The lander’s orbit needs to achieve an exactly 90° inclination before it lands
After this, Lander Vikram would slowly begin to prepare for its powered descent on the moon
NEW DELHI :
After spending more than six weeks in space, lander Vikram separated from the Chandrayaan-2 orbiter to prepare for its historic Moon landing on 7 September.
The separation process was completed at 1.15pm on Monday after Indian Space Research Organisation (Isro) brought the spacecraft closer to the moon, the space agency said. The lander is currently located in an orbit of 119x127km, while the Chandrayaan-2 orbiter continues to traverse its existing orbit.
“All the systems of Chandrayaan-2 orbiter and lander are healthy," the space agency said.
Vikram, weighing nearly 1,471kg, also carries the six-wheeled rover Pragyan, which weighs 27kg. It will now prepare for the soft landing near the south pole of the Moon.
But before that, scientists will perform a small three second manoeuvre on Tuesday to check if all the parameters of the lander are normal. This will be followed by two de-orbit manoeuvres to gradually reduce the altitude at which Vikram will orbit the moon and finally achieve an orbit of 36x110km.
The challenge for Isro is to ensure that the orbit of the lander achieves an inclination of exactly 90° before it begins to execute a successful soft landing near the lunar south pole. Even if there is a slight variation, it could miss the landing at the targeted site. And any change of site could raise difficulties, because if it lands on an inclined surface where the slope is more than 12°, the lander could topple.
The powered descent will begin on the intervening night of 6-7 September between 1.30 and 2.30am before which the lander would screen the lunar surface with its sensors and compare those images with what Isro has loaded onto it.
Vikram has the capability to communicate with Indian Deep Space Network (IDSN) at Byalalu, 25km from Bengaluru, as well as with the orbiter and rover. After the landing, all communication between Earth and Vikram will take place only through the orbiter.
The space agency has also made efforts to strengthen the sensor characterization of lander to make it more autonomous. According to Isro chairman K. Sivan, this would help reduce chances of any false decisions on account of human error.
If all goes as planned, the Indian spacecraft would land near the south pole between two craters at 1:55am on 7 September. But it would still take some time before rover Pragyan would roll out from lander Vikram, which is likely to happen between 5.30-6.30am.
Chandrayaan-2 took off from the Satish Dhawan Space Centre in Sriharikota aboard India’s most powerful rocket— the GSLV Mk111—on 22 July in the country’s second mission to the Moon. The orbiter, lander and rover have all been indigenously designed and manufactured.
The stakes are high as it is India’s first attempt a soft landing on the lunar body—a feat achieved by only three nations so far—the US, Russia and China. An Israeli attempt in April was unsuccessful.