## The GPS Mission: Phase II

After the Boost from Phase I of the GPS mission, the apogee of the elliptical transfer orbit is 20,200 km above the surface of the Earth. This is an *elliptical* orbit, however. It will not stay in a circular orbit at that 20,200 km, so a correction is required.

#1 What kind of correction will the satellite require if it is to move from its current *elliptical* orbit into a *circular* orbit? Where should this correction be applied?

#2 Calculate the exact value of the energy boost required.

Now that you have an answer for Phase II of the mission, try the orbit simulation to see if your answer was correct! If so, your GPS satellite should end up
in a circular orbit at an altitude of 20,200 km above the surface of the Earth. Did you successfully complete the mission?

#### OPTIONAL!

#3 How long does the transfer take?

#### OPTIONAL!

#4 What would happen if you tried to correct the GPS satellite's orbit
by firing the GPS boosters when it was at the *perigee* (closest approach to the Earth) in its elliptical orbit, rather than at the apogee? Describe the shape and location of the resulting orbit.

After you've decided upon your answer as a group, try the orbit simulation and see if your answer was correct!

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