Chandrayaan-3, India’s third lunar mission, is set to enter the lunar orbit in approximately 6 days, with another crucial manoeuvre planned between 12 am and 1 am on August 1st. During this manoeuvre, ISRO will skillfully slingshot the spacecraft towards the Moon.
The anticipated midnight trans-lunar injection (TLI) manoeuvre is projected to endure for a period ranging between 28 to 31 minutes. The spacecraft’s onboard thrusters will be activated during the closest point to Earth (perigee), rather than at the farthest point (apogee).
Why does Perigee attempt the slingshot manoeuvre? The Chandrayaan-3 spacecraft is in an elliptical orbit around Earth, moving at velocities ranging between 1 km/second and 10.3 km/second. The highest velocity (10.3 km/second) is achieved at perigee, while the lowest velocity occurs at apogee. During the slingshot attempt, the spacecraft requires a high velocity. Additionally, the spacecraft’s angle must be altered to enable its journey towards the Moon, which can be efficiently achieved if the operation is carried out at perigee.
Around five to six hours before the scheduled thruster firing time, the pre-written and preloaded commands for the trans-lunar manoeuvre will be activated.
Apart from assisting the spacecraft in changing its orientation for the journey towards the Moon, the firing of the thrusters will also increase its velocity. After the trans-lunar injection (TLI) manoeuvre, Chandrayaan-3’s velocity is projected to be approximately 0.5 km/second higher than at perigee.
The journey to cover 1.2 lakh km typically takes around 51 hours. The average distance between Earth and Moon is 3.8 lakh km, although the actual distance may vary daily based on the positions of the Earth and Moon, ranging between 3.6 lakh km and 4 lakh km. Reaching the Moon’s orbit is just one aspect of the mission. ISRO already achieved this feat with the satellites Chandrayaan-1 in 2008 and Chandrayaan-2 in 2019. The more critical phase of Chandrayaan-3 will unfold after the spacecraft successfully reaches the Moon.
Following the successful capture of a lunar orbit, ISRO will execute a series of manoeuvres to decrease the spacecraft’s altitude and stabilize it into a 100 km circular orbit. During this orbital phase, the propulsion module will be separated from the landing module, and this specific operation is planned for August 17. Subsequently, the scheduled landing attempt on the lunar surface is set to take place on August 23.