by Abort To Orbit (ATO). However, in the event of a time-critical failure, or one that would jeopardize crew safety such as a cabin leak or cooling failure, TAL could be called until shortly before main engine cutoff (MECO) or even after MECO for severe underspeed conditions. The shuttle would then have landed at

515-609: A dry lakebed landing on Runway 17 at Edwards Air Force Base, California, on December 6, 1988. Mission duration was 105 hours. The mission is noteworthy due to the severe damage Atlantis sustained to its critical heat-resistant tiles during ascent. On his third flight, Mullane served on the crew of STS-36, which launched from the Kennedy Space Center, Florida, on February 28, 1990, aboard the Space Shuttle Atlantis . This mission carried DOD payloads and

618-459: A full maintenance overhaul at Palmdale and the ejection seats (along with the explosive hatches) had been fully removed. Ejection seats were not further developed for the shuttle for several reasons: ...in truth, if you had to use them while the solids were there, I don’t believe you would [survive]—if you popped out and then went down through the fire trail that’s behind the solids, that you would have ever survived, or if you did, you wouldn't have

721-514: A gearbox. The waste gas, now cooler and at low pressure, was passed back over the gas generator housing to cool it before being dumped overboard. The gearbox drove the fuel pump, its own lubrication pump, and the HPU hydraulic pump. A startup bypass line went around the pump and fed the gas generator using the nitrogen tank pressure until the APU speed was such that the fuel pump outlet pressure exceeded that of

824-646: A greater chance of reaching an emergency runway for various SSME failure scenarios. An ejection escape system, sometimes called a " launch escape system ", had been discussed many times for the shuttle. After the Challenger and Columbia losses, great interest was expressed in this. All previous and subsequent U.S. crewed space vehicles have launch escape systems, although as of 2024 none have ever been used for an American crewed flight. The first two shuttles, Enterprise and Columbia , were built with ejection seats . These two vehicles were intended to be part of

927-502: A hydraulic pump that produced hydraulic pressure for the SRB hydraulic system. The two separate HPUs and two hydraulic systems were located on the aft end of each SRB between the SRB nozzle and aft skirt. The HPU components were mounted on the aft skirt between the rock and tilt actuators. The two systems operated from T minus 28 seconds until SRB separation from the orbiter and external tank. The two independent hydraulic systems were connected to

1030-610: 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 ). 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 . Recovery also allowed post-flight examination of

1133-571: A launch hold. Electrical power distribution in each SRB consisted 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 supplied main DC bus power to corresponding SRB buses A, B and C. In addition, orbiter main DC bus C supplied backup power to SRB buses A and B, and orbiter bus B supplied backup power to SRB bus C. This electrical power distribution arrangement allowed all SRB buses to remain powered in

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1236-442: A liftoff thrust of approximately 2,800,000 pounds-force (12  MN ) at sea level, increasing shortly after liftoff to about 3,300,000 lbf (15 MN). They were ignited after the three RS-25 main engines' thrust level was verified. Seventy-five seconds after SRB separation, SRB apogee occurred at an altitude of approximately 220,000 ft (42 mi; 67 km); parachutes were then deployed and impact occurred in

1339-623: A main-engine failure. After burning sufficient propellant, the vehicle would be pitched all the way around and begin thrusting back towards the launch site. This maneuver was called the "powered pitcharound" (PPA) and was timed to ensure that less than 2% propellant remained in the external tank by the time the shuttle's trajectory brought it back to the Kennedy Space Center . Additionally, the shuttle's OMS and reaction control system (RCS) motors would continuously thrust to burn off excess OMS propellant to reduce landing weight and adjust

1442-483: 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

1545-580: A mission specialist on the crew of STS-41-D in August 1984, on STS-27 in December 1988, and on STS-36 in March 1990. On his first mission Mullane served as a mission specialist on the crew of STS-41-D, which launched from Kennedy Space Center , Florida, on August 30, 1984. This was the maiden flight of the Orbiter Discovery . During this seven-day mission the crew successfully activated

1648-546: A normal landing about 25 minutes after liftoff. If a second main engine failed at any point during PPA, the shuttle would not be able to reach the runway at KSC, and the crew would have to bail out. A failure of a third engine during PPA would lead to loss of control and subsequent loss of crew and vehicle (LOCV). Failure of all three engines as horizontal velocity approached zero or just before external tank jettison would also result in LOCV. The capsule communicator would call out

1751-521: A number of secondary payloads. After 72 orbits of the earth, the STS-36 mission concluded with a lakebed landing at Edwards Air Force Base, California, on March 4, 1990. With the completion of his third flight, Mullane logged a total of 356 hours in space. He retired from NASA and the Air Force July 1, 1990. In 2006, Mullane published an autobiography, Riding Rockets: The Outrageous Tales of

1854-434: A parachute, because it would have been burned up in the process. But by the time the solids had burned out, you were up to too high an altitude to use it. ... So I personally didn't feel that the ejection seats were really going to help us out if we really ran into a contingency. The Soviet shuttle Buran was planned to be fitted with the crew emergency escape system, which would have included K-36RB (K-36M-11F35) seats and

1957-733: A predesignated airstrip across the Atlantic. The last four TAL sites were Istres Air Base in France, Zaragoza and Morón air bases in Spain, and RAF Fairford in England. Prior to a shuttle launch, two sites would be selected based on the flight plan and were staffed with standby personnel in case they were used. The list of TAL sites changed over time because of geopolitical factors. The exact sites were determined from launch to launch depending on orbital inclination. Preparations of TAL sites took four to five days and began one week before launch, with

2060-621: A predetermined location in Africa, Western Europe or the Atlantic Ocean (at Lajes Field in the Azores ) about 25 to 30 minutes after liftoff. It was to be used when velocity, altitude, and distance downrange did not allow return to the launch point by Return To Launch Site (RTLS). It was also to be used when a less time-critical failure did not require the faster but more dangerous RTLS abort. For performance issues such as engine failure(s),

2163-440: A predetermined time, an isolating valve would be selected, excluding it from the force-sum entirely. Failure monitors were provided for each channel to indicate which channel had been bypassed, and the isolation valve on each channel could be reset. Each actuator ram was equipped with transducers for position feedback to the thrust vector control system. Within each servoactuator ram was a splashdown load relief assembly to cushion

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2266-603: A progressive hydraulic failure, a cabin leak, and an external tank leak. There were four intact abort modes for the Space Shuttle. Intact aborts were designed to provide a safe return of the orbiter to a planned landing site or to a lower orbit than that which had been planned for the mission. Return to launch site (RTLS) was the first abort mode available and could be selected just after SRB jettison. The shuttle would continue downrange to burn excess propellant, as well as pitch up to maintain vertical speed in aborts with

2369-654: 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

2472-478: A specific energy density of about 31.0 MJ/kg . The propellant had an 11-pointed 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 provided high thrust at ignition and then reduced the thrust by approximately a third 50 seconds after lift-off to avoid overstressing the vehicle during maximum dynamic pressure (max. Q). SRB ignition can occur only when

2575-478: A switching valve that allowed the hydraulic power to be distributed from either HPU to both actuators if necessary. Each HPU served as the primary hydraulic source for one servoactuator, and a secondary source for the other servoactuator. Each HPU possessed the capacity to provide hydraulic power to both servoactuators within 115% operational limits in the event that hydraulic pressure from the other HPU should drop below 2,050 psi (14.1 MPa). A switch contact on

2678-754: A switchover was made from the SRB RGAs to the orbiter RGAs. The SRB RGA rates passed through the orbiter flight aft multiplexers/demultiplexers to the orbiter GPCs. The RGA rates were then mid-value-selected in redundancy management to provide SRB pitch and yaw rates to the user software. The RGAs were designed for 20 missions. Made out of 2-cm-thick D6AC high-strength low-alloy steel . The rocket propellant mixture in each solid rocket motor consisted of ammonium perchlorate ( oxidizer , 69.6% by weight), atomized aluminum powder ( fuel , 16%), iron oxide ( catalyst , 0.4%), PBAN (binder, also acts as fuel, 12.04%), and an epoxy curing agent (1.96%). This propellant

2781-399: A technical malfunction (such as an engine failure) was very unlikely, although a medical emergency on board could have necessitated an AOA abort. This abort mode was never needed during the entire history of the Space Shuttle program. An abort to orbit (ATO) was available when the intended orbit could not be reached but a lower stable orbit above 120 miles (190 km) above Earth's surface

2884-500: A vehicle used for human spaceflight . 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. The Space Launch System (SLS) SRBs, adapted from

2987-474: Is commonly referred to as ammonium perchlorate composite propellant (APCP). This mixture gave the solid rocket motors a specific impulse of 242 seconds (2.37 km/s) at sea level or 268 seconds (2.63 km/s) in a vacuum. Upon ignition, the motor burned the fuel at a nominal chamber pressure of 906.8 psi (6.252 MPa). Aluminum was chosen as a propellant due to high volumetric energy density, and its resilience to accidental ignition. Aluminum has

3090-400: Is held for four seconds, and SRB thrust drops to less than 60,000 lbf (270 kN). 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

3193-574: 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

Space Shuttle abort modes - Misplaced Pages Continue

3296-434: Is less than or equal to 50 psi (340 kPa). 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 100,000 lbf (440 kN). Orbiter yaw attitude

3399-458: The Strizh full-pressure suit, qualified for altitudes up to 30,000 metres (98,000 ft) and speeds up to Mach three. Buran flew only once in fully automated mode without a crew, thus the seats were never installed and were never tested in real human space flight. An alternative to ejection seats was an escape crew capsule or cabin escape system where the crew ejected in protective capsules, or

3502-686: The OAST-1 solar cell wing experiment, deployed three satellites , operated the CFES-III experiment, the student crystal growth experiment, and photography experiments using the IMAX motion picture camera . STS 41-D completed 96 orbits of the Earth in 145 hours before landing at Edwards Air Force Base, California, on September 5, 1984. Mullane then was assigned to STS-62-A , the first Shuttle mission scheduled to launch from Vandenberg Air Force Base , but

3605-567: 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

3708-424: The SRB. The solid rocket motor ignition commands were 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 provided the ignition to the hold-down NSDs. The launch processing system monitored the SRB hold-down PICs for low voltage during the last 16 seconds before launch. PIC low voltage would initiate

3811-486: 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. A range safety system (RSS) provides for destruction of

3914-444: The boosters, identification of anomalies, and incremental design improvements. The two reusable SRBs provided 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 carried the entire weight of the external tank and orbiter and transmitted the weight load through their structure to the mobile launcher platform . Each booster had

4017-467: The burn time of the remaining engine), as would a triple SSME failure at any point during an RTLS abort. After the loss of Challenger in STS-51-L, numerous abort enhancements were added. With those enhancements, the loss of two SSMEs was now survivable for the crew throughout the entire ascent, and the vehicle could survive and land for large portions of the ascent. The struts attaching the orbiter to

4120-423: The bypass line, at which point all the fuel was supplied to the fuel pump. When the APU speed reached 100%, the APU primary control valve closed, and the APU speed was controlled by the APU controller electronics. If the primary control valve logic failed to the open state, the secondary control valve assumed control of the APU at 112% speed. Each HPU on an SRB was connected to both servoactuators on that SRB by

4223-489: The commands to each servoactuator of the main engines and SRBs. Four independent flight control system channels and four ATVC channels controlled six main engine and four SRB ATVC drivers, with each driver controlling one hydraulic port on each main and SRB servoactuator. Each SRB servoactuator consisted of four independent, two-stage servovalves that received signals from the drivers. Each servovalve controlled one power spool in each actuator, which positioned an actuator ram and

Space Shuttle abort modes - Misplaced Pages Continue

4326-621: The earlier abort options. There was an order of preference for abort modes: Unlike with all other United States orbit-capable crewed vehicles (both previous and subsequent, as of 2024), the shuttle was never flown without astronauts aboard. To provide an incremental non-orbital test, NASA considered making the first mission an RTLS abort. However, STS-1 commander John Young declined, saying, "let's not practice Russian roulette " and "RTLS requires continuous miracles interspersed with acts of God to be successful." Contingency aborts involved failure of more than one SSME and would generally have left

4429-511: 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

4532-558: The entire cabin is ejected. Such systems have been used on several military aircraft. The B-58 Hustler and XB-70 Valkyrie used capsule ejection, while the General Dynamics F-111 and early prototypes of the Rockwell B-1 Lancer used cabin ejection. Like ejection seats, capsule ejection for the shuttle would have been difficult because no easy way existed to exit the vehicle. Several crewmembers sat in

4635-509: The event of a loss of communication, the spacecraft commander could have made the abort decision and taken action independently. A hydrogen fuel leak in one of the SSMEs during the STS-93 mission resulted in a slight underspeed at main engine cutoff (MECO) but did not necessitate an ATO, and Columbia achieved its planned orbit; if the leak had been more severe, it might have necessitated one of

4738-444: The event of an abort with a TALCOM , or astronaut flight controller aboard for communications with the shuttle pilot and commander. This abort mode was never used during the entire history of the Space Shuttle program. An abort once around (AOA) was available if the shuttle was unable to reach a stable orbit but had sufficient velocity to circle Earth once and land at around 90 minutes after liftoff. Around five minutes after liftoff,

4841-474: The event one orbiter main bus failed. The nominal operating voltage was 28 ± 4 volts DC. There were two self-contained, independent Hydraulic Power Units (HPUs) on each SRB, used to actuate the thrust vector control (TVC) system. Each HPU consisted of an auxiliary power unit (APU), fuel supply module, hydraulic pump , hydraulic reservoir and hydraulic fluid manifold assembly. The APUs were fueled by hydrazine and generated mechanical shaft power to drive

4944-488: The external tank were strengthened to better endure a multiple SSME failure during SRB flight. Loss of three SSMEs was survivable for the crew for most of the ascent, although survival in the event of three failed SSMEs before T+90 seconds was unlikely because of design loads that would be exceeded on the forward orbiter/ET and SRB/ET attach points, and still problematic at any time during SRB flight because of controllability during staging. A particularly significant enhancement

5047-467: The first four flights of Columbia had this as a crew abort option as well. With STS-5 marking the end of Columbia's test flight program, and as an operational mission with four crew members, the two cockpit ejection seats had their rocket motors removed for the flight. Columbia' s next flight ( STS-9 ) was likewise flown with the seats disabled in this manner. By the time Columbia flew again ( STS-61-C , launched on January 12, 1986), it had been through

5150-656: The first, there would have been insufficient energy to cross the Atlantic. Without bailout capability, the entire crew would have been killed. After the loss of Challenger , those types of failures were made survivable. To facilitate high-altitude bailouts, the crew began wearing the Launch Entry Suit and later the Advanced Crew Escape Suit during ascent and descent. Before the Challenger disaster, crews for operational missions wore only fabric flight suits. Another post- Challenger enhancement

5253-401: 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,

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5356-476: 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,

5459-407: 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 boosted the hydrazine pressure and fed it to a gas generator. The gas generator catalytically decomposed the hydrazine into hot, high-pressure gas; a two-stage turbine converted this into mechanical power, driving

5562-411: The ground launch sequence is terminated. 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

5665-426: The ground station. The RSS was used only when the shuttle vehicle violates a launch trajectory red line. Mike Mullane Richard Michael Mullane (born September 10, 1945; Col , USAF , Ret.) is an engineer and weapon systems officer, a retired USAF officer, and a former NASA astronaut . During his career, he flew as a mission specialist on STS-41-D , STS-27 , and STS-36 . Richard Michael Mullane

5768-430: 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

5871-402: The hold-down stud. The stud traveled downward because of the release of tension in the stud (pretensioned before launch), NSD gas pressure and gravity. The stud was stopped by the stud deceleration stand, which contained sand. The hold-down stud was 28 in (710 mm) long and 3.5 in (89 mm) in diameter. The frangible nut was captured in a blast container mounted on the aft skirt of

5974-404: The landings at these three sites have been emergency landings. These sites are listed in bold below. Algeria Australia Bahamas Barbados Canada Cape Verde Chile France The Gambia Germany Space Shuttle Solid Rocket Booster The Space Shuttle Solid Rocket Booster ( SRB ) was the first solid-propellant rocket to be used for primary propulsion on

6077-621: The majority of personnel from NASA, the Department of Defense and contractors arriving 48 hours before launch. Additionally, two C-130 aircraft from the space flight support office from the adjacent Patrick Space Force Base (then known as Patrick Air Force Base) would deliver eight crew members, nine pararescuemen , two flight surgeons , a nurse and medical technician, and 2,500 pounds (1,100 kg) of medical equipment to Zaragoza, Istres, or both. One or more C-21S or C-12S aircraft would also be deployed to provide weather reconnaissance in

6180-479: The manufacturer and then shipped to Kennedy Space Center by rail for final assembly. The segments were fixed together using circumferential tang, clevis, and clevis pin fastening, and sealed with O-rings (originally two, changed to three after the Challenger Disaster in 1986) and heat-resistant putty. Each solid rocket booster had four hold-down posts that fit into corresponding support posts on

6283-432: 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 ,

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6386-403: The middeck, surrounded by substantial vehicle structure. Cabin ejection would work for a much larger portion of the flight envelope than ejection seats, as the crew would be protected from temperature, wind blast, and lack of oxygen or vacuum. In theory an ejection cabin could have been designed to withstand reentry, although that would entail additional cost, weight and complexity. Cabin ejection

6489-467: The mission was canceled after the Space Shuttle Challenger disaster . After the Shuttle returned to service, he flew aboard the Orbiter Atlantis , on STS-27 , which launched from Kennedy Space Center, Florida, on December 2, 1988. The mission carried a Department of Defense (DOD) payload, as well as a number of secondary payloads. After 68 orbits of the earth, the mission concluded with

6592-411: The mobile launcher platform. Hold-down studs held the SRB and launcher platform posts together. Each stud had a nut at each end, the top one being a frangible nut . The top nut contained two explosive charges initiated by NASA standard detonators (NSDs), which were ignited at solid rocket motor ignition commands. When the two NSDs were ignited at each hold down, the frangible nut fractured, releasing

6695-489: The most unlikely to occur as only a very narrow range of probable failures existed that were survivable but nevertheless so time-critical as to rule out more time-consuming abort modes. Astronaut Mike Mullane referred to the RTLS abort as an "unnatural act of physics", and many pilot astronauts hoped that they would not have to perform such an abort because of its difficulty. A transoceanic abort landing (TAL) involved landing at

6798-467: The nozzle at water splashdown and prevent damage to the nozzle flexible bearing. Each SRB contained three rate gyro assemblies (RGAs), with each RGA containing one pitch and one yaw gyro. These provided 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,

6901-432: The nozzle rock and tilt servoactuators . The HPU controller electronics were located in the SRB aft integrated electronic assemblies (IEAs ) on the aft external tank attach rings. The HPUs and their fuel systems were isolated from each other. Each fuel supply module (tank) contained 22 lb (10.0 kg) of hydrazine. The fuel tank was pressurized with gaseous nitrogen at 400  psi (2.8  MPa ), which provided

7004-417: The nozzle to control the direction of thrust. The four servovalves operating each actuator provided a force-summed majority-voting arrangement to position the power spool. With four identical commands to the four servovalves, the actuator force-sum action prevented, instantaneously, a single erroneous input affecting power ram motion. If differential-pressure sensing detected the erroneous input persisting over

7107-495: The ocean approximately 122 nautical miles (226  km ) downrange, after which the two SRBs were recovered. The SRBs helped take the Space Shuttle to an altitude of 28 miles (45 km) and a speed of 3,094 mph (4,979 km/h) along with the main engines. The SRBs committed the shuttle to liftoff and ascent, without the possibility of launch abort, until both motors had fully consumed their propellants and had simultaneously been jettisoned by explosive jettisoning bolts from

7210-406: The orbiter unable to reach a runway. These aborts were intended to ensure the survival of the orbiter long enough for the crew to bail out. Loss of two engines would have generally been survivable by using the remaining engine to optimize the orbiter's trajectory so as to not exceed structural limits during reentry. Loss of three engines could have been survivable outside of certain "black zones" where

7313-406: The orbiter would have failed before bailout was possible. These contingency aborts were added after the destruction of Challenger . Before the Challenger disaster during STS-51-L , ascent abort options involving failure of more than one SSME were very limited. While failure of a single SSME was survivable throughout ascent, failure of a second SSME prior to about 350 seconds (the point at which

7416-405: The orbiter would have sufficient downrange velocity to reach a TAL site on just one engine) would mean an LOCV, since no bailout option existed. Studies showed that an ocean ditching was not survivable. Furthermore, the loss of a second SSME during an RTLS abort would have caused an LOCV except for the period of time just prior to MECO (during which the orbiter would be able to reach KSC by prolonging

7519-433: The orbiter's center of gravity. Just before main engine cutoff, the orbiter would be commanded to pitch nose-down to ensure proper orientation for external tank jettison, since aerodynamic forces would otherwise cause the tank to collide with the orbiter. The main engines would cut off, and the tank would be jettisoned, as the orbiter used its RCS to increase separation. Cutoff and separation would occur effectively inside

7622-478: The orbiter's nose up to level off the orbiter once it reached thicker air, while at the same time ensuring that the structural limits of the vehicle were not exceeded (the operational load limit was set to 2.5 Gs, and at 4.4 Gs the OMS pods were expected to be torn off the orbiter). Once this phase was complete, the orbiter would be about 150 nmi (278 km) from the landing site and in a stable glide, proceeding to make

7725-441: The point in the ascent at which an RTLS was no longer possible as "negative return", approximately four minutes after liftoff, at which point the vehicle would be unable to safely bleed off the velocity that it had gained in the distance between its position downrange and the launch site. The RTLS abort mode was never needed in the history of the shuttle program. It was considered the most difficult and dangerous abort, but also among

7828-542: 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

7931-415: 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

8034-591: The remainder of the vehicle. Only then could any conceivable set of launch or post-liftoff abort procedures be contemplated. In addition, failure of an individual SRB's thrust output or ability to adhere to the designed performance profile was probably not survivable. The SRBs were 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 weighed approximately 1,300,000 lb (590 t) at launch. The two SRBs constituted about 69% of

8137-442: 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 25.5 in (650 mm) measured at the tip of the external tank, with movement towards the external tank). The fire 2 commands cause

8240-519: The shuttle reaches a velocity and altitude sufficient for a single orbit around Earth. The orbiter would then proceed into re-entry; NASA could choose to have the orbiter land at Edwards Air Force Base , White Sands Space Harbor , or Kennedy Space Center . The time window for using the AOA abort was very short, just a few seconds between the TAL and ATO abort opportunities. Therefore, taking this option because of

8343-571: The shuttle test program and would fly with a crew of two test pilots or astronauts. Subsequent shuttles Challenger , Discovery , Atlantis , and Endeavour were built for operational missions with a crew of more than two, including seats in the lower deck, and ejection seat options were deemed to be infeasible. The type used on the first two shuttles were modified versions of the Lockheed SR-71 seat. The approach and landing tests flown by Enterprise had these as an escape option, and

8446-411: The shuttle's SRBs were ignited, the vehicle was committed to liftoff. If an event requiring an abort happened after SRB ignition, it was not possible to begin the abort until after SRB burnout and separation, about two minutes after launch. There were five abort modes available during ascent, divided into the categories of intact aborts and contingency aborts. The choice of abort mode depended on how urgent

8549-573: The shuttle, surpassed it as the most powerful solid rocket motors ever flown, after the launch of the Artemis 1 mission in 2022. Each Space Shuttle SRB provided a maximum 14.7  MN (3,300,000  lbf ) thrust, 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

8652-410: The situation was and what emergency landing site could be reached. The abort modes covered a wide range of potential problems, but the most commonly expected problem was a main engine failure, causing the vehicle to have insufficient thrust to achieve its planned orbit. Other possible failures not involving the engines but necessitating an abort included a multiple auxiliary power unit (APU) failure,

8755-418: 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

8858-523: The south of Bermuda). An ECAL/BDA abort was similar to RTLS, but instead of landing at the Kennedy Space Center , the orbiter would attempt to land at another site along the east coast of North America (in the case of ECAL) or Bermuda (in the case of BDA). Various potential ECAL landing sites extended from South Carolina into Newfoundland, Canada. The designated landing site in Bermuda was Naval Air Station Bermuda (a United States Navy facility). ECAL/BDA

8961-455: The staff working there were given no special training to handle a shuttle landing. If they were ever needed, the shuttle pilots would have had to rely on regular air traffic control personnel using procedures similar to those used to land a gliding aircraft that has suffered complete engine failure. Numerous other abort refinements were added, mainly involving improved software for managing vehicle energy in various abort scenarios. These enabled

9064-495: The switching valve closed when the valve was in the secondary position. When the valve was closed, a signal was sent to the APU controller, that inhibited the 100% APU speed control logic and enabled the 112% APU speed control logic. The 100-percent APU speed enabled one APU/HPU to supply sufficient operating hydraulic pressure to both servoactuators of that SRB. The APU 100-percent speed corresponded to 72,000 rpm, 110% to 79,200 rpm, and 112% to 80,640 rpm. The hydraulic pump speed

9167-468: The terms solid rocket motor and solid rocket booster are often used interchangeably, in technical use they have specific meanings. The term solid rocket motor applied to the propellant, case, igniter and nozzle. Solid rocket booster applied to the entire rocket assembly, which included the rocket motor as well as the recovery parachutes, electronic instrumentation, separation rockets, range safety destruct system, and thrust vector control. Each booster

9270-644: The total lift-off mass. The primary propellants were ammonium perchlorate ( oxidizer ) and atomized aluminum powder ( fuel ), and the total propellant for each solid rocket motor weighed approximately 1,100,000 lb (500 t) (see § Propellant ). The inert weight of each SRB was approximately 200,000 pounds (91 t). Primary elements of each booster were the motor (including case, propellant, igniter, and nozzle ), structure, separation systems, operational flight instrumentation, recovery avionics, pyrotechnics , deceleration system, thrust vector control system, and range safety destruct system. While

9373-511: The upper atmosphere at an altitude of about 230,000 ft (70,000 m), high enough to avoid subjecting the external tank to excessive aerodynamic stress and heating. The cutoff velocity would depend on the distance still to be traveled to reach the landing site and would increase based on the distance of the orbiter at cutoff. In any case, the orbiter would be flying too slowly to glide gently at such high altitude, and would start descending rapidly. A series of maneuvers in quick succession would pitch

9476-404: The vehicle automatically adjusts its orientation in response to its dynamic control command inputs. The SRBs are jettisoned from the space shuttle at an altitude of about 146,000 ft (45 km). 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

9579-502: The vehicle in all three axes (roll, pitch, and yaw). The ascent thrust vector control portion of the flight control system directed 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 were transmitted to the Ascent Thrust Vector Control (ATVC) drivers, which transmitted signals proportional to

9682-470: Was 3,600 rpm and supplied hydraulic pressure of 3,050 ± 50 psi (21.03 ± 0.34 MPa). A high pressure relief valve provided overpressure protection to the hydraulic system and relieved at 3,750 psi (25.9 MPa). The APUs/HPUs and hydraulic systems were reusable for 20 missions. Each SRB had two hydraulic gimbal servoactuators, to move the nozzle up/down and side-to-side. This provided thrust vectoring to help control

9785-467: Was a contingency abort that was less desirable than an intact abort, primarily because there was so little time to choose the landing site and prepare for the orbiter's arrival. All of the pre-designated sites were either military airfields or joint civil/military facilities. ECAL emergency sites were not as well equipped to accommodate an orbiter landing as those prepared for RTLS and TAL aborts. The sites were not staffed with NASA employees or contractors and

9888-508: Was attached to the external tank at the SRB's aft frame by two lateral sway braces and a diagonal attachment. The forward end of each SRB was attached to the external tank at the forward end of the SRB's forward skirt. On the launch pad, each booster also was attached to the mobile launcher platform at the aft skirt by four holddown studs, with frangible nuts that were severed at liftoff. The boosters were composed of seven individually manufactured steel segments. These were assembled in pairs by

9991-444: Was bailout capability. Unlike the ejection seat in a fighter plane, the shuttle had an inflight crew escape system (ICES). The vehicle was put in a stable glide on autopilot, the hatch was blown, and the crew slid out on a pole to clear the orbiter's left wing. They would then parachute to earth or the sea. While this at first appeared only usable under rare conditions, there were many failure modes where reaching an emergency landing site

10094-661: Was born September 10, 1945, in Wichita Falls, Texas . At the time of his birth, his father, Hugh, was serving as a flight engineer on a B-17 in the Pacific War . His family moved regularly until his father was diagnosed with polio and lost the use of his legs, causing the family to move to Albuquerque, New Mexico . He was a Second Class Scout in the Boy Scouts of America . He graduated from St. Pius X High School , Albuquerque, New Mexico, in 1963, then received

10197-455: Was later determined to be an inadvertent engine shutdown caused by faulty temperature sensors. The moment at which an ATO became possible was referred to as the "press to ATO" moment. In an ATO situation, the spacecraft commander rotated the cockpit abort mode switch to the ATO position and depressed the abort push button. This initiated the flight-control software routines that handled the abort. In

10300-446: Was not possible yet the vehicle was still intact and under control. Before the Challenger disaster, this almost happened on STS-51-F , when a single SSME failed at about T+345 seconds. The orbiter in that case was also Challenger . A second SSME almost failed because of a spurious temperature reading; however, the engine shutdown was inhibited by a quick-thinking flight controller. If the second SSME had failed within about 69 seconds of

10403-475: Was not pursued for several reasons: Source: Predetermined emergency landing sites for the orbiter were chosen on a mission-by-mission basis according to the mission profile, weather and regional political situations. Emergency landing sites during the shuttle program included: An orbiter has landed at three sites that are also designated as emergency landing sites: Edwards Air Force Base , Kennedy Space Center , and White Sands Space Harbor . However, none of

10506-400: Was possible. This occurred during mission STS-51-F , when Challenger 's center engine failed five minutes and 46 seconds after liftoff. An orbit near the craft's planned orbit was established, and the mission continued despite the abort to a lower orbit. The Mission Control Center at Johnson Space Center observed an SSME failure and called " Challenger -Houston, abort ATO." The engine failure

10609-528: Was the addition of East Coast/Bermuda abort landings (ECAL/BDA). High-inclination launches (including all ISS missions) would have been able to reach an emergency runway on the East Coast of North America under certain conditions. Most lower-inclination launches would have landed in Bermuda (although this option was not available for the very lowest-inclination launches—those to an orbital inclination of 28.5°—which launched due east from KSC and passed far to

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