1

Orbit Dynamics

by

Eng\ A.Farrag

ADCS Team Leader

By Ahmad farrag

2

Overview

Kelper’s laws

Orbital elements

Orbit types

Reference co-ordinate system

Two body problem

By Ahmad farrag

3

Solar System

Are the positions of the planets and other solar system

objects random?

Do they obey certain laws?

What can these laws tell us about the history and

evolution of the solar system?

By Ahmad farrag

4

Kepler’s Laws

"The orbit of every planet is an ellipse

with the sun at a focus .“

"A line joining a planet and the sun

sweeps out equal areas during equal

intervals of time."

"The square of the orbital period of a

planet is directly proportional to the

cube of the semi-major axis of its orbit."

By Ahmad farrag

5

What is a satellite anyway?

A satellite is any object that orbits or

revolves around another object.

For example, the Moon is a satellite of

Earth, and Earth is a satellite of the Sun.

By Ahmad farrag

6

Understanding Orbits

By Ahmad farrag

8

Orbital “Keplerian” elements

The traditional orbital elements are the

six Keplerian elements

By Ahmad

farrag

9

By Ahmad farrag

10

12

Orbit types

Centric classifications– Galactocentric orbit: An orbit about the center of

a galaxy. Earth's sun follows this type of orbit.

– Heliocentric orbit: An orbit around the Sun. Inour Solar System, all planets, comets, and asteroidsare in such orbits.

– Geocentric orbit: An orbit around the planetEarth, such as the Moon or artificial satellites.

By Ahmad farrag

13

By Ahmad farrag

Orbit types

Altitude classifications

– Low Earth Orbit (LEO): Geocentric orbits ranging in

altitude from 100–1000 km

– Medium Earth Orbit (MEO): Geocentric orbits ranging

in altitude from 1000 km to just below geosynchronous orbit

at 35786 km .

– High Earth Orbit (HEO): Geocentric orbits above the

altitude of geosynchronous orbit 35786 km.

14

Orbit types

Inclination classifications

– Inclined orbit: An orbit whose inclination is not zero

degrees.

– Polar orbit: An orbit that passes above or nearly above

both poles of the planet on each revolution. Therefore it

has an inclination of 90 degrees.

By Ahmad farrag

15

Orbit types

Eccentricity classifications

– Circular orbit: An orbit that has an eccentricity of 0

and whose path traces a circle

– Elliptic orbit: An orbit with an eccentricity greater

than 0 and less than 1 whose orbit traces the path of

an ellipse .

• Molniya orbit: A highly elliptic orbit with inclination of

63.4° and orbital period of half of a sidereal day (roughly

12 hours). Such a satellite spends most of its time over a

designated area of the planet

By Ahmad farrag

16

17

By Ahmad farrag

Orbit types

Synchronous classifications

– Sun-synchronous orbit: An orbit which combines altitude and inclination in such a way that the satellite passes over any given point of the earth surface at the same local solar time. Such an orbit can place a satellite in constant sunlight and is useful for imaging, spy, and weather satellites

– geosynchronous orbit is an orbit around the Earth with an orbital period matching the Earth's sidereal rotation period.

18

Reference Co-ordinate System

Earth-Centered Inertial Frame (ECI)

or Inertial Co-ordinate System (ICS)

By Ahmad farrag

19

Reference Co-ordinate System

Earth-Centered Earth-Fixed Frame (ECEF) or

Greenwich Co-ordinates System (GCS)

By Ahmad farrag

20

Reference Co-ordinate System

Orbital Co-ordinate System OCS

By Ahmad farrag

21

Reference Co-ordinate System

Body Co-ordinate System BCS

By Ahmad farrag