Indian Space Research Organisation aims to revive lander, rover during lunar sunrise

With a new lunar dawn on the horizon, Indian Space Research Organisation (Isro) scientists are now gearing up for their ambitious attempt to revive Chandrayaan-3's Vikram lander and Pragyan rover after two weeks of "sleep" to see if it survived the frigid temperatures of the lunar night.

The "hopeful" reboot of the modules on Thursday and Friday will offer the chance for a bonus extension over and above what has already been an entirely successfully completed mission, Isro scientists said.

S Somanath, Isro chairman, said that they are hoping when the sun rises on the Shivshakti Point, where lander and rover are parked, the equipment will come back to life. The teams will be attempting to revive the instruments on September 21 and 22 — at lunar dawn. "We can only hope to see the equipment back to life on 22 September," Somanath said.

Isro officials said that before the equipment on-board Vikram and Pragyan were put to sleep — in a phased manner starting September 2 — the batteries, that are powered by sunlight, were left charged and solar panels were oriented in a way that they receive light at dawn.

If the on board instruments survive the low temperatures of lunar night – around -200°C – it can come back to life and continue collecting more data from the lunar surface for another 14 days.

In a best-case scenario, when the commands are fed into the lander and the rover to bring the systems back to life, the rover will start moving around the lunar surface again and the equipment on-board the lander will also repeat the process of collecting data.

On Thursday, when the sunlight on the landing spot is bright enough to power the instruments, teams from ISRO Telemetry, Tracking and Command Network (ISTRAC) will start the process of entering commands to revive the instruments. If the machines respond upon recharging itself, the mission will have an extended life and scientists will be able to bag more samples.

The feat might, however, not be as easy as it sounds. Nighttime temperatures on the lunar surface can drop to as low as -200°Celsius, and closer to the poles these temperature recordings go even lower, around -250°C.

While spacecrafts before Chandrayaan-3 have also successfully braved such low temperatures — for instance, China's Chang'e 4 lander and rover in 2019 revived after braving around -190°C — but these crafts were equipped with radioisotope heating units (RHU), which ensure that the temperature on the craft needed for the effective functioning of devices is maintained even as the temperature outside the craft falls.

RHUs are small devices that use the decay of plutonium-238 to provide heat to keep spacecraft components and systems warm so that the equipment can survive in the cold space environment. Neither Chandrayaan-3 lander nor the rover is equipped with these heating devices.

"If we had RHUs, we would not be hopeful, we would be confident of a revival," said a senior Isro official.

Scientists confirmed that Isro is working to develop RHUs for long interplanetary missions, which will ensure that temperatures are maintained at a certain level so that equipment can survive long durations in cold, frigid conditions. The technology demonstration of these devices is expected soon, Isro officials said.