Human factors dictate that an RHC deflection produce a rotation in the same direction as the flight crew member's line of sight. The aft flight station RHC is used only on orbit. An aft sense -Z switch on panel A6 selects the line-of-sight reference about the minus Z axis (overhead windows), and the -X position selects the line-of-sight reference about the minus X axis (aft windows) in order for aft RHC commands to be correctly transformed to give the desired orbiter movement.
Several switches are located on the RHC. A backup flight system (BFS) mode button on the commander's and pilot's RHCs engage the BFS when depressed. The commander's, pilot's, and aft flight station RHCs have a two-contact trim switch that can be pushed forward or aft to add a trim rate to the RHC pitch command; pushing it left or right adds a roll trim rate. The aft RHC's trim switch is inactive. The communications switch on each RHC is a push-to-talk switch that enables voice transmission when the switch is depressed.
Each RHC contains nine transducers: three redundant transducers sense pitch deflection, three sense roll deflection and three sense yaw deflection. The transducers produce an electrical signal proportional to the deflection of the RHC. The three transducers are called channels 1, 2 and 3; the channel selected by redundancy management provides the command. Each channel is powered by a separate power supply in its associated display driver unit. Each controller is triply redundant; thus, it takes only one good signal from a controller for the controller to operate.
Each RHC has an initial dead band of 0.25 of a degree in all three axes. To move the RHC beyond the dead band, an additional force is required. When the amount of deflection reaches a certain level, called the softstop, a step increase in the force required for further deflection occurs. When a software detent position is exceeded, that RHC assumes control.
The softstop occurs at 19.5 degrees in the roll and pitch axes and at 9.5 to 10.5 degrees in the yaw axis. To reach the softstop in the roll axes, 40.95 inch-pounds of static torque deflection are required; 38.2 inch-pounds are needed in pitch and 7 inch-pounds in yaw.
The mechanical hardstop that can be obtained in an axis is 24.3 degrees in the roll and pitch axis and 14.3 degrees in the yaw axis.
Software normally flows from the RHCs to the flight control system through redundancy management and a SOP before it is passed to the aerojet digital autopilot.
In a nominal mission, the flight crew has manual control of the RHC during every major mode except terminal countdown. When an RHC deflection exceeds the detent in an axis, the RHC SOP generates a discrete signal that converts the RHC from the automatic mode to control stick steering, or hot stick. However, during ascent when the ascent digital autopilot is active, a CSS pitch and/or roll/yaw mode push button light indicator on panel F2 or F4 must be depressed in order for manual inputs to be implemented into the flight control system from the commander's or pilot's RHC. When a CSS pitch or roll/yaw push button light indicator is depressed on panels F2 or F4, the white light for the push button indicator will be illuminated and that axis will be downmoded from automatic to CSS.
When the flight crew commands three-axis motion using the RHC, the GPCs process the RHC and motion sensor commands; and the flight control system interprets the RHC motions (fore and aft, right and left, clockwise and counterclockwise) as rate commands in pitch, roll and yaw and then processes the flight control law (equations) to enhance control response and stability. If conflicting commands are given, no commands result.
During orbital flight, any one of the three stations can input three-axis control commands to the flight control system. During entry and landing, the commander and pilot have two-axis (roll and pitch only) capability. Roll, pitch and yaw aerosurface deflection trim is controlled by the panel trim switches, while roll and pitch vehicle rate trim is controlled with the trim switches on the RHC. For a return-to-launch-site abort, both the commander's and pilot's RHC have three-axis capability during major mode 601 and roll and pitch during major modes 602 and 603.
The commander's RHC is powered when the flt cntlr (controller) on/off switch on panel F7 is positioned to on . The pilot's RHC is powered when the flt cntlr on/off switch on panel F8 is positioned to on. The aft RHC is powered when the flt cntlr on/off switch on panel A6 is positioned to on .
If a malfunction occurs in the commander's or pilot's RHC, the red RHC caution and warning light on panel F7 is illuminated.
The RHC contractor is Honeywell Inc., Clearwater, Fla.
TRANSLATIONAL HAND CONTROLLER There are two translational hand controllers: one at the commander's station and one at the aft flight deck station. The commander's THC is active during orbit insertion, on orbit and during deorbit. The aft flight deck station THC is active only on orbit. The THCs are used for manual control of translation along the longitudinal (X), lateral (Y) and vertical (Z) vehicle axes using the RCS.
Each THC contains six three-contact switches, one in the plus and minus directions for each axis. Moving the THC to the right commands translation along the plus Y axis and closes three switch contacts (referred to as channels 1, 2 and 3). Redundancy management then selects the channel and provides the command.
An aft sense switch on panel A6 selects the line-of-sight reference along the minus X or minus Z axis of the orbiter for the aft THC. The aft sense switch must be in the -X position for aft windows and -Z for the overhead windows in order for the aft THC commands to be correctly transformed to give the desired orbiter movement.
The normal displacement of a THC is 0.5 of an inch from the center null position in both directions along each of the three THC axes. A force of 2 pounds is required to deflect either THC 0.5 of an inch in all axes.
The redundant signals from the forward and aft THC pass through a redundant management process and a SOP before being passed to the flight control system. If both the forward and aft THCs generate conflicting translation commands, the output translation command is given.
In what is referred to as the transition digital autopilot mode, the commander's THC is active and totally independent of the flight control orbital digital autopilot ( DAP ) push buttons on panel C3 or A6 or the position or status of the RHC. Whenever the commander's THC is out of detent plus or minus X, Y or Z, translation acceleration commands are sent directly to the RCS jet selection logic for continuous RCS thrusting periods. Rotational commands may be sent simultaneously with translation commands within the limits of the RCS jet selection logic; if both plus X and minus Z translations are commanded simultaneously, plus X translation is given priority.
The commander's THC is powered when the flt cntlr on/off switch on panel F7 is positioned to on . The aft THC is powered when the flt cntlr on/off switch on panel A6 is positioned to on .
The THC contractor is Honeywell Inc., Clearwater, Fla.
CONTROL STICK STEERING PUSH BUTTON LIGHT INDICATORS The pitch auto, CSS and roll/yaw auto , CSS push button light indicators are located on panel F2 for the commander and on panel F4 for the pilot. Each push button light indicator is triply redundant. During entry, depressing a CSS push button light indicator will mode flight control to augmented manual in the corresponding axis, illuminate both CSS lights and extinguish both auto lights for that axis. Depressing a CSS push button light indicator to auto will return flight control in that axis to auto, extinguish both CSS lights and illuminate both auto lights. During ascent, depressing any of the four CSS push button light indicators will mode flight control to augmented manual in all axes, illuminate all four CSS push button light indicators and extinguish all four auto lights. Depressing any of the four push button light indicators to auto will mode flight control to automatic, illuminate all four auto push button light indicators and extinguish the CSS push button light indicators.
RUDDER PEDALS There are two pairs of rudder pedals: one each for the commander and pilot. The commander's and pilot's rudder pedals are mechanically linked so that movement on one side moves the other side. When a pedal is depressed, it moves a mechanical input arm in a rudder pedal transducer assembly. Each RPTA contains three transducers-channels 1, 2 and 3-and generates an electrical signal proportional to the rudder pedal deflection. An artificial feel is provided in the rudder pedal assemblies.
The rudder pedals command orbiter rotation about the yaw axis by positioning the rudder during atmospheric flight. In atmospheric flight, flight control software performs automatic turn coordination; thus the rudder pedals are not used until the wings are level before touchdown.
The RPTA SOP converts the selected left and right commands from volts to degrees; selects the largest of the left and right commands for output to flight control software after applying a dead band; and if redundancy management declares an RPTA bad, sets that RPTA to zero.
The rudder pedals can be adjusted 3.25 inches forward or aft from the neutral position in 0.81-inch increments (nine positions). The breakout force is 10 pounds. A pedal force of 70 pounds is required to depress a pedal to its maximum forward or aft position.
The rudder pedals provide two additional functions unrelated to software after touchdown. Rudder pedal deflections provide nose wheel steering, and depressing the upper portion of the pedals by applying toe pressure provides braking. Differential braking may be used for nose wheel steering.
The commander's RPTA is powered when the flt cntlr on/off switch on panel F7 is positioned to on . The pilot's RPTA is powered when the flt cntlr on/off switch on panel F8 is positioned to on .
The RPTA contractor is Honeywell Inc., Clearwater, Fla.
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.
BODY FLAP SWITCH There are two body flap switches: one for the commander on panel L2 and one for the pilot on panel C3. Each switch is a lever-locked switch spring loaded to the center position. The body flap switches provide manual control for positioning the body flap for SSME thermal protection and for reducing elevon deflections during the entry phase.
The body flap can be switched from its automatic mode to its manual mode by moving either switch from the auto/off position to the up or down position. These are momentary switch positions; when released, the switch returns to auto/off . The white body flap man (lower half) of the push button light indicator on panel F2 or F4 is illuminated, indicating manual control of the body flap. To regain automatic control, the body flap push button light indicator on panel F2 or F4 is depressed, extinguishing the man white light and illuminating the auto white light. The push button indicator can also be depressed to man for manual body flap control. The push button light indicator is triply redundant.
The up and down positions of each switch have two power supplies from a control bus.
If the commander and pilot generate conflicting commands, a body-flap-up command will be output to flight control because up has priority.
RHC/PANEL ENABLE/INHIBIT The dual-redundant trim RHC/panel enable/inhibit switches on panel F3 provide signals to the GPCs, prohibiting software execution of the associated RHC and panel trim switch inputs while in the inhibit position. The enable position is not wired to the GPCs, permitting the RHC and panel trim switch inputs, which allows trimming.
When the trim RHC/panel switch on the left side of panel F3 is in enable, the commander's RHC trim switches command vehicle pitch and roll rates in major modes 304 and 305 (entry) and major modes 602 and 603 (return to launch site). The three trim switches on panel L2 for the commander are used to move the aerosurfaces in roll, pitch and yaw.
When the trim RHC/panel switch on the right side of panel F3 is in enable, the pilot's RHC trim switches command vehicle pitch and roll rates in major modes 304, 305, 602 and 603. The three trim switches on panel C3 for the pilot are used to move the aerosurfaces in roll, pitch and yaw.
Redundancy management processes the two sets of switches. If two switches generate opposing commands, the resultant trim command in that axis is zero.
TRIM SWITCHES The commander's trim roll l (left), r (right); the yaw trim l, r; and trim pitch up, down switches are located on panel L2. The pilot's switches are located on panel C3. The commander's trim switches on panel L2 are enabled when the trim panel on/off switch on the left side of panel F3 is positioned to on . The pilot's trim switches on panel C3 are enabled when the trim panel on/off switch on the right side of panel F3 is positioned to on. The corresponding trim RHC/panel enable/inhibit switch must be in enable in order for trimming to take place.
Each of the three trim switches on panels L2 and C3 are spring loaded to the center off position.
Redundancy management processes the two sets of switches. If two switches generate opposing commands, the resultant trim command in that axis is zero.
AEROSURFACE SERVOAMPLIFIERS Aerosurface servoamplifiers are electronic devices that receive aerosurface commands during atmospheric flight from the flight control system software and electrically position hydraulic valves in aerosurface actuators, causing aerosurface deflections.
Each aerosurface is driven by a hydraulic actuator controlled by a redundant set of electrically driven valves (ports). There are four of these valves for each aerosurface actuator, except the body flap, which has only three. These valves are controlled by the selected ASAs.
There are four ASAs located in aft avionics bays 4, 5 and 6. Each ASA commands one valve for each aerosurface, except the body flap. ASA 4 does not command the body flap.
In addition to the command channels from the ASAs to the control valves, there are data feedback channels to the ASAs from the aerosurface actuators. Each aerosurface has four associated position feedback transducers that are summed with the position command to provide a servoloop closure for one of the four independent servoloops associated with the elevons, rudder and speed brake. The body flap utilizes only three servoloops. The path from an ASA to its associated servovalve in the actuators and from the aerosurface feedback transducers to an ASA is called a flight control channel; there are, thus, four flight control channels, except for the body flap.
Each of the four elevons located on the trailing edges has an associated servoactuator that positions it. Each servoactuator is supplied with hydraulic pressure from the three orbiter hydraulic systems. A switching valve is used to control the hydraulic system that becomes the source of hydraulic pressure for that servoactuator. The valve allows a primary source of pressure (P1) to be supplied to that servoactuator. If the primary hydraulic pressure drops to around 1,200 to 1,500 psig, the switching valve allows the first standby hydraulic pressure (P2) to supply that servoactuator. If the first standby hydraulic pressure drops to around 1,200 to 1,500 psig, the secondary standby hydraulic source pressure (P3) is then supplied to that servoactuator. The yellow hyd press caution and warning light will be illuminated on panel F7 if the hydraulic pressure of system 1, 2 or 3 is below 2,400 psi and will also illuminate the red backup caution and warning alarm light on panel F7.
Each elevon servoactuator receives command signals from each of the four ASAs. Each actuator is composed of four two-stage servovalves that drive a modulating piston. Each piston is summed on a common mechanical shaft, creating a force to position a power spool that controls the flow of hydraulic fluid to the actuator power ram, controlling the direction of ram movement, thus driving the elevon to the desired position. When the desired position is reached, the power spool positions the mechanical shaft to block the hydraulic pressure to the hydraulically operated ram, locking the ram at that position. If a problem develops within a servovalve or it is commanded to a position different than the positions of the other three within an actuator, secondary delta pressure should begin to rise to 2,200 psi. Once the secondary delta pressure is at or above 2,200 psia for more than 120 seconds, the corresponding ASA sends an isolation command to the servovalve, opening the isolation valve, bypassing the hydraulic pressure to the servovalve, and causing its commanded pressure to the power spool to drop to zero, effectively removing it from operation. The pressure differential is sensed by a primary linear differential pressure transducer across the modulating piston when the respective FCS channel switch on panel C3 is in auto . This automatic function prevents excessive transient motion to that aerosurface, which could result in loss of the orbiter due to slow manual redundancy.
The FCS channel yellow caution and warning light on panel F7 will be illuminated to inform the flight crew of a failed channel. A red FCS saturation caution and warning light on panel F7 will be illuminated if one of the four elevons is set at more than plus 15 degrees or less than minus 20 degrees.
There are four FCS channel switches on panel C3- FCS channels 1, 2, 3 and 4; each has an override, auto and off position. The switch for a channel controls the channel for the elevons, rudder/speed brake and body flap, except channel 4, which has no body flap commands. When an FCS channel switch is in auto and that channel was bypassed, it can be reset by positioning the applicable switch to override . When an FCS channel switch is positioned to off , that channel is bypassed.
In each elevon servoactuator ram, there are four linear ram position transducers and four linear ram secondary differential pressure transducers. The ram linear transducers provide position feedback to the corresponding servoloop in the ASA, which is then summed with the position command to close the servoloop. This feedback is then summed with the elevon ram linear secondary differential pressures to develop an electrohydraulic valve drive current that is proportional to the error signal in order to position the ram. The maximum elevon deflection rate is 20 degrees per second.
During ascent, the elevons are deflected to reduce wing loads caused by rapid acceleration through the lower atmosphere. In this scheme, the inboard and outboard elevons are deflected together. By the time the vehicle reaches approximately Mach 2.5, the elevons have reached a null position, where they remain. This is accomplished by the initialized-loaded program.
The rudder/speed brake, which consists of upper and lower panels, is located on the trailing edge of the orbiter's vertical stabilizer. One servoactuator positions the panels together to act as a rudder; another opens the panels at the rudder's flared end so it functions as a speed brake.
The rudder and speed brake servoactuator receives four command signals from the four ASAs. Each servoactuator is composed of four two-stage servovalves that function like those of the elevons. The exception is that the rudder's power spool controls the flow of hydraulic fluid to the rudder's three reversible hydraulic motors and the power spool for the speed brake controls the flow of hydraulic fluid in the speed brake's three hydraulic reversible motors. Each rudder and speed brake hydraulic motor receives hydraulic pressure from only one of the orbiter's hydraulic systems. Each hydraulic motor has a hydraulic brake. When the motor is supplied with hydraulic pressure, the motor's brake is released. When the hydraulic pressure is blocked to that hydraulic motor, the hydraulic brake is applied, holding that motor and the corresponding aerosurface at that position.
The three hydraulic motors provide output to the rudder differential gearbox, which is connected to a mixer gearbox that drives rotary shafts. These rotary shafts drive four rotary actuators, which position the rudder panels.
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