Nilanjan
Nation’s euphoria got no bound as soon as Chandrayaan-3 successfully made a soft landing close to the moon’s South Pole. However, it was the first step of India’s lunar mission that seeks to explore more about the moon’s dark side where descending was more than simply challenging. India is the first country to have accomplished the mission.
According to the latest report, Chandrayaan-3 rover Pragyan has overcome a 100mm deep crater, its first obstacle on the lunar surface. The news came to a big relief of the ISRO control room that has kept a watchful eye on the rover since it came out of spacecraft’s belly after Chadrayaan-3’s soft landing on the moon.
Chandrayaan-3 project director P Veeramuthuvel told TOI that the success of the scientific experiments had made them confident about the possibility of expected outcomes, adding that relentless effort of ISRO colleagues, especially those working on the subsystems – sensors, propulsion, navigation-guidance-and-control and all the mainframe subsystems – and guidance from the ISRO top management and URSC director M Sankaran made the mission possible.
When talking about the rover operations, Veeramuthuvel pointed out that these were not fully autonomous and there were multiple challenges in Pragyan’s movements, adding that each of these challenges needs to be handled one at a time, with the ground team’s involvement.
Turnaround time between two consecutive movements
Veeramuthuvel explains it in more detail. Moving Pragyan between two points involves multiple steps. For planning every path, it needs to download navigation camera data to ground for a digital elevation model (DEM). The ground and the mechanism team decide which path to adopt and uplink the common path for Pragyan to follow. Each time the navigation camera generates images, the maximum DEM that can be generated, considering Pragyan’s limitations, is for five meters.
“This means every time the rover is commanded to move, it can at best cover five metres. Even there, there are challenges of obstacles, etc. We were very anxious about the first crater, but that obstacle has been overcome,” Veeramuthuvel said.
He insists that ISRO has done several rover movements. Pragyan is not a big rover. However, with limited resources, ISRO has put in state-of-the-art miniature systems. He emphasizes that there are limitations including 24z7 hours’ telecommunication and non-available telemetry, which necessitate continuous tracking of the sun and so, the turnaround time between two consecutive movements is nearly five hours.
“The Sun is not static there. Each day, there’s a 12° rotation, which needs to be accounted for, as unlike the lander which has solar panels covered on three sides, the rover has deployable solar panel, where one side is fully mounted with solar cells but on the other side, only half the space is available,” he said.
Given that the rover can communicate with only the lander, the data rate from Pragyan is also limited. ISRO control room needs to download the data to ground. It consumes a significant amount of time as the scientists have to go through the data streaming from the payloads. Therefore, each movement of Pragyan is carefully planned and ISRO is confident of excellent performance, according to Veeramuthuvel.
