MA 4362 Astrodynamics

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MA 4362 Astrodynamics
Orbit Perturbations and Orbit Decay
Chapter 8,Sellers sections 8.2, 8.3 (pp. 272-283)
Week 9
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The N-Body Problem
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What are Other factors that Perturb the Orbit?

• Any disturbance in the regular motion of a
  satellite resulting from a force other than those
  causing regular motion
• Non-spherical earth (Oblateness)
• Sun/moon/planets gravity(Third bodies)
• Atmospheric drag

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The Earth is Not a Perfect Sphere
In actuality, Earth is an Ellipsoid
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Equatorial Bulge
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Gravitational Potential Theory
Irregularities in the Earths Gravitational Field
are modeled by a complex mathematical Model
referred to as Potential Theory (Laplaces
equation)

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Gravitational Potential Theory
J1 --gt Gravitational Potential of Spherical
earth J2 --gt Accounts for Equatorial Bulge
So-named J2 Effect
J2 -- torques the orbit
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Precession of the Right Ascension(J2 Nodal
Regression)
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Precession of the Right Ascension(Nodal
Regression)
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Sun-Synchronous Orbit

• Approx 98 degree Inclination
• Circular or Elliptical LEO
• Sun Angle is Always same (more later)
• Missions
• Electro Optical Imaging
• Weather (DMSP)

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GROUND TRACE
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Sun Synchronous Orbit
Takes Advantage of the fact that precession of
the line of nodes is the same rate as the earths
angular velocity around the sun (about 0.9856?
per day) (retrograde orbits)
Summer
Spring
Fall
Winter
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Sun Synchronous Orbit (concluded)
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Another J2 Effect Perigee Rotation

• Orbit rotates in orbital plane

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Variation of Argument of Perigee
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Variation of Argument of Perigee
Perigee does not rotate
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Molniya Orbits
Molniya Orbits exploit this quirk of nature

• 63.4 /116.6 Degree Inclination
• 500 km perigee - 40,000 km apogee
• Missions Comm / Surveillance

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Atmospheric Drag
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Numerical Example Orbit Decay of Russian Zarya
Module WHAT IF ENGINE QUIT WORKING ?
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Russian Zarya Module

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Russian Zarya Module

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Russian Zarya Module

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Russian Zarya Module

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