India - Chandrayaan to enter lunar orbit on Saturday evening

Srinivas Laxman

MUMBAI: Saturday evening would mark the D-day for India’s prestigious Rs 386-crore moon mission, Chandrayaan-1 , when the tricky lunar orbit
insertion (LOI) takes place – expectedly between 5 pm and 6 pm. The success of the moon mission, which lifted off on October 22, depends on this.

According to space experts, LOI is not without danger because it means traversing through an area in which the gravitational forces of the earth and moon nearly cancel each other out. Consequently, even a small deviation could send the spacecraft into a crash course towards the moon or earth – or on a path leading into deep space. Experts recall that about 30% of unmanned moon missions of the US and the former Soviet Union failed during an LOI.

On the eve of Chandrayaan’s LOI, an Isro official said: “Despite the challenging manouevre on Saturday, the professionalism of scientists and engineers makes us approach the task with optimism , although I admit to a feeling of nervous apprehension . It will be a test for everyone , including the deep space network at Byalalu and the electronic brain of the Chandrayaan spacecraft,’’ he said.

He said the main challenge before LOI was targetting the spacecraft accurately to pass near the moon on Saturday at a “safe’ ’ distance of a few hundred kilometres. The distance between the earth and the moon is 3,86,000 km. “At that distance, it will be a big challenge for us to track the spacecraft, because the moon itself will be moving around the earth at the speed of 3,600 km per hour,’’ he said. It will take about 1.3 seconds for a signal to travel from Isro’s command network at Bangalore to Chandrayaan.

Other Isro officials said that during an LOI, the orientation of the spacecraft, while firing its liquid apogee motor for about 800 seconds, will be very important.