Chandrayaan-3 leaves Earth's influence after 17 days in orbit. Next stop: Moon

After spending 17 days in orbit around the Earth, India's third lunar spacecraft Chandrayaan-3 has bid goodbye to its orbit around the home planet and set course for its destination - Earth's Moon. By performing a Trans-Lunar Injection (TLI), a long-duration burn of its engines (around 20 minutes), Chandrayaan-3 has completely slingshot itself out of Earth'sorbit and influence, thereby putting it on a path that will eventually lead it to the moon.

This crucial manoeuvre has been performed on the intervening night of Monday and Tuesday (31 July and 1 August between midnight hour and 1 am Indian Standard Time).

"Chandrayaan-3 completes its orbits around the Earth and heads towards the Moon. A successful perigee-firing performed at ISTRAC, ISRO has injected the spacecraft into the translunar orbit. Next stop: the Moon. As it arrives at the moon, the Lunar-Orbit Insertion (LOI) is planned for Aug 5, 2023," the Indian space agency posted on X, formerly known as Twitter at 00:32 hrs on 1 August, Indian Standard Time.

So far, during its orbit around the earth, as per commands from ISRO's tracking, telemetry and command facility (ISTRAC), the spacecraft fired its onboard engines on five pre-planned occasions. During each of these engine firings, the craft slingshot itself into a higher orbit and moved further away from the Earth. But now, the craft has exited the earth's influence and set course for the moon.

To get its spacecraft to destinations far away from the Earth (Moon, Mars), the Indian space agency has been using the Slingshot method, scientifically known as Hohmann Transfer Orbits. This is an energy-efficient technique to get a spacecraft to its destination, in the absence of powerful and heavy-lifting rockets.

With extremely powerful rockets (such as America's Space Launch System), it is possible to propel a massive craft(weighing close to 40 tonnes) to the moon in less than a week. Given that India's LVM3 rocket has around only a fraction of the lifting power of global super-heavy rockets, the Indian space agency is using a time-consuming method (which takes more than a month) to get its 3.9-tonne craft to the moon, using available resources.

Having heavier and more powerful rockets offers the performance to carry heavy and more capable spacecraft. The combination of heavy rockets and heavy spacecraft will ensure that the craft is able to develop the velocity and departure energy required to rapidly exit the earth's influence and set course for the moon(Trans Lunar Injection).

Here on, the craft will travel around five days to reach a pre-determined point in space, where the moon will also be at the time. Remember, the moon is also circling the earth and the spacecraft is also circling the earth, so the craft and the moon will have to meet at a certain ideal time and place. Once that meeting happens, the craft will be captured by the moon's gravity and it would begin to orbit the moon.

Thereafter, during the ideal time and day, the lunar craft is allowed to de-boost itself and progressively get closer to the moon's surface, slow itself down gradually and prepare for a lunar landing. ISRO has planned Chandrayaan-3's lunar landing at 5:47 pm Indian Standard Time on 23rd August.