The official wait for reviving Vikram gets over on Friday, when the lunar day (14 Earth days) ends. (File imag... Read More

CHENNAI: While the rest of India waited two weeks for Chandrayaan-2 lander Vikram to ‘wake up’, top Isro scientists knew that the lunar craft had died in the crash in the early hours of September 7. The failure analysis team is inclined to believe that an error in the automatic landing programme (ALP) caused the accident.

Isro insiders told TOI that the 1,471kg Vikram, with the 27kg rover Pragyan in its belly, had crashed on the lunar surface at more than 200kmph, and that the onboard systems are unlikely to have survived the impact. Scientist who saw an image of Vikram after the crash-landing said the lander was either upturned or tilted, but not damaged beyond recognition.

“What I saw appeared like a shadow of Vikram,” said a scientist who analysed the image. “It was definitely not on its legs. I could see at least two of its four legs protruding. It was either upturned or tilted.”

Another scientist privy to the failure analysis said Vikram must have spun out of control sometime during the final 10km descent, and lost contact with the mission control when it was about 330m above the lunar surface (not 2.1km as Isro had earlier said). “When it was upside down, the thrusters which were supposed to act as brakes would’ve worked as accelerators and hit the lunar surface at more than 200kmph, maybe faster,” he said.

Another Isro source said even at that altitude, Vikram could’ve escaped without much damage had it been upright and the thrusters brought down the speed to 10m/s (36kmph). “Had it crashed on its legs, the ‘shoes’ would’ve acted as a shock absorber,” he said. “But since there has been no signal from Vikram, the onboard computer and other systems must have been damaged.”

Two scientists said there could have been an error in the landing program written by a team at the UR Rao Satellite Centre, Bengaluru. “Teams are going through the program. We have to see if it was properly reviewed before execution,” said a scientist who did not want to be named. The software program was to guide the various systems for altitude and velocity control throughout Vikram’s 15-minute descent from Moon ’s 30km orbit to the surface to ensure a soft landing.

The official wait for reviving Vikram gets over on Friday, when the lunar day (14 Earth days) ends. The lander and the rover were designed to work for these 14 Earth days, after which the systems would anyway have shut down during the long, frigid lunar night when temperature dips to minus 183 degrees Celsius.

Soft-landing has remained a challenge for even pioneers in lunar exploration, including the US, Russia and China, as landers, often asymmetric with shifting centres of gravity, had to be manoeuvred from great speeds to near-zero velocity to touch down on the lunar surface upright.

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