The Soviet Union launches Sputnik 3.

On May 15, 1958, the USSR launched its Third Artificial Satellite. While two previous Soviet orbiters were propelled into space by mostly political considerations, Sputnik-3, as it became known in the West, was designed to be a true scientific laboratory. According to original plans, it was supposed to be the first Soviet satellite, but, as it transpired decades later, it became the fourth, after its sibling crashed in a botched launch less than three weeks earlier.

A 8A91 rocket No. B1-1 with the second copy of Object D lifted off on the morning of May 15, 1958. This time, the ride to orbit went without a hitch. (473) A total of four objects were detected by Western radars after the launch: the satellite itself, the core stage of the R-7 rocket and two halves of a payload fairing, while the front tip of the fairing was probably too small to be registered.

On May 29, a press-release dedicated to the mission revealed general dimensions of the satellite and boasted that the third Soviet spacecraft was 2.5 times heavier than the second satellite and 16 times heavier than the first. (199)

As it transpired decades later, most systems onboard the third satellite functioned for more than two weeks, even though its data recorder failed earlier. The onboard system for orbit tracking was misbehaving in the first days of the mission.