Transcript 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