Chapter 8 :

Question 1

What does COE stand for and what are the 6 COEs?

Answer 1

Classical Orbital Elements

1. a- semi major axis
2. e - eccentricity
3. i - inclination
4. Ω - right ascension of the ascending node
5. ω - argument of perigee
6. ν - true anomaly

Question 2

What are perturbations?

Answer 2

changes in the COEs due to other forces

Question 3

Explain the affects atmospheric drag has on orbits

Answer 3

> atmospheric drag occurs up to 600 km or 375 miles
semi major axis gets smaller (dec in energy)
eccentricity decreases (orbit becomes more circular)

Question 4

Oblateness is?

Answer 4

oblateness is a “squashed circle/sphere” which is the true geometric shape of Earth

Question 5

what is the J-2 effect?

Answer 5

related to oblateness, Earth is fatter at equation than at the poles

Question 6

What are some perturbations studies in EA204?

Answer 6

> atmospheric drag
> Earth's oblateness / J-2 effect
> solar radiation pressure
> third body gravitational force
> unexpected thrusting

Question 7

What effect does J-2 have on Ω (right ascension of the ascending node)

Answer 7

Ω motion is westward for i < 90
Ω motion is eastward for i > 90
Ω motion is 0 for polar orbits, i = 90

Ω will have the greatest effects at lower altitudes with low inclinations
Ω effects become weaker as you move north/south away from the equator

Question 8

What effect does J-2 have on ω (argument of perigee)

Answer 8

ω effect causes the major axis to rotate in direction of spacecraft, 116.6 < i < 63.4
ω effect causes the major axis to rotate in opposite direction of spacecraft, 63.4 < i < 166.6

Question 9

What is a Sun-synchronous orbit?

Answer 9

orbit in which the spacecraft has the same angle of the sun on Earth, so there are never changing shadows.
Ideal for reconnaissance, weather, mapping etc.

Question 10

Describe Molniya Orbit

Answer 10

> i = 63.4
> perigee doesn't rotate
> 12 hours in northern hemisphere, 1 hour else where
> 13 hour period
> originally created by the Russians