There are three rotational hand controllers on the orbiter crew compartment flight deck: one at the commander's station, one at the pilot's station and one at the aft flight deck station. Each RHC controls vehicle rotation about three axes: roll, pitch and yaw. During ascent, the commander's and pilot's RHCs may be used to gimbal the SSMEs and SRBs. For insertion and deorbit, the commander's and pilot's RHCs may be used to gimbal the orbital maneuvering system engines and to command thrusting of the reaction control system engines. On orbit, the commander's, pilot's and aft flight station RHCs may be used to command RCS engine thrusting. During entry, the commander's and pilot's RHCs may be used to command RCS engine thrusting during the early portion of entry and may be used to position the orbiter elevons in roll and pitch axes in the latter portion of entry.

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.