BENGALURU: Forty-seven days after it left Earth, Chandrayaan-2 lander Vikram will decide on the exact landing spot on Moon when it would be 100m above the lunar surface between 1.30am and 2.30am on Saturday. If all goes well, it'll touch down 78 seconds later.Isro had chosen a primary landing site and a secondary one, now Vikram will approach the primary landing site, which in turn has two landing zones. "Vikram will be selecting one of these landing zones at the primary site after analysing data at that moment," said an Isro scientist.Chandrayaan-2's preferred landing site is between two craters, Manzinus and Simpelius, about 350km north of Moon's south pole.At a height of 100m, Vikram will hover for a few seconds before the final descent. "Within each landing site, two zones are identified of size 500m x 500m, separated by 1.6km. The prime target will be the first zone," says an Isro paper.Isro considered that both the primary and backup site should have Sun's elevation at more than six degrees on the landing day to ensure enough illumination for the lunar craft to capture images. The lander has been taking pictures of the preferred landing sites since Tuesday."If it can land on the first zone, Vikram will, in 65 seconds, reach a height of 10m directly. In case it has to pick the second landing site, it will use 40 seconds to first descend to a height of 60m, then, drop to 10m in the next 25 seconds," the scientist explained. Once Vikram reaches 10m, it takes about 13 seconds for the touchdown.Vikram's final descent from the lunar orbit would've started from an altitude of 35km. As per Isro's plan, about 10 minutes after the descent is initiated, Vikram would have dropped to a height of 7.4km from the lunar surface. In the next 38 seconds, it will reach a height of 5km and another 89 seconds later Vikram's altitude will be 400m. Here, Vikram will hover for a few seconds to collect data before plunging to 100m in 66 seconds.A successful soft-landing would make India the fourth country after the US, Russia and China to do so. Only 37% of all Moon landing attempts have been successful.