Constellation aerobraking
Constellation aerobraking (note: not a widely used technical term) is a reasonably novel technique in small satellite operations in which multiple satellites in a constellation alter their orientation to receive different amounts of drag to cancel out their relative velocities. Satellites experience minute amounts of drag in the upper atmosphere based on their altitude, surface area, and mass, and satellites with non-cubic form factors can alter their orientation relative to their velocity to create a range of thrusts without active propulsion. Unconfirmed reports suggest that flocks of Planet Labs' Dove satellites employ this technique in order to achieve stable orbital separation around the Earth.
Atmospheric drag is typically an undesirable phenomenon in low Earth orbit, where nontrivial amounts of air molecules are still present, and collisions between satellites and these particles produce a nontrivial force when integrated over times on the order of weeks. All satellites experience this deceleration, and its magnitude can be calculated to reasonable accuracy. Two identical satellites placed into orbit together but with different areas (i.e. two 2U CubeSats, where one points a 1U face into the "wind" and the other orients a 2U face forward) should thus experience different amounts of drag, and will accelerate relative to each other. This is important as if they are launched together, upon separation they will have a relative velocity that needs to be canceled out in order for them to maintain a fixed distance apart from each other. Zeroth-order calculations suggest that separation distances in the hundreds of kilometers can be achieved between two satellites after several weeks in orbit after separation.