Confident of the lander and rover coming back to life when night ends: ISRO Scientist

After sending in scientific data every day for the past week, the Chandrayaan-3 lander and rover have spent roughly half of their intended time on the lunar surface. The two are designed to last one lunar day i.e 14 days on earth. Although, there are mechanisms to spring them back to life when the sun rises again after the long night.

M Srikanth, Chandrayaan-3 mission operations director, in an interview with TOI said that the performance of Vikram and Pragyan so far and the overall health of all systems have increased hopes of the two coming back to life after the night (14 Earth days) passes.

“Our priority is to ensure that the project objective of getting scientific data for one lunar day is achieved. We’re focusing on rover mobility and payload operations. This will continue for another seven days after which they (systems) will go to sleep when the Sun sets. So far, all margins are looking good and we are confident of the lander and rover coming back to life when night ends. If that happens, that will be a bonus and in case that cannot be achieved, the mission is still complete,” Srikanth said.


Why systems sleep at night?
Both Vikram and Pragyan are solar-powered and are designed only to operate during sunlit periods, when the temperatures (in the polar area) are upwards of 54° Celsius.

When the Sun sets, the temperatures could go as low as -203° Celsius and the systems on the lander and rover do not get any power to stay on. “They should turn on once the sun returns provided they have survived the cold. This is especially true with all the electronic components in the lander and rover. Our ground tests show that this is possible,” Isro chairman Somanath had said earlier.

Battery power & eclipse
Srikanth further explained: “One night is equivalent to 14 Earth days. Batteries with such high capacity cannot be included. The capacity of the lander battery is 62.5 Ampere-hour while the rover battery is 10 Ampere-hour, which is enough to meet the mission’s primary objective of doing science for one lunar day.”

He said that the batteries have sufficient capacity to tackle smalle eclipses. This was done in anticipation of a situation where the systems need to go without power. “Sometimes, there are short periods of eclipse, our batteries can typically handle those. However, they are not powerful enough to keep the systems warm throughout a lunar night,” Srikanth said.

Rover positioning for dawn
Assuming that the electronics and other systems on Vikram and Pragyan survive the lunar night, the procedure to spring them back to life is autonomous.

“When sunlight comes back, there’s an autonomous logic pre-loaded on both the lander and rover. Once there is sufficient solar regeneration, they are expected to come back to life provided that they have survived the night,” Srikanth said.

While the lander, which has large solar panels on three sides, can do it more easily, Isro will need to carry out a manoeuvre before the night begins to give the rover a chance of coming back.

“The rover only has a deployable solar panel. Therefore, we will have to do calculations to see where the Sun is likely to rise after 14 days. Once we have this, we will have to position the rover in a place where it can get the best sunlight at dawn to give it the best chance to restart. This positioning has to be done before the current lunar day ends,” Srikanth said.

(With inputs from TOI)