Magnetospheric Multiscale Mission

The Magnetospheric Multiscale (MMS) Mission is a NASA robotic space mission to study the Earth's magnetosphere, using four identical spacecraft flying in a tetrahedral formation. The spacecraft were launched on 13 March 2015 at 02:44 UTC. The mission is designed to gather information about the microphysics of magnetic reconnection, energetic particle acceleration, and turbulence⁠ — processes that occur in many astrophysical plasmas.

Source: Wikipedia — Magnetospheric Multiscale Mission (CC BY-SA 4.0)