Explorer 21

<p>Explorer 21, also called IMP-B, IMP-2 and Interplanetary Monitoring Platform-2, was a <a href="/facts/NASA/TIMCV0yV">NASA</a> satellite launched as part of <a href="/facts/Explorer_program/UAWJXqxP">Explorer program</a>. Explorer 21 was launched on 4 October 1964, at 03:45:00 <a href="/facts/Greenwich_Mean_Time/JpSIdWsn">GMT</a> from <a href="/facts/Cape_Canaveral_Space_Force_Station/dwJ9MCPH">Cape Canaveral</a> (CCAFS), <a href="/facts/Florida/cF245A3Q">Florida</a>, with a <a href="/facts/Delta_(rocket_family)/gQH4EUYB">Thor-Delta C</a> <a href="/facts/Launch_vehicle/g1GCGFJB">launch vehicle</a>. Explorer 21 was the second satellite of the <a href="/facts/Interplanetary_Monitoring_Platform/j1UkG4XX">Interplanetary Monitoring Platform</a>, and used the same general design as its predecessor, <a href="/facts/Explorer_18/ASoPAR2Y">Explorer 18</a> (IMP-A), launched the previous year, in November 1963. The following <a href="/facts/Explorer_28/BlAwqMQK">Explorer 28</a> (IMP-C), launched in May 1965, also used a similar design.
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Explorer 21 open-in-new

Explorer 21