Environmental Engineering Reference
In-Depth Information
The following is a list of the traditional FSW functions:
1.
Attitude determination and control
2.
Sensor calibration
3.
Orbit determination/navigation (traditionally orbit maneuver planning
has been a ground function)
4.
Propulsion
5.
Executive and task management
6.
Time management
7.
Command
processing
(target
scheduling
is
traditionally
a
ground
function)
8.
Engineering and science data storage and handling
9.
Communications
10.
Electrical power management
11.
Thermal management
12.
SI commanding
13.
SI data processing
14.
Data monitoring (traditionally no trending)
15.
FDC
16.
Safemode (separate ones for spacecraft and payload instruments)
2.2.1 Attitude Determination and Control, Sensor
Calibration, Orbit Determination, Propulsion
Often in the past, attitude determination and control, sensor calibration, or-
bit determination/navigation, and propulsion functions have resided within a
separate ACS processor because of the high central processing unit (CPU) de-
mands of its elaborate mathematical computations. As OBC processing power
has increased, this higher cost architecture has become more rare, and nowa-
days, a single processor usually hosts all the spacecraft bus functions. Attitude
determination includes the control laws responsible for keeping the spacecraft
pointing in the desired direction and reorienting the spacecraft to a new di-
rection. Currently, at GSFC, onboard attitude sensor calibration is limited to
gyro drift-bias calibration (and for some spacecraft, a coarse magnetometer
calibration).
Orbit determination may be accomplished by measurement (global posi-
tioning system (GPS) for example), solving the equations of motion, or by
use of an orbit propagator. Traditionally, orbit maneuver planning has been
the responsibility of the ground, but some experiments have been performed
migrating routine stationkeeping-maneuver planning onboard, e.g., Earth
Observing-1 (EO-1). Regardless of whether the orbit-maneuver planning is
done onboard or on the ground, the onboard propulsion subsystem has re-
sponsibility for executing the maneuvers via commands to the spacecraft's
thrusters, which also at times may be used for attitude control and momen-
tum management.
