Aeronautics and astronautics – Spacecraft – Attitude control
Patent
1994-06-10
1997-01-28
Barefoot, Galen L.
Aeronautics and astronautics
Spacecraft
Attitude control
244170, B64G 124
Patent
active
055971431
DESCRIPTION:
BRIEF SUMMARY
The invention relates to the improvement of devices for controlling the spinning direction and damping of nutation vibrations of spacecraft which have a stored spin. Various devices have become known for controlling the desired value and stabilizing the vibrations of spinning bodies, which are freely movable about their rotatory axes, with respect to two body axes (X-, Z-axes), which are situated transversely to the spinning axis, by means of one or several attitude sensors, which measure the angular deviations of the first (X-) and/or second lateral axis (Z-axis) from its desired attitude, and actuators, such as reaction nozzles which generate controlling torques about one or both lateral axes, in particular, operate discontinuously and whose control interventions cannot fall below preset minimal pulse increments. One of these devices, specifically the one known from International Patent Document WO89/02622, is characterized in that, from the measuring signals for the deviations (.epsilon..sub..phi., .epsilon..sub..psi.) of one or both lateral axes from their desired angular position, signal fractions are formed which are separated via regulator networks and which are representative of the orbital movement or spinning direction in space (.phi..sub.0, .psi..sub.0) or for the nutation movement (.phi..sub.N) and are linked in the spin and nutation regulators in such a manner that the first-mentioned signal fraction determines the size or number and preceding signs of the control interventions, and the second signal fraction, which represents the nutation movement (.phi..sub.N) is responsible for the points in time or the phase angle (.beta..sub.N) of the control interventions within a nutation period.
The present invention relates to improvements of devices for the lateral axis control of the above-mentioned type. The reason is that these devices have some significant deficiencies:
According to the characteristics of such devices, a control intervention is triggered only when the spinning deviation from the normal line of the path (H.sub.X, H.sub.Z) in space--illustrated by the orbital movement fraction (.phi..sub.0, .psi..sub.0) of the deviation signals--exceeds predetermined threshold values (d.sub..phi., d.sub..psi.) preset by dead zones, irrespective of how large the nutational vibration amplitude (A.sub.N) may be which is superimposed on the orbital movement fraction. It is known that, in the case of communication or application satellites, for maintaining the inclination of the orbit and the attitude of the spacecraft on its path, path correcting maneuvers must be carried out at regular intervals in the course of which environmental torques act upon the spacecraft which are by approximately 5 powers of ten higher than in the normal operation of the satellite and therefore result in a correspondingly violent actuating of the reaction nozzles for generating controlling torques about all spacecraft axes. After their end, considerable nutation amplitudes may occur according to the size and time-related assignment of the control pulses last emitted about the lateral axes in the phase of the transition to the normal-operation control of the type existing here, while, at the same time, the position of the spin vector is arbitrary, particularly also within the above-mentioned dead zone limits, which do not trigger control interventions before they are exceeded, which control interventions will then, however, also equally cause an optimal reduction of nutation. For a typical three-axis stabilized satellite equipped with a fixed spin wheel of nominally 50 Nms and in the case of an environmental torque of 10.sup.-5 Nm under normal operating conditions, for example, such a residual nutation vibration, which is subjected to no passive or active damping, would continue to exist for up to 1, 2 hours if the spin orientation were just within a permissible dead zone range of 0.025.degree., specifically until the spin deviation has travelled from one response threshold (such as -d.sub..phi.) to another (+d.sub..psi.). In
REFERENCES:
patent: 3937423 (1976-02-01), Johansen
patent: 4174819 (1979-11-01), Bruderle et al.
patent: 4424948 (1984-01-01), Muhlfelder et al.
patent: 5042752 (1991-08-01), Surauer et al.
Bittner Helmut
Surauer Michael
Barefoot Galen L.
Deutsche Aerospace AG
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