Chinese scientists have reported a milestone in space laser communications, sustaining a high-speed, hours-long laser link with a satellite more than 40,000km (25,000 miles) above the Earth. The capability is seen as critical to future deep-space networks. According to the Chinese Academy of Sciences’ Institute of Optics and Electronics, which led the project, researchers used a 1.8-metre (6-foot) aperture telescope in Yunnan province to lock onto a geostationary satellite within four...