Landing & Rover Deployment

BENGALURU: In his July 28 address to the nation, Prime Minister Narendra Modi had said that Chandrayaan-2 , launched on July 22, has taught India two lessons: Faith and fearlessness. Forty-one days have since passed, and, scientists at Isro’s mission operations complex here in Peenya are clinging on to faith on systems they built, while the world sits in anticipation of a successful Moon landing .Vikram, Chandrayaan-2's lander, with rover Pragyan inside it, is expected to make a touchdown on the lunar surface between 1.30am and 2.30am Saturday (September 7), after the powered descent from its current orbit, a process Isro chairman K Sivan describes as “15 minutes of terror.”If Vikram lands successfully, India will be the fourth country after US, Russia and China to have achieved such a feat, and, as Isro had claimed, the first ever to so to Moon's south pole. That India did in its first attempt will make it more special, given that only 37% of all Moon landing attempts have been successful.“Final preparations are on, and we are confident of a controlled, soft landing,” Sivan told TOI on Wednesday.As per Isro’s original plan, Vikram had to be in a 30kmX100km orbit before the final descent. However, after the last de-orbit manoeuvre early on Wednesday (September 4), it is in a of 35kmX101km orbit which, Isro said was the “required orbit for Vikram to commence its descent.”Vikram, which was sitting on top of the oribter separated on September 2. The next day, Isro carried out its first de-orbit manoeuvre, while also performing another operation to bring down the perigee (closest point to Moon) of the orbiter to 96km.Before these operations, Isro had performed a series of manoeuvres around Earth between July 22 and August 13, and, the trans-lunar insertion (TLI) on August 14 put the the spacecraft in a straight path towards Moon.On August 20, Chandrayaan-2 entered Moon’s orbit, and between August 21 and September 1, a series of lunar-bound manoeuvres decreased its orbit.The mission, cleared by former prime minister Manmohan Singh on September 18, 2008, was initially planned to be a joint venture with Russia, whose space agency Roscosmos was to provide the lander. However, that deal fell through and Isro decided to go solo in 2012.Post midnight, Vikram will begin the 15-minute final descent between 1am and 2am. As per Isro’s plan, about 10 minutes later, it would have dropped to reach 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.At 400m, Vikram will hover for about 12 seconds to collect some data from the lunar surface and then further reduce its altitude in the next 66 seconds, to reach a height of 100m.At this height (100m), Vikram will hover again to decide if it must land on the first preferred site or the second one. Its onboard instruments will tell Vikram what to do.If it can land on the first site, 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, further drop down to 10m in the next 25 seconds. From the height of 10m, it will take Vikram 13 seconds to touchdown on Moon.“This is the plan. There could be slight variations as in all missions, but the landing is expected to be smooth,’ a senior scientist said.Two hours after Vikram’s landing, the ramp will roll out completely and touch the lunar surface. And, about an hour and ten minutes after that, the solar panels of Pragyan will be turned on and five minutes later, Pragyan will start moving, and about 45 minutes later, it will make a touchdown on the lunar surface.