GRACE-FO is a collaboration of the US and the German Research Centre for Geosciences (GFZ), which is managing the German involvement in the mission and is contributing the launch vehicle and launch services. Some important factors in selecting a launch vehicle are reliability, cost, availability, and capability of lifting the satellite to its desired orbit.
GRACE-FO will be injected into a 490 km (304 mile) altitude, near circular polar orbit. Many of the satellites in NASA's Earth Observing System have a nearly polar orbit. In this orbit, the satellite moves around the Earth from pole to pole, taking about 99 minutes to complete an orbit. During one half of the orbit, the satellite views the daytime side of the Earth. At the pole, satellite crosses over to the nighttime side of Earth.
As the satellites orbit, the Earth turns underneath, and Earth does most of the work of traveling! By the time the satellite crosses back into daylight, it is over the region neighboring the area seen in its last orbit. In a 24-hour period, polar orbiting satellites will view most of the Earth twice: once in daylight and once in darkness.
GRACE-FO will continue the important work of tracking the movement of water and ice around the planet.