The Indian Space Research Organisation (ISRO) is gearing up to launch the highly anticipated Chandrayaan-3 mission to the Moon on July 13. The spacecraft will embark on a nearly two-month-long journey, aiming to achieve a successful “soft landing” on the lunar surface. This mission holds significant importance for India, as it follows the setback experienced during the Chandrayaan-2 mission when the lander and rover crashed on the Moon in 2019.
However, landing on the Moon is an immensely challenging endeavor. It requires the precise alignment and coordination of multiple high-tech systems to function flawlessly. These systems include navigation guidance, flight dynamics, terrain imaging, thruster firings, and the crucial ability to decelerate at the right moment and speed to reach the desired landing spot.
The complexity of this process is highlighted by a senior scientist who worked on the Chandrayaan-2 mission. As the Moon-bound lander separates from the propulsion module and begins its descent, it must carefully control its speed and lateral movement. The lander’s descent speed needs to be reduced autonomously to three meters per second to ensure a soft landing. Thrusters are fired to achieve this reduction in speed and to control the lander’s orientation during descent.
Japan’s ispace encountered a similar challenge earlier this year when its Hakuto-R lunar lander failed to slow down in time due to an altitude miscalculation, resulting in mission failure. Chandrayaan-2 also experienced a comparable setback caused by a software glitch. These incidents highlight the criticality of managing the descent speed accurately due to the Moon’s reduced gravitational force compared to Earth.
The unique nature of lunar gravity necessitates even more precise control over the descent rate, as there is less natural deceleration. The burden of landing falls on the lander’s thrusters, which must fire for the right duration and with the appropriate force. Failure to control the descent speed properly can lead to a rapid and potentially dangerous descent.
The Moon’s challenging surface, marked by numerous craters and loosely held regolith (soil and rocks), adds further complexity to the landing process. Multiple landing options are considered in advance, including primary, alternate, and secondary contingency sites. The terrain within the landing radius plays a crucial role in achieving a successful touchdown.
To aid in the landing process, Chandrayaan-3 is equipped with two lander hazard detection and avoidance cameras. Inputs from these cameras will assist in making the final decision on the landing site. Importantly, while the data will be sent to mission control, the actual decision on where to land will be made by the lander itself due to the time delay in sending inputs from Earth.
These challenges and intricacies make lunar landings extremely difficult. Despite the Moon’s serene appearance in the night sky, it presents treacherous obstacles that must be overcome. Chandrayaan-3 aims to conquer these hurdles and secure its place in the history books as a successful lunar mission.