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Space Shuttle: Difference between revisions
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→Auxiliary Power Unit and Hydraulics System
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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. | 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. | ||
As compared to the rest of the Shuttle's systems, the APU turbines with with 180 kW power each generate a lot of waste heat which ends up warming the hydraulic fluid and the lube oil. The APUs are operated at a temperature of over 390 K (250 F) though, so for an APU cold start it takes a bit more than 10 minutes to reach that temperature. Afterwards, the water spray boiler systems have to be used to cool hydraulic fluid and lube oil - they are supplied by three water tanks containing 142 lb of water each and can spray up to 10 lb / minute for cooling purpose. Overheating APUs can not be run for more than 2-3 minutes before they fail. | |||
When not in use, electrically powered hydraulic circulation pumps keep the hydraulic fluid moving such as to equalize temperatures in the components. | When not in use, electrically powered hydraulic circulation pumps keep the hydraulic fluid moving such as to equalize temperatures in the components. | ||
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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 - refer to Help/Aircraft Checklists for the detailed procedure. <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> | 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 - refer to Help/Aircraft Checklists for the detailed procedure. <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> | ||
Operation of the water spray boilers is realistically integrated into the heat transfer model of the Shuttle (see below), including the failure of overheating APUs. | |||
=== Active Thermal Control System === | === Active Thermal Control System === | ||