ISRO's Chandrayaan-3 mission is all set to make its mark by deploying a lander and rover near the south pole of the Moon, a region known for its unique and challenging terrain. The lunar south pole is home to numerous craters. These craters, though not specifically targeted, represent the complex and demanding environment that the lander and rover must face.
The Shackleton crater, which is located at the south pole of the Moon, has been found to contain a vast amount of ice in the form of crystallized water. The presence of water ice on the Moon opens up possibilities for sustaining future human presence and space exploration. However, reaching the south pole and exploring its icy terrain poses a formidable challenge.
Space experts point out that the design of a lunar rover is very crucial as it must be well suited to withstand the harsh conditions of the lunar surface, including darkness, extreme cold, radiation, and challenging terrain.
“Rovers can travel much further than humans on foot, allowing them to cover more ground and collect more data. Engineers must carefully consider these factors when designing lunar rovers, as they can all pose significant challenges to a safe and successful operation of a rover on the Moon,” Girish Linganna, space and aerospace expert, told THE WEEK.
The Moon is in synchronous rotation with Earth, meaning that it rotates on its axis at the same rate that it orbits the Earth. This is why, from Earth, we can always see the same side of the Moon. As the Moon orbits the Earth, each side of it is exposed to 14 Earth days of light (lunar day) and 14 Earth days of dark (lunar night).
There are areas on the Moon’s poles that are always dark. These are called ‘permanently shadowed regions’ (PSRs). The Sun is always very low relative to the horizon in these areas, so the craters are always dark. These craters are impact features created when asteroids or comets collide with the Moon’s surface. Craters can vary greatly in size—from a few metres to hundreds of kilometres wide. There are millions of craters on the Moon and they are found all over the surface.
“Rovers rely on solar panels for power, so they cannot operate in darkness. Without power, rovers cannot move, use their instruments, or communicate with Earth. Solar panels work only when there is sunlight. Solar panels are delicate and need to be protected during launch and landing. The vibrations and forces of the launch can damage solar panels, and a hard landing on the Moon could also cause their breakage. Engineers must design solar panels strong enough to withstand the rigours of space travel and must pack them carefully to protect them from damage,” explained Linganna.
Linganna said in order to survive the lunar night, rovers must recharge their batteries in sunlight. This allows them to run their heaters during the long, cold lunar night. Rovers can also recharge their batteries using a nearby lunar lander. The lander acts as a home base for the rovers, providing them with a place to dock and recharge. The rovers use docking software to find the lander and, once they are docked, can use wireless charging to recharge their batteries.
The Moon’s surface experiences extreme temperature swings between day and night. During the day, the temperature can reach a scorching 127°C, but it can plummet to a frigid -173°C at night. The temperature can drop even lower inside craters, which are constantly in shadows. The coldest place in the solar system is found at the bottom of the Hermite Crater on the Moon and at the Moon’s poles. NASA’s Lunar Reconnaissance Orbiter (LRO) measured the temperature in the Hermite Crater to be about -250°C.
“The lunar rovers can also be painted with gold to prevent heat from being transferred by radiation similar to how a thermos flask retains heat. Rovers can also use aerogel, a type of insulation that is 99.8 percent air. Air is a good insulator and aerogel is very lightweight, making it ideal for space missions.
"Rovers have temperature control systems that include heaters and heat rejection systems. The heaters are controlled by a thermostat that can automatically switch them on and off. The heat rejection system uses a pump and tubing to release heat out into space, similar to how an air-conditioning system in a car works,” said Linganna.
Moon also has high levels of radiation that can cause the insulation on the rover wires to become brittle, leading to short circuits. Hence, lunar rovers need special shielded wires that are resistant to radiation damage. To overcome this, they normally use a shielded cable which has a black plastic jacket on the outside, a braided wire shield underneath and a white insulating material underneath that. Different coloured wires extend out from the end.
“The Moon’s surface appears flat and smooth from Earth, but is actually quite varied. There are some flat areas, but there are also steep, rocky landforms and deep craters. To explore the varied terrain of the Moon, rovers need to be able to climb and manoeuvre over obstacles. They also need to be able to avoid getting stuck in soft soil or sand,” remarked Linganna.
Experts point out that the distance between the Earth and the Moon—approximately 384,000 kilometers—adds to the complexity of the mission. “The communication software must be sophisticated, allowing for complex command structures and intelligent decision-making processes to facilitate the rover's movements on the lunar surface. This level of autonomy is crucial, as there is no room for error in the harsh and unforgiving environment of Space,” remarked Srimathy Kesan, founder and CEO of Space Kidz India, which is into design, fabrication and launch of small satellites, spacecraft and ground systems.
Choosing to target the lunar south pole, known for its challenging conditions, is a testament to India's ambition and determination. “Success in this endeavor would be a significant milestone, demonstrating India's ability to achieve remarkable feats in a cost-effective and efficient manner. The Chandrayaan-3 mission has a budget of approximately Rs 610 crore, making it a highly economical project given the scope of its objectives,” said Kesan.
Besides, rovers exploring the Moon need special wheels that can withstand the sharp rocks and jagged, microscopic shards of rock found in the lunar regolith. Rovers need wheels with good treads to grip the powdery lunar regolith, which can be slippery to drive on. To see how a rover will work on the Moon, engineers test drive them on a fake Moon surface. This fake surface is made of a material that feels like real lunar soil. Rover wheels need to be designed to help the rover climb and descend steep crater walls. Rovers have wheels with deep grooves, spikes, or mesh. Drivers are taught to avoid places where the rover can get stuck. DuAxel is a new rover design from NASA that can climb steep slopes. It is made of two two-wheeled vehicles that are connected by a cable. This allows the rover to move one vehicle at a time, which helps it to stay stable.
The moon also has fine dust and if the dust gets on a rover’s cameras, the driver will not be able to see well. This could cause the rover to crash. Dust can also get into the rover’s mechanical parts and make them stop working. Engineers are working on ways to keep dust off astronaut spacesuits and rovers. They are experimenting with different methods, including creating electrical charges to repel dust and applying dust-resistant coatings.
The rover for Chandrayaan-3 is named Pragyan, which means ‘wisdom’ in Sanskrit. The rover will carry out in situ chemical analysis of the lunar surface during the course of its mobility. The rover is six-wheeled and about 1.6 metres long and 1 metre wide. The first of the two payloads—Alpha Particle X-ray Spectrometer (APXS) and Laser-Induced Breakdown Spectroscope (LIBS)—will be used to analyze the elemental composition of the lunar surface, while the second will be used to study the mineralogy of the surface.
The rover is designed to travel up to 500 metres on the lunar surface. It is expected to operate for about one lunar day, which is about 14 Earth days, as its electronics are not designed to endure the frigid lunar night. The rover will be deployed from the Vikram lander after it has successfully landed on the lunar surface. The rover module will generate 50 watts and weighs only 26 kg. The rover-Earth communication will be carried out through an orbiter that had earlier been deployed by Chandrayaan-2.
