Luna 10

Luna 10 conducted extensive research in lunar orbit, gathering important data on the strength of the Moon's magnetic field, its radiation belts, and the nature of lunar rocks (which were found to be comparable to terrestrial basalt rocks), cosmic radiation, and micrometeoroid density. Perhaps its most important finding was the first evidence of mass concentrations (called "mascons")—areas of denser material below the lunar surface that distort lunar orbital trajectories. The craft's gamma-ray spectrometer allowed the detection of radioactive uranium, thorium, and potassium-40 on the Moon. Part of the E-6S series, Luna 10 was battery powered and had an on-orbit dry mass of 540 kg. Scientific instruments included a gamma-ray spectrometer for energies between 0.3–3 MeV (50–500 pJ), a triaxial magnetometer, a meteorite detector, instruments for solar-plasma studies, and devices for measuring infrared emissions from the Moon and radiation conditions of the lunar environment. Gravitational studies were also conducted. Luna 10 launched towards the Moon on 31 March 1966 at 10:48 GMT. After a midcourse correction on 1 April, the spacecraft entered lunar orbit on 3 April 1966 and completed its first orbit three hours later (on 4 April Moscow time).