Satellite orbit raising using electric propulsion
Apparatus and methods for raising the orbit of a satellite having electric propulsion thrusters, an Earth sensor and an inertial reference sensor such as a gyro. A satellite positioning system generates orbital data and a profile generator generates an ideal electric orbit raising profile of the satellite. The ideal profile is one that the satellite must follow so that the perigee, apogee and inclination of the satellite can be adjusted simultaneously in a mass-efficient manner. A state machine processes the ideal profile and a true anomaly to generate a desired electric orbit raising profile. Steering apparatus generates signals that are used to control the attitude of the satellite to follow the desired profile. The desired profile places the satellite in an Earth-pointed attitude when the satellite is at a predefined point in the orbit, slews the satellite from the Earth-pointed attitude to an ideal orbit raising attitude, steers the satellite according to the ideal profile during orbit raising, and steers the satellite from the desired attitude to the Earth-pointed attitude.
1. A satellite comprising:
one or more electric propulsion thrusters and an attitude sensor, the attitude sensor including one or more of an earth sensor, a star tracker, a gyro and an inertial reference sensor; the satellite including:
a positioning system that computes a position of the satellite in a dynamically changing orbit;
a profile generator coupled to the positioning system that computes an ideal electric orbit raising profile of the satellite, to achieve target orbit values of perigee, apogee and inclination;
steering apparatus, coupled to the attitude sensor, that generates error signals that are used to control the attitude of the satellite; wherein
onboard the satellite, the ideal electric orbit raising profile and a true anomaly of the dynamically changing orbit are processed in order to compute a desired electric orbit raising steering profile to steer the satellite, the desired electric orbit raising profile including an electric thruster ignition phase, a burn phase, and a shutdown phase that are autonomously repeated, wherein during the burn phase, perigee, apogee and inclination of the satellite are simultaneously driven towards the target orbit values.
2. The satellite recited in claim 1 wherein the positioning system comprises an orbit propagator.
3. The satellite recited in claim 1 wherein the positioning system comprises a global positing system.
4. The satellite recited in claim 1 wherein the electric propulsion thrusters comprise Hall effect thrusters.
5. The satellite recited in claim 4 wherein the electric propulsion thrusters further comprise a bi-propulsion thruster.
6. The satellite recited in claim 1 , wherein the inertial reference sensor comprises a gyro that is reset to remove drift when the satellite is in an Earth pointed orientation.
7. The satellite recited in claim 1 , wherein the attitude sensor comprises a star tracker.
8. The satellite recited in claim 1 , wherein the thrust profile steers the satellite in and out of the orbital plane.
9. The satellite recited in claim 1 , wherein the satellite is steered around the thrust vector.
10. The satellite recited in claim 1 , wherein two dual axes thruster positioning mechanisms are actuated to dump momentum in three axes simultaneously.
11. The satellite recited in claim 1 , wherein a single dual axes thruster positioning mechanism is actuated to dump two axes of momentum, and the satellite itself is steered in inertial space, resulting in full three axis momentum dumping.
12. An electric propulsion orbit raising method for use with a satellite having one or more electric propulsion thrusters, and an attitude sensor, the attitude sensor including one or more of an earth sensor, a star tracker, a gyro, and an inertial reference sensor, the method comprising:
dynamically computing, on board the satellite, an orbital position of the satellite in a dynamically changing orbit;
dynamically computing, onboard the satellite, an ideal electric orbit raising profile of the satellite based on the orbital position, to achieve target orbit values of perigee, apogee and inclination;
dynamically processing, the ideal electric orbit raising profile and a true anomaly of the dynamically changing orbit, and computing, a desired electric orbit raising steering profile to steer the satellite, the desired orbit raising profile including an electric thruster ignition phase, a burn phase, and a shutdown phase, that are autonomously repeated, wherein during the burn phase, perigee, apogee and inclination of the satellite are simultaneously driven towards the target orbit values.
13. The method recited in claim 12 wherein the satellite is steered using a gyro.
14. The method recited in claim 12 wherein the satellite is steered using a star tracker.
15. The method recited in claim 13 wherein the electric propulsion thrusters comprise Hall effect thrusters.
16. The method recited in claim 14 wherein the electric propulsion thrusters further comprise a bi-propulsion thruster.
17. The method recited in claim 13 , wherein the inertial reference sensor comprises a gyro that is reset to remove any drift when the satellite is in an Earth pointed orientation.
18. The method recited in claim 12 , wherein the attitude sensor comprises a star tracker.
19. The method recited in claim 12 , wherein the thrust profile steers the satellite in and out of the orbital plane.
20. The method recited in claim 12 , wherein the satellite is steered around the thrust vector.
21. The method recited in claim 12 , wherein two dual axes thruster positioning mechanisms are actuated to dump momentum in three axes simultaneously.
22. The method recited in claim 12 , wherein a single dual axes thruster positioning mechanism is actuated to dump 2 axes of momentum, and the satellite is steered in inertial space, resulting in 3 axes momentum dumping.
23. An electric propulsion orbit raising method for use with a satellite having a positioning system for generating orbital data relating to the satellite, the positioning system including one or more electric propulsion thrusters, and an attitude sensor, the attitude sensor including one or more of an earth sensor, a star tracker, a gyro and an inertial reference sensor, the method comprising:
computing an orbital position of the satellite in a dynamically changing orbit;
computing, based on the orbital position, an ideal electric orbit raising (EOR) profile, to achieve target orbit values of perigee, apogee and inclination;
processing the ideal electric orbit raising profile and a true anomaly of the dynamically changing orbit, and computing a desired electric orbit raising steering profile to steer the satellite, the desired orbit raising profile including an electric thruster ignition phase, a burn phase, and a shutdown phase that are autonomously repeated, wherein, during the burn phase, perigee, apogee and inclination of the satellite are simultaneously driven towards the target orbit values.
24. The method recited in claim 23 wherein the electric propulsion thrusters are fired after the satellite is slewed from an Earth-pointed attitude to an ideal electric orbit raising attitude, and are shut down prior to the satellite being placed in the Earth-pointed attitude.