S-45 (satellite)

S-45 was an American satellite, which was lost in a launch failure in 1961. The satellite was intended to operate in a highly elliptical orbit, from which it was to have provided data on the shape of the ionosphere, and on the Earth's magnetic field. It was part of the Explorer programme, and would have been designated Explorer 10 had it reached orbit. A second identical satellite, S-45A, also failed to achieve orbit when it was launched.

S-45 was launched aboard a Juno II rocket, serial number AM-19F. The launch took place from Launch Complex 26B at the Cape Canaveral Air Force Station at 00:13:16 UTC on 25 February 1961. The rocket malfunctioned after the second stage separated, and contact with the payload was lost. The third and fourth stages subsequently failed to ignite, resulting in the satellite failing to achieve orbit.