March 11, 2017
—For a space program that’s made impressive strides in recent years, the early death of Chandrayaan-1 likely came as a disappointment. The Indian Space Research Organization (ISRO) expected this lunar orbiter – the country’s first – to last for two years when it launched in 2008. But on Aug. 29, 2009, just 312 days into its mission, contact with the probe was lost.

Even so, scientists could console themselves with the knowledge that they had completed 95 percent of the mission’s primary science goals, according to The Indian Express. And on Thursday, they got a second piece of good news: NASA researchers have found the probe continuing its silent orbit around the moon’s poles.

“Chandrayaan-1 was our first interplanetary mission and I am delighted that it has been found,” former ISRO chair Krishnaswamy Kasturirangan told The Times of India.

The Chandrayaan-sighting isn’t just good news for India. In pinpointing this spacecraft, NASA honed a technique for tracking errant spacecraft that’s likely to see action again soon.

“Finding derelict spacecraft and space debris in Earth’s orbit can be a technological challenge,” NASA’s Jet Propulsion Laboratory explained in a press release. That challenge grows as the size of the object in question shrinks. In 2014, space policy expert Brian Weeden warned Congress that “CubeSats” – inexpensive satellites that can measure as small as 11 centimeters on a side – posed a threat to other spacecraft.

“Their small size … makes them difficult to track with conventional radars and telescopes,” he explained, keeping ground controllers from planning evasive maneuvers.

Chandrayaan 1 measured a relatively bulky 1.5 cubic meters. But it had ventured far beyond the low Earth orbit where most Cubesats fly; the moon orbits Earth at a distance of nearly 239,000 miles.

“Detecting these objects in orbit around Earth’s moon is even more difficult,” NASA explains. In addition to the greater distance, the gravitational tug of mountains and other surface features could easily shift an orbiter’s path, and “Optical telescopes are unable to search for small objects hidden in the bright glare of the moon.”

But NASA doesn’t just rely on optical telescopes. It also has the Deep Space Network (DSN), a system of three high-powered radio antennae, to keep in touch with its far-flung space probes.

To search for Chandrayaan 1, JPL used a DSN antenna in California, along with radio telescopes in West Virginia and Puerto Rico. They pointed their super-sized radar ears at a region 100 miles above the Moon’s north pole, which the space probe had passed over every two hours and eight minutes during its mission.

Twice within a four-hour span, the researchers picked up “something that had a radar signature of a small spacecraft:” India’s long-lost lunar orbiter.

“It turns out that we needed to shift the location of Chandrayaan-1 by about 180 degrees, or half a cycle from the old orbital estimates from 2009,” explained Ryan Park, the manager of JPL’s Solar System Dynamics group. “But otherwise, Chandrayaan-1’s orbit still had the shape and alignment that we expected.”

Expect to see more ventures like these in coming decades, as deep space gets more crowded and more cosmopolitan. According to the Planetary Society, there are currently four active spacecraft – two American and two Chinese – in orbit around the moon. Both countries aim to send humans there in coming decades, and India, Russia, and China are all planning to launch more unmanned missions in coming years.

Protecting these spacecraft from each other and their predecessors will require a high-powered tracking system, and NASA says that its “interplanetary radar” is up to the task. “Ground-based radars could possibly play a part in future robotic and human missions to the moon, both for a collisional hazard assessment tool and as a safety mechanism for spacecraft that encounter navigation or communication issues,” JPL predicts.

And while finding Chandrayaan-1 isn’t the same as reviving it, NASA’s earned the respect and gratitude of India’s space scientists.

“To be declared lost and then found after eight years is a great accomplishment,” Dr. Kasturirangan said.