A week after they had to postpone the launch of Chandrayaan-2 less than an hour before lift-off, scientists of the Indian Space Research Organisation (ISRO) will try to make use of an extremely narrow window of opportunity Monday afternoon to make another attempt at sending India’s first lander mission to the Moon.
A 20-hour countdown for the launch started 6.43 pm Sunday for the scheduled launch at 2.43 pm Monday. This time, scientists have very little flexibility in terms of time as the suitable slot during which the spacecraft can be launched lasts barely a few minutes.
“The most suitable launch window this month was between July 9 and 16. On these days, the time slot during which the mission could be launched extended to about an hour or more. But on Monday, this launch opportunity exists for barely a couple of minutes. So, all operations in the run-up to the launch have to be completed with extreme precision. There is no room for any delay. I am sure the mission control can do this,” said a former ISRO scientist.
The scientist said similar narrow time slots were available on a few other days this month but after that, a suitable widow would be available only in September.
PTI quoted ISRO chairman K Sivan as saying Sunday that Chandrayaan-1 had revealed the presence of water molecules on the Moon and that there were possibilities of the latest mission returning successful scientific experiments.
“It is because of these reasons that Chandrayaan-2 has attracted attention not only from Indian scientists but also global scientists,” Sivan told reporters at the Chennai airport during a stopover enroute to Sriharikota in Andhra Pradesh, the launch site.
The launch was originally scheduled for the early morning of July 15, but scientists noticed a sudden drop in pressure in a chamber filled with helium gas with about two hours to go. Unable to immediately ascertain the reason, and unwilling to take chances with the prestigious mission, they decided to abort the launch.
An expert committee was constituted to assess the problem and recommend corrective measures. On Thursday, ISRO said the committee had rectified the problem and that all systems were functioning normally. It had then announced that the spacecraft would be launched on July 22.
“Whatever technical snag we observed on July 15 has been rectified. The vehicle is in good health… The (pre-launch) rehearsal has been successfully completed,” PTI quoted Sivan as saying.
Rocket holds key to first step in mission
The problem that aborted last week’s launch was in GSLV Mk-III, the rocket that will go on its first operational flight in this mission. Chandrayaan-2’s composite module — Orbiter, Lander and Rover — and other instruments were normal. The rocket’s job is only to deliver the spacecraft in Earth’s orbit.
Despite the delay, there is no change in the September 6 date on which the lander and rover modules of the mission would land on the Moon. But the path it would take would be different, since there would now be 48 days between launch and landing instead of the original 54 days.
There is also a possibility that by the time it lands on the Moon, the date in India would have changed to September 7. This is because the lander might take some time in locating the right spot to land, an ISRO scientist said.
According to the revised flight sequence, Chandrayaan-2 would spend 23 days in the Earth’s orbit instead of 17 in the original schedule.
After incrementally raising its orbit during this period, the spacecraft would embark on its journey towards the Moon, which will take seven days. For the next 13 days, it would remain in lunar orbit, going around the Moon in an orbit of 100 km. Earlier, it was supposed to spend 28 days in lunar orbit.
The lander module would separate from the Orbiter on Day 43, or September 2, and could continue to go around the Moon for another few days in a lower orbit. The actual landing would happen on September 6, as originally scheduled, or in the early hours of September 7.
Chandrayaan-2 is India’s first attempt to land on the lunar surface. Its first Moon mission Chandrayaan-1, which was launched in 2008, was an Orbiter mission. But one of the instruments on board, called Moon Impact Probe (MIP) was made to crashland on the lunar surface. The MIP was one of the two instruments of Chandrayaan-1 that provided irrefutable evidence of the presence of water on the Moon.
With Chandrayaan-2, India will become the fourth country to soft-land a rover on the Moon after Russia, the US and China.