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.