The European Space Agency (Esa) is to place instruments aboard two Chinese satellites in a project to study "space weather".

The Double Star programme will be just the first step... Luan Enjie Chinese National Space Administration

The agency signed a deal with the Chinese National Space Administration in Paris on Monday, the first time that it has decided to put experiments on board Chinese satellites.

"We will integrate the units in Europe and then finally they will be integrated on to the satellites in China," Giuseppe Giampalmo, Esa's head of international co-operation, told BBC News Online.

"We think that it may be a world first," he said.

Magnetic 'bubble'

The Chinese project, Double Star, will explore the Earth's magnetosphere - the magnetic "bubble" which surrounds the planet.

The first two Cluster satellites were launched by a Russian Soyuz rocket in July 2000

Storms in the magnetosphere can disrupt power supplies and communications on Earth.

Esa already has a programme to study the magnetosphere with its Cluster satellites, a series of four that went into orbit in 2000.

It will be putting duplicates of the Cluster instruments on the Chinese missions, in some cases using spare instruments from the Cluster launches.

Different orbits

"By and large, they are the same instruments measuring the same parameters.

"We have four Cluster satellites in the tail of the magnetosphere, whereas the Chinese satellites will have polar and equatorial orbits very close to the Earth in a very active area of the magnetosphere," Mr Giampalmo explained.

Esa was asked by the Chinese space authorities to provide some of the instruments for China's Double Star programme.

It is spending eight million euros (�4.8m) on refurbishing spare Cluster instruments, getting them ready for launch and monitoring them.

'Landmark' agreement

"This agreement ... is one of the most important landmarks in scientific collaboration since the Esa and the People's Republic of China first agreed to exchange scientific information more than 20 years ago," Esa Director General Antonio Rodotà said.

"The Double Star programme will be just the first step in substantial cooperation between the Chinese National Space Administration (CNSA) and Esa," CNSA director Luan Enjie said.

The first Chinese satellite will investigate the Earth's magnetic tail, where particles are accelerated towards the planet's magnetic poles, while the second will concentrate on the poles themselves and the development of aurorae.

They are due to go into orbit aboard Long March 2C rockets in December 2002 and March 2003.