A formation of small and large satellites orbits the Earth along the same ground track every 98 minutes in a 705-kilometer sun-synchronous orbit, crossing the equator at 1:30 a.m. and p.m. Termed the “A-Train” (short for the Afternoon Train), this carefully planned and coordinated constellation operates as a single, powerful, virtual observatory. This is a spectacular success story — our understanding of Earth system science has significantly improved due to the synergies from this diverse and complementary suite of instruments.