On October 13, 2015, China started the 24 hour test flight of its largest airship yet in Xilinhot, Inner Mongolia. The Yuanmeng has a volume of 18,000 cubic meters, length of 75 meters and 22 meters height. It will fly to 20,000 meters to test its control systems and near space flight performance. With solar panels installed on its top, the Yuanmeng will be one of the largest solar powered airships in existence, using solar power to drive its rotors will save additional weight in order to increase payload. Solar power also gives it a total flight endurance of six months. The Yuanmeng’s 5-7 ton payload of data relays, datalinks, cameras and other sensors would also be powered by the sun.
Yu Quan, a scientist of the Chinese Academy of Engineering, notes that airships are ideal for long duration flights in near space (the atmosphere between 20km to 100km altitude) though thermal expansion from day and night temperature differentials are a design issue. Operating higher in near space means that the Yuanmeng would have constant line of sight over a hundred thousand square miles, an important requirement for radar and imaging. Increased sensor coverage means increased warning time against stealthy threats such as cruise missiles, giving Chinese forces a greater opportunity to detect and shoot down such threats. It would also be harder for fighters and surface to air missiles to attack near space objects.
Full article: China Tests its Largest Airship (Popular Science)