page_title: Space Shuttle
section_title: Launch
hierarchical_section_title: Space Shuttle / Mission profile / Launch
caption_attribution_description: Polski: Silnik na paliwo stałe oddzielający się od promu. English: Solid Rocket Boosters separating from space shuttle.
context_page_description: The Space Shuttle was a partially reusable low Earth orbital spacecraft system that was operated from 1981 to 2011 by the National Aeronautics and Space Administration as part of the Space Shuttle program. Its official program name was Space Transportation System, taken from a 1969 plan for a system of reusable spacecraft of which it was the only item funded for development. The first of four orbital test flights occurred in 1981, leading to operational flights beginning in 1982. Five complete Space Shuttle orbiter vehicles were built and flown on a total of 135 missions from 1981 to 2011, launched from the Kennedy Space Center in Florida. Operational missions launched numerous satellites, Interplanetary probes, and the Hubble Space Telescope; conducted science experiments in orbit; and participated in construction and servicing of the International Space Station. The Space Shuttle fleet's total mission time was 1322 days, 19 hours, 21 minutes and 23 seconds.
context_section_description: The mission crew and the Launch Control Center (LCC) personnel completed systems checks throughout the countdown.  Two built-in holds at T−20 minutes and T−9 minutes provided scheduled breaks to address any issues and additional preparation. After the built-in hold at T−9 minutes, the countdown was automatically controlled by the Ground Launch Sequencer (GLS) at the LCC, which stopped the countdown if it sensed a critical problem with any of the Space Shuttle's onboard systems. At T−3 minutes 45 seconds, the engines began conducting gimbal tests, which were concluded at T−2 minutes 15 seconds. The ground launch processing system handed off the control to the orbiter vehicle's GPCs at T−31 seconds. At T−16 seconds, the GPCs armed the SRBs, the sound suppression system (SPS) began to drench the MLP and SRB trenches with 1,100,000 L (300,000 U.S. gal) of water to protect the orbiter vehicle from damage by acoustical energy and rocket exhaust reflected from the flame trench and MLP during lift-off. At T−10 seconds, hydrogen igniters were activated under each engine bell to quell the stagnant gas inside the cones before ignition. Failure to burn these gases could trip the onboard sensors and create the possibility of an overpressure and explosion of the vehicle during the firing phase. The LH₂ prevalves were opened at T−9.5 seconds in preparation for engine start.
  Beginning at T−6.6 seconds, the main engines were ignited sequentially at 120-millisecond intervals. All three RS-25 engines were required to reach 90% rated thrust by T−3 seconds, otherwise the GPCs would initiate an RSLS abort. If all three engines indicated nominal performance by T−3 seconds, they were commanded to gimbal to liftoff configuration and the command would be issued to arm the SRBs for ignition at T−0. Between T−6.6 seconds and T−3 seconds, while the RS-25 engines were firing but the SRBs were still bolted to the pad, the offset thrust caused the Space Shuttle to pitch down 650 mm (25.5 in) measured at the tip of the external tank; the 3-second delay allowed the stack to return to nearly vertical before SRB ignition. At T−0, the eight frangible nuts holding the SRBs to the pad were detonated, the final umbilicals were disconnected, the SSMEs were commanded to 100% throttle, and the SRBs were ignited. By T+0.23 seconds, the SRBs built up enough thrust for liftoff to commence, and reached maximum chamber pressure by T+0.6 seconds. At T−0, the JSC Mission Control Center assumed control of the flight from the LCC.
  At T+4 seconds, when the Space Shuttle reached an altitude of 22 meters (73 ft), the RS-25 engines were throttled up to 104.5%. At approximately T+7 seconds, the Space Shuttle rolled to a heads-down orientation at an altitude of 110 meters (350 ft), which reduced aerodynamic stress and provided an improved communication and navigation orientation. Approximately 20−30 seconds into ascent and an altitude of 2,700 meters (9,000 ft), the RS-25 engines were throttled down to 65−72% to reduce the maximum aerodynamic forces at Max Q. Additionally, the shape of the SRB propellant was designed to cause thrust to decrease at the time of Max Q.  The GPCs could dynamically control the throttle of the RS-25 engines based upon the performance of the SRBs.
  At approximately T+123 seconds and an altitude of 46,000 meters (150,000 ft), pyrotechnic fasteners released the SRBs, which reached an apogee of 67,000 meters (220,000 ft) before parachuting into the Atlantic Ocean. The Space Shuttle continued its ascent using only the RS-25 engines. On earlier missions the Space Shuttle remained in the heads-down orientation to maintain communications with the tracking station in Bermuda, but later missions, beginning with STS-87, rolled to a heads-up orientation at T+6 minutes for communication with the tracking and data relay satellite constellation. The RS-25 engines were throttled at T+7 minutes 30 seconds to limit vehicle acceleration to 3 g. At 6 seconds prior to main engine cutoff (MECO), which occurred at T+8 minutes 30 seconds, the RS-25 engines were throttled dow
caption: Solid rocket booster (SRB) separation during STS-1
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