Meet the Indian space enthusiast who helped NASA find the crash site of the Vikram lander on the cratered surface of the moon.
We finally know where Chandrayaan-2’s Vikram lander crashed on the cratered surface of the moon in the pre-dawn hours of 7 September.
National Aeronautics and Space Administration (NASA) said late on Monday that it had spotted the lander’s impact site and its debris in the images captured over the last few months by its Lunar Reconnaissance Orbiter (LRO). NASA managed to do it with help from an Indian engineer, Shanmuga Subramanian.
On 17 September, little over a week after the Indian Space Research Organisation (ISRO) lost contact with the Vikram lander, NASA’s LRO passed over and photographed the area around the point it was supposed to land.
However, at the site, the end of the lunar day, which is equivalent to 14 earth-days, was nearing. This means that, at the landing site, the sun is low on the horizon and it is near dusk in the region.
Moreover, near the lunar south pole, where Vikram was to land (around 71 degree south of the lunar equator), the sun does not rise higher than around 19 degree in the sky. (Sunlight strikes at low angles in these regions of the moon, only skimming the rims of craters and leaving the interiors cold in shadow.)
These conditions created long shadows on the surface, covering the lander. As a result, LRO couldn’t capture the details it could have otherwise, and NASA was unable to spot the Vikram lander on the surface of the moon.
NASA released the first set of pictures on 26 September. Many, including Subramanian, a mechanical engineer based in Chennai, immediately got to work.
“It was something challenging as even NASA couldn’t find out. So why can't we try out? And that's the thought that led me to search for Vikram lander,” he told Swarajya soon after NASA named him in its press release.
A graduate of the Government College of Engineering in Tamil Nadu’s Tirunelveli district, Subramanian works for an “L & IT Architect” in Chennai.
“I am crazy about rockets from my childhood and never missed watching a rocket launch on television until I reached college. That got interested and hooked me in space exploration always,” he wrote in an email.
Finding the hint, which he passed on to NASA, wasn’t easy, Subramanian said.
“There was no data available about the path of Vikram lander. I eventually concluded it would have come from North Pole as one of the tweets from Cees Bassa (astronomer ASTRON, the Netherlands Institute for Radio Astronomy) said Vikram has crossed North Pole of Moon,” he told this correspondent.
Subramanian “searched NASA’s pictures for four to five days, every night”.
He got “false positives” initially and was corrected by Twitterati. One such tweet led him to a reddit forum, where he got the information he was looking for.
Then, from ISRO’s “live images”, Subramanian concluded that the Vikram lander must have “stopped short of around 1 km from the landing spot so it eventually lead to me searching around 2 square km around the landing area,” he wrote.
“I searched around North of the landing spot as Vikram approached the landing spot only from North and though there was lot of false positives,” he added.
But, eventually, Subramanian spotted a little bright spot and contacted the scientists working with the LRO’s camera.
“I found a tiny little dot. After comparing with LRO images from the last 9 years, which confirmed it would be the debris, I reached out NASA,” he said.
After receiving the information, LRO scientists scoured the area in which Subramanian had spotted the bright pixel. They compared the images of the area taken before the Vikram lander’s attempted soft-landing and those taken by the LRO camera on 11 November (over a month after the hard landing).
In the process, NASA was able to find the spot of impact nearly 2,500 feet southeast of Vikram lander’s designated landing site, “and a spray of debris emanating outward”.
It was one of these pieces of debris that Subramanian had located.
The debris he spotted (marked ‘S’ in the picture below) is around 750 metres northwest of the main crash site of the Vikram lander. It was a single bright pixel identification in the first mosaic (1.3 metre pixels, 84 degree incidence angle) that had been released by NASA as early as 26 September.
John Keller, the deputy project scientist for the LRO project, confirmed Surbamanian’s contribution. “Thank you for your email informing us of your discovery of debris from the Vikram lander. The LRO team confirmed that the location does exhibit changes in images taken before and after the date of the landing,” he wrote to him.
“Using the information, the LRO team did additional searches in this area and located the site of the primary impact as well as other debris around the impact location and has announced the sighting on the Nasa and ASU pages where you have been given credit for your observation,” he wrote to Subramanian.
Subramanian says he couldn’t have spotted the debris without LRO data.
“They (LRO’s team) replied only today after they confirmed. The surface was not illuminated and I do know that before going public they need to be 100 per cent sure that it was Vikram lander. So I was waiting for the confirmation and eventually got it today,” he told Swarajya.
“I don't think Vikram lander would have made such impact on minds of Indian public if it had landed successfully,” Subramanian added.