Early technology satellite. None reached orbit.

Typical orbit: 1041 km circular orbit, 60.4 deg inclination. Mass: 56 kg (123 lb). Associated Launch Vehicle: Scout X-4.

• 1964 October 10 - Explorer 22 - Program: Explorer. Launch Site: Vandenberg. Launch Vehicle: Scout X-4. Mass: 52 kg (114 lb). Perigee: 872 km (541 mi). Apogee: 1,053 km (654 mi). Inclination: 79.70 deg. Period: 104.30 min.

  Ionospheric and geodetic data. Spacecraft engaged in research and exploration of the upper atmosphere or outer space.

• 1965 April 29 - Explorer 27 - Program: Explorer. Launch Site: Wallops Island. Launch Vehicle: Scout X-4. Mass: 60 kg (132 lb). Perigee: 932 km (579 mi). Apogee: 1,309 km (813 mi). Inclination: 41.20 deg. Period: 107.70 min.

  Battery failed in 1968; ionospheric research and geodetic data. Spacecraft engaged in research and exploration of the upper atmosphere or outer space.

• McDowell, Jonathan, Launch Log, October 1998. Jonathan McDowell's complete on-line listing of all objects orbited since Sputnik. Accessed at: http://hea-www.harvard.edu/~jcm/space/log/launch.html.

• McDowell, Jonathan, Jonathan's Space Home Page, Harvard University, 1997-present. Jonathan McDowell's complete on-line listing of all objects orbited and over 20,000 rocket launches Accessed at: http://www.planet4589.org/jsr.html.

• NASA Report, Early Electrostatic Probe Results From Explorer Xxii, . Accessed at: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660012932_1966012932.pdf. -right click to download pdfs!

• JPL Mission and Spacecraft Library, Jet Propulsion Laboratory, 1997. Accessed at: http://msl.jpl.nasa.gov/home.html.

• Krebs, Gunter, Gunter's Space Page, University of Frankfurt, 1996. Accessed at: http://www.skyrocket.de/space.

• USAF Satellite Database, USAF Institute of Technology, 1995. Accessed at: ftp://archive.afit.af.mil/pub/space/.