Chapter 14

Satellite Motion

Basic Concept of Satellite Motion:

• A projectile has two components of motion

(1) vertical distance d = ½ g t2

(2) horizontal distance d = v t

If the vertical distance an object falls matches the curvature of the earth, then the object will orbit the earth as a satellite.

The Earth’s curves about 5 meters for every 8000 meters.

Orbits of Satellites (Circular)

• “In circular orbit the speed of a circling satellite is not changed by gravity. We can understand this by comparing a satellite in circular orbit to a bowling ball rolling along a bowling alley. Why doesn’t the gravity that acts on the bowling ball change its speed? The answer is that gravity is pulling neither forward nor backward – it pulls straight downward.” Hewitt, p. 202

Orbits of Satellites

• For satellites close to Earth, the time for a complete orbit is about 90 minutes

• For higher altitude orbits, the orbital speed is less and the period is longer

• The moon is the only natural satellite of Earth. It has a period of 27.3 days

Orbits of Satellites (Eliptical)

• A projectile that travels faster than 8 km/s will overshoot a circular path and trace an oval-shaped path or elipse

• “An elipse is a specific curve: the closed path taken by a point that moves in such a way that the sum of its distances from two fixed points is constant.” (p. 203)

Apogee (farthest point)Perigee (closest point)

Escape Velocity

• Velocity required to escape the pull of gravity from an object