A general name given the U. S. Series of polar-orbiting satellites beginning in 1966 with the launch of ESSA-1. The series continued with eight additional satellites in the TOS series (ESSA-1 through -9), six satellites in the ITOS series between 1970 and 1976, and evolving into the current series of TIROS- N satellites, beginning 1978. An improved version of TIROS-N was introduced in 1983, termed Advanced TIROS-N. With the launch of NOAA-K (renamed NOAA-15 after launch) in May 1998, POES moved to another new generation of spacecraft with a full complement of new and improved instruments. POES satellites are sometimes referred to as the NOAA series of satellites, based on the name (e.g., NOAA-15) given to POES satellites since 1970.