The joint Chinese-European space mission, Double Star, will blast off on 27 December. In a column for BBC News Online, Dr Chris Carr of Imperial College London looks at the wealth of new data its instruments will provide about the Sun-Earth environment.
Last month, the European Space Agency and its counterpart the Chinese National Space Administration met in Beijing to review the readiness of the first Double Star spacecraft.
The Double Star launch site in Southern China (Image: European Space Agency)
Named Explorer 1, the first of two satellites will be launched at the end of this month from a base in Southern China.
It is a collaboration between Europe and China which sees the launcher and the satellites made by China, whilst Europe provides a number of scientific instruments, plus a contribution to the network of data systems on the ground.
The first dedicated space science mission launched by China, Double Star is the invention of Professor Zhenxing Liu of the Centre for Space Sciences in Beijing.
Liu has long been involved with a European mission called Cluster which comprises four spacecraft in a close-formation orbit above the Earth.
Cluster's job is to analyse the magnetosphere - the bubble of magnetised and charged gas which surrounds our planet - in small-scale detail.
Professor Liu's idea was to complement Cluster's measurements by launching two additional spacecraft.
DOUBLE STAR MISSION
Launch date: 27 December
Launch vehicle: Chinese Long March 2C rocket
Aim: To study the effects of the Sun on the Earth's environment
However, whilst the Cluster spacecraft are separated by some few hundred kilometres, Double Star will be tens of thousands of kilometres apart.
The intention is to bring a global context to the measurements. Physics of the Sun-Earth environment has developed rapidly since the dawn of the Space Age.
Indeed, the term magnetosphere was coined as late as 1959 to describe the region around our planet which is protected from the radiation of the Sun (the so-called solar wind) by the Earth's magnetic field.
This extends to about 60,000 kilometres from the Earth, and the orbits of both Cluster and Double Star are designed to clip this boundary.
Though seemingly remote, there are a lot of processes going on here which have an impact for us on the ground.
The Aurora Borealis, or Northern Lights, is an example of the solar wind leaking through our protective magnetic barrier.
The aurora is a fantastic light-show, but as our life becomes more dependent on technology, we face practical problems.
Cutaway diagram of spacecraft
For example, changes in the Sun's activity can send huge amounts of energy towards the Earth which buffet and reconfigure the magnetosphere, causing disruption to communications, power-line failures and even the destruction of satellites.
A new branch of physics called "space weather" has emerged to study these effects; Double Star will contribute to our understanding of these physical processes.
Each spacecraft is a spinning cylinder about two metres across and one metre high, crammed with instrumentation.
Three of the eight instruments on Explorer 1 come from UK universities in London (Imperial College London and University College London); and Sheffield, France, Austria and Ireland are also providing hardware.
The instruments will measure the diffuse mixture of charged particles and fields which exist in the near-vacuum between the Earth and the Sun.
So tenuous is this mixture that the instruments require an exceptional level of sensitivity.
The magnetic-field instrument (Imperial College) will measure a field 1,000 times weaker than the field which, at the Earth's surface, is responsible for the slow movement of a compass needle.
European scientists and engineers are gathering in China for the launch and switch-on of their first spacecraft.
The culmination of many years' intensive work, the satellite will sit atop a Long-March 2C rocket which will loft it into a highly elliptical orbit traversing the Earth's poles.
Six months later, Explorer 2 will follow. The spacecraft are expected to survive just one or two years in the harsh radiation of space, but in this time they will beam back to Earth a wealth of new data about the Sun-Earth environment.