China and the European Union have launched a space mission to study the Earth's magnetic fields.
The first of two probes has been launched onto orbit
The Double Star mission - which involves two spacecraft - is the first joint project between China and the European Space Agency.
The first spacecraft blasted off early on Tuesday aboard a Chinese Long March 2C/SM rocket from a base in the town of Xichang in south-west China.
The second will be launched in about six months' time.
The spacecraft will study how the magnetised and charged particles streaming off the Sun affect Earth.
In extreme cases, this ejected material can interfere with communications and power lines, and even damage electronic components on orbiting satellites
The joint venture sees China provide the launch rockets and the chassis for each spacecraft, and a number of instruments.
Europe is spending 8m euros (£5.6m) on complimentary scientific instruments and a contribution to the network of data systems on the ground.
Explorer 1, or Tan Ce 1 as China calls it, is two metres in diameter
Seven of the instruments on Double Star will actually be identical to those currently flying on the four Cluster spacecraft put in orbit in 2000 by the European Space Agency (Esa) to study the Earth's magnetosphere.
Conducting joint studies with similar instruments on Cluster and Double Star should increase the overall scientific return from both missions, researchers believe.
The term magnetosphere refers to the region around the planet which is protected by the Earth's magnetic field from the radiation and matter ejected by the Sun.
This huge, tadpole-shaped region of space extends to about 60,000 kilometres from the Earth, and the orbits of both Cluster and the Double Star duo are designed to clip its boundary.
Though seemingly remote, there are a lot of processes going on in and around the magnetosphere that have direct consequences on Earth.
The arrival of huge clouds of magnetised and charged particles at the Earth buffet and reconfigure the magnetosphere.
The satellites will take up orbits thousands of km apart
The interaction can give rise to the beautiful aurorae - the Northern and Southern Lights - but it can also lead to communications disruption, power-line failures and even satellite damage.
The magnetosphere also helps reduce some of the more harmful - in health terms - cosmic radiation from reaching the Earth's surface.
The Double Star duo will sit thousands of kilometres apart from each other in space.
One spacecraft will fly in a polar orbit and the other close to Earth's equator.
But it will be possible to synchronise these orbits with those of the four Cluster satellites so that all six spacecraft can study near-Earth space together to give the most detailed, multi-dimensional view of the complex magnetosphere ever obtained.
The Cluster quartet have been operational since 2000
"On its own, Double Star would be scientifically important because it will provide new measurements in key regions of magnetosphere," said Andrew Fazakerley from University College London and one of the principal scientific investigators from the UK.
"For example, it will provide important new information on the Earth's changing radiation belts.
"However, the really exciting part is that the orbits of the two spacecraft are explicitly designed for co-ordinated measurements with Cluster.
"So, when Cluster is in the distant magnetic tail and Double Star is in the near tail, we shall be able to see simultaneously for the first time what happens in both of these key regions when the huge amounts of energy that drive the aurora are released."