quasistationary orbit

A quasistationary orbit is an orbit that almost but not quite a geostationary orbit (GSO). In a quasistationary orbit a satellite does not hang still relative to Earth, but moves in a complex elliptical trajectory. As seen from the ground, the path of the satellite has the form of a closed intersecting loop, elongated along the horizon, and having angular dimensions of around 30° in azimuth and 5–6° in elevation. Quasistationary orbits offer a number of advantages for carrying out reconnaissance (spy) tasks, including a large monitoring area and the possibility of taking multiposition bearings on radio emitters to pinpoint their location. They were first proved out by the Canyon series and have become a characteristic feature of American SIGINT (signals intelligence) satellites. In distinction to a GSO, which has an altitude of 35,800 kilometers and an inclination of 0°, quasistationary orbits used by SIGINT satellites have a perigee (low point) of 30,000–33,000 kilometers, an apogee (high point) of 39,000–42,000 kilometers, and an inclination of 3–10°.