000A: How do you move around in space?

The main way of changing the velocity of a spacecraft is to take part of the mass of the spacecraft, and eject it; anything but small plane changes require a lot of energy, which can make such manoeuvres prohibitive; the Earth’s diameter is almost 43km more at the equator than between the poles; Sun-synchronous orbits are used in Earth observation missions to maintain consistent illumination of the ground throughout the year.