In the Earth's upper ionosphere and higher in space are strong electric fields which accelerate the particles responsible for the auroral lights. These electric fields may be thought of as voltages like you would find across two battery terminals.

To measure these electric fields, the UC Berkeley Rocket deploys long antennas with spherical voltage probes on the end. These probes measure the electric potential in space that may be responsible for accelerating charged particles to higher velocities. These electric fields can also be in the form of radio waves, and lower-frequency waves which heat our ionosphere.