NASA
17th July 2015, 03:30
On July 11, 2015 we received our first images in over three months from NASA's Solar TErrestrial RElations Observatory Ahead spacecraft, or STEREO-A. Since March 24, 2015, STEREO-A has been on the far side of the sun, where it has had to operate in safe mode, collecting and saving data from its radio instrument.
The three-month safe mode period was necessary because of the geometry between Earth, the sun, and STEREO-A. STEREO-A orbits the sun as Earth does, but in a slightly smaller and faster orbit. The orbit ensured that over the course of years, Earth and the spacecraft got out of sync, with STEREO-A ending up on the other side of the sun from Earth, where it could show us views of our star that we couldnÕt see from home. Though the sun only physically blocked STEREO-A from EarthÕs line of sight for a few days, STEREO-A was close enough to the sunÑfrom our perspective -- that from March 24 until July 8, the sun interfered with STEREO-AÕs data transmission signal, making it impossible to interpret.
More... (http://www.nasa.gov/feature/goddard/stereo/return-of-the-stereo-a-spacecraft)
The three-month safe mode period was necessary because of the geometry between Earth, the sun, and STEREO-A. STEREO-A orbits the sun as Earth does, but in a slightly smaller and faster orbit. The orbit ensured that over the course of years, Earth and the spacecraft got out of sync, with STEREO-A ending up on the other side of the sun from Earth, where it could show us views of our star that we couldnÕt see from home. Though the sun only physically blocked STEREO-A from EarthÕs line of sight for a few days, STEREO-A was close enough to the sunÑfrom our perspective -- that from March 24 until July 8, the sun interfered with STEREO-AÕs data transmission signal, making it impossible to interpret.
More... (http://www.nasa.gov/feature/goddard/stereo/return-of-the-stereo-a-spacecraft)