Planetary and Satellite Motion(Math Excluded– Concept only)

•Satellite: any object that is orbiting a massive body.

2 Types:•Natural Satellites include moons, comets, planets.•Man-made Satellites are any man-made satellite.

(common sense).

•A satellite is a projectile.•The only force acting on it is gravity.•Speed must be great enough to prevent it from

crashing to Earth.

What’s the minimum speed?•The Earth’s surface curves about 5 m for every 8000

m.• It must travel 8000 m horizontally for every 5 m of

vertical fall.

• It so happens that the vertical distance that a horizontally launched projectile would fall in its first second is approximately 5 meters (1/2gt2).

•A satellite launched at 8000 m/s can orbit in a circular path (launched in an area w/o air drag).

•As the projectile travels tangentially a distance of 8000 m in 1 s, it will drop app. 5 m towards Earth.

• It will remain the same height above the Earth due to the fact that the planet curves at the same rate.

Weightlessness in Space•Astronauts in orbit often experience weightlessness.•Same sensation you get when you are suspended over

your seat on a roller coaster.

Remember contact vs. action at a distance forces

•You don’t feel an action at a distance force pulling on you in the same way as you do a contact force.

•Ex: sliding across a tennis court (friction) being pushed by a jerk (applied) swinging from a rope (tension)•But, on a trampoline, you don’t really feel gravity

pulling you in the same way.•But it’s there.

Scales and Weight

•Astronauts in orbit are weightless for the same reason riders of a free-fall coaster or elevator are.

•There are no external contact forces acting on them.

•Without gravity, they would not be orbiting. They’d be flying into space towards their DEATH.

•Weightlessness does not mean gravity-less!•Repeat this 29x in your head.

•Misconception: the astronauts are weightless because the force of gravity is reduced in space. The reasoning goes as follows: "with less gravity, there would be less weight and thus they would feel less than their normal weight.“

•True, but it does not explain their sense of weightlessness.

•Yes, they experience less g, but the weightlessness comes from “having the floor pulled out from under them.”

•Due to being projectiles.

•Others think there’s no gravitational force because there’s no air.

•Gravity DOES exist in a vacuum.

Geosynchronous satellites•Geosynchronous: always above the same area of

sky.

http://upload.wikimedia.org/wikipedia/commons/3/3a/Geostationaryjava3Dsideview.gif

•They have an orbital period the same as the Earth's rotation period.

•Period: amnt of time to complete one orbit•An idea popularized by Arthur C. Clarke (wrote

2001: A Space Odyssey and other sci-fi books).

•Over 600 GS satellites in orbit.•High altitude…means slight signal delay.•Uses: global communication, satellite tv, weather

forecasting, defense apps, GPS.