Inner space is getting more crowded. Since the 1980s, the Global Positioning System constellation of satellites has been in medium orbit some 20,000 kilometers above the Earth and now numbers more than 30. Since 2006 it has been joined by almost the same number of Russian GLONASS counterparts. The first examples of Europe's Galileo satellite network have been launched and China's BeiDou equivalent will add a further 40 over the next decade. But what happens if they stop working? GPS has become such an integral part of the world's commercial aviation community that doing without it seems almost inconceivable. However, there have been concerns for years that multiple satellites could be put out of commission by particularly energetic solar flares.
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