At about the same time the Apollo 11 astronauts were completing their historic first human moonwalk, Luna 15, a robotic space mission of the Soviet space programme, began its descent to the surface of the moon from lunar orbit. Tasked with the objective of gathering lunar samples and returning them to Earth, Luna 15 crashed on the lunar surface and was destroyed on impact.
Luna 15 was one among a string of failures in the Soviet space programme in its attempt to bring lunar samples back to Earth. They eventually succeeded with Luna 16, which became the first mission to retrieve samples from the moon’s surface without direct human involvement.
Two stages
The Luna 16 spacecraft consisted of two stages – an ascent stage and a descent stage. While the descent stage was mainly concerned with providing course corrections, lunar orbital insertion and the landing manoeuvre; the ascent stage was responsible for propelling the sample container back to Earth.
The descent stage, which had four legs to support the craft on the surface, acted as a launch pad for the ascent stage. The descent stage also housed fuel tanks and a landing radar, while the ascent stage held the radio equipment and the spherical sample return container.
Launched on September 12, 1970, Luna 16 travelled to the moon without incident, save for one midcourse correction. Entering orbit on September 17, it required two further orbital adjustments in the next two days to alter its altitude and inclination in preparation for descent to the moon. Luna 16 began its descent on September 20 by firing its main engine and six minutes later, it landed softly in its target area.
Drilling for samples
Less than an hour after landing, Luna 16 used an automatic drill to dig through the lunar surface. Seven minutes later, the drill reached a depth of 35 mm before hitting rock. The core sample was withdrawn and lifted to the top of the spacecraft, before the collected rocks were safely deposited in the small spherical capsule.
Having accomplished half of what it set out to do, Luna 16 now had to safely return its invaluable cargo back to Earth. A little over 25 hours after landing on the moon, the return stage’s rocket motor was fired and the spacecraft’s upper stage lifted off from the moon with its 105 g of lunar soil.
Over the next three days, the ascent stage traversed directly back to Earth, needing no midcourse corrections during its journey. Reentering the Earth’s atmosphere at a velocity of 11 km/second, the capsule then parachuted to the surface. It landed 80 km southeast of Zhezkazgan, a town in Kazakhstan, on September 24.
Completely automated
Even though Apollo 11 astronauts had retrieved lunar samples during their historic moonwalk in July 1969 and Apollo 12 astronauts had repeated the feat in November 1969, Luna 16 was special in its own right. This mission was not only the first time the Soviets had managed to collect rock and soil samples from the surface of the moon, but also the first time any nation had managed to bring back samples in a completely automated manner.
The lunar samples collected were then analysed by scientists, who found out in what way the rocks and soil were similar and different from those collected in the Apollo 11 and 12 missions. While the dark, powdery basalt material closely resembled the soil recovered by Apollo 12 from another lunar mare (large, dark, basaltic plains on our moon) site, Luna 16’s samples slightly differed from those collected by Apollo 11 in the levels of titanium and zirconium oxide.
Even though some Luna missions had failed as they either ended in crashes or failed to reach orbit, the programme as a whole was largely a great success. The programme achieved a series of firsts from the time Luna 1 managed the first lunar flyby in 1959. Luna 16 joined the list of successes by achieving the first robotic sample return.
