The Cluster mission is a non-tripulated mission that studies the magnetosphere over the course of an entire solar cycle. The mission is composed of four identical spacecrafts flying in a tetrahedral formation. A replacement for the original Cluster spacecraft which was lost in a launch failure in 1996, was the four Cluster II spacecrafts which were successfully launched in pairs in July and August 200,onboard two rockets. In february 2011, Cluster II celebrated 10 years of successful scientific operations in space. The mission has been extended until December 2016.
Double Star Mission
Double star was a joint Chinese-European mission directed by ESA and the Chinese space agency (CNSA) also with the objective of studying the magnetosphere complementing Cluster. It was proposed in 1997 and the 1st of July of 2001 they signed an agreement on the mission.
The mission consisted of two satellites. They were both designed, developed and launched by the China Space Administration, flying in different orbits around the earth. The ESA built 8 measuring instruments onboard of each satellite, seven of which were instruments meant to be used in the cluster mission.
Envisat (environmental satellite) Mission
Envisat is an inoperative Earth-observing satellite still in orbit. It was launched on March 1, 2002 aboard an Ariane 5. It is at an altitude of 790 km being in a Sun synchronous polar orbit. It orbits the earth in about 101 minutes with a repeat cycle of 35 days. After loosing contact with the satellite on April 8, 2012, ESA formally announced the end of Envisat's mission on the 9th of May 2012. Envisat is the largest civilian Earth observation satellite put into space.
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