Chandrayaan-3, India's third lunar mission, has reached a significant milestone as it completed its orbits around the Earth and is currently situated in the translunar orbit. Chandrayaan-3 is set to head towards its next destination, the Moon, with the lunar orbit insertion (LOI) planned for August 5, 2023, as per the Indian Space Research Organisation (ISRO).
Following its launch on July 14, the Chandrayaan-3 mission underwent a series of five sequential orbit raises to gradually elevate the spacecraft's orbit.
The spacecraft has changed its course to reach the Moon by using its perigee engine, which acts like a rocket to accelerate the spacecraft. The perigee refers to the point in an orbit that is closest to the Earth. By firing the perigee engine, the spacecraft gains speed and energy to travel towards the moon.
“The firing of the perigee engine is done at this specific point because it helps maximize the spacecraft's efficiency. By firing the engine at the perigee, the spacecraft can take advantage of the Earth's gravitational pull to boost its speed and propel itself towards the Moon. This is called trans-lunar injection. After the firing of the perigee engine, the spacecraft will enter into a new orbit around the moon on 5th of August and continue to orbit for a few days to further adjust its trajectory and get closer to the Moon's surface viz 100kms circular orbit above the moon surface. This allows the spacecraft to ensure a proper landing by carefully positioning itself before descending onto the lunar surface,” explained space and aerospace expert Girish Linganna.
ISRO has set a plan to separate the landing module from the propulsion module on August 17. The landing module, named Vikram, carries the Rover called Pragyaan. ISRO will then aim to safely land Vikram on the Moon's surface on August 23. This separation is crucial as it allows the landing module to independently navigate and make a precise touchdown on the Moon.
Approximately four hours after a successful soft landing, the Rover Pragyaan is scheduled to detach from the Lander Vikram. Both Vikram and Pragyaan will then proceed to conduct in situ experiments on the lunar surface. In situ experiments refer to conducting tests and analysis directly on the Moon's surface without bringing samples back to Earth. These experiments will provide valuable data and insights regarding the lunar environment, composition, and other scientific measurements, helping to expand our understanding of the Moon and its potential for future exploration.
“The propulsion module, which contains scientific instruments, will continue to orbit the Moon. This means that after the successful landing of Vikram and the deployment of Pragyaan, the propulsion module will not land on the lunar surface but instead remain in the Moon's orbit. By staying in orbit, the propulsion module can continue to gather valuable data and conduct scientific experiments. It allows for a comprehensive exploration of the Moon's environment and enables further study of the lunar gravitational field, mapping of the lunar surface, and other scientific measurements. This data will contribute to our understanding of the Moon's geological composition, its evolution, and potentially aid future missions and human explorations,” said Linganna.
Though Chandrayaan-3 is taking more than a month to reach the Moon, if one has to go back in history, the Apollo 8 mission was the fastest journey to the moon, taking 69 hours and 8 minutes. Every mission after Apollo 8 took at least 74 hours to reach the moon. The Apollo 17 mission was the last mission to land on the Moon, taking 86 hours and 14 minutes. The USSR's Luna-2 craft took just 34 hours to reach the moon in 1959.
To travel long distances in space, one needs high speeds and straight trajectories. The Apollo 11 mission used a super heavy-lift launcher called Saturn V to travel at more than 39,000 kilometres per hour. The Saturn V rocket could lift 43 tonnes, including the lunar module, service module, and command module. The third stage of the Saturn V rocket put the modules into a trans-lunar trajectory after orbiting Earth for the second time. The launcher and the lunar craft used powerful engines to reach the Moon in just four days, covering 3,80,000km. The Apollo missions between 1969 and 1971 cost NASA $185 million each, or $1.2 billion in 2016. Of this, $110 million was spent on building each Saturn V rocket.
“Unlike previous missions that prioritised speed, Chandrayaan-3 takes a different approach, focusing on cost optimisation and safety considerations while still accomplishing its research objectives. The Apollo mission, which brought humans to the Moon, achieved faster travel times but incurred high fuel consumption costs. The specially designed Saturn 5 rockets were used to accomplish this feat, but their construction came with exorbitant expenses. In contrast, ISRO aims to strike a balance between efficiency and affordability,” remarked Srimathy Kesan, founder and CEO of Space Kidz India.