Van Allen belts (in yellow) in 2013 illustration released by NASA's Goddard Space Flight Center
Wiley J. Larson and James R. Wertz (Editors), Space Mission Analysis and Design, 3rd Edition, Section 8.2, "Hardness and Survivability Requirements," 1 October 1999.Fox, Karen. “NASA's Van Allen Probes Discover a Surprise Circling Earth,"
NASA press release, 28 February 2013.
Bille and Lishock, The First Space Race (Texas A&M), 2004.