As the Chandrayaan-3 mission rover 'Pragyan' is on the prowl collecting crucial data, images, and sharing them back with the rover and then to the Earth, establishing communication between the rover and lander on the lunar surface using Rx/Tx antennas poses significant challenges. These challenges arise from factors as the lunar environment’s harsh conditions, signal interference, maintaining line-of-sight communication and ensuring reliable data transmission over varying distances. Considering these factors, ISRO has implemented high-gain Rx/Tx antennas to address the communication challenges and minimize latency.
“Setting up communication between Earth-based ground stations and the lunar surface lander is a task fraught with multiple challenges. The distance between the Earth and moon as the moon is about 3,84,400 kilometres (238,900 miles) away from Earth. This means that radio waves, which are used for communication, would take about 1.2 seconds to travel between the two bodies. This long delay makes it difficult to have real-time conversations and to control spacecraft in real-time. Besides this, the moon has no atmosphere, so radio waves can travel unimpeded. This means that there is no interference from the atmosphere. But, it also means that there is no protection from solar radiation and other space weather events. These events can damage spacecraft and disrupt communication signals. Additionally, the lunar surface is covered in rocks and dust, which can scatter and absorb radio waves. This can make it difficult to maintain a clear signal between Earth and the moon,” explained space and aerospace expert Girish Linganna. He added that as the moon’s gravity is much weaker than Earth’s, it is difficult to keep the spacecraft in orbit around the moon. This can make it difficult to maintain a reliable communication link.
Having perfectly achieved the soft landing on the south pole of the moon the Chandrayaan-3 mission is gearing up for a remarkable lunar expedition. In a span of 14 days, its rover will cover around half a kilometre distance on the moon, collecting crucial data and images along the way. Over the next two weeks, the 6-wheeled Pragyan rover module from Chandrayaan-3 is scheduled to share data with the scientific community. Subsequently, the moon will experience a 14-day night-time period during which the Vikram lander and Pragyan rover, both of which are dependent on sunlight, will become inactive. Nonetheless, the chances of the pair reactivating upon the return of sunlight have not been dismissed by ISRO scientists.
Derived from the Sanskrit word for ‘Wisdom’, Pragyan is a six-wheeled rover aimed at conducting a sequence of lunar surface experiments. The rover features a rectangular 91.7 x 75.0 x 39.7cm chassis, supported by a 6-wheel rocker-bogie drive system. Equipped with navigation cameras and a 50W solar panel, Pragyan communicates directly with the lander through Rx/Tx antennas.
“The 6-wheel rocker-bogie drive system is a type of vehicle propulsion mechanism that allows for better mobility over rough terrain. It employs a flexible suspension system which ensures that all six wheels can maintain contact with the ground, enhancing stability and manoeuvrability. An Rx/Tx antenna is a type of antenna that can both transmit and receive radio waves. It is typically used in applications where both functions are required, such as in wireless communication systems,” remarked Linganna.
This expert further adds that there are many ways communication can be streamlined from the lunar surface. “As radio waves travel differently at different frequencies, by using multiple frequencies, it is possible to find a frequency that is less affected by the lunar environment. Redundancy techniques can be used to send the same data over multiple channels. This can help to ensure that the data is received even if one of the channels is disrupted,” pointed out Linganna.
