India’s most ambitious space mission will get under way at 2.51 a.m. on July 15 when its powerful Geosynchronous Satellite Launch Vehicle-Mark III (GSLV-MK III) soars into the sky from the spaceport at Sriharikota with the Chandrayaan-2 spacecraft on board. Technologically, it will be the most challenging mission that the Indian Space Research Organisation (ISRO) has undertaken because ISRO will not only be sending a spacecraft to the moon but attempting to soft-land a contraption called the lander on the lunar surface.
On September 6 or 7, the lander, sitting on top of the spacecraft, will separate from the spacecraft that is going around the moon at an altitude of 100 km. After coming down to an altitude of 30 kilometres above the moon, the lander will descend ever so slowly in a controlled fashion and settle on the lunar surface on its four legs. From the lander will emerge a rover, a one-metre-long robotic vehicle which will drive about on the tricky lunar soil to a maximum distance of 500 metres. Both the lander, which will be static, and the peripatetic, six-wheeled rover, will carry instruments to conduct scientific experiments on the moon.
The Chandrayaan spacecraft, also called the orbiter, which will be orbiting above, has its own payloads that will map the lunar surface, prospect for minerals, search for buried water and so on. The lander has been named Vikram, after Vikram Sarabhai, the pater familias of India’s space programme. The rover is called Pragyan, the Sanskrit word for knowledge. Both the lander and the rover will have a life of one lunar day. In other words, they will conduct experiments on the lunar soil for 14 earth days. The mission life of Chandrayaan spacecraft is one year. The Moon is 3.84 lakh km from the earth.
The Chandrayaan-2 mission is a 100 per cent indigenous project. The GSLV-Mk III rocket, the Chandrayaan spacecraft, the lander Vikram and the rover Pragyan are all ISRO-made. Out of the 14 scientific instruments on the orbiter, the lander and the rover, 13 are from various laboratories in India. A last-minute addition on board the lander (14th instrument) is from NASA.
K. Sivan, ISRO Chairman, described the 15 minutes that the lander will take to descend from an altitude of 30 km and make a soft-landing on the moon as “the most terrifying moments not only for all the people in ISRO but for all Indians”. He added, “These 15 minutes will be the most complex mission ISRO has ever undertaken.” The lander has its own propulsion system to control its descent and touch down gently on the moon. ISRO has developed throttleable engines for this. Sivan told a press conference in Bengaluru on June 12: “The lander’s propulsion system will function in a throttleable manner. This is a new [technology] development for us. The throttleable engines will break the velocity of the lander in a controlled fashion. They will slowly bring down the lander and make it land at a place near the South Pole of the moon.” The lunar South Pole is a place to which no moon-faring country, including the U.S., Russia and China, has gone so far.
Thus, ISRO’s Chandrayaan-2 mission is more complex by an order of magnitude than Chandrayaan-1, which was India’s first spacecraft to the moon. It was a Polar satellite Launch Vehicle (PSLV-C11) that put the Chandrayaan-1 spacecraft into its initial earth-parking orbit on October 22, 2008. The spacecraft later reached the Moon and was inserted into an orbit of 100 km above it. An instrument called Moon Impact Probe (MIP) separated from the spacecraft and was commanded to crashland on the moon to signal that India had arrived there. The MIP had India’s national flag painted on it.
Now, 11 years later, India has decided to put a lander on the South Pole of the moon for two reasons: communication and science. South Pole has good visibility. Good solar light is available there. The rover is powered by batteries which get their energy from its solar panel. This solar panel will be exposed to the sun’s light falling on the moon’s South Pole. Besides, as Sivan said, the South Pole does not have many craters or boulders. It is not “very slopy”. So the lander will not topple.
“From the science point of view, the Moon’s South Pole is more in the shadow region than its North Pole…. Water is expected more there. Some minerals may be there. So new science is expected,” the ISRO Chairman said.
The Chandrayaan-2 spacecraft and Vikram and Pragyan will totally feature 14 payloads or scientific instruments. The spacecraft/orbiter has eight payloads, including cameras to take pictures of the moon’s surface, search for water-ice and study the lunar exosphere. Vikram will have four payloads, including a NASA instrument. The three Indian instruments will study the properties of the landing site and seismic activity, that is, lunar quakes. The NASA payload will measure the distance from the lander to the earth. The Pragyan rover has two instruments to compute the minerals and chemical composition of the lunar surface.
The GSLV-MKIII, a three-stage vehicle that weighs 640 tonnes and has a cryogenic upper stage, is India’s most powerful launcher to date. The 44-metre-long rocket has been declared an operational vehicle after two consecutively successful developmental flights on June 5, 2017 and November 14, 2018.