Upload
priscila-turnock
View
217
Download
0
Tags:
Embed Size (px)
Citation preview
Orbital PertubationsOrbital Pertubations
AtmosphereOrbital Decay
Effect of the AtmosphereEffect of the Atmosphere
Height (km) Life
200 2 weeks
1000 1000yrs
36000 1Myrs
Effect of the Earth’s ShapeEffect of the Earth’s Shape
TOP VIEWTOP VIEW SIDE VIEWSIDE VIEW
15m15m
15m15m
7.5m7.5m 7.5m7.5m
EQUATOREQUATOR
12 714 km12 714 km
12 756 km12 756 km
N Pole
Orbital PertubationsOrbital PertubationsThese 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’.
Applications of OrbitsApplications 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
Persistence………Persistence………
………….versus Resolution.versus Resolution
Orbital RequirementsOrbital Requirements
LEO
Coverage
Dwell Time
Revisit Time
Resolution & Power Requirements
GEO c.700
Achieving OrbitAchieving Orbit
Initial LaunchInitial Launch
Direct ascent into low altitude orbit
Data TableData TableEarth Gravitational
Force Mass of Earth Radius of Earth Orbital Height Orbital Velocity Orbital Period Energy Required to Achieve Orbit
6.67E-11 5.98E+24 6.378E+06 12 7900.7 84.7 3.133E+07
6.67E-11 5.98E+24 6.378E+06 19 7896.3 84.9 3.136E+07
6.67E-11 5.98E+24 6.378E+06 100 7846.8 86.5 3.175E+07
6.67E-11 5.98E+24 6.378E+06 200 7786.9 88.5 3.222E+07
6.67E-11 5.98E+24 6.378E+06 300 7728.4 90.5 3.267E+07
6.67E-11 5.98E+24 6.378E+06 400 7671.2 92.6 3.311E+07
6.67E-11 5.98E+24 6.378E+06 500 7615.2 94.6 3.354E+07
6.67E-11 5.98E+24 6.378E+06 600 7560.5 96.7 3.396E+07
6.67E-11 5.98E+24 6.378E+06 700 7506.9 98.8 3.436E+07
6.67E-11 5.98E+24 6.378E+06 800 7454.4 100.9 3.475E+07
6.67E-11 5.98E+24 6.378E+06 900 7403.0 103.0 3.514E+07
6.67E-11 5.98E+24 6.378E+06 1000 7352.7 105.1 3.551E+07
6.67E-11 5.98E+24 6.378E+06 1100 7303.3 107.3 3.587E+07
6.67E-11 5.98E+24 6.378E+06 1200 7255.0 109.4 3.622E+07
6.67E-11 5.98E+24 6.378E+06 20000 3888.6 710.6 5.498E+07
6.67E-11 5.98E+24 6.378E+06 35789 3075.6 1436.3 5.781E+07
Hohman Transfer OrbitHohman Transfer Orbit
Initial Orbit
Transfer Orbit
Final Orbit
On Orbit On Orbit ManoeuvreManoeuvre Basics 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:
RepositioningRepositioning
• 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:
Skynet 5A Launch SimulationSkynet 5A Launch Simulation