Unit 2.6 Orbital Perturbations

Question 1

Orbital Perturbation

Answer 1

A deviation from a normal or expected motion.

Question 2

Perturbation Theory

Answer 2

A highly irregular system can be solved by taking a well-known system and adding on the irregularities.

Question 3

Gravitational Perturbations

Answer 3

Central Body Effects:
- J2 Effect: Nodal regression/Perigee Rotation

3rd Body Effects:
- 3rd Body perturbations/Lagrange Points

Question 4

Non-Gravitational Perturbation

Answer 4

• Atmospheric Drag
• Solar radiation
• Unexpected Thrusting

Question 5

Central-Body Effects

Answer 5

Largest perturbing force present for near-earth objects due to the oblate-ness of earth

Question 6

J2 Effect

Answer 6

Caused by earth’s oblate-ness. Earth’s rotation causes mass to be compressed building at its center (equator).
RAAN, argument of perigee and Mean Anomaly are most affected.
Causes:
- Nodal regression
- Perigee rotation

Question 7

Nodal Regression

Answer 7

Because of earth’s equatorial bulge, gravitational force created by the added mass attracts satellites more than at its poles.
Causes the plane of motion to precess due to the change in the RAAN
Prograde will precess West
Retrograde will precess East
**Depends on the altitude (higher altitude= least effect) and inclination (closer to the equator= more effect) of the orbit.

Question 8

Perigee Rotation

Answer 8

Continuous shift in the location of the perigee.

Perigee location is zero at critical inclination of 63.4 and 116.6

Question 9

Mass Assymetry

Answer 9

Mountain ranges contain more concentrated mass than ocean; thereby causing more irregularities.
Triaxiality of earth - major axis of through the equator causes gravity wells at 77E and 135W

Question 10

Third Body Effects

Answer 10

Additional celestial bodies whose gravitational force affect the satellite/object orbiting earth. Increases as altitude increases.
Affects GEO mostly

Question 11

Lagrangian Points

Answer 11

Five locations caused by the earth’s and the sun’s gravitational forces where small third bodies can maintain relative motion.
L1, l2, and L3 are unstable points where telescopes, deep space telescopes can be placed. L4 and L5 are stable points where it may be possible to placed a space base for interstellar travel.

Question 12

Atmospheric Drag

Answer 12

LEO satellites most affected by earth atmosphere which may cause satellites to reenter earth.
Lowers eccentricity - due to more effect at perigee than apogee
Low mass/high surface - most affected satellites

Question 13

Solar Radiation

Answer 13

Photons hitting the satellite’s surface producing pressure that changes orbital characteristics slightly
Low mass/high surface more affected