PBS Satellite Service (also known as the PBS National Program Service; formerly known as PBS Schedule X in Eastern Time, with the West Coast delay signal designated PBS-XP) are feeds relayed from PBS by satellite. The service was launched in September 1978. The service provides a mixed variety of programming selected from PBS's regular network services. In the X/XP years a satellite feed was multicast by some PBS member stations on an over-the-air DTV sub-channel 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. PBS currently utilizes two transponders on the AMC-21 satellite. Transponder 24 is a MCPC (multiple channel per carrier) which currently has seven channels upli