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Module That Powered Historic Moon Mission Has Returned to Earth’s Orbit

The propulsion module that powered India’s spacecraft to a historic moon landing just transitioned back into Earth’s orbit, according to the country’s space agency. The move aims to test how the growing space power might one day return samples of lunar soil.

The propulsion module had more fuel left over than the Indian Space Research Organization, or ISRO, had expected. So, researchers decided to move forward with an attempt to bring the module back toward home, the agency said Monday.

And the module is now back in Earth’s orbit.

The propulsion module — a unit shaped like a large box with a solar panel and an engine strapped to its bottom — propelled the Chandrayaan-3 mission’s lunar landerduring most of its trek to the moon after the spacecraft launched in mid-July.

After reaching lunar orbit three weeks later, the lander separated from the propulsion module and achieved touchdown on August 23 — making India only the fourth country to land a vehicle on the moon’s surface. Only the United States, China and the former Soviet Union had previously accomplished such a feat.

The Vikram lander — and Pragyan, a six-wheeled rover it deployed — spent nearly two weeks carrying out all the mission’s planned science experiments before they were put to sleep for the lunar night, a two-week period when sunlight doesn’t reach the moon’s surface.

Both the lander and the rover have remained in slumber on the moon after prior attempts to awaken the vehicles failed. If the vehicles had reawakened, it would have been an added bonus for the mission, which was deemed wholly successful by India’s space agency.

Meanwhile, the propulsion module remained in lunar orbit. The component served as a relay point, pinging data back from the lander to Earth. And the module carried a single experiment: the Spectro-polarimetry of HAbitable Planet Earth, or SHAPE.

Chandrayaan bonus mission

The SHAPE experiment was designed to observe Earth from lunar orbit, capturing in near-infrared light the characteristics of our home planet that make it habitable for humans. The study was meant to give scientists a blueprint for how to search for similar characteristics — called “biosignatures” — elsewhere in the universe.

The initial plan was to operate the SHAPE experiment for about three months, while the propulsion module continued whirring through lunar orbit.

But because the rocket that launched the Chandrayaan-3 spacecraft delivered it to such a precise orbit, the propulsion module was left with more propellant than expected.

It “resulted in the availability of over 100 kg (220 pounds) of fuel in the (propulsion module, or PM) after over one month of operations in the lunar orbit,” according to the space agency. “It was decided to use the available fuel in the PM to derive additional information for future lunar missions and demonstrate the mission operation strategies for a sample return mission.”

That means the ISRO could use the information gleaned from the propulsion module’s return to map out a future moon landing mission that could return samples of lunar soil back to Earth.

Similarly, India had previously tested a way to vault the Chandrayaan-3 lander back away from the surface of the moon after landing. It amounted to a short “hop” test, sending the vehicle up a few centimeters off the ground. (The trial did not, however, attempt to get back into lunar orbit or reconnect with the propulsion module. The maneuvers were only intended to test out aspects of the vehicle’s design to inform future missions.)

The propulsion module is now orbiting about 96,000 miles (154,000 kilometers) above Earth, where it will make one lap of the planet about every 13 days.

In its statement, the space agency said the propulsion module’s path back toward Earth was mapped out to consider “collision avoidance such as preventing the PM from crashing on to the Moon’s surface or entering into the Earth’s GEO belt at 36000 km and orbits below that.”

GEO, or geostationary orbit, is an area of space populated by large, expensive satellites that provide television and other communications services to people on Earth.