The upper atmosphere is the most relevant to global warming and yet
the most difficult to study.

Aircraft and weather balloons are limited to a ceiling of 25Km. The only existent practical means of sampling these upper regions is by attaching instruments to rockets, most commonly military test flights.

It is ironic that one of the worst upper atmospheric pollutants is solid rocket fuel emission; by studying the effects of pollution we exacerbate the problem. A relatively small prototype of HYPACC 2 could deliver probes to the upper atmosphere at minimal cost in financial and environmental terms.
The use of a super gun for atmospheric research is by no means a new one. The HARP (High Altitude Research Project) of the 1960's was the brainchild of Gerald Bull, infamous for the Babylon Gun of the late Saddam Hussien. The HARP project was a resounding success especially considering its modest cost.

A modern version of HARP would help our understanding of the atmosphere. The project may also assist in the development of scramjet technology by providing a hypersonic accelerator for test purposes (as with the SHARP gun).