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.
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
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.
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.