ISRO 2023 Rewind - To the Moon and back, in preparation for Chandrayaan-4

By making India the fourth nation to soft-land a craft on the moon and the first to do so near the unexplored Lunar south pole, the Indian Space Agency ISRO showcased its capability and determination in remarkably rising from the setback of Chandrayaan-2 (2018). For India, Chandrayaan-3 is almost like a gift that keeps on giving and it has already set the ball rolling for Chandrayaan-4. From the flawless launch on July 14 to the autonomous landing sequence that lasted 19 minutes (on August 23), the mission progressed in textbook fashion. The icing on the Lunar cake was the "India, we are on the Moon" quote from the ISRO Chief, in his post-landing address. In addition to swelling Indian hearts with pride, it also left an indelible mark on cyberspace, as the Chandrayaan-3 live stream by ISRO continues to be the most-viewed on YouTube. On the face of it, Chandrayaan-3 was all about soft-landing safely, deploying the rover there and leaving India's imprint on the moon. While the science data from Chandrayaan-3 continues to be scrutinised and processed, some of the achievements and findings of the mission are worth re-emphasising. Lunar hop Chandrayaan-3 landed vertically like a helicopter. In the words of ISRO, VSSC Director Dr. S.Unnikrishnan Nair, "It was a feather-like soft-landing". Let's imagine that the Chandrayaan-3 lander wants to take off again and come back. In that case, it would have to fire its engines and almost launch itself like a rocket and reach Lunar orbit. Related video: Year Ender 2023: A look back at this year's space exploration and what lies ahead in 2024 (India Today) As a minor step or hop towards that ambitious future goal, the Vikram lander of Chandrayaan-3 was commanded to perform a hop test, which it successfully performed. Think of the hop as an exercise move - jumping up from a point and landing a few centimetres beside where you started from. By performing this manoeuvre, ISRO has re-fired the engines of the Vikram lander and gathered valuable data on engine firings on the Lunar surface. WATCH | Moon landings, giant leap on Mars, & more... NASA reveals its 2024 plans Notably, the liquid-fuelled engines of the lander module were fired almost 10 days after they last fired (during the landing on August 23). Propulsion Module returns! All talk about Chandrayaan-3 had come to an end by October, as it became evident that the craft had completed its planned 14-day mission life (One Lunar day) and did not show signs of waking up (which ISRO had partially hoped for, as a bonus). While there was no response from the lander and rover on the moon, the craft that continued to circle the moon, the Propulsion Module had more tricks up its sleeve. The Propulsion module is the vehicle that carried the Chandrayaan-3 craft from the earth orbit to the Lunar orbit. Therefore, it has its own set of engines and fuel tank. Watch: NASA's Curiosity rover records 'dawn to dusk' video on Mars While the Propulsion module was not a full-fledged orbiter like that of the Chandrayaan-2 orbiter, ISRO carried out a significant feat with the Propulsion module. Realising that the Propulsion module had at least 100 kilograms of fuel in its tank, after one month of circling the moon, ISRO chose to not waste a drop of fuel and wanted to derive the proverbial maximum mileage from the mission. The craft that was circling the moon was gradually steered out of the moon's sphere of influence and brought closer to the earth. The moon is around 3.84 lakh kilometres away from the Earth. From the Lunar orbit, the Propulsion Module traveled a distance of 2.34 lakh kilometres to reach an orbit very high above the earth. According to ISRO, the module was brought to an orbit that is almost 1.15-1.54 lakh kilometres above the Earth. This is a very safe orbit with hardly any satellites operating in the region and it means that the Propulsion module can remain there till the end of its life and beyond, without any risk of collision. Watch | Report: Tesla to set up manufacturing plant in Gujarat, India × Just like the hop test, this return flight of the propulsion module helps ISRO's future Lunar exploration plans. It would prove crucial in future missions such as Chandrayaan-4 that involve bringing samples back from the moon. It also validates ISRO's spacecraft mission operations planning, which involved the sophisticated and meticulous calculations required to return a craft from one celestial body's orbit to another. Simply put, ISRO has derived much more value out of Chandrayaan-3, than what was initially expected and publicly known.