17 July 2019
India’s second lunar probe
Source: By Amitabh Sinha: The Indian Express
Chandrayaan-2 is India’s second lunar probe, and its first attempt to make a soft landing on the Moon. It has an Orbiter, which will go around the Moon for a year in an orbit of 100 km from the surface, and a Lander and a Rover that will land on the Moon. Once there, the Rover will separate from the Lander, and will move around on the lunar surface. Both the Lander and the Rover are expected to be active for one month.
The Orbiter, Lander and Rover are each fitted with several instruments to carry out experiments. While Chandrayaan-2 is expected to yield a wealth of new information about the Moon, apart from demonstrating ISRO’s new capabilities, here are a few things that are likely to be discussed the most in the coming days.
How is Chandrayaan-2 different from Chandrayaan-1?
Chandrayaan Lander: Named Vikram after Dr Vikram A Sarabhai, Father of the Indian Space Programme. The Vikram Lander has been designed to be able to communicate with the Indian Deep Satellite Network near Bengaluru, as well as with the Orbiter and Rover.
The Indian Space Research Organisation (ISRO) was forced by circumstances to develop its own Lander and Rover for Chandrayaan-2. Originally scheduled to launch in 2011, Chandrayaan-2 was supposed to carry a Russian-made lander and rover, since ISRO did not then have the technology to develop these. The type of lander and rover that Russia was building for Chandrayaan-2, however, developed problems on another mission, forcing it to make design corrections. But then, the proposed new design would not have been compatible with Chandrayaan-2. Russia eventually pulled out, and ISRO began to develop its own Lander and Rover, a task that delayed the Mission by a few years.
How has the landing been scheduled?
The Lander and Rover were scheduled to descend on September 6, more than 50 days after the launch early July 15. The launch, however, got delayed due to technical issues. Most of the other lander missions have taken considerably less time to reach the Moon. The human missions, in fact, all landed within three to four days. Chandrayaan-1 had taken 12 days to enter the Moon’s orbit. The time taken to reach the Moon is dictated by many factors, such as the strength of the rocket carrying the spacecraft, the nature of experiments to be carried out, and the position of the Moon in its orbit.
Chandrayaan-2’s launch vehicle, GSLV-Mk-III, is the most powerful rocket ISRO has built — however; it is still not powerful enough to reach the Moon’s orbit in one shot. Therefore, the spacecraft will go around the Earth several times, successively raising its orbital height, before transferring itself into the lunar orbit. Once there, it will orbit the Moon for several days before ejecting the Lander and the Rover. The date, September 6, was chosen because the landing site will remain well illuminated by sunlight over the next one month while the Lander and Rover work and collect data. Also, there is no lunar eclipse during this period.
How is a soft landing achieved?
In terms of technology, landing is the most complicated part of the Mission. Travelling at nearly 6,000 km per hour at the time of their ejection from the Orbiter, the Lander and Rover would have to slow down to roughly about 3 km/hr. This 15-minute exercise will mark the “most terrifying moments” for the mission, as ISRO chairman K Sivan put it. The Moon does not have an atmosphere to provide drag, so the use of parachute-like technologies to slow down the Lander cannot be used. Instead, thrusters will be fired in the opposite direction to slow it down. All this while, the Lander will also be imaging the lunar surface to look for a safe site to land.
What new information will the Mission look for?
South Pole: Chandrayaan-2 is attempting to go where no spacecraft has gone before — to the south pole of the Moon. There have been 28 landings on the Moon so far, including six human landings. All these landings have taken place in the equatorial region. Studies have, however, indicated that the unexplored Polar Regions could hold much greater scientific potential.
Chandrayaan Rover: A 6-wheel robotic vehicle named Pragyan (wisdom). It can travel up to 500 m and will leverage solar energy for its functioning. It can only communicate with the Lander.
The polar regions of the Moon are understood to be filled with small and large craters, ranging from a few cm to several thousands of km. These craters make it extremely hazardous for a spacecraft to land. This region is also extremely cold, with temperatures in the range of –200°C. Unlike the Earth, the Moon does not have a tilt around its axis. It is almost erect, because of which some areas in the polar region never receive sunlight. Anything here is frozen for eternity. Scientists believe that rocks found in these craters could have fossil records that can reveal information about the early Solar System.
Chandrayaan-2 will carry out extensive three-dimensional mapping of the topography of the region, and will also determine its elemental composition and seismic activity.
Quest for Water: Two instruments on board Chandrayaan-1 provided irrefutable evidence of water on the Moon, something that had been elusive for more than four decades. Chandrayaan-2 will take the search further, trying to assess the abundance and distribution of water on the surface. The large craters in the South Polar Region are believed to hold large amounts of ice — in millions or billions of tonnes, by one estimate.
Equally important would be the attempt to determine the origins of water on the Moon — whether it has been produced on the Moon, or has been delivered from an outside source. This would also offer a clue on how reliable the water resources could be. Studies show that the water detected on the Moon could have been formed in a few different ways. It is known that the lunar surface is full of oxides of multiple elements. These oxides could react with hydrogen ions in the solar wind to make hydroxyl molecules, which could combine with hydrogen to make water.
The water could also come from external sources. Comets and asteroids that contain water vapour are known to have collided with the Moon in the past, and could have transferred traces of this water to the Moon, which could have got trapped inside the extremely cold regions.
It is the discovery of water on the Moon by Chandrayaan-1, and by a NASA mission a year later, that has rekindled interest in the Moon, and given rise to hopes that it could finally be used to set up a permanent scientific mission, and also as a possible launchpad for going deeper into space. Finding adequate water, and being able to extract it economically, is crucial to this dream.
Timeline: India in space, through the years
February 16, 1962: The Indian National Committee for Space Research is formed under the leadership of Vikram A Sarabhai and physicist Kalpathi Ramakrishna Ramanathan.
November 21, 1963: India’s space programme takes off with launch of a sounding rocket from Thumba Equatorial Rocket Launching Station in Kerala. It was for probing upper atmospheric regions and space research.
August 15, 1969: ISRO is formed.
April 19, 1975: Aryabhata, India’s first satellite, is launched from a Soviet Kosmos-3M rocket from Kapustin Yar in then Soviet Union. It was designed and built in India.
June 7, 1979: Bhaskara-I, the first experimental remote-sensing satellite built in India, is launched. Images taken by its camera were used in hydrology, forestry and oceanography.
July 18, 1980: Satellite Launch Vehicle-3, India’s first experimental satellite launch vehicle, takes off with Rohini Satellite RS-D2. Camera had ability to use data for classifying ground features like water, vegetation, bare land, clouds and snow.
April 10, 1982: Insat-1A is launched. Was abandoned in September 1983, when its attitude control propellant was exhausted.
April 2, 1984: Rakesh Sharma, former IAF pilot, becomes the first Indian in space. In a joint India-Soviet Union mission, Sharma boards the Soyuz T-11 spacecraft to the Salyut 7 Orbital Station.
October 22, 2008: Launch of Chandrayaan-1. It orbits the Moon but does not land. It performs high-resolution remote sensing aiming, among various missions, to prepare a 3D atlas of both the near and far sides of the Moon.
November 5, 2013: Launch of Mangalyaan, the Mars Orbiter Mission. Orbiting and studying Mars since September 24, 2014.