Aeronautics and astronautics – Spacecraft – Attitude control
Reexamination Certificate
2002-02-20
2003-09-23
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Spacecraft
Attitude control
C701S013000, C244S169000
Reexamination Certificate
active
06622969
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a maneuver device for an artificial satellite, which can greatly and speedily change an attitude angle and an angular velocity of the artificial satellite by means of an attitude control actuator such as a thruster and a reaction wheel mounted on the artificial satellite.
BACKGROUND OF THE INVENTION
Artificial satellites are conventionally provided with a maneuver device which controls the attitude of the artificial satellite.
FIG. 9
is a block diagram showing a configuration of an exemplary conventional maneuver device.
In the
FIG. 9
, the conventional maneuver device is provided with a feed forward torque instruction signal generator
107
for outputting a feed forward torque instruction signal
110
according to a pre-programmed maneuver plan, and a thruster
108
for generating control torque based on the input feed forward torque instruction signal
110
and applying the generated control torque to satellite dynamics
100
. The satellite dynamics
100
represent the dynamic behavior of the artificial satellite incorporating this maneuver device. The maneuver device is further provided with an attitude angle detector
101
for detecting an attitude angle of the satellite dynamics
100
and outputting it as a detected attitude angle signal, an angular velocity detector
102
for detecting an angular velocity of the satellite dynamics
100
and outputting it as a detected angular velocity signal, a target attitude angle value generator
103
for generating a target value of the attitude angle of the satellite dynamics
100
and outputting it as a target attitude angle signal, and a target angular velocity value-generator
104
for generating a target value of the angular velocity of the satellite dynamics
100
and outputting it as a target angular velocity signal. The device is yet further provided with an attitude control signal calculator
105
for outputting an attitude control signal
111
based on inputs of an attitude angle error signal
112
(a difference signal between the target attitude angle signal and the detected attitude angle signal) and an angular velocity error signal
113
(a difference signal between the target angular velocity signal and the detected angular velocity signal), and a reaction wheel
106
for generating control torque based on the input attitude control signal
111
.
Next, operations performed by this conventional maneuver device will be described. First, the feed forward torque instruction signal generator
107
generates a feed forward torque instruction signal
110
as torque to be applied to each axis of the satellite dynamics
100
at each time point according to the maneuver plan, and outputs the feed forward torque instruction signal
110
to the thruster
108
. The thruster
108
is driven based on the input feed forward torque instruction signal
110
to generate and apply control torque to the satellite dynamics
100
.
The feed forward torque instruction signal generator
107
outputs the feed forward torque instruction signal
110
according to the pre-calculated maneuver plan regardless of the state of the satellite dynamics
100
. Thus, the accuracy of controlling the attitude may strikingly be deteriorated due to, for example, disturbance torque applied from the external environment to the satellite dynamics
100
, an error of the feed forward torque instruction signal
110
, an output error of the reaction wheel
106
and a control error caused by discrete outputs generated by the thruster
108
.
The disturbance torque applied to the satellite dynamics
100
includes solar radiation pressure torque caused by pressure of sunlight, gravity gradient torque caused by gravity of the earth and the like, torque caused by control gas jet injected from the thruster striking against the artificial satellite (i.e., torque caused by a plume of the thruster), residual magnetic torque caused by interaction between the magnetism of the artificial satellite and the geomagnetic field, and aerodynamic torque caused by impact of a slight amount of aeromolecules existing in the orbit of the artificial satellite.
In order to compensate for attitude errors caused by such disturbance torque and control errors, the conventional maneuver device employs a system including the attitude angle detector
101
, the angular velocity detector
102
, the target attitude angle value generator
103
, the target angular velocity value generator
104
, the attitude control signal calculator
105
, and the reaction wheel
106
which compensates for the attitude error during maneuver.
During the maneuver carried out by the feed forward torque instruction signal generator
107
and the thruster
108
, the target attitude angle value generator
103
generates and outputs a target value of the attitude angle of the artificial satellite to the attitude control signal calculator
105
at each time point. At the same time, the target angular velocity value generator
104
generates and outputs a target value of the angular velocity of the artificial satellite to the attitude control signal calculator
105
at each time point. The attitude angle detector
101
detects the actual attitude angle of the artificial satellite and outputs it as a detected attitude angle signal to the attitude control signal calculator
105
. At the same time, the angular velocity detector
102
detects the actual angular velocity of the artificial satellite and outputs it as a detected angular velocity signal to the attitude control signal calculator
105
. Then, the attitude control signal calculator
105
generates an attitude control signal
111
based on an attitude angle error signal
112
generated as a difference signal between the target attitude angle signal and the detected attitude angle signal as well as an angular velocity error signal
113
generated as a difference signal between the target angular velocity signal and the detected angular velocity signal, and outputs the generated signal
111
to the reaction wheel
106
. Here, the attitude control signal calculator
105
generates the attitude control signal
111
only with the input of the attitude angle error signal
112
and the angular velocity error signal
113
, according to a generally-employed control logic such as PID (Proportional-plus-Integral-plus-Derivative) control rule. Then, the reaction wheel
106
is driven based on the attitude control signal
111
to generate and apply control torque to the artificial satellite. As a result, maneuver takes place in the satellite dynamics
100
while the attitude error caused by the thruster
108
during the maneuver is compensated by the control torque from the reaction wheel
106
. The attitude of the satellite dynamics
100
is controlled during the maneuver by the sum of the control torque generated by the thruster
108
and the control torque generated by the reaction wheel
106
.
FIG. 10
is a block diagram showing a configuration of another exemplary conventional maneuver device. The maneuver device shown in
FIG. 10
represents those without a thruster. The configuration of the maneuver device shown in
FIG. 10
differs from the maneuver device shown in
FIG. 9
in that it has no thruster, and that a feed forward torque instruction signal
110
generated by a feed forward torque instruction signal generator
107
is added to an attitude control signal
111
generated by an attitude control signal calculator
105
, and the resulting signal is input to a reaction wheel
106
. Other than these differences, the configuration of the device shown in
FIG. 10
is the same as that shown in FIG.
9
.
In the maneuver device shown in
FIG. 10
, the reaction wheel
106
generates torque based on a sum signal of the feed forward torque instruction signal
110
and the attitude control signal
111
, and uses the torque to perform maneuver. The maneuver device shown in
FIG. 10
has an advantage in that it only uses the reaction wheel
106
as an attitude control actuator and thus can save an amount of fuel required by the t
Barefoot Galen L.
Whitham Curtis & Christofferson, PC
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