Operations phase: completed; data archiving: ongoing.
Double Star is a joint ESA/Chinese project to study the effects of the Sun on Earth's environment, and in particular the 'magnetotail', where storms of high-energy particles are generated.
Double Star follows in the footsteps of ESA's ground-breaking Cluster mission by studying the effects of the Sun on Earth's environment. It explores Earth's magnetosphere - the magnetic 'bubble' that surrounds our planet.
As its name suggests, Double Star involves two satellites - each designed, developed, launched and operated by the China National Space Administration - flying in complementary orbits around the Earth. One of the Double Star spacecraft flies in a polar orbit and the other close to Earth's equator.
This orbital configuration enables scientists to obtain simultaneous data on the changing magnetic field and population of electrified particles in different regions of the magnetosphere.
The duo were launched from two different launch sites in China in December 2003 and July 2004. This schedule enabled them to operate alongside ESA's Cluster mission - a mini flotilla of four identical spacecraft launched into elliptical orbits around Earth.
Conducting joint studies with Cluster and Double Star should increase the overall scientific return from both missions.
A key aspect of ESA's participation in the Double Star project is the inclusion of seven instruments that are identical to those currently flying on the four Cluster spacecraft. One additional European instrument is an imager that monitors energetic neutral atoms (ENAs) in Earth's magnetosphere. A further eight experiments are provided by Chinese institutes.
By flying experiments identical to those on Cluster, the costs and development time can be reduced.
The equatorial spacecraft (TC-1) was launched at 20:06 CET, 29 December 2003, into an elliptical orbit of 550 kilometres by 66 970 kilometres, inclined at 28.5 degrees to the equator. This enables it to investigate Earth's huge 'magnetotail', the region where particles are accelerated towards the planet's magnetic poles by a process known as 'reconnection'.
The polar satellite (TC-2) was launched at 15:15 CET, 25 July 2004. This concentrates on physical processes taking place over the magnetic poles and the development of aurorae. It has a 700 kilometre by 39 000 kilometre orbit taking it round Earth once every 11.7 hours.
The collaboration between the National Commission of Science and Technology of the People's Republic of China and ESA started in 1980 when the first agreement to exchange scientific and technical information on space programme and projects of mutual interest was signed.
Then in 1992, the Chinese Academy of Science signed an agreement with ESA to collaborate on the Cluster mission. Since then several Chinese scientists were hosted in Europe at ESA establishments and in European institutes and became co-investigators
In September 1999, the ESA Director-General was invited by the Administrator of the China National Space Administration (CNSA) to discuss the collaboration on the Double Star programme. In May 2001, ESA approved funding for collaboration and recommended the co-operation with China.
Finally in July 2001, ESA and CNSA signed the agreement on the Double Star programme, the first time that it was decided to put ESA experiments on board Chinese satellites.
Double Star is being developed by the China National Space Administration.
ESA has agreed to contribute 8 million Euros to the Double Star programme. This funding has been used for refurbishment and pre-integration of the European instruments, acquisition of data for four hours per day and co-ordination of scientific operations.