Luna 4

Luna 4 (E-6 series) was the USSR's first successful spacecraft of their "second generation" Luna program. The spacecraft, rather than being sent on a straight trajectory toward the Moon, was placed first in a low Earth orbit (167 to 182 km altitude) and then the rocket stage reignited to send it on a curving path towards the Moon.

Luna 4, the second attempt of this program, achieved the desired trajectory but a failure to make a required midcourse correction resulted in it missing the Moon by 8336.2 km at 13:25 UT on April 5, 1963. It then entered a barycentric 90,000 × 700,000 km Earth orbit. The intended mission of the probe is not known, it was speculated the probe was designed to land on the Moon with an instrument package based on the trajectory and on the later attempted landings of the Luna 5 and Luna 6 spacecraft and successful landing of Luna 9. (A lecture program entitled "Hitting the Moon" was scheduled to be broadcast on Radio Moscow at 7:45 p.m. the evening of April 5 but was cancelled.) The spacecraft transmitted at 183.6 MHz at least until April 6.