AA 4362 Astrodynamics Orbital Groundtracks

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AA 4362 AstrodynamicsOrbital Groundtracks
Week 7 Vallado Chapter 3
Sections 3.4, 3.5, 3.6, 3.7

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Groundtracks
A ground track is the projection of a satellites
orbit onto the earths surface
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Orbital Ground Tracks (contd)
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Transforming from Inertial to Earth Fixed
Coordinates
Lets Look at this first
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Precession of the Equinoxes

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Nutation of the Precession Cycle
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Computing the Rotation Matrix

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Computing the Hour Angle

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Universal Time (GMT)

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Relating GMST to UT1

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Computing the Julian Day
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Pulling it All Together

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Pulling it All Together(contd)

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Pulling it All Together(contd)

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Pulling it All Together(contd)
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Pulling it All Together(contd)

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How Does Earth Radius Vary with Latitude

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How Does Earth Radius Vary with Latitude(contd)

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How Does Earth Radius vary with Latitude(contd)

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Earth Radius Versus Latitude

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What is the Earths Mean Radius

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Earth Radius Based on Volume

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Earth Radius (contd)

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Gaussian Surface
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Geocentric vs Geodetic Coordinates

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Geocentric vs Geodetic Coordinates(contd)

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Geocentric vs Geodetic Coordinates(contd)

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Geocentric vs Geodetic Coordinates(contd)

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Geocentric vs Geodetic Coordinates(contd)

Whitmore, Stephen A., and Haering, Edward A.,
Jr., FORTRAN Program for the Analysis of Ground
Based Range Tracking Data--Usage and Derivations,
NASA TM 104201, December, 1992
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Geocentric vs Geodetic Coordinates(contd)
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Geocentric vs Geodetic Coordinates(contd)
Whitmore, Stephen A., and Haering, Edward A.,
Jr., FORTRAN Program for the Analysis of Ground
Based Range Tracking Data--Usage and Derivations,
NASA TM 104201, December, 1992
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Pulling it all together
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Pulling it all together (contd)
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Pulling it all together (concluded)
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Numerical Example

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Numerical Example (contd)

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Numerical Example (contd)

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Numerical Example (contd)

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Numerical Example (contd)

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Numerical Example (contd)

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Numerical Example (contd)
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(No Transcript)
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Groundtrack Examples
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Types of 3-D Orbits
Low-Earth Orbit (LEO)

• Inclined / Polar Orbits
• 160 - 6000 km
• Missions
• Manned (Shuttle)
• Reconnaissance / Weather
• Communications

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Types of 3-D Orbits (contd)

• Medium Earth Orbit (MEO)
• Semi-Synchronous Orbit
• 20,000 km
• Missions Navigation (GPS)

Satellite Footprint
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Types of 3-D Orbits (contd)
GEO
Geosynchronous
Geostationary

• Period 24 hrs
• Any inclination
• Does not need to be a circular orbit

• Period 24 hours
• Inclination near zero
• Circular (e zero)
• Altitude 35,780 km

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Geostationary
Satellite Stationary With respect to Earth Surface
i 0 e 0 T 24hrs
Satellite Footprint
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Geosynchronous (eccentric orbit)
Satellite No Longer Stationary With respect
to Earth Surface
i 0 e 0 T 24hrs
Satellite Footprint
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Geosynchronous (Inclined orbit)
Satellite No Longer Stationary With respect
to Earth Surface
i 0 e 0 T 24hrs
Satellite Footprint
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Geosynchronous (Inclined orbit)
Satellite No Longer Stationary With respect
to Earth Surface
i 0 e 0 T 24hrs
Satellite Footprint
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How Big is a GEO Orbit?
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Specialized Orbits(Molniya)

• Hangs over One
• Hemisphere for
• Most of its period
• then whips
• Through other
• portion

• Highly Eccentric
• 63.4 /116.6 Degree Inclination
• 500 - 40,000 km Altitude
• Missions Comm Relay (Molniya)
• Polar Coverage

Satellite Footprint