Solar storms – or Coronal mass ejections (CMEs) – are caused by the sudden release of built-up magnetic stress in the Sun's atmosphere. On Earth, we see the results of small versions of these when plasma streaming from the sun strikes our upper atmosphere and creates the Northern and Southern Lights (the Aurora Borealis and the Aurora Australis). Sometimes, however, these ruptures can be inordinately large and have the potential to wreak havoc on orbiting satellites, radio networks, and national power grids. In an effort to be prepared well in advance of such events, a UK consortium has proposed a satellite system that can provide as much as five days warning of potentially damaging CMEs.

When the Sun flares, it does not necessarily eject large amounts of coronal mass. However, when a particularly large eruption occurs, the release of material can often be a billion tonnes or more spewing out from the sun’s interior at over 2,500 kilometers per second (5,500 mph). The effect of all of this material and its driving energy slamming into the protective magnetic field of the Earth is to cause large plasma flares and very strong versions of the two borealis. But it also causes a huge electromagnetic field pulse that can disrupt radio communications, satellite systems, and even disable entire national power grids – as happened in a particularly large solar storm of March 1989 that blacked out the whole of Quebec.

In light of the potentially devastating consequences of these phenomena, in 2011 the UK government added solar storms to their National RIsk Register of Civil Emergencies. To monitor such events, they then also created the Met Office Space Weather Operations Centre (MOSWOC) to develop and implement ways to alert the nation using the likes of the SOHO, STEREO , and SDO solar-observing satellites.

Given that none of these craft are designed or deployed as continuous monitoring stations, however, and that one of them – STEREO – is currently on the opposite side of the Sun from Earth, the information received is limited. As some of these satellites have also been in space for more than twenty years, the technology is outmoded and the longevity limited for these space-based solar monitors.

To help alleviate this problem, the consortium (consisting of Airbus Defence and Space (UK), in collaboration with the Met Office, Mullard Space Science Laboratory, Rutherford Appleton Laboratory, and Imperial College London), has set a target to source new data currently provided by the STEREO satellites, via a new mission able to provide continuous data from a stable orbit. The mission, dubbed Carrington-L5, is named after the British scientist – Richard Carrington – who recorded the strongest geomagnetic storm on record, which occurred in 1859.

The L5 in the mission's name designates a particular point of gravitational balance between two bodies in space. These locations are known as Lagrange points, which are numbered L1 to L5 and define specific stable areas where gravitational forces are balanced and allow stable orbits for satellites. In the Carrington-L5 mission, Lagrange point L5 designates a position located in the third corner of an imaginary equilateral triangle, if that triangle was drawn in the plane of orbit with a common base line that lay in the centers of the two masses.

In this case, the two bodies are the Earth and the Sun, and L5 is a site roughly equidistant from both. As such, the Carrington-L5 mission gravitational balance point will allow the satellite to follow the Earth in its orbit around the Sun at a distance of around 150 million km (93 million miles). From this viewpoint, the satellites would be able to monitor events on the surface of the Sun several days in advance of any solar storm activity area before it rotates around to face the Earth.

To minimize costs, the mission aims to reuse systems already developed by Airbus for previous space missions. New instruments will also be designed for the payload, which have all been identified by MOSWOC as critical to the monitoring of CMEs (including coronagraphs, heliometers, gravitometers, and radiation monitors), and must remain operational for a minimum of a decade of extreme space weather conditions.

"Within the UK, we have the heritage and experience to create this mission on a relatively short timescale and at a low overall cost," said Dr. Markos Trichas, Principal Mission Systems Engineer at Airbus Defence and Space (UK). "All components we are planning to use for the Carrington-L5 spacecraft and payload have flown before or are in an advanced stage of development. This will minimize the cost of procurement and massively increase the benefits to our economy while allowing the growth of the UK space industry."

The first satellite in the system is slated for launch in 2021.

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