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## More About Orbits

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**More About Orbits**Orbits can be ellipses, parabolas or hyperbolas**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**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...**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**In Gravity Assist, a Massive Object Causes a less Massive**One to Speed Up or Slow Down