While the United States was fighting to get a man on the Moon by the end of the 1960s, the Soviet Union was working hard to return a sample of lunar soil as part of the robotic Luna program. Some missions were successful and others weren’t, but for decades no one was really sure why. That’s changed: Last week, NASA’s Lunar Reconnaissance Orbiter photographed the remnants of two Luna missions, Luna 23 and 24, and almost 50 years later is helping solve the mysteries these missions opened.
The Luna program was conceived in 1955 by Sergei Korolev, the elusive Soviet Chief Designer responsible for the USSR’s early successes in space. He proposed building a multi-stage version of the R-7 rocket (the one that would launch Sputnik into orbit two years later) that would be powerful enough to deliver a payload to the Moon. He envisioned Soviet probes orbiting, landing on, and photographing the Moon before the Americans. The eventual goal would be for a Luna spacecraft to return a soil sample.
The sample return spacecraft consisted of a descent stage, an ascent stage, and an Earth-return capsule. The entire suite was designed to land on the surface where an instrument would gather the lunar sample and place it in the Earth-return capsule. The ascent stage would fire its main engine and send the mission’s payload back to Earth leaving the descent stage on the surface.
Success came early to the Luna program. In 1959, Luna 2 became the first spacecraft to reach the lunar surface when it crashed at a point in the North near Mare Imbrium (the Sea of Clouds). Luna 3 went into orbit and sent back the first pictures of the Moon’s far side the same year.
Luna 15 marks the Soviet Union’s intersection with Apollo; Luna 15, the third designed for a sample collection and return, was launched three days before Apollo 11. On July 20, 1969, as Neil Armstrong and Buzz Aldrin made history’s first manned lunar landing, the orbiting Luna 15 fired its retrorockets to descend towards the surface. Unfortunately, it crashed while the Apollo 11 crew was partway through their historic moonwalk.
Luna 23 met a similar fate. Launched on October 28, 1974, it malfunctioned halfway through its mission and ended up crashing on the surface in the Mare Crisium (the Sea of Crisis in the northwest on the Earth-facing side). The spacecraft stayed in contact with Earth after its hard landing, but it couldn’t get a sample. Mission scientists expected the spacecraft had tipped over as a result of its landing, but without a way to image the moon at a high resolution, they weren’t able to confirm, and the mystery endured.
It turns out they were indeed right. The whole spacecraft is still on the surface, its ascent engine never fired, and high resolution image from LRO’s cameras show the spacecraft lying on its side.
LRO also captured images of Luna 24, the mission that picked up where Luna 23 left off by landing, collecting, and returning samples from a point less than 2.5km away on 18 August 1976. After less than 24 hours, Luna 24 fired its ascent stage, and sent a 0.375 pound sample of lunar regolith to scientist on Earth.
The sample puzzled scientists — it had unexpected characteristics based on the understanding of Mare Crisium geology at the time. The new picture of the spacecraft’s landing point has shed light on why the sample differed from the observed lunar environment around it.
Images from NASA’s LRO’s Camera have solved the mystery by putting the lander in geographic and geological context. Luna 24 landed near a crater that had brought material up from ancient lava flows. The spacecraft returned a sample not from its environment, but from beneath the surface that hadn’t been exposed to space nearly as long. This accounts for the nearly 40-year-old mystery.
Luna 9 and 13 have yet to be imaged by NASA’s LRO. It’s yet to be seen if it was actually pesky Moon aliens that wrecked their mission, but with the last pair of Luna spacecraft set to be captured by NASA sometime in the near future, we’ll find out soon enough.