Editing Space Shuttle (section)

====Flight systems====
The orbiter was equipped with an [[avionics]] system to provide information and control during atmospheric flight. Its avionics suite contained three [[microwave scanning beam landing system]]s, three [[gyroscope]]s, three [[Tactical air navigation system|TACAN]]s, three [[accelerometer]]s, two [[radar altimeter]]s, two [[barometric altimeter]]s, three [[attitude indicator]]s, two [[Machmeter|Mach indicator]]s, and two [[Aviation transponder interrogation modes|Mode&nbsp;C]] [[Transponder (aeronautics)|transponders]]. During reentry, the crew deployed two [[Air data boom|air data probes]] once they were traveling slower than Mach 5. The orbiter had three [[Inertial measurement unit|inertial measuring units]] (IMU) that it used for guidance and navigation during all phases of flight. The orbiter contains two [[star tracker]]s to align the IMUs while in orbit. The star trackers are deployed while in orbit, and can automatically or manually align on a star. In 1991, NASA began upgrading the inertial measurement units with an [[inertial navigation system]] (INS), which provided more accurate location information. In 1993, NASA flew a [[GPS]] receiver for the first time aboard [[STS-51]]. In 1997, Honeywell began developing an integrated GPS/INS to replace the IMU, INS, and TACAN systems, which first flew on [[STS-118]] in August 2007.<ref name=jenkins />{{rp|402–403}}

While in orbit, the crew primarily communicated using one of four [[S band]] radios, which provided both voice and data communications. Two of the S&nbsp;band radios were [[phase modulation]] [[transceiver]]s, and could transmit and receive information. The other two S&nbsp;band radios were [[frequency modulation]] [[transmitter]]s and were used to transmit data to NASA. As S&nbsp;band radios can operate only within their [[Line-of-sight propagation|line of sight]], NASA used the [[Tracking and Data Relay Satellite System]] and the [[Spacecraft Tracking and Data Acquisition Network]] ground stations to communicate with the orbiter throughout its orbit. Additionally, the orbiter deployed a high-bandwidth [[Ku band|K<sub>u</sub>&nbsp;band]] radio out of the cargo bay, which could also be utilized as a rendezvous radar. The orbiter was also equipped with two [[UHF]] radios for communications with [[air traffic control]] and astronauts conducting EVA.<ref name=jenkins />{{rp|403–404}}

[[File:Space Shuttle General Purpose Computer.jpg|thumb|right|alt=The two computers used in the orbiter|AP-101S (left) and AP-101B general purpose computers]]
The Space Shuttle's [[fly-by-wire]] control system was entirely reliant on its main computer, the Data Processing System (DPS). The DPS controlled the flight controls and thrusters on the orbiter, as well as the ET and SRBs during launch. The DPS consisted of five general-purpose computers (GPC), two magnetic tape mass memory units (MMUs), and the associated sensors to monitor the Space Shuttle components.<ref name=jenkins />{{rp|232–233}} The original GPC used was the IBM [[IBM System/4 Pi#AP-101|AP-101B]], which used a separate [[central processing unit]] (CPU) and input/output processor (IOP), and [[non-volatile memory|non-volatile]] [[Solid-state drive|solid-state memory]]. From 1991 to 1993, the orbiter vehicles were upgraded to the AP-101S, which improved the memory and processing capabilities, and reduced the volume and weight of the computers by combining the CPU and IOP into a single unit. Four of the GPCs were loaded with the Primary Avionics Software System (PASS), which was Space Shuttle-specific software that provided control through all phases of flight. During ascent, maneuvering, reentry, and landing, the four PASS GPCs functioned identically to produce quadruple redundancy and would error check their results. In case of a software error that would cause erroneous reports from the four PASS GPCs, a fifth GPC ran the Backup Flight System, which used a different program and could control the Space Shuttle through ascent, orbit, and reentry, but could not support an entire mission. The five GPCs were separated in three separate bays within the mid-deck to provide redundancy in the event of a cooling fan failure. After achieving orbit, the crew would switch some of the GPCs functions from guidance, navigation, and control (GNC) to systems management (SM) and payload (PL) to support the operational mission.<ref name=jenkins />{{rp|405–408}} The Space Shuttle was not launched if its flight would run from December to January, as its flight software would have required the orbiter vehicle's computers to be reset at the year change. In 2007, NASA engineers devised a solution so Space Shuttle flights could cross the year-end boundary.<ref name="YERO">{{cite web |last=Bergin |first=Chris |title=NASA solves YERO problem for Shuttle |url=http://www.nasaspaceflight.com/content/?cid=5026|website=NASASpaceflight.com |archive-url=https://web.archive.org/web/20080418182718/http://www.nasaspaceflight.com/content/?cid=5026 |archive-date=April 18, 2008 |date= February 19, 2007 |access-date=December 22, 2007}}</ref>

Space Shuttle missions typically brought a portable general support computer (PGSC) that could integrate with the orbiter vehicle's computers and communication suite, as well as monitor scientific and payload data. Early missions brought the [[Grid Compass]], one of the first laptop computers, as the PGSC, but later missions brought [[Apple Inc.|Apple]] and [[Intel]] laptops.<ref name=jenkins />{{rp|408}}<ref name="GRiD">{{cite web |url=http://www.computerhistory.org/events/index.php?id=1139464298 |title=Pioneering the Laptop: Engineering the GRiD Compass |access-date=October 25, 2007 |publisher=The Computer History Museum |year=2006 |author=The Computer History Museum |url-status=dead |archive-url=https://web.archive.org/web/20071204034101/http://www.computerhistory.org/events/index.php?id=1139464298 |archive-date=December 4, 2007}}</ref>