Chandrayaan 2: Giant leap for ISRO

In what will be the most technologically complex mission ISRO has undertaken so far, Chandrayaan-2 will attempt to land a rover near the South Pole of the moon.

Published : Jul 09, 2019 11:27 IST

Scientists work on the orbiter and lander of Chandrayaan-2 at the ISRO Satellite Integration and Test Establishment (ISITE) in Bengaluru on June 12.

Scientists work on the orbiter and lander of Chandrayaan-2 at the ISRO Satellite Integration and Test Establishment (ISITE) in Bengaluru on June 12.

EXCITED photographers and reporters scrimmaged to take pictures or have a glimpse of the two vehicles in the cavernous clean room of the big facility. They were the Chandrayaan-2 spacecraft/orbiter and the lander. The Indian Space Research Organisation’s (ISRO) engineers were milling around the lander, named Vikram after the founder of India’s space programme, Vikram Sarabhai. Inside the lander was a rover called Pragyaan, a one-metre-long robotic car with six wheels. The orbiter, the lander and the rover were undergoing a battery of tests in the massive clean room of the ISRO Satellite Integration and Testing Establishment (ISITE) in Bengaluru. Weighing 3.8 tonnes, the orbiter, the lander and the rover are together called the composite module.

At 2:51 a.m. on July 15, the Geosynchronous Satellite Launch Vehicle-Mark III (GSLV-Mk III) with the Chandrayaan-2 orbiter, lander and rover aboard will soar into the sky from the second launch pad at Sriharikota in the most ambitious mission undertaken by ISRO, its second shot at the moon. The first took place in October 2008 when it put the Chandrayaan-1 spacecraft into a circular orbit above the moon at an altitude of 100 kilometres.

Challenging mission

The comparison ends there. For, in ISRO’s history, the Chandrayaan-2 mission will be the most challenging and technologically complex because ISRO will not only be putting the orbiter around the moon but also soft-landing the lander on lunar soil and deploying the rover, which will be driven around the moon’s surface. The lander, with the rover inside, after separating from the orbiter circling above the moon, will slowly descend and gently land on the South Pole of the moon, on September 6 or 7. So, Chandrayaan-2 will take 53 to 54 days to travel the 3.84 lakh km from the earth to the moon’s surface.

What is audacious is that India will be the first country to soft-land a lander on the South Pole of the moon. Even the United States, Russia and China have not attempted it.

From separation from the orbiter to touchdown on the moon, the lander will take about 15 minutes. It has throttleable engines to control its descent. Besides, it has sensors that will decide where the lander should touch down avoiding boulders and craters. Four and a half hours after touchdown, the rover will emerge from the lander and slide down a ramp on to the lunar soil. It will be driven about on the moon’s surface, conducting experiments. The orbiter, the lander and the rover together have 14 instruments to take pictures of the moon, prospect for minerals, look for helium, search for buried water-ice, investigate the lunar exosphere, and so on.

K. Sivan, ISRO Chairman, said the 15 minutes from the separation from the orbiter to the soft-landing “will be the most terrifying moments”. During a press conference in Bengaluru on June 12, he said: “These 15 minutes will form the most complex mission that ISRO has ever undertaken. The throttleable engines are a new [technology] development for us.”

The moon’s South Pole “is a place to which nobody has gone earlier. So, a lot of new science is expected from this mission,” he added. Sivan emphasised that Chandrayaan-2 was “a 100 per cent indigenous mission” because the launch vehicle, the orbiter, the lander and the rover were all built at ISRO facilities.

“This is the first time we are attempting to soft-land on the moon. This is the crucial part of the Chandrayaan-2 mission,” said S. Ramakrishnan, former Director, Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram. The VSSC designed and built the GSLV-Mk III, which is the most powerful vehicle that India has built so far. The three-stage rocket weighs 640 tonnes. Ramakrishnan played an important part in designing and building it. He said: “The new technology we are attempting in the Chandrayaan-2 mission is the soft-landing. From the lunar orbit, we should descend in a programmed manner and land precisely. The velocity of the descent of Vikram and the velocity at which it should soft-land should take place as per plans. The lander should stand on its four legs. Otherwise, it will topple. We have to calculate everything…. About 30 to 40 events should take place precisely during the descent phase. Only then the mission will be successful.”

According to ISRO literature, the challenges in landing on the moon include navigating large distances accurately, conducting trans-lunar injection of the composite module, preventing damage from lunar dust and accomplishing the first landing on the moon’s South Polar region.

On June 24, hectic activity was under way at the Satish Dhawan Space Centre (SDSC) in Sriharikota in Andhra Pradesh, the spaceport from where the GSLV-Mk III will lift off. The three stages of the rocket had already been stacked up in the Vehicle Assembly Building (VAB) of the second launch pad. The orbiter arrived at Sriharikota from ISITE, Bengaluru, on June 15. Then came the lander with the rover. They are now undergoing a variety of tests at Sriharikota. After the lander with the rover inside is stapled to the top of the orbiter, the entire module will be mated with the GSLV-Mk III in the first week of July. The composite module will be encased in the heat shield of the launcher. The launcher will move from the VAB to the launch pad three days before the launch date. “Preparations for the launch are progressing fast,” said an SDSC official on June 24.

July is the most favourable period for launching Chandrayaan-2, with the launch originally set for any day from July 9 to 16. The launch window spanned 10 minutes on each of these dates. During the remaining days of July, the launch window available was just one minute.

About 17 minutes after lift-off, the third, upper cryogenic stage of the rocket will inject the composite module into an initial earth-parking orbit with a perigee of 170 km and an apogee of 38,000 km. In the next 16 days, the propulsion system on board the orbiter will fire five times. They are called earth-bound burns. This will enable the composite module to perform five manoeuvres and go into an orbit of 150 km by 1,41,000 km.

“After the five earth-bound manoeuvres, an important manoeuvre called trans-lunar burn will take place, with the propulsion system on the orbiter firing,” said Sivan. “It will put the composite module’s trajectory towards the moon.” For the next five days, the composite module will travel towards the moon. Once it reaches the moon, the propulsion system will once again fire and a retro-burn will happen. This burn/firing will put the composite module into an orbit with a perilune of 150 km and an apolune of 18,000 km. Said Sivan: “Subsequently, there will be four lunar-burn manoeuvres. Then the lunar orbit insertion will happen. Thus, the composite module will be captured in a circular orbit of 100 km around the moon.” The composite module will go around the moon in this orbit for 27 days.

The real action

After the 27th day, the real action will begin, which makes the Chandrayaan-2 mission more complex by an order of magnitude than the Chandrayaan-1 mission. For, it will be time for the lander to hive off from the orbiter. After separating itself from the orbiter, the lander will use its propulsion system to reduce its circular orbit of 100 km by 100 km around the moon to 100 km by 30 km. The lander will stay in this orbit for four days. Sivan explained: “During these four days, we will do many checks to see whether the lander system is working perfectly. On D-Day, that is, on the fourth day, when the lander is 30 km above the moon, the real event will take place. At the D-instant, the lander’s propulsion system will function in a throttleable manner. It will break the velocity of the lander in a controlled fashion that will bring down the lander slowly and make it land at a place near the South Pole. This will take about 15 minutes.”

Four and a half hours after the lander touches down, its door will open and the ramp will be deployed. The rover will emerge from the lander, slowly roll down the ramp on to the lunar soil. While all this is happening, the orbiter will be circling the moon at an altitude of 100 km. Both the static lander and the roving Pragyaan will have a life of one lunar day, that is, 14 earth days. Pragyaan, powered by solar batteries, will travel a maximum distance of 500 metres during those 14 days. Its velocity will be one centimetre a second, or 36 metres an hour.

Out of a total of 14 instruments in the composite module, 13 are Indian payloads and one payload is from the United States’ National Aeronautics and Space Administration (NASA). The orbiter, which weighs 2.4 tonnes, has eight instruments. From its 100-km orbit around the moon, its terrain-mapping camera and high-resolution camera can take pictures of the moon’s surface. Its imaging infrared spectrometer will look for minerals. The orbiter’s instruments will especially look for rock-forming elements such as magnesium, calcium, iron, and so on. Its synthetic aperture radar will hunt for buried water-ice on the moon. Another instrument will study the moon’s exosphere. Indeed, in a huge breakthrough, Chandrayaan-1 had discovered water-ice on the moon. Sivan described it as “the greatest achievement of the Chandrayaan-1 mission”.

The lander, which weighs 1.4 tonnes, has four payloads, including the one from NASA. The three Indian instruments will conduct experiments on lunar quakes and study the landing sites’ thermo-physical properties. The payload for studying the moon’s seismic activity is called Instrument for Lunar Seismic Activity. The NASA payload, a last-minute addition, is called Laser Retroreflector Array. It will try to understand the dynamics of the earth-moon system and measure the distance from the lander on the moon to the earth.

The rover, which weighs about 27 kg, has two payloads including an Alpha Particle X-ray Spectrometer. They will compute the mineral and chemical composition of the moon’s surface.

Sivan explained why ISRO preferred to go to the moon’s South Pole. ISRO selected it for its convenience, communication and science, he said. The rover depended on solar energy to charge its battery. Good visibility and plenty of sunlight are available to it in the South Pole. The landing site should not have a slope of more than 12 degrees. The lander would topple otherwise. The South Pole had good landing characteristics, visibility and sunlight. It was more under the shadow regime than the North Pole. So, there was a better chance of the presence of water-ice than in the North Pole. “So, new science is expected,” he said.

About 500 industries across the country have contributed to the making of the GSLV-Mk III. Another 120 took part in providing the hardware and the software in the building of the composite module.

Sivan said: “It is not only ISRO’s mission but the entire country’s programme. The entire country [including the academia and research institutions] has contributed to it and is looking for science from this mission. The whole nation will benefit from the Chandrayaan-2 programme.”

The cost of the entire mission is about Rs.1,000 crore. This includes Rs.603 crore for building the composite module and the payment to agencies abroad for providing tracking and navigation support to ISRO. The cost of building the GSLV-Mk III is around Rs.375 crore.

The Project Directors for the Chandrayaan-2 composite module and the Mission Director are two women, M. Vanitha and Ritu Karidhal respectively.

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