Chandrayaan-3 mission: Two vehicles have done their job, two more to go

As the Indian lunar mission Chandrayaan-3 entered its third and final phase, the Chandrayaan-3 lunar lander has now taken over the reins of the high-profile mission. Around 1 pm IST, on Thursday (August 17), the Indian space agency ISRO announced that the Chandrayaan-3 integrated spacecraft had separated into two parts - the propulsion module and the lander module.

While the propulsion module continues to orbit the moon for a few years, the lander module is headed towards the Lunar surface, in preparation for its lunar soft-landing scheduled for August 23.

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"LM is successfully separated from the Propulsion Module (PM). LM is set to descend to a slightly lower orbit upon a deboosting planned for tomorrow around 1600 Hrs., IST," ISRO tweeted.

With the Chandrayaan-3 propulsion module included, India now has three of its crafts circling the moon. This includes Chandrayaan-1 (defunct), Chandrayaan-2 orbiter and the Chandrayaan-3 propulsion module. India commenced its lunar exploration journey in 2008 with Chandrayaan-1 and then followed it up with Chandrayaan-2 in 2019, and Chandrayaan-3 in July this year.

Four vehicles in Chandrayaan-3 mission

Any spacefaring mission is like a relay race — there are many performers and each one completes their task and hands over to the next. On July 14, the LVM3 rocket was the vehicle that carried the 3.9-tonne spacecraft (comprising the propulsion module, lander and rover) into the earth's orbit. Performing its task in about 16 minutes, India's largest rocket injected the satellites into the desired orbit.

Then on, the craft's propulsion module gradually pushed and steered the craft away from the Earth, using its onboard engines. Until July 31, the craft orbited the earth and then fired its engines to gain more velocity, pushing itself to rendezvous with the moon in a few days (lunar transfer trajectory). On August 5, the craft reached the vicinity of the moon and fired its engines to slow itself down, reduce its orbit and get captured by lunar gravity.

From August 5 till August 17, the craft has been circling the moon. Once in a few days, the craft retro-fired its engines to slow down and reduce its orbit and get closer to the lunar surface. On Thursday, as the craft was in a 153 km x 163 km orbit, the propulsion module and lander module separated. This means that the propulsion module has completed its core task of getting the craft into an orbit around the moon.

Watch |Chandrayaan-3 to land on the moon on August 23

Henceforth, it will be the responsibility of the Vikram lander to test its cameras, sensors and engines, as it prepares for a lunar soft landing. The lander craft will commence reducing its orbit on Friday (August 18) and eventually cut down its velocity from a few kilometres/second to one metre/second, which is the ideal speed for lunar soft-landing.

After the successful soft landing, the lander is meant to open its ramp and allow the 'Pragyan' rover to roll out onto the lunar surface. In close coordination with each other, the lander, rover and propulsion module would then carry out their respective scientific tasks and send their data back to Earth.

As far as the lander and rover are concerned, ISRO is looking at an operational life of one lunar day or two weeks on Earth. However, after the lunar night passes and the new dawn breaks, when the sunlight is available, it is possible that the lander and rover come back to life.

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