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Space Shuttle: Difference between revisions
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→Avionics and guidance systems
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[[File:Shuttle-approach06.jpg|600px|thumbnail|none|Touchdown and drag chute deployed]] | [[File:Shuttle-approach06.jpg|600px|thumbnail|none|Touchdown and drag chute deployed]] | ||
== Systems == | |||
=== Auxiliary Power Unit and Hydraulics System === | |||
Thrust vector control of the SSMEs during ascent, movement of the various aerosurfaces, deployment of the landing gear and brakes/nose wheel steering all rely on hydraulic pressure to operate. | |||
The Space Shuttle is equipped with three independent hydraulics systems, each of them powered by an Auxiliary Power Unit (APU), a turbine utilizing hydrazine as propellant. Under normal load conditions, each APU utilized about 3 - 3.5 lb of propellant per minute. With a hydrazine load of 332 lb, this means the system can be operated for about 90 minutes under nominal conditions or be run in a power-saving mode for 110 minutes during an once around abort. This means that the APUs have to be switched off when not used - they are powered down as part of the post-MECO operations and powered up as part of the atmospheric entry preparations. | |||
When not in use, electrically powered hydraulic circulation pumps keep the hydraulic fluid moving such as to equalize temperatures in the components. | |||
As of June 2015, the APU and hydraulic system is modeled with a fair amount of detail and operated from a dedicated menu. APUs need to be started as part of the pre-launch checklist. <b>If the hydraulic system is not available during ascent, this will result in loss of the vehicle after SRB separation as there is no control over the Shuttle if the SSMEs can not be gimbaled.</b> | |||
== Avionics and guidance systems == | == Avionics and guidance systems == | ||