Orbital Pertubations Effect of the Atmosphere Orbital Decay

Orbital Pertubations

Effect of the Atmosphere Orbital Decay Atmosphere Height (km) 200 1000 36000 Life 2 weeks 1000 yrs 1 Myrs

Effect of the Earth’s Shape 15 m N Pole 7. 5 m 12 714 km EQUATOR 12 756 km TOP VIEW SIDE VIEW 15 m

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’.

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

Persistence………

……. versus Resolution

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

Achieving Orbit

Initial Launch Direct ascent into low altitude orbit

Data Table Earth Gravitational Force Mass of Earth Radius of Earth Orbital Height Orbital Velocity Orbital Period Energy Required to Achieve Orbit 6. 67 E-11 5. 98 E+24 6. 378 E+06 12 7900. 7 84. 7 3. 133 E+07 6. 67 E-11 5. 98 E+24 6. 378 E+06 19 7896. 3 84. 9 3. 136 E+07 6. 67 E-11 5. 98 E+24 6. 378 E+06 100 7846. 8 86. 5 3. 175 E+07 6. 67 E-11 5. 98 E+24 6. 378 E+06 200 7786. 9 88. 5 3. 222 E+07 6. 67 E-11 5. 98 E+24 6. 378 E+06 300 7728. 4 90. 5 3. 267 E+07 6. 67 E-11 5. 98 E+24 6. 378 E+06 400 7671. 2 92. 6 3. 311 E+07 6. 67 E-11 5. 98 E+24 6. 378 E+06 500 7615. 2 94. 6 3. 354 E+07 6. 67 E-11 5. 98 E+24 6. 378 E+06 600 7560. 5 96. 7 3. 396 E+07 6. 67 E-11 5. 98 E+24 6. 378 E+06 700 7506. 9 98. 8 3. 436 E+07 6. 67 E-11 5. 98 E+24 6. 378 E+06 800 7454. 4 100. 9 3. 475 E+07 6. 67 E-11 5. 98 E+24 6. 378 E+06 900 7403. 0 103. 0 3. 514 E+07 6. 67 E-11 5. 98 E+24 6. 378 E+06 1000 7352. 7 105. 1 3. 551 E+07 6. 67 E-11 5. 98 E+24 6. 378 E+06 1100 7303. 3 107. 3 3. 587 E+07 6. 67 E-11 5. 98 E+24 6. 378 E+06 1200 7255. 0 109. 4 3. 622 E+07 6. 67 E-11 5. 98 E+24 6. 378 E+06 20000 3888. 6 710. 6 5. 498 E+07 6. 67 E-11 5. 98 E+24 6. 378 E+06 35789 3075. 6 1436. 3 5. 781 E+07

Hohman Transfer Orbit Initial Orbit Transfer Orbit Final Orbit

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

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

Skynet 5 A Launch Simulation