MMS: Mission Implementation (III)

Spacecraft Formation

The sketches used in scientific papers and textbooks to illustrate the concept of reconnection are generally two-dimensional. Yet reconnection, like other natural phenomena, occurs in three dimensions, not two, and unraveling its physics requires simultaneous observations of the magnetic field and plasma at, ideally, a minimum of four locations. Thus, MMS is being implemented with four spacecraft, which will be launched together on a single launch vehicle and inserted sequentially into Earth orbit. As they explore the dayside and nightside reconnection regions, the spacecraft will fly in a tetrahedron formation, allowing them to capture the three-dimensional structure of the reconnection sites they encounter. Onboard propulsion will be used to adjust the separation among the spacecraft, from hundreds of kilometers to as close as 10 kilometers, to achieve the optimum interspacecraft separation for probing the diffusion region.