Extra brake thrust may have sent Vikram lander out of control in home stretch

BENGALURU: When silence descended on the Isro mission control and millions of Indian homes minutes before Vikram was to touch down on the Moon at 1.53am on Saturday, many thought the lander had too little thrust to brake to a halt. A day later, Isro scientists are looking at whether Vikram had too much braking thrust, which spun it out of control.

"We thought one of the thrusters may have underperformed," said an Isro scientist. "But after some preliminary analysis, it looks like a thruster overperformed."

Descending from its orbit 30km from the Moon, Vikram had achieved perfect roughbraking for 10 minutes, reducing its velocity from 1,680 metres per second to 146 metres per second. Soon after the fine-braking that signalled Vikram's last 5km descent to the Moon, mission control lost contact with the lander.

Officially, Isro maintained that data was still being analysed. However, a scientist told TOI, "Vikram's legs were to be horizontal during the roughbraking and had to be rotated by 90 degrees to bring them vertical to the landing surface before fine-braking. At this point, the thrust might have been more than optimal, impacting the lander's orientation. It's like a car losing direction due to sudden braking at high speed."

When Vikram went silent, Isro mission control searched for links from Nasa's deep space network centre in Madrid and the Indian station in Mauritius, but to no avail.