Chennai: New challenges in soft-landing a heavier lander and a rover on the moon have forced Indian Space Research Organisation ( Isro ) to make considerable improvements to Chandrayaan-2 , delaying the launch beyond this year.

The national committee that reviewed Chandrayaan-2 in March this year felt soft-landing would be a tricky proposition unless some improvements are made to the lander.

“We decided to add another liquid engine to the lander, revisit the mission sequence and conduct more tests. We realized that the deadlines set earlier were impossible to meet,” said a senior scientist present at the review.

The Chandrayaan-2 team also decided to have more electronic packages as standby. These additions increased the weight of the spacecraft.

“We could still carry this extra weight using an upgraded version of GSLV-MII, but we decided to go in for GSLV-MIII. And once this was decided, we could build in more redundancies for a safer flight as GSLV-MIII could take much more,” said a scientist. In effect, the ground mass of Chandrayaan-2 went up from 3,250kg to 3,850kg.

The lander weight went up from 1,250kg to about 1,350, the six-wheeled rover’s weight from 20kg to 25kg. For every extra kilogram of the payload, the lift-off weight of the vehicle increases by 4kg, as more propellent is needed.

“Soft-landing is a big process,” said one of the scientists. “The orbiter (that carries the lander and the rover) will be moving at 6,000kmph around the moon. From this speed, we have to bring the lander to touch down gently on a terrain that it will be able to assess only immediately before the landing,” another scientist said.

A senior member of the Chandrayaan-2 team said the first turning point was when Russian space agency Roscosmos, which was to provide the lander, met with a failure in a joint venture with China on a mars mission.

“The failed system was similar to the lander Russia had promised us. They had to make changes which added to the weight, and we decided to make our own lander,” he said.

Before finalizing GSLV-MIII as the Chandrayaan-2 launcher, Isro had decided to ‘uprate’ GSLV-MII. “We had to uprate the cryogenic system and the liquid engine,” said the review panel member. “But then, we cannot afford to fly Chandrayaan as a test flight of the uprated GSLV-MII. Hence we have decided to use GSLV-MIII. There is a MIII launch scheduled in a couple of months. That launch will give us the confidence to go ahead with Chandrayaan-2.”

The launch, scheduled for December 2016, missed three deadlines and was last planned for October this year. Further delay of Chandrayaan-2 may help Israel, which is planning a moon mission in December, to beat India and be the fourth nation to soft-land on the lunar surface, after the US, Russia and China.

Isro is treading cautiously after two satellite mission failures in less than a year. Navigation satellite IRNSS-1H got stuck in the heat shield in August, 2017 and Gsat-6A communication satellite went out of control soon after the launch in April this year.

