The orbit of Chandrayaan-2 around the Earth was raised for a third time on Monday at 3:12 pm to reach a highly elliptical orbit of 276 x 71792 km. The on-board propulsion system was fired for 989 seconds, according to Indian Space Research Organisation (ISRO).
“The third manoeuvre was completed successfully on Monday and the spacecraft parameters are all normal for now,” said an official from ISRO, on condition of anonymity.
The propulsion systems have to be fired two more times on August 2 and 6 to increase the apogee or the point on the orbit farthest from the Earth.
A total of six manoeuvres had been planned in the 23-day duration that Chandrayaan 2 would spend going around the earth – one to increase the perigee or the point on the orbit closest to the Earth and five others to the apogee. However, the rocket carrying Chandrayaan 2, India’s heaviest GSLV Mark III, “over-performed” on the day of the launch giving a boost of 6,000 km to the spacecraft.
This reduced the number of manoeuvres to five – one to increase the perigee and four to increase the apogee – till the spacecraft left Earth-orbit and started its journey towards the moon.
The spacecraft will be injected in a trans-lunar orbit (orbit between Earth and moon) on August 14 with the parameters 266 x 4,13,623 km. The spacecraft is scheduled to reach a lunar orbit of August 20.
“The teams here recalculate the orbit every hour and there is round-the-clock simulation to plan for the next move to ensure the spacecraft is on track. Unlike a launch vehicle which we cannot guide once launched, we can keep adjusting the orbit of the spacecraft as needed,” the official said.
The propulsion systems would be fired four more times in the lunar orbit to lower the spacecraft into a circular 100x 100 km orbit around the moon with a two-hour orbital time or time taken for the satellite to complete one orbit.
After this, the lander-rover will separate and move to a 100x30km orbit. During this period, the optical high-resolution camera on-board will be turned on to scout for a suitable landing site in the lunar south pole.
The images taken will be transmitted to Earth and processed after which the landing site map will be uploaded to the lander-rover before its powered descent to the moon on Sept 7 at 2.58am.