Two German radar satellites are now flying in tight formation as they prepare to make the most detailed ever 3D map of the Earth's entire surface.
From the BBC News article: "TanDEM-X and TerraSAR-X have moved to within 350m of each other as they sweep around the planet at 7km/s. [...] TerraSAR-X was launched in 2007. TanDEM-X was put in space in June, since when it has been brought closer and closer to its more established sibling. [...] The fully finished DEM of the Earth's surface should be available in 2014. [...] With the TanDEM mission, the intention is to go down to a spatial resolution of 12m by 12m with a relative vertical accuracy of less than two metres."