Greicius, Tony (January 30, 2008). "Explorer 1 Mission Overview". Explorer 1: America's first spacecraft. Washington: NASA. Archived from the original on April 19, 2012. Retrieved May 11, 2012.
nssdc.gsfc.nasa.gov
Grayzeck, Dr. Ed (April 20, 2012). "Vanguard 1". National Space Science Data Center. Washington: NASA. Retrieved May 11, 2012.
Greicius, Tony (January 30, 2008). "Explorer 1 Mission Overview". Explorer 1: America's first spacecraft. Washington: NASA. Archived from the original on April 19, 2012. Retrieved May 11, 2012.