Aeronautics and astronautics – Aircraft control – Automatic
Patent
1994-06-07
1996-07-16
Barefoot, Galen L.
Aeronautics and astronautics
Aircraft control
Automatic
244171, B64G 136
Patent
active
055359655
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a three-axis stabilized, earth-oriented satellite according to the preamble of claim 1 as well as to a process for implementing the sun and earth acquisition in the case of such a satellite.
A satellite of this type is known from H. Bittner, et al. "The Attitude Determination and Control Subsystem of the Intelsat V Spacecraft", published in Proceedings of AOCS Conference, Noordwijk, Oct. 3 to 6, 1977, ESA SP-128, November, 1977. By means of its attitude control system, it is capable of carrying out many different maneuvers which are required in the transfer orbit and in the geostationary orbit, such as the sun acquisition; that is, the alignment of the X-axis of its satellite-fixed system of coordinates (X, Y, Z) with the sun; the earth acquisition; that is the alignment of the Z-axis with the center of the earth; the apogee maneuver; that is the alignment of the Z-axis in the direction of the geostationary orbit in the apogee of the transfer orbit before the injection into the apogee; and finally all simple attitude control maneuvers for continuously maintaining the desired orientation as well as all reacquisition maneuvers when attitude references, such as the sun and/or the earth are lost.
The attitude control system of this known satellite comprises a regulator for using the respective required control laws; actuators, specifically attitude control nozzles, for generating controlling torques about each of the principal axes (X, Y, Z) of the satellite according to control signals emitted by the regulator; as well as sun sensors, an earth sensor, and a redundantly designed gyroscope package, which measures in three axes, for the direct measuring of the components of the rotational speed vector of the satellite with respect to the principal axes of the satellite. The sun sensors have a first field of view which comprises about the negative Z-axis, overall, one half of the XZ-plane and a specific width perpendicularly to it, and a second field of view which comprises about the X-axis overall one third of the XY-plane and a specific width perpendicularly to it. The earth sensor is oriented by means of its optical axis, as customary, in the direction of the Z-axis which, in the geostationary orbit, must be continuously aligned with the center of the earth (earth orientation).
The measured value generator used in the attitude control system include as an essential element a gyroscope package, which measures in three axes, for the direct measuring tracking of the components of the rotational speed vector .omega. (.omega..sub.X, .omega..sub.Y, .omega..sub.Z).sup.T of the satellite relative to the satellite-fixed system of coordinates. In the case of the known satellites, these measured values are required because there the control is designed correspondingly in order to be able to carry out the desired attitude control maneuvers. However, the use of gyroscopes of this type has the significant disadvantage that they are electromechanical components on which very high demands are to be made, particularly under the extreme condition of space, and which are very susceptible to disturbances and wear. The resulting required redundant design represents a considerable cost factor.
It is therefore an object of the invention to provide a satellite of the above-mentioned type whose attitude control system is designed as cost-effectively as possible and is nevertheless functionally reliable.
According to the invention, this object is achieved by the characteristics contained in the characterizing part of claim 1.
Accordingly, a sun sensor arrangement is now used whose field of view in a plane of the satellite-fixed system of coordinates--called "field of view plane"60 here--, for example, the XZ-plane, comprises the full angle of o.ltoreq..alpha..sub.1 .ltoreq.Z.pi., wherein .alpha..sub.1 is an angle which extends around in this plane from an arbitrarily selected reference direction, approximately the X-axis. Thus, an all-around view is required in the field of view plane. Perpendicularly to it, th
REFERENCES:
patent: 5080307 (1992-01-01), Smay et al.
patent: 5255879 (1993-10-01), Yocum et al.
"The Attitude Determination and Control Subsystem of the Intelsat V Spacecraft" published in Proceedings of AOCS Conference, Noordwijk, Oct. 3-6, 1977, ESA SP-128, Nov. 1977, pp. 1-20.
Bittner Helmut
Fichter Walter
Fischer Horst-Dieter
Surauer Michael
Barefoot Galen L.
Deutsche Aerospace AG
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