This simulation shows the paths followed by the STEREO-A and STEREO-B spacecraft.
The two STEREO (Solar TErrestrial RElations Observatory) spacecraft were launched on 26th October 2006 and placed in highly eccentric and almost identical orbits around the Earth. The two spacecraft flew past the Moon on December 15th 2006, with STEREO-A being deflected into an orbit around the Sun with period slightly less than one year, and STEREO-B being deflected into a less eccentric orbit around the Earth. STEREO-B flew past the Moon for a second time on January 21st 2007, and was deflected into an orbit around the Sun with period slightly greater than one year. The two spacecraft then continued to follow their orbits around the Sun, with STEREO-A (with period slightly less than one year) moving ever further ahead of the Earth, and STEREO-B (with period slightly more than one year) moving ever further behind the Earth.
The simulation also contains the Sun, together with all known planets and the Moon.
The starting date for the simulation is 1st January 2007 - a few weeks after the launch of the two spacecraft, and in between STEREO-B's two encounters with the Moon. If you run the simulation forward, you can watch STEREO-B's second encounter with the Moon, after which both spacecraft move into orbits around the Sun. If you run the simulation backward, you can watch the two spacecraft's first encounter with the Moon, before which both spacecraft had highly eccentric and almost identical orbits around the Earth. You can see how the paths (orbits) followed by the two spacecraft are dramatically changed by the encounters with the Moon, enabling them to be moved into their desired orbits around the Sun.
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