Chandrayaan-3 takes off: How the moon mission compares with 2019’s Chandrayaan-2

Chandrayaan-3 takes off: How the moon mission compares with 2019’s Chandrayaan-2


Context- India’s third mission to the moon took off on Friday at 2:35 pm, The mission aims to achieve what its predecessor could not — land softly on the lunar surface and explore it with a rover.

A successful soft landing will make India the fourth country, after the United States, Russia, and China, to achieve the feat. The position remains vacant after the missions from Israel and India in 2019 crash-landed and the spacecraft carrying a lander-rover from Japan and a rover from UAE failed in 2022.

The mission

  • 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.

(Credits- Indian Express)

  • This whole process is likely to take around 42 days, with the landing slated for August 23 at the lunar dawn. Lunar days and nights last for 14 earth days. The lander and rover are built to last only one lunar day — they can’t survive the extreme drop in temperatures during lunar nights — and hence have to land right at dawn.
  • As for the landing site, it has been moved slightly from the previous location on a plateau between two craters. The site, at around 70 degree S near the Southern pole of the moon, was selected as there are several craters here that remain permanently in shade, and can be the store-house of water ice and precious minerals. The change in the current landing site has been made on the basis of the pictures captured by the Chandrayaan-2 orbiter, which have provided a very clear map of the moon.
  • Despite the current mission not carrying an orbiter — it will use data from the Chandrayaan-2 orbiter — the weight of the payload is slightly more than the previous mission, with the lander making up most of the excess weight. This is most probably due to the modifications made for a safe landing.

Changes in the mission, design

  • Isro chairperson S Somanath recently said the changes to the current mission were “failure-based.” He said, “Instead of a success-based design in Chandrayaan-2, we are doing a failure-based design in Chandrayaan-3 —we are looking at what can go wrong and how to deal with it.”
  • During Chandrayaan-2, the lander and rover had crashed on the moon, instead of landing softly on it. Explaining the reason for it, Somanath said the main issue was that the five engines on the lander developed a slightly higher thrust than expected. The lander had to click pictures to determine the landing site, remaining stable during the period, and the errors accumulated.
  • When the course corrections began, the spacecraft needed to turn very fast but its ability to turn was limited by its software. Also, the spacecraft faced contradictory requirements of slowing down the velocity at which it was coming down but accelerating forward in order to reach the correct landing site. So, when it did land, it hit the ground with a higher velocity.

The changes to the current mission have been made keeping this in mind

  • One, the landing area has been expanded. Instead of trying to reach a specific 500mx500m patch for landing as targeted by Chandrayaan-2, the current mission has been given instructions to land safely anywhere in a 4kmx2.4km area.
  • Second, the lander has been provided more fuel so it can travel longer distances to the landing site or an alternate landing site, if need be.
  • Third, the lander will no longer depend only on the pictures it clicks during the descent to determine a landing site. High resolution images from the Chandrayaan-2 orbiter have been fed into the lander and it will click images just to confirm that it has reached the correct location.
  • Then, changes have also been made to the physical structure of the lander. The central thruster on the lander has been removed, reducing the number from five to four. The legs have been made sturdier to ensure it can land even at a higher velocity. More solar panels have been added to the body of the lander.

Experiments on board

  • The payloads on the lander and rover remain the same as the previous 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.
  • A new experiment has been tacked on to the propulsion module that will remain in orbit around the moon for three to six months. Called Spectro-polarimetry of Habitable Planet Earth (SHAPE), it will look for smaller planets that might be habitable in the reflected light.

Conclusion- While the objectives of the mission remain the same, scientists at the Indian Space Research Organisation Isro have learnt from the previous mission. The lander’s design was improved after a series of tests to see how it performs under various circumstances, such as inability to reach the landing spot, failure of electronics or sensors, velocity being higher than needed, among others.

Syllabus- GS-3; Science and Tech

Source- Indian Express