Aeronautics and astronautics – Spacecraft – Attitude control
Patent
1994-06-23
1995-07-18
Barefoot, Galen L.
Aeronautics and astronautics
Spacecraft
Attitude control
244169, 364434, 364459, B64G 126
Patent
active
054334020
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to a device and process for controlling the attitude of a spacecraft to be rotated about an axis of its body, i.e., the axis of rotation, and more particularly to an attitude control device comprising actuators for generating torques about the axis of rotation as well as about two lateral axes which are orthogonal with respect to the axis of rotation and to one another. Sensors are provided for the formation of angular velocity signals with respect to the three axes. Two modulators, which are in each case connected in front of the actuators assigned to one of the two lateral axes emit controlling signals to the actuators and have a variable dead zone. Two regulator networks, which receive one of the two lateral-axis angular velocity signals respectively, furnish a control signal for one of the two modulators and have a first signal path as well as a second signal path which is connected in parallel to the first one and contains an integrator.
This type of a device and this type of a process are known from U.S. Pat. No. 4,725,024. The object of U.S. Pat. No. 4,725,024 is to send a three-axis stabilized satellite, which is on a low, almost circular orbit, into an elliptic transfer path by igniting a perigee power unit. The apogee of this transfer path coincides with the radius of the endeavored geostationary orbit. Before igniting the perigee engine, for reasons of stability, the satellite must be rotated about a body axis of rotation which is to coincide with the thrust vector of the thrust exercised by the perigee power unit. In this case, the perigee power unit is still docked to the satellite, and the axis of symmetry of the power unit is congruent with an axis of symmetry of the satellite. In the case of U.S. Pat. No. 4,725,024, this is the roll axis. As known, the roll axis is one of the body's three axes of the satellite forming a rectangular system of coordinates, which also include the yaw axis as well as the pitch axis as the lateral axes. In the final operating condition of the satellite on the geostationary orbit, the roll axis must be oriented in the flight direction; the yaw axis must be oriented toward the center of the earth; and the pitch axis must be oriented perpendicularly to the two as well as to the plane of the orbit.
The attitude control system of a three-axis stabilized satellite includes a number of actuators, for example, fuel nozzles, which are capable of furnishing in a targeted manner torques or controlling torques about the three above-mentioned axes. The known attitude control device according to U.S. Pat. No. 4,725,024 also has sensors in the form of gyroscopes which furnish angular velocity signals with respect to rotations about the three axes of the body. Each of the two lateral-axis angular velocity signals is fed into a regular network which furnishes a control signal for a modulator which comprises a dead zone and, in turn, has the task of generating discrete control signals for the actuators assigned to the respective lateral axis. The two regulator networks have a first signal path as well as a second signal path which is connected in parallel to the first and contains an integrator. The two signal paths are fed together in front of the assigned modulator in a summation element.
Before being discharged from the space tug, the satellite with the docked perigee power unit already rotates slowly at approximately two revolutions per minute about the axis of rotation. After the discharge of the thus formed spacecraft from the loading bay of the space tug, via the actuating of the corresponding actuators, the rotation about the axis is continuously increased to a value of approximately forty revolutions per minute. If possible, care must be taken during this spin-up phase that the inevitably occurring nutation is controlled to a constant amplitude and the direction of the axis of rotation in the inertial space is maintained as precisely as possible.
The excitation of nutation vibrations may have different causes
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Bittner Helmut
Surauer Michael
Barefoot Galen L.
Deutsche Aerospace AG
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