Editing Space Shuttle (section)

===Solid Rocket Boosters===
{{main|Space Shuttle Solid Rocket Booster}}
[[File:Two Space Shuttle SRBs on the Crawler transporter.jpg|thumb|right|alt=Two Solid Rocket Boosters that are not attached to an external tank or orbiter|Two SRBs on the mobile launcher platform prior to mating with the ET and orbiter for [[STS-134]]]]

The Solid Rocket Boosters (SRB) provided 71.4% of the Space Shuttle's thrust during liftoff and ascent, and were the largest [[solid-propellant motor]]s ever flown.<ref name=SRB_largest>{{cite web |url=http://www.nasa.gov/returntoflight/system/system_SRB.html |title=Solid Rocket Boosters |publisher=NASA |date=March 5, 2006 |last=Dunbar |first=Brian |access-date=July 19, 2021 |archive-date=April 6, 2013 |archive-url=https://web.archive.org/web/20130406193019/http://www.nasa.gov/returntoflight/system/system_SRB.html |url-status=live}}</ref> Each SRB was {{convert|149.2|ft|m|abbr=on|order=flip|sigfig=2}} tall and {{convert|12.2|ft|m|abbr=on|order=flip|sigfig=2}} wide, weighed {{convert|150000|lb|kg|abbr=on|order=flip|sigfig=3}}, and had a steel exterior approximately {{convert|.5|in|mm|abbr=on|order=flip|sigfig=2}} thick. The SRB's subcomponents were the solid-propellant motor, nose cone, and rocket nozzle. The solid-propellant motor comprised the majority of the SRB's structure. Its casing consisted of 11 steel sections which made up its four main segments. The nose cone housed the forward separation motors and the parachute systems that were used during recovery. The rocket nozzles could gimbal up to 8° to allow for in-flight adjustments.<ref name=jenkins />{{rp|425–429}}

The rocket motors were each filled with a total {{convert|1106640|lb|kg|abbr=on|order=flip|sigfig=2}} of solid rocket propellant ([[Ammonium perchlorate composite propellant|APCP]]+[[Polybutadiene acrylonitrile|PBAN]]), and joined in the [[Vehicle Assembly Building]] (VAB) at KSC.<ref name=jenkins />{{rp|425–426}} In addition to providing thrust during the first stage of launch, the SRBs provided structural support for the orbiter vehicle and ET, as they were the only system that was connected to the [[mobile launcher platform]] (MLP).<ref name=jenkins />{{rp|427}} At the time of launch, the SRBs were armed at T−5&nbsp;minutes, and could only be electrically ignited once the RS-25 engines had ignited and were without issue.<ref name=jenkins />{{rp|428}} They each provided {{convert|2800000|lbf|kN|abbr=on|order=flip|sigfig=3}} of thrust, which was later improved to {{convert|3000000|lbf|kN|abbr=on|order=flip|sigfig=3}} beginning on [[STS-8]].<ref name=jenkins />{{rp|425}} After expending their fuel, the SRBs were [[Jettison (aviation)|jettisoned]] approximately two minutes after launch at an altitude of approximately {{convert|150000|ft|km|sigfig=2|abbr=on|order=flip}}. Following separation, they deployed drogue and main parachutes, landed in the ocean, and were recovered by the crews aboard the ships [[MV Freedom Star|MV ''Freedom Star'']] and [[MV Liberty Star|MV ''Liberty Star'']].<ref name=jenkins />{{rp|430}} Once they were returned to Cape Canaveral, they were cleaned and disassembled. The rocket motor, igniter, and nozzle were then shipped to Thiokol to be refurbished and reused on subsequent flights.<ref name=shuttle_manual />{{rp|124}}

The SRBs underwent several redesigns throughout the program's lifetime. [[STS-6]] and [[STS-7]] used SRBs {{convert|5000|lb|kg|abbr=on|order=flip|sigfig=2}} lighter due to walls that were {{convert|.004|in|mm|abbr=on|order=flip|sigfig=2}} thinner, but were determined to be too thin to fly safely. Subsequent flights until [[STS-26]] used cases that were {{convert|.003|in|mm|abbr=on|order=flip|sigfig=2}} thinner than the standard-weight cases, which reduced {{convert|4000|lb|kg|abbr=on|order=flip|sigfig=2}}. After the ''Challenger'' disaster as a result of an [[O-ring]] failing at low temperature, the SRBs were redesigned to provide a constant seal regardless of the ambient temperature.<ref name=jenkins />{{rp|425–426}}