Quantum Experiments at Space Scale (QUESS; Chinese: 量子科学实验卫星; pinyin: Liàngzǐ kēxué shíyàn wèixīng), also known as Quantum Space Satellite, and nicknamed Micius or Mozi (Chinese: 墨子) after the ancient Chinese philosopher and scientist, is a joint Austrian-Chinese satellite operated by the Chinese Academy of Sciences, in co-operation with the University of Vienna and the Austrian Academy of Sciences. QUESS is a proof-of-concept mission designed to facilitate quantum optics experiments over long distances to allow the development of quantum encryption and quantum teleportation technology. Quantum encryption uses the principle of entanglement to facilitate communication that is totally safe against eavesdropping and decryption. By producing pairs of entangled photons, QUESS will allow ground stations separated by many thousands of miles to establish secure quantum channels. QUESS itself has limited communication capabilities: it needs line-of-sight, and can only operate when not in sunlight. If QUESS is successful, further Micius satellites will follow, allowing a European–Asian quantum-encypted network by 2020, and a global network by 2030.