Rate Gyro Assemblies
rate gyro assemblies are used by the flight control system during
ascent, entry and aborts as feedbacks to final rate errors that
are used to augment stability and for display on the commander's
and pilot's attitude director indicator rate needles on panels F6
and F8. The four orbiter RGAs are referred to as RGAs 1, 2, 3 and
The RGAs sense
roll rates (about the X axis), pitch rates (about the Y axis) and
yaw rates (about the Z axis). These rates are used by the flight
control system to augment stability during both ascent and entry.
Each RGA contains
three identical single-degree-of-freedom rate gyros so that each
gyro senses rotation about one of the vehicle axes. Thus, each RGA
contains one gyro-sensing roll rate (about the X axis), one gyro-sensing
pitch rate (about the Y axis) and one gyro-sensing yaw rate (about
the Z axis).
Each gyro has
three axes. A motor forces the gyro to rotate about its spin axis.
When the vehicle rotates about the gyro input axis, a torque results
in a rotation about the output axis. An electrical voltage proportional
to the angular deflection about the output axis-representing vehicle
rate about the input axis-is generated and transmitted through the
flight aft MDMs to the GPCs and RGA SOP. This same voltage is used
within the RGA to generate a counteracting torque that prevents
excessive gimbal movement about the output axis. The maximum output
for roll rate gyros is plus or minus 40 degrees per second; for
the pitch and yaw gyros, the maximum output is plus or minus 20
degrees per second.
The RGA SOP
converts the voltage rate into units of degrees per second.
The RGA 1,
2, 3 and 4 on/off power switches are located on panels O14, O15,
O16 and O15, respectively. The redundant power supplies for RGAs
1 and 4 prevent the loss of more than one rate gyro assembly if
main bus power is lost.
The RGAs remain
off on orbit except during flight control system checkout to conserve
The RGAs afford
fail-operational redundancy during both ascent and entry. A quad
mid value software scheme selects the best data for use in redundancy
management and failure detection.
red caution and warning light on panel F7 will be illuminated to
inform the flight crew of an RGA failure.
The RGAs are
located on the aft bulkhead below the floor of the payload bay.
They are mounted on cold plates for cooling by the Freon-21 coolant
loops. The RGAs require a five-minute warm-up time.
The RGA contractor
is Northrop Corp., Electronics Division, Norwood, Mass.