STEREO spacecraft observing the Sun
(Credit: NASA)
The sun occasionally ejects vast gas clouds into space, known as coronal mass ejections (CMEs). Each cloud may carry 1,000,000,000 tonnes of gas into space at several hundred km/s. Despite the importance of CMEs scientists don't fully understand their origin or evolution, nor their structure or extent in interplanetary space. When these clouds engulf earth they can disrupt power, navigation, communication and satellite control systems.
The NASA STEREO mission was launched in October 2006 and is providing a totally new perspective on solar eruptions by imaging CMEs and background events from two observatories simultaneously. The two identical probes are offset from one another, one flying ahead of the earth in its orbit and the other behind the earth, using a series of lunar swingbys. The spacecraft look back at the sun and the space between the sun and the earth. This two-platform view allows 3D images of the sun to be produced.
It is the RAL Space-led Heliospheric Imagers (HI) on STEREO that look at the space between the sun and the earth, using wide-angle telescopes. They are being used to detect the CMEs as they propagate through interplanetary space.
When combined with data from observatories on the ground or in low-earth orbit, STEREO's data will allow scientists to track the buildup and lift-off of magnetic energy from the sun and the tragectory of earth bound CMEs in 3D. In addition to leading the HI instruments, all of the imaging instruments aboard the two STEREO spacecraft use a CCD based camera system developed by RAL Space.
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