The thermosphere is an upper region of Earth's atmosphere that includes the ionosphere and extends from an altitude of 85 kilometers (above the mesopause), where the temperature is about –33°C, to the lower level of the exosphere at 500 kilometers, where the temperature is about 1,500°C. The thermosphere is known be very active with waves and vertical tides of very thin air far above the highest clouds and storms of charged particles. However, it is still poorly understood and difficult to explore. Weather balloons and research aircraft cannot reach it. Sounding rockets do travel through the upper atmosphere, however they can at best take short snapshots of a specific region, and do not provide global mapping. Furthermore, the Space Shuttle orbits in a region well above the lower thermosphere; upon reentry, the Space Shuttle does pass through the lower thermosphere, however only briefly. A promising alternative approach is to tether a probe from a larger orbiting platform, and then lower the probe into the region of the thermosphere. The feasibility of this technique has already been demonstrated by NASA's SEDS experiments.