Efficient stationkeeping strategy for the three apogee (TAP) orbit

1. A method of maintaining at least one satellite in an operational orbit having a nominal orbital period, the method comprising:

executing a stationkeeping strategy that controls parameters of the operational orbit such that, for a constellation of two satellites disposed in the operational orbit, separated by one half the nominal orbital period, the constellation provides substantially continuous coverage of a polar region, wherein:

the nominal orbital period is sixteen hours, and the operational orbit has (i) an inclination of greater than 60°; (ii) a nominal eccentricity of at least 0.4; (iii) an initial argument of perigee (ARGP) of 90°+/−4° or 270°+/−4°; (iv) an operational orbit apogee altitude in the range of 35,000 km to 50,000 km; and (v) an operational orbit perigee altitude in a range of 7000 to 15000 km; and

the stationkeeping strategy includes:

establishing an initial Right Ascension of Ascending Node (RAAN) of the operational orbit such that naturally caused orbital drift results in a mid-life RAAN of 0 degrees; and

controlling the ARGP, only indirectly, by performing, with a propulsion subsystem of the spacecraft, orbit maintenance maneuvers only to directly control one or both of the operational orbit apogee altitude and the operational orbit perigee altitude within a respective required range.

2. The method of claim 1 , wherein, during a mission life of ten or more years, the orbit maintenance maneuvers exclude direct control of the inclination for at least seven years.

3. The method of claim 2 , wherein the stationkeeping strategy includes establishing each of: an initial value of orbital inclination and an initial value of ARGP, such that substantially continuous coverage of a polar region is maintained throughout the mission life.

4. The method of claim 3 , wherein the initial value of orbital inclination is less than 63°.

5. The method of claim 3 , wherein the initial value of ARGP is such that a mid-life ARGP is 90° or 270°.

6. The method of claim 3 , wherein the initial value of ARGP is 274° and ARGP at end of expected mission life is 266°.

7. The method of claim 1 , wherein RAAN at end of life is approximately 250°.

8. The method of claim 1 , wherein a total impulse required for the stationkeeping strategy is allocated such that at least 70% of the total impulse is to control the operational orbit perigee altitude and the operational orbit apogee altitude and less than 30% is to control the inclination.

9. The method of claim 1 , wherein more than 70% of the orbit maintenance maneuvers are performed at either perigee or apogee of the orbit.

10. The method of claim 1 , wherein the stationkeeping strategy excludes performance of the orbit maintenance maneuvers for a period of at least twelve months proximate to mid-life.

11. An earth-orbiting satellite comprising a propulsion subsystem and a spacecraft controller, wherein:

the spacecraft is configured to be disposed in an operational orbit, and

the spacecraft controller is configured to execute a stationkeeping strategy that controls parameters of the operational orbit such that, for a constellation of two satellites disposed in the operational orbit, separated by one half the nominal orbital period, the constellation provides substantially continuous coverage of a polar region, wherein:

the nominal orbital period is sixteen hours, and the operational orbit has (i) an inclination of greater than 60 degrees; (ii) a nominal eccentricity of at least 0.4; (iii) an initial argument of perigee (ARGP) of approximately 90°+/−4° or approximately 270°+/−4°; (iv) an operational orbit apogee altitude in the range of 35,000 km to 50,000 km; and (v) an operational orbit perigee altitude in the range of approximately 7000 to 15000 km; and

the stationkeeping strategy includes:

selecting an initial Right Ascension of Ascending Node (RAAN), such that naturally caused orbital drift results in a mid-life RAAN of approximately 0 degrees; and

controlling Argument of Perigee (ARGP) only indirectly, by causing the propulsion subsystem to execute orbit maintenance maneuvers only to directly control one or both of the operational orbit apogee altitude and the operational orbit perigee altitude within a respective required range.

12. The satellite of claim 11 , wherein, during a mission life of ten or more years, the orbit maintenance maneuvers exclude direct control of the inclination for at least seven years.

13. The satellite of claim 12 , wherein the stationkeeping strategy includes establishing each of: an initial value of orbital inclination and an initial value of ARGP, such that substantially continuous coverage of a polar region is maintained throughout the mission life.

14. The satellite of claim 13 , wherein the initial value of orbital inclination is less than 63°.

15. The satellite of claim 13 , wherein the initial value of ARGP is such that a mid-life ARGP is 90° or 270°.

16. The satellite of claim 13 , wherein the initial value of ARGP is 274° and ARGP at end of expected mission life is 266°.

17. The satellite of claim 11 , wherein RAAN at end of life is 250°.

18. The satellite of claim 11 , wherein a total impulse required for the stationkeeping strategy is allocated such that at least 70% of the total impulse is to control the operational orbit perigee altitude and the operational orbit apogee altitude and less than 30% is to control orbital inclination.

19. The satellite of claim 11 , wherein more than 70% of the orbit maintenance maneuvers are performed at either perigee or apogee of the orbit.

20. The satellite of claim 11 , wherein the stationkeeping strategy excludes performance of the orbit maintenance maneuvers for a period of at least twelve months proximate to mid-life.