Two-and-a-half months later, the Indian Space Research Organisation (ISRO) has finally admitted publicly that the Vikram lander on Chandrayaan-2 mission made a “hard-landing” on the moon.
In a written answer to a question posed to the Department of Space in Lok Sabha, Minister of State in the Prime Minister’s Office (PMO) Jitendra Singh said the “reduction in velocity” of the Vikram lander during the final phase of its descent on the moon’s surface “was more than the designed value”. As a result, Vikram “hard-landed” on the moon “within 500 metres of the designated landing site”, he said.
The fact that Vikram, which was supposed to touch down on the moon’s surface in the early hours of September 7, had crash-landed was no secret. That was the only fate possible after it was seen to be unable to slow down its velocity at the required rate when it was barely 2 km from the moon’s surface.
ISRO, however, had so far avoided any comment on the fate of the Vikram lander. It had maintained that communication with the lander was lost when it was 355 metres above the moon, and efforts were being made to restore contact. Three days after the incident, ISRO had said the Orbiter module of Chandrayaan-2, which is functioning normally and circling the moon, had spotted Vikram and taken thermal images, but did not say anything about the condition of the lander. At that time too, it had said that it was trying to re-establish communication signal.
Early in the morning of September 7, the Vikram lander, which had already separated from the main spacecraft a few days earlier, had begun its descent to the moon from an orbit about 30 km from the lunar surface. A soft landing on the moon involved the slowing down of Vikram from a speed of 1,683 metres per second (over 6,000 km per hour) with which it was moving just before the descent to about 2 metres per second (5 to 7 km per hour) ahead of touchdown.
The descent had proceeded smoothly till Vikram was about 2.1 km from the surface, after which it was unable to slow down at the required rate. When the lander was 355 metres above the moon, the ground control room lost its communication link with it. At the time the communication was lost, Vikram was hurtling towards the moon at a speed of over 200 km per hour.
“The first phase of descent was performed nominally from an altitude of 30 km to 7.4 km above the moon surface. The velocity was reduced from 1,683 m/s to 146 m/s. During the second phase of descent, the reduction in velocity was more than the designed value. Due to this deviation, the initial conditions at the start of the fine braking phase (final phase below 7.4 km altitude) were beyond the designed parameters. As a result, Vikram hard-landed within 500 m of the designated landing site,” the minister said in a written answer in the Lok Sabha.
The minister said apart from the landing, most of the objectives of the Chandrayaan-2 mission, which was India’s first attempt to soft-land on the moon, were successful.
“Most of the components of technology demonstration, including the launch, orbital critical manoeuvres, lander separation, de-boost and rough braking phase were successfully accomplished. With regards to scientific objectives, all the eight state-of-the-art scientific instruments of the Orbiter are performing as per the design and providing valuable scientific data. Due to the precise launch and orbital manoeuvres, the mission life of the Orbiter is increased to seven years. The data received from the Orbiter is being provided continuously to the scientific community. The same was recently reviewed in an all-India user meet organised in New Delhi,” the minister said.