The Indian Space Research Organisation’s (ISRO’s) Chandrayaan 2 mission will near the close of its journey phase at the end of today. On September 5, the Vikram lander detached itself from the orbiter in a circular orbit around the Moon and began preparations to descend on the lunar surface. It is expected to attempt this landing between 1.30 am and 2.30 am later tonight, i.e. the early hours of September 7.
If the landing is completed as planned, ISRO will have achieved a significant milestone, rendering India only the fourth country in history to successfully soft-land a payload on the Moon.
Obviously it is easier said than done. Vikram, a trapezoidal box weighing 1.4 tonnes – will first descend up to a height of 30 km over the surface using four thrusters. Then its computer will shut them off to prevent the dust they kick up from the surface from damaging its onboard sensors. The lander will then shift to using just one thruster and descend slowly, using the sensors to provide guidance feedback.
K. Sivan, the chairman of ISRO, has said that this phase will be ’15 minutes of terror’ as the lander will autonomously – i.e. without the active assistance of its scientists – attempt to land.
Once it has touched down, scientists will perform health checks over the next few hours to ensure all its components are working as intended. If they are, the lander will drop a ramp over the surface to allow the Pragyan rover to exit and descend, beginning the scientific operations phase of the Chandrayaan 2 mission.
Sticking the landing is expected to bring great accolades for ISRO from space scientists, analysts and entrepreneurs from around the world. Apart from joining an elite club of spaceflight agencies, the feat will also signal ISRO’s mastery of many of the technologies required to achieve interplanetary travel and remote robotic operations.
ISRO signalled this to some extent with its Mars Orbiter Mission (MOM) of 2014, but as many experts have acknowledged, Chandrayaan 2 is much more complicated as well as is fitted with a richer suite of analytical instruments. And while MOM was a technology demonstrator, Chandrayaan 2 is a scientific mission, with its primary goal being to expand its predecessor’s knowledge of the Moon’s water content.
Success would also make Chandrayaan 2 the southernmost lunar surface mission in history. Vikram’s landing spot of choice is located on the 70.9º S latitude, near the south polar region. In 2011, one of Chandrayaan 1’s instruments had spotted an abundance of water in the lunar soil near the Moon’s south pole.
The Chandrayaan 2 stack – comprising the orbiter, lander and rover – carries a total of 13 instruments plus a small retroreflector provided by NASA. While the orbiter will revolve around the Moon for more than a year to come, Vikram and Pragyan will be online only for 14 Earth days, or one lunar day. This is because the lithium-ion batteries that store the power generated by their solar cells are not likely to survive the extreme cold of the lunar night.
ISRO has said it will provide a live telecast of the landing event (corresponding to events on Earth) via Doordarshan, on its website and via its social media accounts from 1:10 am. Sivan is expected to address the media around 9 am tomorrow, September 7, morning with more details.