The area of the upper atmosphere between 50,000 ft and 200,000 ft has been referred to as "Near Space" because it is above the altitudes generally used by aircraft and below the altitudes used by satellites.

Balloons and airships have been identified as primary candidates for the exploitation of this region because of their potential for ease of deployment, low cost and long-term loitering capabilities.

The most ambitious use of stratospheric Lighter Than Air (LTA) vehicles in the near-space regime is in the area of station keeping airships.

These vehicles will have the ability to be propelled against the wind in order to maintain persistence in a single area for the duration of the mission.

http://www.aerostar.com/aerospace.htm