Kennelly–Heaviside layer Kennelly–Heaviside layer The Kennelly–Heaviside layer, named after Arthur E. Kennelly and Oliver Heaviside, also known as the E region or simply the Heaviside layer, is a layer of ionised gas occurring between roughly 90–150 km (56–93 mi) above the ground — one of several layers in the Earth's ionosphere. It reflects medium-frequency radio waves. Because of this reflective layer, radio waves radiated into the sky can return to Earth beyond the horizon. This "skywave" or "skip" propagation technique has been used since the 1920s for radio communication at long distances, up to transcontinental distances. Propagation is affected by time of
Atmospheric entry often travelling quite fast relative to the Earth simply because their own orbital path is different from that of the Earth before they encounter Earth's gravity well. Most controlled objects enter at hypersonic speeds due to their suborbital (e.g., intercontinental ballistic missile reentry vehicles), orbital (e.g., the Soyuz), or unbounded (e.g., meteors) trajectories. Various advanced technologies have been developed to enable atmospheric reentry and flight at extreme velocities. An alternative low velocity method of controlled atmospheric entry is buoyancy which is suitable for planetary entry where thick atmospheres, strong gravity, or both factors complicate high-velocity hyperbolic entry, such as the