The Magnetospheric Multiscale ( MMS ) mission is a formation flying mission that consists of four distinct phases : phases 1 and 2 are low - inclination highly elliptical orbits ( HEO ) , phase 3 is a double - lunar swingby which transfers phase 2 to phase 4 , a high - inclination HE0 orbit . Phase 2 is designed to reach the first lunar swingby of phase 3 in the most efficient fashion . It is shown that when the orientation of the line of apsides of phase 2 is properly chosen , no extra Delta - V is required beyond what is typically needed to raise apogee to lunar distance .