Method and apparatus for steering the attitude of a satellite
First Claim
1. A method of controlling the attitude of a satellite, comprising the steps of:
- (a) providing a duster of CMGs on a satellite, said CMGs having respective wheels each rotatably mounted on a gimbal and said gimbals being mounted on a satellite platform to rotate about gimbal axes having different fixed directions, (b) from starting conditions and desired end conditions regarding attitude of the satellite and angular speed of the satellite and from an imparted time duration, determining set orientations of the gimbals about the axes thereof which correspond to a new configuration of the cluster of CMGs that is remote from any singular configuration and is such that exchange of angular momentum between the cluster of CMGs and the satellite during said imparted time duration will give rise to an attitude maneuver resulting into the desired end conditions; and
(c) simultaneously and independently controlling the orientation of said gimbals about the axes thereof to bring said gimbals into the set orientations by applying an angular position reference in open loop in a local servo-control of the orientations of all gimbals.
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Abstract
A method is disclosed for controlling the attitude of a satellite by controlling the speed of the gimbals of CMGs in a cluster of CMGs, the CMG having respective wheels mounted on gimbals that are mounted on a satellite platform to rotate about different orientation axes. From starting conditions and end conditions relating to attitude and angular speed and time, a cluster configuration is determined that is remote from any singular configuration such that exchanging angular momentum between the cluster of CMGs and the satellite during a given length of time will give rise to the desired attitude maneuver. The orientation of each gimbal is changed in simultaneous and independent manner into its reference orientation by using an angular position reference, applied in an open loop in the local servo-control of the angular positions of the gimbals.
58 Citations
10 Claims
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1. A method of controlling the attitude of a satellite, comprising the steps of:
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(a) providing a duster of CMGs on a satellite, said CMGs having respective wheels each rotatably mounted on a gimbal and said gimbals being mounted on a satellite platform to rotate about gimbal axes having different fixed directions, (b) from starting conditions and desired end conditions regarding attitude of the satellite and angular speed of the satellite and from an imparted time duration, determining set orientations of the gimbals about the axes thereof which correspond to a new configuration of the cluster of CMGs that is remote from any singular configuration and is such that exchange of angular momentum between the cluster of CMGs and the satellite during said imparted time duration will give rise to an attitude maneuver resulting into the desired end conditions; and
(c) simultaneously and independently controlling the orientation of said gimbals about the axes thereof to bring said gimbals into the set orientations by applying an angular position reference in open loop in a local servo-control of the orientations of all gimbals. - View Dependent Claims (2, 3, 4, 5, 6, 7)
maximizing the square root for a determinant of (AA′
), which amounts to maximizing margin relative to singularities, A′
being the Jacobian matrix defined by the formula ∂
ij=∂
Hi/∂
σ
j where i=1 to 3 and j=1 to 4;
minimizing the norm defined by a vector s of norms of the rows of matrix A′
(A.A)−
1, whereby maximizing the three-axis torque controllability of said new configuration;
minimizing the infinite norm of σ
, which corresponds to minimizing time required for reconfiguring the cluster; and
minimizing norm 2 of σ
, whereby obtaining minimum-energy reconfiguration.
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7. A method according to claim 1, wherein step (b) includes taking account of a constraint consisting in limiting an orientation domain angle of each of said gimbals to a predetermined range.
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8. Apparatus for steering attitude of a satellite, the apparatus comprising:
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a cluster of at least three CMGs for three-axis steering and of at least two CMGs for two-axis steering, the CMGs having respective wheels mounted on gimbals that are mounted on a satellite platform for rotation about different orientation axes by respective gimbal motors;
means for determining, from starting and desired end conditions in terms of satellite attitude and angular velocity and from allowed time duration for attitude change, a new configuration of orientations of the gimbals in the cluster that is remote from any singular configuration and is such that exchange of angular momentum between the cluster of CMGs and the satellite within said allowed time duration will cause a desired attitude maneuver from said starting conditions to said end conditions to take place; and
means for simultaneously and independently driving the gimbal motors in such a manner as to bring the orientation of each gimbal about the orientation axis thereof into a set orientation corresponding to the new configuration by applying an angular position reference in open loop in an on-board local angular position servo-control of all gimbals. - View Dependent Claims (9, 10)
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Specification