With the launch of Chandrayaan-3 today (July 14), the Indian Space Research Organisation (Isro) is set to make its second attempt to land a spacecraft on the Moon. Earlier in 2019, due to problems that had emerged during the last stage of the descent, Chandrayaan-2’s lander and rover crashed on the moon’s surface. Should this mission see a successful “soft” landing, India will become only the fourth country – after the United States, Russia, and China – to have done so. We explained what is being planned this time around in this explainer. But what is the larger aim of India’s moon missions, and what are the parts – the propulsion module, the lander module and the rover – involved for helping Isro “bring the moon closer to us”, as the space agency says? Firstly, how do space missions work? Any space mission essentially has two parts – the rocket, or the carrier, and the spacecraft, which could be a satellite or any other payload. The rocket has the limited job of transporting the spacecraft into space. In most missions, the rockets get destroyed after completing their job. The spacecraft continues to operate as designed. As NASA explains, “The launch of a spacecraft comprises a period of powered flight in the beginning, during which the vehicle rises above Earth's atmosphere and accelerates" with the help of a rocket. The rocket is powered by a propellant, which is a mix of fuel and oxidisers (that allow for burning to happen), all meant to generate enough energy to help the spacecraft lift-off. Once that happens, this powered flight continues and ends only when the rocket's last stage burns out and the spacecraft separates. The payload should have been, ideally, placed into the orbit of the planetary body that it is supposed to reach by this time. This video from Isro shows how this process was to happen in the case of Chandrayaan-2. What are the Chandrayaan missions? India’s Chandrayaan missions are aimed at lunar exploration, beginning with Chandrayaan-1 that launched on October 22, 2008. “The primary science objective of the mission was to prepare a three dimensional atlas of both near and far side of the Moon and to conduct chemical and mineralogical mapping of the entire lunar surface with high spatial resolution,” Isro said at the time. It made more than 3,400 orbits around the moon and was operational for at least 312 days, until August 29, 2009, when radio contact with the spacecraft was lost. However, the fact that it used indigenously developed technology was a major achievement. On November 14, 2008, a payload named MIP (Moon Impact Probe) carried by the spacecraft was separated and it struck the lunar South Pole in a controlled manner. India was then able to make discoveries related to the detection of water (H2O) and hydroxyl (OH) on the lunar surface. The data also revealed their enhanced abundance towards the polar region. It further found ice in the North polar region of the Moon. What happened with Chandrayaan-2? Chandrayaan-2 brought together an Orbiter (to orbit the planetary body and not land on it), Lander (to land on its surface) and Rover (to move on the surface) with the goal of exploring the south pole of the Moon. It was launched in July 2019 and was only a partial success, because on September 7 that year, its lander, Vikram, and rover, Pragyaan, crashed on the Moon’s surface. While Vikram was supposed to lose most of its velocity by the time it was 400m from the lunar surface, system errors led to it having a high velocity, resulting in a crash. Nevertheless, its Orbiter functioned well and was able to gather data. It built on the discovery of water from Chandrayaan-1, and found signatures of water at all latitudes. The Large Area Soft X-Ray Spectrometer (CLASS), which measures the Moon’s X-ray spectrum to examine the presence of major elements such as magnesium, aluminium, silicon, calcium, titanium, iron, etc., found the minor elements chromium and manganese for the first time through remote sensing. And what does Chandrayaan-3 aim to do? Mainly, the Chandrayaan-3 mission is to demonstrate India's growing technical capabilities in the field and conduct a successful soft landing on the moon. Amitabha Ghosh, a scientist for NASA's Rover mission to Mars, explained what this means in The Indian Express thus: “Imagine a spacecraft hurtling through space, at 10 times the speed of an airplane, having to nearly come to a standstill in order to land gently on the Earth — all in a matter of a few minutes and, more importantly, without any human intervention. This, in a nutshell, is a soft landing.” The payloads on the lander and rover remain the same as the last mission. There will be four scientific payloads on the lander to study lunar quakes, thermal properties of the lunar surface, changes in the plasma near the surface, and a passive experiment to help accurately measure the distance between Earth and moon. The fourth payload comes from NASA. There are two payloads on the rover, designed to study the chemical and mineral composition of the lunar surface and to determine the composition of elements such as magnesium, aluminium and iron in the lunar soil and rocks. Notably, the landing site of the latest mission is more or less the same as the Chandrayaan-2: near the south pole of the moon at 70 degrees latitude. If everything goes well, the Chandrayaan-3 will become the world’s first mission to soft-land near the lunar south pole. But why land near the south pole? As NASA says, “Extreme, contrasting conditions make it a challenging location for Earthlings to land, live, and work, but the region’s unique characteristics hold promise for unprecedented deep space scientific discoveries.” It also noted the importance of Lunar polar volatiles. Volatiles are chemical elements or compounds in a solid state that melt or evaporate at moderately warm temperatures and can be found on the moon. Space missions could help understand their distribution on the moon. If they contain elements like Hydrogen and Oxygen, this “could have a profound impact on the future of deep space exploration and commerce", NASA says. It would reduce the amount of supplies that would have to be sent from Earth to support humans in deep space. What is a launch window, and why is it so precise? The launch window refers to the time period in which a particular mission must be launched. Chandrayaan-3 took off at 2:35 pm. According to the European Space Agency (ESA), if the spacecraft intends to get close to another spacecraft, a planet, or other point in space, the launch must be carefully timed so that their orbits overlap at some point in the future. If the weather is bad or a malfunction occurs during a launch window, the mission must be postponed until the next launch window appropriate for the flight. It illustrates with an example: “Imagine the Solar System as an athletics race track. If you were watching the 400 metres race from the centre of the track and wanted to intercept one of the runners taking part, one way would be to simply chase the runner you wish to stop. If you were fast enough, you might eventually catch up but only after expending a lot of energy and travelling a long way. A much better way to intercept your athlete is simply to walk across the centre to the other side of the circular track. It is a much shorter distance and you use a lot less energy and time getting there. You calculate your walk so that you arrive at the other side of the track at the same time as they do. Too early, and you are waiting around for them. Too late, and you have missed them completely - you'd have to wait one lap until they came around again. In spaceflight, straight-line paths do not exist for the same reason. All planets move in long, curved paths around the Sun that take the shape of circular and elliptical orbits.” Further, the Earth and other planetary bodies are also not stationary and their constant movement needs to be calculated to devise the shortest, most fuel-efficient path for the spacecraft. Why will it take so many days for the lander to reach the moon? This whole process is likely to take around 42 days, with the landing slated for August 23 at the lunar dawn. The Chandrayaan-3 mission will be launched into space by the Launch Vehicle Mark-III, (LVM-III). After launching into an orbit around the Earth at an altitude of 179 km on Friday, the spacecraft will gradually increase its orbit in a series of manoeuvres to escape the Earth’s gravity and slingshot towards the moon. After reaching close to the moon, the spacecraft will need to be captured by its gravity. Once that happens, another series of manoeuvres will reduce the orbit of the spacecraft to a 100×100 km circular one. Thereafter, the lander, which carries the rover inside it, will separate from the propulsion module and start its powered descent towards the moon's surface. The craft lander and rover have a mission life of one Lunar day. Each Lunar day lasts for 14 earth days, as does each Lunar night, as it takes around one month (close to 28 earth days) for the moon to complete one rotation on its axis (and one revolution around the earth). The rover and lander cannot survive the extreme drop in temperatures during lunar nights, which is why they are being landed right at dawn. And finally, why do we want to go to the moon? The Moon is the closest cosmic body to earth, where space discovery can be attempted and documented, said Isro at the time of Chandrayaan-2. It was also described as a promising test bed to demonstrate technologies required for future deep-space missions. It would further help “stimulate the advancement of technology, promote global alliances and inspire a future generation of explorers and scientists”, it said. For live updates of the launch, click here.
