How Are We Supposed to Get Signals From Chandrayaan-3?

Now, all eyes are on the Chandrayaan-3, as Russia's Luna-25 crashed during landing.

Generally, Earth–Moon–Earth communication or EME (also regarded as Moon bounce), is a type of radio communications technique. In this method, a radio waves propagates from an Earth-based transmitter directed through reflection from the surface of the Moon back to an Earth-based receiver. As Chandrayaan-3 is on the verge of landing, you might be thinking, how it's possible to get information immediately. Is the method of sending information like running commentary or something else. If you are eager to know how this transmission system is actually going to be, go through this article.

Difference between Radio waves and electromagnetic waves:

Before understanding the transmission, it's important to know about wave properties. Radio broadcasts are generally done through audio waves. Usually, audio waves require a medium like the air for propagation. However, signals through space are sent in the form of electromagnetic waves. This is basically progession of energy, which don’t require any medium to travel. Electromagnetic waves are a type of transverse waves, indicating that they are measured by their amplitude or height and wavelength or distance between the highest/lowest points of two consecutive waves.

How ISRO is getting signal?

Chandrayaan-3 mission was launched on July 14, 2023. Since then, Indian Space Research Organisation (ISRO) is getting updates on spacecraft’s health via ground stations of the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA).

The Moon is more than 238,855 miles (384,400 km) away from the Earth. For such distance, it will take around 2.6 seconds for two-way radio communication to travel.

The Mission Operations Complex (MOX) at ISRO Telemetry, Tracking and Command Network (ISTRAC), Bengaluru is going to face this time lag while transmitting and receiving signals to and from the Chandrayaan-3 Vikram lander encircling the Moon.

The Pragyan rover would receive its commands to perform experiments and traverse the lunar surface, through Vikram lander. However, ISRO has a backup plan. If direct communication between the lander and earth station is not possible, Chandrayaan-2 will mediate the process.

ESA and ISRO collaboration:

"Since the launch of Chandrayaan-3, ESA has been supporting the mission by utilising two of the ground stations in the ESTRACK network to track the satellite in its orbit, receive telemetry from the spacecraft and forward it to the Mission Operations Centre in Bengaluru, and forward commands sent from Bengaluru to the flying satellite," Ramesh Chellathurai, ground operations engineer at ESOC Darmstadt, said.

"The ESA’s 15-metre antenna in Kourou, French Guiana, and the 32-metre antenna belonging to Goonhilly Earth Station, U.K., were selected for the support, based on their technical capabilities as well as their periods of geometric visibility to the satellite," the statement added.

"These two stations have been communicating with the Chandrayaan-3 mission on a regular basis, providing a complete communication channel between the Mission Operations Team in Bengaluru and the Chandrayaan-3 satellite," Mr. Chellathurai added.

"It will be this telemetry that is used to confirm the success of the landing. This type of back-up support is common during the key moments of a space mission, such as a landing. After a successful landing, data collected by the mission’s Rover will be routed via the Lander Module to the ground stations. These valuable scientific data will be received by the antennas in Kourou and Goonhilly and forwarded to the Mission Operations Centre in Bengaluru," Mr. Chellathurai said.

Support from NASA:

NASA's 'Deep Space Station' (DSS)-36 and DSS-34, Canberra Deep Space Communications Complex are providing telemetry and tracking coverage during the powered descent phase. This Deep Space Network is also supported by DSS-65 at Madrid Deep Space Communications Complex.

"We receive the telemetry from the spacecraft that has the data on the health and status as well as instrument measurements and pass them on to ISRO in practically real-time. We also monitor the radio signal itself for the Doppler effect, which is the primary tool for navigating the spacecraft. This is the critical information during the landing phase and tells us in real-time how it is doing," Sami Asmar, Jet Propulsion Laboratory’s Interplanetary Network Directorate Customer Interface Manager, said.

He added that "primary support for the mission comes from the DSN complex in California because that is exactly on the other side of the Earth from India and can be in view of the Moon when the station in India cannot see the Moon."

ISRO has a 32-metre deep space tracking operation station in India. It helps to locate, track, command and receive telemetry along with scientific data from its distant spacecraft. However, ISRO needs support from others to track or command a spacecraft when it is outside the 'field of view' of this antenna.

"Thanks to its global 'Estrack' network of deep space stations, ESA can help its partners track, command and receive data from spacecraft almost anywhere in the Solar System via its ESOC (European Space Operations Centre) mission control centre in Darmstadt, Germany," ISRO said in a statement.