Radiation decay data satellite. May also have been a cover for some NRL ELINT satellites.

Typical orbit: 480 km x 2416 km at 70.3 to 81.4 degrees inclinati.

• 1961 June 29 - Injun 1 - Launch Site: Cape Canaveral. Launch Complex: LC17B. Launch Vehicle: Delta. Mass: 25 kg (55 lb). Perigee: 869 km (539 mi). Apogee: 992 km (616 mi). Inclination: 66.80 deg. Period: 103.60 min.
  Dual launch; failed to separate from Solrad 3; still returned radiation data. Space craft engaged in investigation of spaceflight techniques and technology (US Cat A).

• 1962 January 24 - Injun 2 - Launch Site: Cape Canaveral. Launch Complex: LC17B. Launch Vehicle: Delta. FAILURE: Failure.
  

• 1962 December 13 - Injun 3 - Launch Site: Vandenberg. Launch Complex: SLC2E. Launch Vehicle: Delta. Mass: 52 kg (114 lb). Perigee: 240 km (140 mi). Apogee: 2,406 km (1,495 mi). Inclination: 70.30 deg. Period: 112.10 min.
  Radiation decay data. Space craft engaged in investigation of spaceflight techniques and technology (US Cat A).

• 1964 November 21 - Explorer 25 - Program: Explorer. Launch Site: Vandenberg. Launch Complex: SLC5. Launch Vehicle: Scout. Mass: 40 kg (88 lb). Perigee: 526 km (326 mi). Apogee: 2,319 km (1,440 mi). Inclination: 81.30 deg. Period: 114.30 min.
  Radiation data. Spacecraft engaged in research and exploration of the upper atmosphere or outer space (US Cat B).

• 1968 August 8 - Explorer 40 - Program: Explorer. Launch Site: Vandenberg. Launch Complex: SLC5. Launch Vehicle: Scout. Mass: 70 kg (154 lb). Perigee: 679 km (421 mi). Apogee: 2,489 km (1,546 mi). Inclination: 80.70 deg. Period: 117.80 min.
  Injun Explorer; radiation data. Spacecraft engaged in research and exploration of the upper atmosphere or outer space (US Cat B).