India's Chandrayaan-3 moon rover swerves to avoid crater

The six-wheeled Pragyan rover had to change course to avoid a 4-metre-wide crater on the surface of the moon, as the Vikram lander has returned temperature readings from the lunar surface

India’s moon rover has successfully steered around a small crater and carried on exploring uncharted territory near the south pole, while its mothership lander has transmitted its first scientific data, as the Chandrayaan-3 mission approaches its halfway point.

Four hours after the Indian Space Research Organisation (ISRO) spacecraft landed on 23 August, and once the sun had risen on the landing site, the six-wheeled Pragyan rover – which weighs just 26 kilograms – rolled off the Vikram lander and onto the lunar surface.

The rover sat near the lander while ISRO engineers carried out tests and waited for its solar panel to begin producing power, before it set off across the surface. On 27 August, Pragyan came across a 4-metre-wide crater, requiring a change in course. The rover is now “safely heading on a new path”, ISRO tweeted on 28 August.

The Chandrayaan-3 mission has also provided its first useful scientific data, with a device on the lander called ChaSTE (Chandra’s Surface Thermophysical Experiment) sampling the temperature of the moon dust below the surface. At a depth of 20 millimetres, the temperature was around 40°C (104°F), but this dropped off rapidly because the dust is a poor thermal conductor, with the temperature falling to -10°C (14°F) at a depth of 80 millimetres.

This means there could be liquid or frozen water just beneath the surface, with huge implications for crewed missions, as water can be drunk by astronauts or used to create breathable oxygen and rocket fuel.

John Bridges at the University of Leicester, UK, says that due to the low pressure on the moon it would be unlikely to find liquid water near to the surface – even in areas where the temperature was above freezing point so water would not be trapped in ice – because it would boil away, although at lower depths the pressure could rise enough to allow liquid water. But he says that it’s too early to interpret readings from Chandrayaan-3.

“But it’s fantastic they’re getting data,” says Bridges. “You can’t help comparing it to certain other space agencies; engineers are just getting on now and doing it. They’re sort of overtaking Russia.”

A significant portion of the Chandrayaan-3 mission’s official lifespan has already passed: both the lander and rover are expected to operate for one lunar day (equivalent to 14 Earth days), which began on 23 August. This is limited by sunset cutting their ability to harvest energy from solar panels, but also by the freezing temperatures that the equipment will have to endure overnight, dropping as low as –238°C.

ISRO didn’t respond to a request for comment, but mission operations director M Srikanth told the Times of India that engineers are currently “confident” that the rover and lander will revive after the coming lunar night.

“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,” said Srikanth. “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.”

If the hardware isn’t damaged by the cold, both the rover and lander are designed to harvest solar power when available, boot up and resume transmission with Earth. The rover will be parked in a position prior to sunset that will give it the best chance of achieving this when the sun rises again, said Srikanth.

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