TESS

The Transiting Exoplanet Survey Satellite was not built to study Earth. It carried four wide-field cameras aimed at nearby stars, designed to catch the faint dimming that signals a planet crossing in front of its sun. On 18 April 2018, a Falcon 9 launched TESS from Cape Canaveral into a highly elliptical orbit — the spacecraft then used its own propulsion, including a lunar flyby, to settle into a stable 2:1 resonance orbit with the Moon that kept it clear of Earth's radiation belts and stably positioned for decades.

TESS was the first NASA astrophysics satellite mission launched under contract with SpaceX, cleared for flight after SpaceX received the agency's Category 2 Launch Services Program certification earlier that year. Where Kepler surveyed a fixed patch of sky, TESS was designed to scan 85 percent of the celestial sphere, monitoring around 200,000 bright nearby stars. Its initial two-year mission expected to catalog over a thousand confirmed exoplanets — targets close enough for follow-on telescopes to study in detail.