1,360
edits
Space Shuttle: Difference between revisions
Jump to navigation
Jump to search
→The Main Engines
| Line 83: | Line 83: | ||
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. | ||
=== A note on aerodynamics of the mated vehicle === | |||
With the ET and SRBs attached, the launch stack has quite different aerodynamical characteristics than the OV alone, for instance the stack is more yaw-stable than the orbiter and its pitching moment as function of alpha and rolling moment as function of beta are very different. Where such data could be obtained from wind tunnel tests with the mated stack, it has been used in the simulation. | |||
As in reality, the simulated shuttle has an automated downward elevon deflection schedule with Mach number upon ascent to provide further load relief for the wings (with corresponding aerodynamical forces acting). | |||
In general though, aerodynamical effects are subleading, the ascent dynamics is dominated by the thruster forces and the flight control systems have a large margin to compensate for them. | |||
=== CSS DAP schemes for ascent === | |||
During ascent, the stick controls thrust vectoring for both SSMEs and SRBs. The following two DAP schemes are available: | |||
<b>Thrust vectoring:</b> This is the real CSS ascent mode for the shuttle in which stick motion controls rate, stick to neutral commands an attitude hold. Internally a PID controller vectors the thrusters and uses the stick input as a bias for the error. This is a very stable scheme and can be easily used to achieve high precision in controlling ascent speed or orbital inclination. | |||
<b>Thrust vectoring (gimbal):</b> This is an educational scheme in which the stick motion directly controls the engine gimbal, i.e. the pilot needs to do the task of the PID controller himself. To make things somewhat easier, the engines are automatically vectored through the stack's CoG, i.e. outside the atmosphere stick neutral corresponds to zero moments acting on the stack. In the atmosphere, the control input hence needs to compensate for aerodynamical forces. Launch in this scheme is fairly rough and it is not possible to reach high precision, but it is possible to fly into orbit and gain a first-hand experience of the forces acting on the stack. | |||
=== Ascent structural and aerodynamical limits === | === Ascent structural and aerodynamical limits === | ||