The mission

An illustration of the Double Star spacecraft. Image: Chinese National Space Administration The Double Star Programme (DSP) is a joint mission between the European Space Agency (ESA) and the Chinese National Space Administration (CNSA).

It is designed to study the effects of the Sun on the magnetosphere, the region around the Earth that contains charged particles controlled by the terrestrial magnetic field. Double Star is a follow up to the highly successful Cluster mission that began operations in 2000.

The spacecraft

Double Star consists of 2 satellites designed, developed, launched and operated by CNSA.

Each DSP spacecraft is cylindrical in shape with a height of 1.4m, a diameter of 2.1m and a weight of 330 kg. They both spin at a rate of 15 revolutions per minutes (rpm).

The satellites each have a total of 16 instruments, half from Europe and half from from China. 7 of the 8 European instruments are identical to those currently flying on the four Cluster spacecraft. Reusing the Cluster designs reduced the costs and development time and also minimised the risks associated with using newly developed instruments.

Launch and operation

The two Double Star probes fly along complementary paths. DSP-1 orbits above the tropics while DSP-2 travels in a polar orbit. Image: Chinese National Space Administration The equatorial spacecraft (DSP-1) and the polar satellite (DSP-2) are scheduled for launch on-board Chinese Long March 2C rockets in December 2003 and June 2004 respectively. This allows them to operate alongside Cluster. However both Double Star spacecraft will have an orbit which brings them much closer to the Earth than the four satellites making up Cluster, operating within a zone not covered by any other missions.

DSP-1 will be launched into an elliptical orbit with a closest approach to the Earth (perigee) of 550km and a maximum altitude (apogee) of 63780km. The orbit is inclined at 28.5° to the equator.

This probe will look at the Earth's huge magnetospheric tail, the nightside region of the magnetosphere where particles accelerate towards the North (N) and South (S) poles and substorms (events lasting one hour or less, during which energy is rapidly released in the magnetospheric tail) take place. DSP-1 is expected to last about 18 months.

DSP-2 will be launched into a polar orbit with a perigee of 700km, an apogee of 39000km and an inclination of 90°. This probe will have a lifetime of 12 months. It will investigate the physical processes taking place over the magnetic poles, the development of auroras and the energy input from the solar wind (the flow of electrons, protons and the nuclei of elements from the Sun) into the polar ionosphere (layers of ionised particles and electrons found at altitudes of 80–250 km in the atmosphere of the Earth).