NEW DELHI: At 2.21am on Wednesday, Chandrayaan-2 said goodbye to Earth and left the planet’s orbit to enter a straight path towards Moon. The Indian space research organisation (Isro) successfully conducted the ‘trans lunar injection (TLI) manoeuvre. During the TLI manoeuvre, the spacecraft’s liquid engine was fired for about 1,203 seconds to make it enter the lunar trajectory after it had spent 22 days in Earth’s elliptical orbit.
Explaining the lunar trajectory journey, Isro chairman K Sivan told TOI, “Chandrayaan-2 will take six days to travel in the lunar trajectory to reach Moon (lunar orbit) on August 20.” The total distance from Earth to Moon is 3.84 lakh kilometre.
To put Chandrayaan-2 in the lunar trajectory from perigee (the point in the orbit when the craft is nearest to Earth), Isro had first raised the elliptical orbit of the lunarcraft around Earth by conducting five manoeuvres. The fifth manoeuvre was conducted successfully on August 6 when the propulsion system was fired for a duration of 1,041 seconds, following which Isro had said all the lunarcraft’s parameters were normal. Out of 3,850kg (launch) mass of Chandrayaan-2, 2.542kg is just the weight of fuel.
On entering Moon’s sphere of influence, the onboard propulsion system of Chandrayaan-2 will be fired again to slow down the craft, which will enable it to be captured into a preliminary orbit around Moon.
Through a set of manoeuvres, the orbit of Chandrayaan-2 around Moon will be circularised at a height of 100 km from the lunar surface. Sivan said, “Like we had raised the Earth orbit of Chandrayaan-2 with the help of the propulsion system to take the craft away from Earth, we will use the propulsion system to lower the lunar orbit of Chandrayaan-2. We will do five to six manoeuvres to reduce its orbit.” Thereafter, Lander ‘Vikram’, named after the father of Indian space programme Vikram Sarabhai, will separate from the orbiter and enter into a 100kmx30km orbit around Moon. Once the lander reaches 30km altitude on September 6, the final descent to the lunar surface will begin.
The Isro chief told TOI, “The final descent of 30km for 15 minutes will be the most terrifying moments for Team Isro as we will be handling this most complex operation for the first time. The final descent of Chandrayaan-2, when its thrusters will move into reverse direction so as to reduce the spacecraft’s speed, will be shaky. “It will be just like holding a newborn baby for the first time,” he said.
If the Chandrayaan-2 team, led by project director M Vanitha and mission director Ritu Karidhal, is able to land the lunarcraft successfully in the wee hours of September 7, India will become the fourth country in the world to land its spacecraft on Moon.
After landing, Pragyan rover, housed within Vikram lander, will come out of it after four hours. It will roll out at a speed of 1cm per second. During its lifespan of one lunar day (14 Earth days), Pragyan will move up to 500 metre on the lunar surface. It will take images and analyse content on the lunar surface and send back data via Vikram or the orbiter to Earth within 15 minutes.
While Vikram and Pragyan will last for a lunar day, the orbiter will continue to circle around Moon for over a year during which it will also map Moon and take images of different areas to look for water and “new science”. A passive payload of Nasa, Laser Retroreflector Array, attached to Vikram will calculate the distance between the Earth and Moon and help detect the exact location of the lander on Moon.
Chandrayaan-2 is loaded with 13 desi payloads that will do a detailed study of topography, seismography, mineral identification and distribution, surface chemical composition, thermo-physical characteristics of top soil and composition of the tenuous lunar atmosphere for a new understanding of the origin and evolution of Moon.