PBS Satellite Service or "HD01" (formerly PBS Schedule X in Eastern Time, with the west coast delay signal designated PBS-XD) is the 24-hour network feed from the PBS that provides a mixed variety of programming selected from PBS's regular network service. In the X/XD years was multicast by some PBS member stations on an over-the-air DTV subchannel along with their regular programming, or during overnight hours on their main channel to provide a second opportunity for viewers to watch or record primetime programming.
As of 2015, the PBS Satellite Service can be received unscrambled via satellite on these coordinates:
In the context of spaceflight, a satellite is an artificial object which has been intentionally placed into orbit. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as Earth's Moon.
The world's first artificial satellite, the Sputnik 1, was launched by the Soviet Union in 1957. Since then, thousands of satellites have been launched into orbit around the Earth. Some satellites, notably space stations, have been launched in parts and assembled in orbit. Artificial satellites originate from more than 40 countries and have used the satellite launching capabilities of ten nations. About a thousand satellites are currently operational, whereas thousands of unused satellites and satellite fragments orbit the Earth as space debris. A few space probes have been placed into orbit around other bodies and become artificial satellites to the Moon, Mercury, Venus, Mars, Jupiter, Saturn, Vesta, Eros, Ceres, and the Sun.
Satellites are used for a large number of purposes. Common types include military and civilian Earth observation satellites, communications satellites, navigation satellites, weather satellites, and research satellites. Space stations and human spacecraft in orbit are also satellites. Satellite orbits vary greatly, depending on the purpose of the satellite, and are classified in a number of ways. Well-known (overlapping) classes include low Earth orbit, polar orbit, and geostationary orbit.