Navigation and Guidance

The navigation function is to determine the vehicle position and velocity
as input to the guidance and control system

The guidance system determines the proper vehicle attitude and issues
steering commands to the control system..

Inertial Reference Unit (IRU) contains a 4 gimbal all attitude,
gyro-stabilized platform wupporting three orthogonal
accelerometers. A crystal oscillator with 800 pulses per second given
navigation function timing. The IRU triggers
an interrupt every 20msec.

NAVIGATION System
ELEMENTS:

      - Inertial Measurements Group aMG)

            Inertial Reference Unit (IRU)
            System Electronics Unit (SEW)

      - Digital Computer Unit (DCU)



FUNCTION: - Determine Vehicle Position and Velocity for Use by Guidance and
Control

Navigation is the process of determining vehicle position and velocity.
This is done on board the Centaur D-1 by
inertially measuring accelerations, computing a gravity correction, and
integrating.

A stable platform and its electronics unit make up the inertial measurement
group gMG). The IMG measures
acceleration and provides a time reference for the digital computer unit
(DCU) to make the navigation computations.

SYSTEM OPERATION. The navigation function is to measure sensed
acceleration, compute gravity contributions to
vehicle accelerations, determine time, and integrate the net vehicle
accelerations to maintain continuous values of
position and velocity. These values are stored for use by other functions.

A reference inertial coordinate system is maintained in the IRU by gyros
mounted on a platform. The platform is the
inner gimbal of a 4-gimbal assembly. It is kept fixed in space by the
movement of the other gimbals with respect to
it, each other, and the vehicle. The platform itself has unlimited
3-degrees-of-freedom movement. If the platform
rotates from the inertial reference, the gyros sense this and put out an
error signal. The error signal is then used to
drive the platform back to its proper orientation.

In response to disturbances, the platform is stabilized by the three
orthogonallymounted single-degree-of-freedom
gyros (U. V, W) which drive the appropriate gimbals (Figure 4-14) through
resolvers (U and V) and torque motors.
No resolving of W gyro output is required, since the W axis is held fixed
in space by the inner middle and outer
middle gimbals. The torque motors are d-c, direct drive.

GUIDANCE FUNCTION

ELEMENT:

      - Digital Computer Unit


FUNCTION:

      - Determine Proper Vehicle Attitude and Issue Steering
      Commands to the Control System


OPERATION. The vehicle position and velocity, together with information
about the desired trajectory, provide
input to the guidance function. The output is the desired vehicle attitude,
stated in terms of roll and pitch axes in
inertial coordinates.

The DCU performs computations to determine the desired attitude, expresses
this attitude in inertial coordinate
components of vehicle roll and pitch axes, and outputs these components via
the a-c D/A converters. Figure 4-18 is a
block diagram of the guidance system.