This is a joint mission for China and Europe designed to study the Earth's magnetic environment
By: Maggie McKee, New Scientist (translation: Dikla Oren)
"Double Star", a joint mission for China and Europe designed to study the Earth's magnetic environment, has begun its work.
"Everything looks great," says Philippe Escova, project scientist at the European Space Agency. Scientists began analyzing the information that flows from it, and conducted the longest measurement of the vortex zone, where the first encounter between the solar wind and the Earth's magnetic field takes place.
The first of the mission's two satellites, 1-TC, was launched from China in December 2003. Its twin will join it in July. Double Star will operate for eighteen months at the same time as the mission, which includes four satellites that was launched in 2000 and is called "Cluster".
The cycle time of 1-TC around the Earth is 27 hours, and its orbit is particularly elliptical. At the closest point to the Earth in its orbit, it is 570 km from the Earth - only about a tenth of the Earth's radius - while at the furthest point it is 13 times the Earth's radius.
At this distance, the satellite moves at a relatively slow speed, as it begins to return towards Earth. This means that it spends about ten minutes - twice as much as the previous satellites - in measurements in the "shock arc" area.
This area is a horseshoe-shaped area, where the charged particles from the solar wind first meet the Earth's magnetic field, from which they are pushed aside, similar to how water flows around a pebble.
The arc shock region changes its position depending on the activity of the sun. As the region moved around the satellite, the satellite saw ions from the solar wind, which were expelled from the region back to the Sun.
"We've seen this before, but because the double star stays longer in this region, we see the exquisite arrangement of these ions," Escova told New Scientist.
Double Star is intended to serve as a long-term complement to the European Space Agency's (ESA) Cluster mission. The cluster studies the Earth's magnetosphere in a relatively small range with the help of four satellites, located at intervals of 250 km from each other. The Double Star will perform measurements at distances of up to 40,000 km from the cluster.
Scientists are already comparing the measurements of the effects of giant gas eruptions from the Sun's corona, called Coronal Mass Ejections, from the two missions. The latest outbreaks occurred last January. Such events have affected the operation of satellites in the past and caused the shutdown of power plants on Earth.
Escova also hopes that if the two missions work together, they will be able to map the "magnetopause" region, which is the boundary between the solar wind and the region under the direct influence of the Earth's magnetic field. This area lies within the arc of shock.
Most of the eight science instruments on the 1-TC are working better than expected, but the two magnetometers need further calibration. This is because the magnetic field of the satellite itself turned out to be greater than expected, so the mission scientists are now working on developing software that would compensate for this.
The spacecraft's magnetic field decreases with distance, and since the two magnetometers are located in different places they will measure slightly different magnetic fields. This difference will allow scientists to calculate the effect of the satellite's self-magnetic field and eliminate its effect on the magnetometers.
