Artificial Satellite Orbits


Start with: horizontal acceleration vs. gravity

Fire a bullet and drop another at same time

Which hits ground first? (both same time)


Satellite orbits similar

Velocity of initial trajectory will determine what happens

See fig. 4.1, pg. 60

Obviously, a minimum velocity is required to get through the atmosphere

Anything less, and the object will fall back to earth

Circular satellite velocity: 8 km/sec

Velocity needed to achieve earth orbit

NOT out of gravitational influence

Satellite "falls" around the earth, just like the moon

Apogee vs. perigee: relative orbital distances

Farthest distance vs. closest approach to parent body

Final speed of rocket at burn-out determines resulting orbit

See fig. 4.2, pg. 61

If <8 km/sec: orbit is an ellipse

Will impact earth: works well for ballistic missiles

"Crimson Tide" scene

If > CSV then will achieve earth orbit

If > 11 km/sec then will escape earth's gravitational pull

The "Escape Velocity" needed for interplanetary travel

Also called "parabolic velocity"

Interplanetary travel

Payload weight is critical (payload is anything taken aloft)

Directly affects the amount of fuel needed to achieve escape velocity (F=ma)

Vicious circle: the added fuel also adds weight!

The idea is to minimize the weight of the fuel to allow more payload

Videodisc: "For All Mankind" Ch. 29 (Saturn V), Ch. 25 (Apollo 8 lift-off)

Earth vs. lunar rendezvous debate

We have used flybys to get us to the outer planets, and beyond

See fig. 4.7, pg. 64

Space programs of all countries have been very active

Lots of debris left in orbit (see fig. 4.5, pg. 63)

What to do with it all?

A real problem? or no big deal?