STEREO

STEREO (Solar TErrestrial RElations Observatory) is a solar observation mission. Two nearly identical spacecraft (STEREO-A, STEREO-B) were launched in 2006 into orbits around the Sun that cause them to respectively pull farther ahead of and fall gradually behind the Earth. This enabled stereoscopic imaging of the Sun and solar phenomena, such as coronal mass ejections. Contact with STEREO-B was lost in 2014 after it entered an uncontrolled spin preventing its solar panels from generating enough power. It was briefly resumed in 2016 before being interrupted and eventually declared lost.