Forty years ago today — January 31, 1972 — the HEOS (Highly Elliptical Orbit Satellite) A-2 launched from the Western Space and Missile Center at Vandenberg AFB.
HEOS A-2 was built by the European Space Research Organization, the precursor to today’s European Space Agency, to study “interplanetary space and the high-latitude magnetosphere.”
HEOS 2 provided new data on the sources and acceleration mechanisms of particles found in the trapped radiation belts and in the polar precipitation regions and auroral zones. It also monitored solar activity and cosmic radiation.
According to this Wikipedia page on 1972 spaceflight, this was also the last launch of the Thor-Delta rocket configuration, which itself was part of the family of Delta rockets that are still launching satellites today.
(An early Thor-Delta, from 1961. USAF image from Wikimedia Commons.)
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