The Cluster Mission: A Heliophysics Workhorse Exploring Our Magnetosphere
For 15 years, four satellites have been orbiting Earth, helping us better understand the space around us. Far from being a complete vacuum, Earth's environment is filled with electrical fields, magnetic fields and charged particles that whirl along in concert with these dynamic electromagnetic surroundings.
Cluster is a joint European Space Agency and NASA mission made of four spacecraft. The first two spacecraft launched on July 16, 2000, and the second pair launched on August 9, 2000, to observe just how these particles streamed and gyrated, creating a vast, constantly changing space environment around our planet. Flying four spacecraft – in a tightly controlled pyramid shape – made this the first ever mission capable of gathering 3-dimensional observations of structures in near-Earth space, as well as how they changed over time.
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"When Cluster launched 15 years ago, the orbit was designed to be maneuverable," said Melvyn Goldstein, mission scientist for Cluster at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "They could be maneuvered into a tetrahedral configuration to enable a full 3-dimensional view of structures such as Earth’s bow shock and magnetopause. At perigee they naturally form a string of pearls, useful for observations of something long and thin, like the aurora."
Its journeys over the past 15 years have greatly improved our understanding of the magnetic bubble – the magnetosphere – that surrounds Earth. This is key not only for understanding our place in the solar system, but also to help understand how changes in the space environment can have effects throughout our entire magnetosphere – important information for those who model the space weather events that can affect satellites or interrupt radio communications.
When Cluster launched, scientists had little understanding of the full shape and structure of any given event in space. Today the four spacecraft have traveled right through aurora, crossed in and out of the edges of the magnetosphere, and provided some of our very first glimpses of something called magnetic reconnection in which magnetic field lines explosively realign and transform magnetic energy into fast-moving, energetic particles and heated plasma. By observing magnetic reconnection near Earth, scientists can learn more about how it occurs throughout the universe. In some circumstances, especially in giant explosions on the sun such as solar flares, magnetic reconnection can create huge explosions that can send particles hurtling off at nearly the speed of light. NASA’s Magnetospheric Multiscale mission will extend this initial work from Cluster and focus directly on magnetic reconnection occurring in near-Earth space when it enters science mode later this year.
Cluster continues to provide remarkable science. On July 14, 2015, new results were published based on Cluster's Inner Magnetospheric Campaign, in which the spacecraft were in an orbit optimized to examine waves coursing through Earth’s near-space environment – at times pairs of the spacecraft were just a few miles apart. Understanding such waves can help scientists develop a comprehensive model of the magnetosphere that will enable improved forecasting of potential space weather hazards to spacecraft. New results are also expected soon from Cluster's recent Shock Campaign. In early 2015, Cluster conducted a campaign, in which it gathered observations at the boundaries of the magnetosphere in the search for more information on what processes cause extreme changes in the solar wind as it encounters the magnetosphere's boundaries.
Source : NASA