more about orbits

More About Orbits

Orbits can be ellipses, parabolas or hyperbolas

All Orbit Shapes are Conic Sections

Why Do We Call it a “Focus?”

Escape Velocity• Every object has an escape velocity• Anything launched with less than escape

velocity will fall back• Anything launched with greater than escape

velocity will keep going and never return• Escape velocity from Earth’s surface is 11

km/sec or 25,000 miles per hour.• For anything in a circular orbit, escape

velocity is 1.4 times its orbital velocity.

Orbits and Escape Velocity

• Anything moving with less than escape velocity will travel in an elliptical orbit

• Anything moving exactly with escape velocity will travel in a parabolic orbit (Think of it as an infinitely long ellipse)

• Anything moving with more than escape velocity will travel in a hyperbolic orbit

Orbits and Escape Velocity

What About Three Objects?

• Kepler and Newton solved the problem of one object orbiting about another

• Are there formulas for three interacting bodies?

• Bottom Line: No (After much effort)• Except for a few special cases...

The Lagrangian

Points

Gravity Assist• Gravity assist happens naturally. It can

capture comets into short-period orbits or expel them from the Solar System

• We use gravity assist to speed up, slow down, or redirect spacecraft

• The Cassini mission to Saturn was launched with only one-fifth the energy needed to reach Saturn

We’re Pretty Good At It

In Gravity Assist, a Massive Object Causes a less Massive One to

Speed Up or Slow Down

Gravity Assist Can Speed Objects Up

Gravity Assist Can Slow Things Down