Momentum wheel platform steering system and method
First Claim
1. Apparatus for controlling a spacecraft momentum wheel platform in an on-board computer-controlled rate following mode, said apparatus comprising:
- a roll-yaw state estimator and controller for generating desired momentum wheel platform rates;
a rate integrator coupled to said roll-yaw state estimator and controller for integrating said desired momentum wheel platform rates to produce desired momentum wheel platform angles;
a forward transform computer coupled to said rate integrator and responsive to said desired momentum wheel platform angles for computing desired actuator extensions;
a step computer coupled to said forward transform computer and responsive to desired actuator extensions for producing actuator step command signals; and
a momentum wheel platform having linear actuators coupled to said step computer for actuation of said linear actuators to tilt said momentum wheel platform a predetermined amount;
the output of said rate integrator being fed back to said roll-yaw state estimator and controller as a momentum wheel platform angle feedback signal.
2 Assignments
0 Petitions
Accused Products
Abstract
Method and apparatus for controlling the two-axis rate and position as well as the linear elevation of a momentum wheel platform supported by three jackscrews driven by stepper motors. By tilting the momentum wheel, a control torque is produced in the plane orthogonal to the nominal wheel spin axis. When all three actuators are operational, the control transformations are made unique by constraining the sum of the actuator extensions to be zero. When one actuator has failed, the above constraint is eliminated and the failed actuator is constrained to its measured value. Momentum wheel platform rotational rate commands generated by the roll/yaw control system are first integrated to give desired gimbal angles, and then transformed into jackscrew extensions. Jackscrew step commands are computed as the difference between these desired extensions and the current positions of the jackscrews. The position of each jackscrew is maintained by accumulating the step commands. The desired extensions are also back-transformed to compute gimbal angles that are fed back to the roll-yaw state control system. In ground commanded stepping, the momentum wheel platform steering method operates exactly as described above, except that relative jackscrew step commands from a ground station are utilized instead of the step commands computed in the rate following configuration.
24 Citations
20 Claims
-
1. Apparatus for controlling a spacecraft momentum wheel platform in an on-board computer-controlled rate following mode, said apparatus comprising:
-
a roll-yaw state estimator and controller for generating desired momentum wheel platform rates; a rate integrator coupled to said roll-yaw state estimator and controller for integrating said desired momentum wheel platform rates to produce desired momentum wheel platform angles; a forward transform computer coupled to said rate integrator and responsive to said desired momentum wheel platform angles for computing desired actuator extensions; a step computer coupled to said forward transform computer and responsive to desired actuator extensions for producing actuator step command signals; and a momentum wheel platform having linear actuators coupled to said step computer for actuation of said linear actuators to tilt said momentum wheel platform a predetermined amount; the output of said rate integrator being fed back to said roll-yaw state estimator and controller as a momentum wheel platform angle feedback signal. - View Dependent Claims (2)
-
-
3. Apparatus for controlling a spacecraft momentum wheel platform in an on-board computer-controlled rate-following mode, said apparatus comprising:
-
a roll-yaw state estimator and controller for generating desired momentum wheel platform rates; an on-board computer coupled to said roll-yaw state estimator and controller and responsive to said desired momentum wheel platform rates for computing desired actuator extensions; an actuator step computer coupled to said on-board computer and responsive to said desired actuator extensions for producing actuator step command signals by computing the difference between the desired actuator position and the existing actuator position, where the existing actuator position is determined by taking the sum of the previous actuator step command signals; and a momentum wheel platform having linear actuators coupled to said actuator step computer and responsive to said actuator step command signals for actuation of said linear actuators to tilt said momentum wheel platform a predetermined amount, thereby producing said desired momentum wheel platform rate. - View Dependent Claims (4)
-
-
5. An attitude control system for a spacecraft comprising:
-
a spacecraft; a tiltable platform disposed on said spacecraft; three pivots for supporting said platform disposed equidistantly therearound; three linear actuators each comprising a jackscrew driven by a stepper motor, each of said linear actuator being individually coupled to a different one of said pivots and being adapted to raise or lower its respective pivot; a momentum wheel mounted to said platform and being adapted to spin at high speed about a spin axis to produce a momentum vector, the spin axis of said wheel being initially aligned in a predetermined direction with respect to said spacecraft, said platform and said wheel being adapted to be tilted through small angles to produce a component of the wheel momentum vector in a plane transverse to the spin axis of said wheel; an on-board computer disposed on said spacecraft for computing desired roll-yaw momentum wheel platform rates for said spacecraft; a platform steering computer coupled to said on-board computer for converting said roll-yaw momentum wheel platform rates to jackscrew position commands; a step logic computer coupled to said platform steering computer for converting said jackscrew position commands to jackscrew step commands; and a plurality of stepper motor control drivers coupled from said step logic computer to said linear actuators for applying said jackscrew step commands to said stepper motors. - View Dependent Claims (6, 7, 8, 9, 10)
-
-
11. A method for controlling a spacecraft momentum wheel platform in an on-board computer-controlled rate following mode, said method comprising the following steps:
-
generating desired momentum wheel platform rate commands in a roll-yaw state estimator and controller; integrating said desired momentum wheel platform rate commands to produce desired momentum wheel platform angle commands; forward transforming said desired momentum wheel platform angle commands to produce desired actuator extension commands; computing actuator step command signals from said desired actuator extension commands; applying said actuator step command signals to the spacecraft momentum wheel platform to produce tilt thereof. - View Dependent Claims (12, 13, 14, 15, 17)
-
-
16. A method for controlling platform rates of a momentum wheel platform comprising the following steps:
-
providing desired platform rates to a spacecraft on-board computer; integrating said platform rates; transforming said integrated platform rates to required linear actuator extensions via a forward transformation; providing measurements of existing linear actuator extensions to said spacecraft on-board computer; transforming measured actuator extensions to platform rotations via a backward transformation; constraining the sum of the actuator extensions to be zero; applying actuator position commands to a step logic computer that converts them into step commands; and applying the step commands to the stepper motors of the linear actuator to produce the desired platform rates.
-
-
18. A method of controlling a momentum wheel platform in an on-board computer controlled rate following mode, said method comprising the following steps:
-
generating platform rate commands in an on-board computer; integrating platform rate commands to provide desired platform angles; computing desired jackscrew extensions from desired platform angles; measuring existing jackscrew extensions; generating jackscrew step commands as the difference between desired jackscrew extensions and measured jackscrew extensions; and applying the jackscrew step commands to the jackscrews to tilt the momentum wheel platform.
-
-
19. A method of controlling a momentum wheel platform by ground command, said method comprising the following steps:
-
transmitting desired jackscrew position commands from a ground control to a spacecraft; measuring existing jackscrew extensions; generating a number of jackscrew step commands equal to the desired jackscrew position command from ground; and applying the jackscrew step commands to the jackscrews to tilt the momentum wheel platform. - View Dependent Claims (20)
-
Specification