BANGALORE: Notwithstanding the last-minute scrubbing of Chandrayaan-2 launch on July 15, ISRO may still be able to soft-land Vikram (lander) on the same day as it had initially planned —September 6-7.

“There may be a slight change in strategy, but it won’t affect the actual day of landing,” a senior scientist associated with the mission told TOI on Thursday.

Four days after the cancellation of the first scheduled launch, ISRO said: “Chandrayaan-2 launch is rescheduled on July 22 at 2:43 pm.”

TOI first reported on July 15 that the new launch date could be on July 22.

An expert committee constituted to analyse the issue—the July 15 launch was cancelled after a leak in the cryogenic stage of the launch vehicle was detected—has suggested remedial action, which has been implemented.

Sources said that the new launch date was finalised late Wednesday. “The committee identified the root cause of the snag and corrective actions are implemented,” ISRO said.

‘Buffer Time Around Moon’

The agency will be able to achieve the landing on September 6-7 as its initial plan included a “buffer” time around Moon for two reasons: First, to give itself a second chance in case of hiccups that pushed the launch from July 15.

“This was key to keep time for a relaunch and still carry out the mission without too many changes in the profile and software,” a source said.

And second, because July 15 was the longest launch window (10 minutes), which ISRO felt was the best day for launch, which gave the agency additional days around Moon before the lander separation procedure.

If it was launched on July 15, the spacecraft would have reached Moon in 22 days, after which it would go around Moon for 28 days before Vikram’s separation from the orbiter and then Vikram would go around Moon for four days before finally soft-landing.

“Now, nothing in the initial approach is changing. We’ll still take 22 days to insert Chandrayaan-2 into the lunar orbit because we need 17 days around Earth for five orbit raising manoeuvres, and then five days for the lunar-craft to travel close to Moon,” a senior scientist explained.

Also, the number of days Vikram needs to go around Moon in a 30 km X 100 km orbit before initiating deboosting procedures for landing will also be the same as planned initially—four days. 

The only thing that will change is the number of days the spacecraft goes around Moon before lander separation. According to initial plans, the spacecraft was to go around in a 100 km X 100 km orbit for 28 days before separation, and now it will go around for 21 days.

“Technically, the separation could have happened even after just one day of lunar insertion. The reason the orbiter had 28 days as per the first plan was because the July 15 window meant we reached there much earlier than the most suited day for landing (September 6-7), which gives us 14 full days (1 lunar day) on Moon,” the scientist explained.

“Now, we will reach Moon about seven days later than the initial plan, but still in 22 days from launch. And yet, we have enough time left for landing on the same date,” the scientist added.

So, the total number of days of the mission will be reduced from 54 days to 47 days. A shorter launch window on July 22—ISRO chairman K Sivan had on June 12 said that all days of July after the 15th will only have one minute—another senior scientist said, won’t be a “problem”.

“You don’t need to worry about the length of the launch window. Look at the last 20 missions and you’ll know that we’ve launched on the dot. So the length of the window shouldn’t be a concern even now,” a scientist said.