Orbital Pertubations

1. Orbital Pertubations

2. Effect of the Atmosphere Atmosphere Orbital Decay

3. Effect of the Earth’s Shape 15m N Pole 7.5m 7.5m 12 714 km EQUATOR 12 756 km TOP VIEW SIDE VIEW 15m

4. Orbital Pertubations These are subtle but accumulative effect on an orbit Nodal regression The orbital plane effectively twists around the earth This is because of the shape of the Earth. This effect is known as Orbital Twist. Perigee Rotation This effect appears as a twisting of the satellites position relative to the Equator. Therefore, satellites need to be managed, in effect ‘flown’.

5. Applications of Orbits LEO Earth Observation with resolution Communications MEO Missions Global Navigation Satellite Systems GEO Communications Earth Observation with persistence HEO Communications Earth Observation with persistence

6. Persistence………

7. …….versus Resolution

8. Orbital Requirements GEO LEO c.700 Coverage Dwell Time Revisit Time Resolution & Power Requirements

9. Achieving Orbit

10. Initial Launch Direct ascent into low altitude orbit

11. Data Table

12. Hohman Transfer Orbit Initial Orbit Transfer Orbit Final Orbit

13. On Orbit Manoeuvre Basics Attain initial on-orbit station. Maintain assigned position (all Geo satellites). Modify orbit to meet new mission requirements. On-board motors (“thrusters”) are fitted to modify the satellite’s orbit to:

14. Repositioning Primarily for GEO satellites . Using fuel shortens life. Takes weeks or months to complete the manoeuvre. Takes capability away from users. Moving satellite to a higher or lower orbit:

15. Skynet 5A Launch Simulation