STEREO Spacecraft return to Earth

In October 2006 the NASA twin STEREO spacecraft were launched from Cape Canaveral aboard a Delta II rocket and subsequently injected into solar orbits with one spacecraft behind the Earth in its orbit, and the other in front, both drifting away from Earth by about 22.5 degrees per year (Earth-Sun-spacecraft angle).

The two spacecraft carried identical payloads which, for over 16 years have imaged solar activity and the passage of solar ejecta (specifically billion tonne plasma clouds known as coronal mass ejections) from their source on the Sun, through the inner Solar System and their impacts in the vicinity of Earth.

The spacecraft passed behind the Sun, as seen from the Earth, in 2014/15 and have been slowly coming round towards the Earth again.

After a mission that has gone way beyond the original planned lifetime, only one of the spacecraft, known as STEREO-A, is still in operation, but in August this year both STEREO spacecraft will fly by the Earth as they begin their second revolution of the Sun with respect to the Earth.