This week in rocket history: the first successful robotic sample return from the Moon, Luna 16. But first, some background.
The Soviet Union made several attempts starting in 1969 to return samples from the Moon with robotic spacecraft as part of their wider Luna program, which included flybys, impactors, and lunar rovers. Most of the first five attempts at sample return failed and were either not acknowledged by the Soviets or given really generic code names like “Kosmos 300” to hide their true purpose. However, one of them, Luna 15, almost made it.
Luna 15 was the second attempt by the Soviets to do a sample return, and it launched on July 13, 1969, and successfully burned for the Moon. It was in lunar orbit at the same time as the crewed Apollo 11 mission and even attempted to land the day after Neil and Buzz. Unfortunately, it crashed on the surface of the Moon some 553 kilometers (that’s 344 miles) northwest of where Apollo 11 landed. That’s a little more than the distance between Houston and New Orleans in the U.S.
The next attempt, Luna 16, was the sixth attempt by the Soviets to conduct a fully autonomous sample return mission from the moon.
Luna 16 was launched on a Proton K- Blok D rocket from Baikonur on September 12, 1970. The spacecraft weighed a massive 5,750 kilograms at launch. Most of that mass was propellant for its lunar descent stage.
Five days after launch, Luna 16 entered lunar orbit to study lunar gravity and the terrain around the landing site. This extra step was necessary to prevent another failure — Luna 15 had crashed into the side of a mountain that the Soviets didn’t even know about.
Lunar descent was initiated on September 20. The entire landing sequence took six minutes and was conducted using two different sets of engines: the main engine for the majority of the landing sequence and a different set of easier-to-control lower thrust landing engines for the final twenty meters. Luna 16 landed successfully at 05:18 UTC in the Sea of Fertility. This was the first landing on the Moon in the dark.
Only one hour after landing, the spacecraft set to work drilling and collecting its sample. The drill managed to go 35 centimeters into the lunar surface before hitting a rock. The collected regolith was transferred into the return capsule, and the upper stage of the lander blasted off of the Moon’s surface at 07:43 UTC on September 21, after spending nearly 27 hours on the surface.
The return trajectory was very simple: a direct burn back to the Earth’s atmosphere. The return capsule landed back in Kazakhstan at 03:26 UTC on September 24. During reentry, the capsule was subjected to a maximum of 350 Gs of force, or about 175 times more than a shuttle astronaut experienced.
With the successful return of the samples to Earth, planetary scientists were able to get to work.
Scientific analysis of the Luna 16 regolith samples demonstrated that these soils were different from many of the other samples thus far collected on the Moon and suggested a far more complicated geologic history for our only natural satellite. Although the rocks collected were basaltic, which is a common volcanic rock type on both the Earth and the Moon, these rocks contained iron-rich pyroxene. The higher iron content showed that these rocks originated from a different volcanic process than the Apollo samples that had been collected at that time.
In fact, high iron content is often an indication of longer-term volcanic processes than had been previously known to have happened on the Moon. The volcanic rocks in the regolith were also ancient, with radioisotope ages of around 3.4 billion years. For reference, the first bacterial life is thought to have originated on the Earth around that time. This kind of iron-rich basalt shows that volcanic systems on the Moon lasted for long periods of time, rather than short melting and eruption events as had been previously thought.
So there you have it: the Soviets didn’t crash their spacecraft into a mountain and brought back evidence of ancient lunar volcanism.
PDF: Luna 16 Core (LPI)
Precambrian Time (National Geographic)