Over 10 000 artificial satellites circle above our heads. About 1000 of these concern classified military satellites, many of these launched by the NRO (National Reconnaissance Office). The NRO is the USA’s `unknown` military Space Agency operating in the shades of NASA. Amateur satellite trackers around the word classify these `secret` satellites. Marco Langbroek will explain how and why these satellites are traced, but also what the NRO has contributed to space technology nowadays. Langbroek has been awarded several prices and even has his own asteroid named after him. Come to his lecture at 17:00 in De Sitterzaal. There will be a free borrel afterwards.