A polar orbit.

A polar orbit is a satellite orbit that passes over, or very close to, both poles of the Earth. During a 12-hour day, a satellite in such an orbit can observe all points on the Earth.

Polar orbits are 90-degree inclination orbits, meaning that the orbit is at 90-degrees to the plane of the equator. This type of orbit is useful for spacecraft that perform mapping or surveillance operations, such as the NOAA Tiros satellites and the Landsat satellites. Since the orbital plane is nominally fixed in space, the planet rotates below a polar orbit, allowing the spacecraft low-altitude access to virtually every point on the surface.

To achieve a polar orbit requires more energy, thus more propellant, than does an orbit of low inclination. A polar orbit cannot take advantage of the "free ride" provided by the Earth's rotation, and thus the launch vehicle must provide all of the energy for attaining orbital speed.