everal teams are already at work on such telescopes. NASA is developing a project called the Ultra Long Duration Balloon (ULDB), which would be able to stay aloft for 100 days at a time. However, its telescope is designed to be dangled from a cable. The slight swaying of the cable means the telescope would not be able to produce very high-resolution images.
Another team from the Southwest Research Institute in San Antonio, Texas, US, has already tested its design. It flew an airship called HiSentinel to 22.5 km in November 2005.
HiSentinel is 45 metres long, and Fesen says two such airships could be lashed together to carry a 0.3-metre telescope. But its developers are already designing larger airships that could loft even more ambitious observatories to the edge of space.