The environment is often studied from here on Earth. But why not a top-down rather than a bottom-up approach? NASA’s Earth Observing System (EOS) grew out of an idea proposed by astronaut Sally Ride, who, after observing Earth from outer space, envisioned “Mission to Planet Earth,” a coordinated global research effort to preserve the planet. The A-Train is a group of satellites orbiting some 400 miles above the Earth’s surface. Courtesy of NASA. The EOS program subsequently launched a series of satellites to provide researchers and scientists around the globe with data that forms a snapshot of our planet. Dubbed the “A-Train” because they fly in formation as a flotilla, the satellites travel at low polar orbits about 438 miles above the Earth’s surface – timed to pass over the same point within a few minutes of each other. Onboard are sophisticated state-of-the-art photonic equipment, including lasers, spectrometers, radar, telescopes and optoelectronic imagers.