Science & Technology

Chandrayaan 2 lunar landing: Isro loses contact with lander Vikram

Lander performed as planned up to 2.1 km above the lunar surface during its descent

By Akshit Sangomla
Published: Saturday 07 September 2019
Isro Chairman K Sivan. Photo: Twitter

Vikram, Chandrayaan 2’s lander, lost contact with Indian Space Research Organisation’s (Isro) mission control centre just a few minutes before it had to soft-land on the lunar surface. After that the scientists went into a huddle and Prime Minister Narendra Modi was informed by ISRO Chairman K Sivan about the loss of communication. Scenes of heightened tension among the scientists could be seen in the mission control. The data is still being analysed by them to conclude what happened to the lander.  

The lander performed as planned by Isro up to a point when it was 2.1 kilometres (km) above the Moon’s surface. This was in the fine-breaking phase of the descent process, in which the craft had to be brought down from a height of 5 km to about 400 metres. Before this, the descent operation started from the height of around 30 km.

In the first rough-breaking phase, the orbit was brought down from 30 km to 7.4 km in about 10 minutes. The velocity of Vikram was also bought down from 1,680 m per second to 146 m/sec during this phase. In the next absolute navigation (altitude control) phase, the orbit was further reduced to 5 km from 7.4 km and the velocity slowed even more. When communication was lost Vikram was still travelling at around 50 m/sec.

Vikram had successfully detached from the orbiter on September 2. The next day, the lander reduced its orbit to 100 km x 30 km and then all the systems were self-checked onboard for the subsequent three days. 

Years of hard work and planning by Isro scientists and Chandrayaan 2’s 48-day journey from Earth to Moon finally had come down to the last few ‘minutes of terror’ that Vikram was seemingly not able to overcome. With this India would have become only the fourth country to have successfully soft-landed a human-made object on another planet or natural satellite after the United States, Russia and China.

A soft-landing protects the object from impact while a hard landing doesn't. Soft-landing ensures that the object is able to carry out further experimentation on the target planet or satellite, mostly with the help of a rover vehicle.

Soft-landing on any planetary surface is complicated. Vikram was to use five thrusters — four at the corners and one at the centre to make its final descent. Maintaining the required velocity with such thrusters is difficult as a fine balance among them needs to be maintained. Then there is the issue of moon dust which could wreck the engines of the thrusters.

At the moment, Isro scientists are non committal about the fate of Vikram. It could have landed successfully despite losing communication because the landing process was programmed into the lander itself without being micromanaged by ground control. Else it could have crash landed on the lunar surface. The final conclusion can be drawn only after careful analysis.

With Vikram's landing India would have become the only country to have landed a craft near the south pole of the Moon. The spot where Vikram was to land was a highland that rises between two craters called Manzinus C and Simpelius N. It's about 600 km from the Moon’s south pole. A couple of hours after the landing Isro's six-legged rover Pragyan was to roll out onto the lunar surface and start its exploration for the next 14 lunar days or one Earth day. It was to conduct experiments on chemistry, mineralogy and exosphere, especially collecting more evidence for the existence of water.

Exploration of this part of the Moon was very crucial to understand the characteristics of the satellite planet in full as all the other missions have conducted experiments and returned samples from regions closer to the equator. This was mainly because it is pretty difficult to land at the poles. To land at the poles the orbit of the lander has to remain at a 90-degree angle to the lunar surface.

This is not required in the equatorial regions where soft landings have been attempted before. Even there only 37 percent of attempted landings have been successful till date. Every correction in the orbit of Vikram to land near the south pole came with a penalty of wasted fuel which cannot be then used for other processes. But the lander carried 60-70 kg extra fuel for such exigencies. This fuel efficiency challenge could have been the point where Vikram could have faltered. 

For Isro, the journey to the Moon has not been without delays and close shaves. The Chandrayaan 2 project has been delayed multiple times in the past year. The original launch date was in March 2018 which was later pushed to April and then to October to conduct further tests on the launch vehicle.

Further deliberations by the fourth comprehensive technical review meeting concluded that the mission's components needed changes, especially in configuration and landing sequence. This pushed the launch date to the first half of 2019. In February 2019, the lander craft named Vikram suffered damage in both its legs during a routine test. After this setback ISRO reworked its systems and finally fixed July 15 as the launch date.

But just 56 minutes before the engines had to fire up, ISRO called off its launch due to a technical snag. The snag turned out to be a leak in the helium tank of the Geosynchronous Satellite Launch Vehicle Mk III M1 (GSLV Mk III M1). The entire process of identifying, analysing and fixing the leak took ISRO’s launch team only 24 hours after which they prepared for the launch, according to Sivan. The final launch took place on July 22 against a narrow window of only a few minutes. 

PM Modi tweeted in support of Isro:

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