BENGALURU: Isro on Monday said that on August 27, Chandrayaan-3 rover Pragyan came across a 4-metre diameter crater positioned 3 metres ahead of its location, causing it to change its path.

“The Rover was commanded to retrace the path.

It’s now safely heading on a new path,” Isro said.

This is the second crater Pragyan has encountered — it has successfully negotiated a small crater with a depth of approximately 100-mm earlier, as first reported by TOI in its August 28 edition.One senior scientist said: “The crater that was first negotiated was a small one.

This is a much bigger crater and a decision was made to avoid it and choose a safe path.”Chandrayaan-3 Rover Pragyan Successfully Crosses First Lunar Obstacle- A 100-mm deep CRATER!As reported by TOI earlier, rover operations on the Moon are semi-autonomous and ground stations need to uplink commands for its mobility.

For every path planning, the rover’s onboard navigation camera data is downloaded to ground for generation of a digital elevation model (DEM), then the ground and mechanisms teams will decide which path to take and uplink the command for the rover to follow.

On August 27 too, a similar operation was carried out to ensure that the rover avoids the new crater.How does rover moveWatch: Chandrayaan-3 Rover Pragyan crosses massive 4-meter diameter crater positioned just 3m aheadPointing out that the rover operations are not fully autonomous and require commands to be sent from Earth, Chandrayaan-3 P Veeramuthuvel told TOIi movement of Pragyan is riddled with multiple challenges, each of which need to be overcome every time the rover moves.“Moving the rover from point A to B involves many steps.

For every path planning, onboard navigation camera data must be downloaded to ground for generation of a digital elevation model (DEM), then the ground and mechanisms team will decide which path to take and uplink the command for the rover to follow,” he explained.

‘5m Eyesight’Stating that the rover simply cannot rove indefinitely, he said just as human eyes can only see up to a certain distance, there are limitations on the rover too.

“The maximum DEM that can be generated is only for 5 metres each time the navigation camera sends images, which means every time the rover is commanded to move, it can at best cover 5 metres.

Even there, there are challenges of obstacles etc.

A small crater has also been crossed, its depth is approximately 100mm.

We were very anxious but that obstacle has been overcome,” Veeramuthuvel said.

5-hr turnaround timeIsro has already done multiple rover movements as of Sunday.

“If you see, it is not like a big rover.

Within the limited resources, we’ve put in place miniature systems that are state-of-the-art.

But there are limitations such as non-availability of telemetry and telecommunications 24/7, the need to track the sun continuously and so, the turnaround time between each movement operation is around five hours,” he said.He added that the turnaround time between one rover mobility and another is around 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 explained.B-20 Summit: PM Modi says Chandrayaan-3's success marks start of India's festive seasonGiven that the rover is packed with telemetry, telecommand, battery, NGC, data handling storage, etc.

power is crucial.

“The data rate is also limited from the rover given that it can only communicate with the lander from where we need to download to ground.

This also consumes time as we need to also look at the science data coming in from the payloads.

So, each movement of the rover is very carefully planned and we are confident of good work being done there,” Veeramuthuvel said.WatchISRO shares Chandrayaan-3 latest images: Pragyan rover navigates Moon's treacherous terrain, avoiding massive crater