TOS spacecraft marked the first operational system of US polar-orbiting meteorological satellites. TOS was a follow-on to the TIROS (Television Infrared Observation Satellite) series, and was itself followed by the ITOS (Improved TIROS) series, and later the NOAA series. TIROS spacecraft were developed by GSFC and managed by ESSA (Environmental Science Services Administration). The objective was to establish a global weather satellite system. The TOS spacecraft are also referred to as ESSA spacecraft. Spacecraft: Body mounted solar cells. Payload: TOS/ESSA spacecraft carried television cameras, APT (Automatic Picture Transmission) systems, and AVCS (Advanced Vidicon Camera System) instruments.

Typical orbit: approx. 1400 km, polar, circular. Length: 0.56 m (1.83 ft). Maximum Diameter: 1.07 m (3.51 ft). Mass: 140 kg (300 lb).

• 1966 October 2 - ESSA 3 - Program: Tiros. Launch Site: Vandenberg. Launch Complex: SLC2E. Launch Vehicle: Delta. Mass: 145 kg (319 lb). Perigee: 1,387 km (861 mi). Apogee: 1,486 km (923 mi). Inclination: 100.90 deg. Period: 114.60 min.
  Environmental Survey Satellite 3; replace ESSA 1. Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

• 1967 January 26 - ESSA 4 - Program: Tiros. Launch Site: Vandenberg. Launch Complex: SLC2E. Launch Vehicle: Delta. Mass: 132 kg (291 lb). Perigee: 1,326 km (823 mi). Apogee: 1,440 km (890 mi). Inclination: 102.00 deg. Period: 113.40 min.
  Replaced ESSA 2. Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

• 1967 April 20 - ESSA 5 - Program: Tiros. Launch Site: Vandenberg. Launch Complex: SLC2E. Launch Vehicle: Delta. Mass: 145 kg (319 lb). Perigee: 1,355 km (841 mi). Apogee: 1,422 km (883 mi). Inclination: 102.00 deg. Period: 113.50 min.
  Replaced ESSA 3. Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

• 1967 November 10 - ESSA 6 - Program: Tiros. Launch Site: Vandenberg. Launch Complex: SLC2E. Launch Vehicle: Delta. Mass: 132 kg (291 lb). Perigee: 1,409 km (875 mi). Apogee: 1,485 km (922 mi). Inclination: 102.10 deg. Period: 114.80 min.
  Returned cloud cover images. Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

• 1968 August 16 - ESSA 7 - Program: Tiros. Launch Site: Vandenberg. Launch Complex: SLC2E. Launch Vehicle: Delta. Mass: 145 kg (319 lb). Perigee: 1,431 km (889 mi). Apogee: 1,473 km (915 mi). Inclination: 101.90 deg. Period: 114.90 min.
  Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

• 1968 December 15 - ESSA 8 - Program: Tiros. Launch Site: Vandenberg. Launch Complex: SLC2E. Launch Vehicle: Delta. Mass: 132 kg (291 lb). Perigee: 1,414 km (878 mi). Apogee: 1,464 km (909 mi). Inclination: 102.00 deg. Period: 114.60 min.
  Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

• 1969 February 26 - ESSA 9 - Program: Tiros. Launch Site: Cape Canaveral. Launch Complex: LC17B. Launch Vehicle: Delta. Mass: 145 kg (319 lb). Perigee: 1,425 km (885 mi). Apogee: 1,505 km (935 mi). Inclination: 101.80 deg. Period: 115.20 min.
  Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).