The story so far: Chandrayaan 2 took off from Sriharikota on July 22 to safe land the ‘Vikram’, carrying its ‘Pragyan’ rover, in a suitable high plain on the lunar surface, at a latitude of about 70º South. But soon after 1.50 a.m. on September 7, in the final minutes of the lander’s descent on its own, the Indian Space Research Organisation (ISRO) team in Bengaluru lost contact with the module.
What went wrong with the mission?
Chandrayaan 2, comprising an orbiter, a lander and a rover, journeyed from earth for eight days and reached the moon’s vicinity on August 20. On September 2, the lander riding on the orbiter was separated and got into a closer orbit around the moon, moving pole-to-pole at a distance of 35 km x 100 km.
Mission planners at ISRO had divided the last critical 15-minute parabolic descent into four smaller phases. At 1.38 a.m. IST on September 7, the lander perfectly cleared the ‘rough braking phase’, swooping down from 30 km to 7.4 km of the lunar surface in 10 minutes. Its velocity had dropped as required from 1,640 metres a second to about 400 metres a second.
It had now entered the second part, the ‘fine braking phase’ of 3 minutes, with the four throttleable motors switching off to further lower the velocity. It had to re-orient itself, take pictures of the landing site to look for hazards like slopes and rocks. The moon was just over 2 minutes and 2.1 km away. But by then, at the command headquarters in Bengaluru, the green lines on the screens showed that it had strayed from its path; mission managers said they were not receiving any signal from the lander.
Vikram had developed a problem, gone silent and had crashed at the fag end of a perfect journey, along with the stillborn rover. Some 20 minutes later, ISRO Chairman K. Sivan announced that contact had been lost with Vikram and that ISRO was piecing together its last set of data.
While the failure analysis committee reconstructs and simulates the last moments to infer the causes, theories abound about what may have caused the crash: did the thruster/s overperform? Did Vikram lose altitude and not recover, losing the earth link? Or was it some other anomaly?
However, since then, ISRO has spoken only once in the last seven days: just to say it had located the crashed Vikram and would try to reconnect with it. It must do so before the lunar night sets in around September 21, cutting off any solar power supply to the spacecraft.
Why was this mission important?
For ISRO this was the second moon mission after Chandrayaan 1 of 2008. The project, approved in 2007 and planned for 2012, had undergone a few twists, turns, delays and redesigns over the last few years. Finally in June, Dr. Sivan formally announced that it would be launched in mid-July.
Chandrayaan 1 was an orbiting mission and died just after eight months in orbit, but not before confirming the exciting presence of water molecules on the lunar surface. Chandrayaan 2 planned to take off from where its precursor left off and look intensively for water deposits from up close. It was a formidable combination of an orbiter, a lander and a robotic rover which aimed to look at the moon’s exterior, surface and interior in that order.
What were the challenges?
Dr. Sivan had repeatedly spoken of the challenges of soft landing on moon — the spacecraft had to land unharmed and intact, remain in touch with earth and do its assigned job. Of nearly 80 missions sent to moon since the early 1960s, less than 40% have succeeded. This year alone, China’s Chang’e 4 mission made the first ever landing on the far side of the moon in January and also deployed a rover. But in April, Israel’s Beresheet craft crashed on the moon.
The lunar terrain is rocky and uneven. The moon’s gravity is about 17% of the earth and the moon dust that slowly rises and falls on landing can disable sensitive instruments of a lander. Many technologies of Vikram are new: the lander and its legs, the autonomous rover, and the four throttleable motors.
What happens after this?
In the end, India did not arrive on the moon. The country had the aim of becoming the fourth member of the lunar club, after the Soviet Union, the U.S. and China. As for Chandrayaan 2, we may have heard the last of the lander and the rover. But the orbiter gliding 100 km above continues to bear the Chandrayaan 2 torch, beaming back pictures of the moon. The information it will send as it revisits the spot where Vikram lies may offer precious lessons for future planetary missions by India and other countries.
