|Mission type||Lunar lander|
|Mission duration||12 days (launch to last contact)|
|Launch mass||1,422 kilograms (3,135 lb)|
|Start of mission|
|Launch date||April 2, 1963, 08:04:00UTC|
|Launch site||Baikonur 1/5|
|End of mission|
|Last contact||April 14, 1963|
|Semi-major axis||394,128 kilometres (244,900 mi)|
|Periapsis altitude||199 kilometres (124 mi)|
|Apoapsis altitude||694,000 kilometres (431,000 mi)|
|Epoch||April 2, 1963|
|Lunar flyby (failed landing)|
|Closest approach||April 6, 1963, 1:24 UT|
|Distance||8,336.2 kilometres (5,179.9 mi)|
Luna 4, or E-6 No.4 (Ye-6 series), sometimes known in the West as Sputnik 26, was a Soviet spacecraft launched as part of the Luna program to attempt the first soft landing on the Moon. Following a successful launch, the spacecraft failed to perform a course correction and as a result it missed the Moon, remaining instead in Earth orbit.
Luna 4 was launched by a Molniya-L carrier rocket at 08:16:37 UTC on April 2, 1963. Launch occurred from Site 1/5 at the Baikonur Cosmodrome. After reaching an initial parking orbit of 167 by 182 kilometres (104 by 113 mi), the rocket's upper stage restarted to place Luna 4 onto a translunar trajectory.
The spacecraft did not perform a required midcourse correction manoeuvre, which resulted in it missing the Moon by 8,336.2 kilometres (5,179.9 mi) at 1:24 UT on April 5, 1963. It then entered a barycentric 90,000 × 700,000 km Earth orbit. 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.
The purpose of this experiment was to obtain information on the characteristics of the lunar surface. These characteristics included the amount of cratering, structure and size of craters, the amount, distribution, and sizes of ejecta, mechanical properties of the surface such as bearing strength, cohesiveness, compaction, etc. Determination and recognition of processes operating to produce the lunar surface features also were among the objectives of this photographic experiment.