India’s first lunar lander about to try for risky touchdown

In a few hours, an Indian spacecraft will attempt something no other mission has achieved before: making a soft, controlled landing in the moon’s south polar region. If all goes well, the robotic lander Vikram—part of the Indian Space Research Organization’s Chandrayaan-2 mission—will touch down on the moon on Friday by 21:25 BST, marking a milestone in the exploration of our closest celestial neighbour.

It’s a risky endeavour: During its 15-minute powered descent, Vikram will have to autonomously scan for obstacles and then take steps to avoid them. If Vikram touches down on a site with more than a 12-degree slope or catches a leg on a boulder, the lander could risk toppling over, bringing the surface portion of the mission to a swift end.

“Even though we got a successful lunar orbital insertion, landing is the terrifying moment,” Kailasavadivoo Sivan, ISRO’s chairman, said in an August press conference. “The powered descent ... that is a first to us.”

In addition to setting a global first, a successful landing would make India just the fourth country to touch down anywhere on the lunar surface, and only the third nation to operate a robotic rover there.

NASA’s Lunar Reconnaissance Orbiter will monitor the landing’s after-effects, such as whether gases from Vikram’s exhaust plume build up in the moon’s tenuous exosphere, notes Dana Hurley, a planetary scientist at Johns Hopkins University’s Applied Physics Laboratory. Until the landing attempt, all she and the world’s other lunar scientists can do is hold their breath—because they know all too well what can go wrong.

“We’re always excited and nervous, because we know it’s very hard to do,” Hurley says. “It’s a tough business.”

Polar placement

Since its launch on July 22, Chandrayaan-2 has spent the last several weeks inching its way to the moon, ultimately entering lunar orbit on August 20. On September 2, Vikram separated from the mission’s orbiter, and the newly freed lander began a series of braking manouvers to lower its orbit and ready itself for landing.

If things proceed without a hitch, Vikram and Pragyaan—the small solar-powered rover it’s carrying—will set down on the moon at a latitude of about 70 degrees South, on a highland between the craters Manzinus C and Simpelius N.

While not technically at the lunar south pole, Chandrayaan-2’s target site is by far the southernmost ever selected for a soft lunar landing. The next southernmost lander, China’s Chang’e-4, sits at a southern latitude of about 45.5 degrees on the moon’s far side, about 1,200 miles from Vikram’s targeted site.

This landing site is “somewhere new that we haven’t seen before, so that makes it another area for ground-truthing remote sensing data,” says Clive Neal, a lunar geologist at the University of Notre Dame. “It’s going to certainly enhance our knowledge of what the moon is like in those areas, so it’s going to be another very good place for science and exploration.”

Chandrayaan-2’s scientific goal is to study the south polar region’s distribution of water ice and other so-called volatile compounds. The results could have implications for future human exploration. Previous lunar missions, including India’s Chandrayaan-1 orbiter, found evidence that soils at the lunar poles contain water ice, which could be an invaluable resource to future lunar astronauts. Lunar ice also archives the history of the early solar system, since water arrived at the moon in one of several ways, including ancient comet impacts. 

“The entire globe is waiting for our data,” Sivan said. “This will be giving input for a future program [that] is concerning humanity in a major way.”

All eyes upward

But landing at such a high latitude is no small feat. During the crewed Apollo missions, NASA designers didn’t attempt any landings near the lunar poles out of safety concerns. If the Apollo spacecraft’s rocket engine had failed during an attempt to get into lunar orbit, NASA wanted to make sure that astronauts could loop around the moon and get back to Earth using gravity alone. This “free return” constraint limited Apollo landing sites to a narrow band north and south of the moon’s equator.

Robots don’t have the same worries about returning to Earth, and from orbit, the moon’s south pole is among the best-studied patches of lunar terrain. Three previous missions, including India’s Chandrayaan-1 orbiter, fired small impactors into the region’s surface to kick up debris clouds that orbiters overhead could analyse.

Even so, no soft landings south of Chang’e-4 have yet been attempted, crewed or uncrewed—and as recent missions underscore, a lot can go wrong on the way to the surface. In April, the Israeli nonprofit SpaceIL’s Beresheet spacecraft crashed during the final moments of its lunar landing attempt. Had Beresheet pulled it off, it would have become the first privately funded spacecraft to land on the moon in a controlled manner.

In August, Sivan said that ISRO had learned lessons from Beresheet and other lunar landing attempts, noting that many other spacecraft have tried, and failed, to make it onto the moon in one piece. “One good thing is, we are learning from their failures,” he said.

Whatever happens, Neal is optimistic about the future of lunar exploration: “It’s exciting to see nations that weren’t involved in the space race of the ‘60s going to the moon,” he says. “It shows that we’re trying to get off this planet and explore—and it’s not just the United States or Russia. It’s other countries that are doing it, too.”