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Space Shuttle: Difference between revisions
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→The Main Engines
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In FG, the throttle controls all three SSMEs during ascent. Engines ignite once throttle is moved above 67%, this triggers the SRB ignition. If the throttle is moved below 67%, the engines will stop, however they will restart once throttle is moved again up as long as fuel is available in the ET. | In FG, the throttle controls all three SSMEs during ascent. Engines ignite once throttle is moved above 67%, this triggers the SRB ignition. If the throttle is moved below 67%, the engines will stop, however they will restart once throttle is moved again up as long as fuel is available in the ET. | ||
=== Ascent structural and aerodynamical limits === | |||
The following structural and aerodynamical limits need to be observed during ascent: | |||
* dynamical pressure qbar < 819 lb/sqf (modeled) | |||
This is a structural limit for the orbiter and mated stack, in actual operations the orbiter should be kept below 650 lb/sqf. | |||
* wing bending moment CBW between -0.019 and 0.019 (not modeled) | |||
At max qbar, the wing bending moment is a function of Mach number and AoA. Since Mach number is close to 1.4 in this phase of the flight, this limit basically translates into alpha between -8 degrees and 2 degrees. This can only be achieved if the orbiter is in inverted flight. | |||
* translational accelerations Nx between 0 and 3.11 g (modeled), Ny between -0.18 and 0.18 g (not modeled) and Nz between -0.06 and 0.73 g (not modeled). | |||
These are structural limits of the mated stack to acceleration rather than aerodynamical forces. Especially the Nx (acceleration along the orbiter axis, i.e. main engine thrust) is important and requires to throttle down the SSMEs towards the end of the burn time. | |||
* late ascent trajectory may not drop below 265.000 ft (modeled) | |||
This is a heat load limit for the external tank insulation, if the thermal protection of the ET fails, it will explode. | |||
== Glossary of acronyms == | == Glossary of acronyms == | ||