Atmospheric satellite

An atmospheric satellite (United States usage, abbreviated atmosat) or pseudo-satellite (British usage) is an aircraft that operates in the atmosphere at high altitudes for extended periods of time, in order to provide services conventionally provided by an artificial satellite orbiting in space.

Atmospheric satellites remain aloft through atmospheric lift, either aerostatic (e.g., balloons) or aerodynamic (e.g., airplanes). By contrast, conventional satellites in Earth orbit operate in the vacuum of space and remain in flight through centrifugal force derived from their orbital speed.

To date, all atmosats have been unmanned aerial vehicles (UAVs).

An atmosat remains aloft through atmospheric lift, in contrast to an artificial satellite in Earth orbit which remains aloft through centrifugal force derived from its high orbital speed. Because of this high speed a satellite must operate in the vacuum of space, is expensive to build and launch, and its path is inflexible once launched. Atmospheric satellites fly much slower and are intended to provide a range of services more economically and with more versatility than current low Earth orbit satellites.

Operating altitudes are expected to be in the tropopause—at approximately 65,000 feet—where winds are generally less than 5 knots and clouds do not block sunlight. It is desirable in the United States to operate above 60,000 feet, above which the Federal Aviation Administration does not regulate the airspace.

There are two classes of atmosat, respectively gaining their lift through either aerostatic (e.g., balloons) or aerodynamic (e.g., airplanes) forces. In order to remain aloft for long periods, the NASA and Titan Aerospace designs use propeller-driven electric airplanes powered by solar cells, in contrast to Google's Project Loon which envisions using helium-filled high-altitude balloons.

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