How will communication link between Chandrayaan-2 orbiter and Chandrayaan-3 lander help ISRO?

The distance between the Earth and Moon is more than 238,855 miles (384,400 km), it could take approximately 2.6 seconds for two-way radio communication to travel that far. That's the kind of lag that the ISRO Mission Operations team at the Mission Operations Complex (MOX) at ISRO Telemetry, Tracking and Command Network (ISTRAC), Bengaluru, would be facing while transmitting and receiving signals to and from the Chandrayaan-3 lander that's circling the Moon.

Given that India has the advantage of having two crafts—Chandrayaan-2 orbiter and Chandrayaan-3 propulsion module—circling the Moon, ISRO would be using one of them as a backup/emergency communication link.

ISRO has designed and developed the Chandrayaan-3 'Vikram' lander in a way that permits the lander craft to directly communicate with the stations back on Earth. In fact, the 26-kg Pragyan rover would also be depending on the lander craft for all its communication with the ground stations back on Earth.

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The rover would also receive its commands to perform experiments and traverse the lunar surface, via the lander. However, ISRO has a contingency plan, in case direct communication between the lander and earth station is not possible. That's where the predecessor mission Chandrayaan-2 comes into play.

5 things that can go wrong at the last moment before Chandrayaan-3’s landing

ISRO Chandrayaan-2 (its Vikram lander) failed to make a lunar soft-landing on September 7, 2019. However, the orbiter from the Chandrayaan-2 mission continues to circle the Moon and carry out its functions, as it contains adequate fuel to remain in its orbit for almost eight years, as estimated by ISRO in 2019.

Therefore, ISRO is using the Chandrayaan-2 orbiter as a backup communication link between its Chandrayaan-3 Vikram lander and the ground stations. Simply put, the Chandrayaan-2 orbiter would act as an intermediary between the lander and the ground stations.

"Welcome, buddy!’ Ch-2 orbiter formally welcomed Ch-3 LM. Two-way communication between the two is established. MOX has now more routes to reach the LM" ISRO posted on X on Monday afternoon.

This tweet explains that ISRO has established contact with the lander via the propulsion module and tested out its emergency communication method.

It must be remembered that the Chandrayaan-3 lander module is circling the Moon in a 25kmx134km orbit, which is its final pre-landing orbit. As it circles the moon, the lander module is testing out is various systems and sensors. This includes altimeters, laser doppler velocimeters, on-board cameras etc.

These sensors are best tested and calibrated when they are at an appropriate altitude from the moon. Hence, ISRO is making all preparations in the run-up to its lunar landing process (powered descent) that is scheduled to commence at 5.45pm (IST) on Wednesday.

In 19 minutes, the craft will reduce its horizontal velocity and vertical velocity, thereby slowing down from a few kilometres/second velocity to 1meter/second landing velocity.

ISRO has made the craft and its landing legs to withstand landing impacts of 2meters/second.

All eyes are on the India’s lunar landing, as Russia's Luna-25, which was meant to land on August 21, failed to make the descent after its manoeuvre to reach its final pre-landing orbit had gone wrong.

The Russian space agency, Roscosmos, officially announced the crash-landing and eventual loss of its craft, which is Russia's maiden standalone lunar mission.

However, the erstwhile Soviet Union has done dozens of Lunar missions, including sample return missions, the last of which was done in 1976.

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