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Speed Brake/Thrust Controller

There are two speed brake/thrust controllers: one on the left side of the flight deck forward on panel L2 for the commander and one on the right side of the center console on panel C3 for the pilot. The SBTCs serve two distinct functions: during ascent, the pilot's speed brake/thrust controller may be used to vary the thrust level of the three SSMEs. During entry, the commander's or pilot's speed brake/thrust controller may be used to control aerodynamic drag (hence airspeed) by opening or closing the speed brake.

Depressing a takeover switch (with three contacts) on each SBTC switches to manual control of the SSME thrust level setting (pilot's only) or speed brake position. Each SBTC contains three transducers-channels 1, 2 and 3, which produce a voltage proportional to the deflection. Redundancy management selects the output.

In the case of the SSME thrust-level setting, the top half of both spd bk/throt push button light indicators on panels F2 and F4 will be illuminated, indicating auto . Only the pilot's SBTC can be enabled for manual throttle control. The pilot depresses the takeover push button on the SBTC, causing the general-purpose computer throttle command to be frozen at its current value. While depressing the takeover button, the pilot moves the SBTC to match the frozen GPC command. Manual control is established when the match is within 4 percent. When the match is achieved, the spd bk/throt man push button light indicator on panel F4 will be illuminated and the auto light extinguished. The takeover push button is then released. If the takeover push button is released before a match is achieved, the system reverts to GPC auto commands. Under manual throttle command, depressing either or both push button light indicators on panel F2 or F4 will cause the system to revert to the GPC auto commands, extinguishing the pilot's man light and illuminating the auto lights on panels F2 and F4. Transferring back to auto during a return-to-launch-site abort leaves the throttle at the last-commanded manual setting until 3 g's, and the vehicle is held at 3 g's.

If the speed brake mode is in automatic and the commander or pilot wishes to control the speed brake manually, momentarily depressing the takeover push button grants control of the SBTC to the crew member who depressed the switch. The speed brake is driven to the position currently commanded by the SBTC. The spd bk/throt man push button light indicator on panel F2 will be illuminated if the commander takes control, extinguishing the auto light. If the pilot takes control, the spd bk/throt man push button light indicator on panel F4 will be illuminated, and the commander's light will be extinguished. To place the speed brake under software control, either or both spd bk/throt push button indicators on panel F2 or F4 can be depressed, and the auto lights on panels F2 and F4 will be illuminated.

At the forward setting, the SSME thrust level is the greatest, and the speed brake is closed. Rotating the SBTC back decreases the SSME thrust level or opens the speed brake.

The SBTC SOP converts the selected SSME throttle command to a setting in percent and the selected speed brake command from volts to degrees. In addition, the SBTC SOP selects the speed brake command from the SBTC whose takeover button was depressed last. If both takeover buttons are depressed simultaneously, the commander's SBTC is given control. If redundancy management declares an SBTC bad, the command is frozen.

The commander's SBTC is powered by the flt cntlr on/off switch on panel F7 when positioned to on . The pilot's SBTC is powered when the flt cntlr on/off switch on panel F8 is positioned to on .

The SBTC contractor is Honeywell Inc., Clearwater, Fla.


Curator: Kim Dismukes | Responsible NASA Official: John Ira Petty | Updated: 04/07/2002
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