* Just after World War II, the US military began exploring the use of high-altitude spy balloons, which led to a large-scale series of missions called Project Genetics. According to government documents, the project flew photographic balloons over Soviet bloc territory in the 1950s.
*Such balloons typically operate at 80,000–120,000 ft (24,000–37,000 m), where commercial air traffic flies – airliners almost never fly above 40,000 ft. The highest performing fighters typically do not operate above 65,000 feet, although spy planes such as the U-2 have a service ceiling of 80,000 feet or more.
* According to a 2009 report by the Air Command and Staff College of the US Air Force, the advantages of balloons compared to satellites include the ability to scan wide areas of territory at close range and being able to spend more time over the target area.