Upper atmosphere

Near space is the region of Earth's atmosphere that lies between 20 and 100 km (65,000 and 328,000 feet) above sea level, encompassing the stratosphere, mesosphere, and the lower thermosphere. It extends roughly from the Armstrong limit above which humans need a pressure suit to survive, up to the Kármán line where astrodynamics must take over from aerodynamics in order to achieve flight. The definition of near space can vary depending on the source, but in general near space comprises the altitudes above where commercial airliners fly but below orbiting satellites.

The terms "near space" and "upper atmosphere" are generally considered synonymous. However, some sources distinguish between the two. Where such a distinction is made, only the layers closest to the Karman line are called near space, while only the remaining layers between the lower atmosphere and near space are called the upper atmosphere.

Near space was first explored in the 1930s. The early flights flew to the edge of space without computers, spacesuits, and with only crude life support systems. Notable people who flew in near space were Jean Piccard and his wife Jeannette, on the nearcraft The Century of Progress. Later exploration was mainly carried out by unmanned nearcraft, although there have been skydiving attempts made from high-altitude balloons.

The area is of interest for military surveillance purposes, scientific study, as well as to commercial interests for communications, and tourism. Craft that fly in near space include high-altitude balloons, non-rigid airships, rockoons, sounding rockets, and the Lockheed U-2 aircraft. The region has been of interest to space travel. Early attempts used a craft known as a rockoon to reach extreme altitudes and orbit. These are still used today for sounding rockets.

...
Wikipedia