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Rumba and Tango head for their sisters
 real 56k

Prof Roger Bonnet, Esa
Esa has stuck to its promises
 real 28k

John Credland, Esa
"It was a beautiful launch"
 real 28k

Wednesday, 9 August, 2000, 11:24 GMT 12:24 UK
Cluster satellites launch
Esa Launch
The rocket left the launch pad on time
The two remaining Cluster spacecraft that will investigate the physics of space weather have blasted off from the Baikonur cosmodrome in Kazakhstan.

Their Soyuz-Fregat launch vehicle lifted off from the space port exactly on time at 1113 GMT (1213 BST).

"It was a beautiful launch," said John Credland, head of the European Space Agency's Scientific Projects Department, who watched the event on a live link in London, UK. "So far, so good."

The Cluster duo, named Rumba and Tango, will rendezvous with the two identical satellites, Salsa and Samba, launched successfully last month.

Together, they will investigate most of the major boundaries and regions of interest within the vast but invisible magnetic field that surrounds our planet - the magnetosphere.

Violent solar events

This magnetic "bubble" protects life on Earth from the stream of charged particles - electrons and protons - that are blasted continuously from the Sun.

Cluster facts
Spin rate: 15 rpm
Spacecraft diameter: 2.9 m
Spacecraft height: 1.3 m
Dry mass: 550 kg
Propellant mass: 650 kg
Solar array power: 224 W
Downlink rate: 2 to 262 kbit/s
Following highly elongated, polar orbits which take them between 19,000 and 119,000 km from the Earth, the Cluster quartet will investigate how the magnetosphere interacts with this solar wind, and the high-energy particles from more violent solar events such as flares and so-called coronal mass ejections (CMEs).

There is currently a great deal of interest in these "space weather" phenomena. The charged particles, which move at hundreds of kilometres a second, can knock out electronics onboard satellites and in extreme cases interfere with power grids on the Earth's surface.

Cluster will give scientists better equations with which to predict space weather in the future.

"All the communication satellites above the Earth are affected by these massive bursts from the Sun," said John Credland. "If we could get pre-warning of these bursts, we could stop knockouts of spacecraft and their circuits. We could also stop power line surges on Earth which have also been responsible for some quite spectacular blackouts in the past."

'Back on track'

Rumba and Tango will follow almost identical manoeuvres to their sister ships to make a rendezvous set for 15 August.

Esa Cluster
Scientists have spent four years rebuilding the Cluster programme
Wednesday's launch was an emotional occasion for Professor Roger Bonnet, Esa's Director of Science.

Cluster II replaces the original mission destroyed in the Ariane-5 explosion in 1996. Speaking to reporters and Esa staff, he proudly announced that Cluster was now "back on track".

"After so many years of expectation, Esa has been able to stick to its promises to the scientists," he said. "We are very pleased to announce that in a few weeks the whole mission will be in operation.

"With Soho (Solar and Heliospheric Observatory) and Cluster, Europe is now fully participating in the investigation of the Sun-Earth relationship and space weather activities."

Giant discs

Each satellite is shaped like a giant disc, 1.3m high and 2.9m across. Most of the 11 instruments on each spacecraft will sit behind reinforced panelling inside the disc. Others have to be slung on booms to avoid interference from the spacecraft themselves.

Esa Cluster
The craft will fly in a pyramid formation
About half the launch weight of each disc will be fuel. Manoeuvrability is the key for Cluster - the craft are designed to take measurements in different locations.

Early in the mission, the spacecraft will spend most of their time flying on the side of the Earth that faces away from the Sun. After six months, they will move in front of the planet to investigate the polar cusps, weak points in Earth's magnetic shield where charged particles penetrate the upper atmosphere and generate the spectacular Northern and Southern Lights.

From the end of December, data will be coming down from the quartet at a rate of one gigabyte (two compact disks) every day.

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Launch console
See also:

16 Jul 00 | Sci/Tech
Cluster satellites go into orbit
05 Jul 00 | Sci/Tech
Black box recorders for satellites
04 Jul 00 | Sci/Tech
Cluster mission launch bumped
20 Feb 00 | Washington 2000
'And here's today's space weather forecast...'
19 Feb 00 | Washington 2000
National grid gets space protection
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