Chandrayaan-3 and other moon missions

Context

  • The Chandrayaan-3 mission is India’s third lunar mission and second attempt to make a soft landing on the surface of the Moon.

    • It’s one of the several space missions lined up to go to the celestial body, including Russia’s Luna 25 mission and NASA’s Artemis II.
    • A successful soft landing will make India the fourth country, after the United States, Russia, and China, to achieve the feat.

Chandrayaan-3 and other moon missions

About the Chandrayaan-3 mission

  • After launching into an orbit around the Earth at an altitude of 179 km, 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.
  • 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.

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.

The different kinds of moon missions that have been launched so far:

  • Flybys: These are the missions in which the spacecraft passed near the Moon but did not get into an orbit around it. These were either designed to study the Moon from a distance or were on their way to some other planetary body or deep space exploration and happened to pass by the celestial body. Some early examples of flyby missions were Pioneer 3 and 4 by the United States and Luna 3 of the then USSR.
  • Orbiters: These were spacecraft that were designed to get into a lunar orbit and carry out prolonged studies of the Moon’s surface and atmosphere. India’s Chandrayaan-1 was an Orbiter, as were 46 other Moon missions from various countries. Orbiter missions are the most common way to study a planetary body. So far, landings have been possible only on the Moon, Mars and Venus. All other planetary bodies have been studied through orbiter or flyby missions. Chandrayaan-2 mission also consisted of an orbiter, which is still operational and orbiting the Moon at an altitude of around 100 km.
  • Impact Mission: These are an extension of Orbiter missions. While the main spacecraft keeps going around the Moon, one or more instruments on board make an uncontrolled landing on the lunar surface. They get destroyed after the impact, but still send some useful information about the Moon while on their way. One of the instruments on Chandrayaan-1, called Moon Impact Probe, or MIP, was also made to crash land on the Moon’s surface in a similar way. ISRO claimed that the data sent by the MIP had presented additional evidence of the presence of water on the Moon, but these findings could not be published because of calibration errors.
  • Landers: These missions involve the soft landing of the spacecraft on the Moon. These are more complicated than the Orbiter missions. In fact, the first 11 attempted lander missions had all ended in failure. The first landing on the moon was accomplished on January 31, 1966, by the Luna 9 spacecraft of the then USSR. It also relayed the first picture from the Moon’s surface.
  • Rovers: These are an extension of the lander missions. The lander spacecraft, because they are bulky and have to stand on legs, remain stationary after landing. The instruments on board can carry out observations and collect data from close quarters but cannot come in contact with the Moon’s surface or move around. Rovers are designed to overcome this difficulty. Rovers are special wheeled payloads on the lander that can detach themselves from the spacecraft and move around on the moon’s surface, collecting very useful information that instruments within the lander would not be able to obtain. The rover onboard Vikram lander in the Chandrayaan-2 mission was called Pragyaan.
  • Human missions: These involve the landing of astronauts on the moon’s surface. So far only NASA of the United States has been able to land human beings on the moon. So far, six teams of two astronauts each have landed on the moon, all between 1969 and 1972. After that, no attempt has been made to land on the Moon. But with NASA’s Artemis III, currently planned for 2025, humanity is set to once again to the lunar surface in more than 50 years.

Reference: IE

https://indianexpress.com/article/explained/explained-sci-tech/chandrayaan-3-launch-tomorrow-the-two-moon-missions-compared-8831747/

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