Success of Chandrayaan-3 Depends on the Design of Lunar Rovers

ISRO’s Chandrayaan-3 mission is to deploy a rover and lander near the south pole of the earth’s only natural satellite. The lunar South Pole is a unique and difficult terrain where the challenge of a safe and successful landing comes with multiplied challenges. The region is full of craters that represent a complex and challenging environment the lander and rover are likely to encounter.

The Shackleton crater is seated at the lunar South Pole. It contains a huge volume of crystalized water, which is actually ice. According to scientists, the presence of water ice creates opportunities for further space exploration and sustaining human lives in the future. However, for all these to come true, a rover needs to reach the South Pole and explore the region, which is still a difficult challenge.

Design of Rover: An Important Criterion

According to experts, the design of a rover is extremely important for the lunar mission to be successful, especially when it comes to landing in the southern region. The rover must withstand several extreme conditions on the lunar surface, such as heavy cold, darkness, powerful radiation etc.

Girish Linganna, a renowned space and aerospace expert, says rovers are machines and so can travel further than astronauts can do on foot and therefore, cover a larger region and collect more information. According to him, engineers must remember these factors when designing a lunar rover. If a rover is not built strong enough to sustain harsh weather and other challenging conditions, the lunar mission will never be successful.

The moon orbits around the earth in a synchronous motion, implying that its speed of rotation on its own axis equals that of its orbiting the earth. This synchronized motion explains why we can see only the same side of the moon from the Earth. The moon takes 30 days to orbit around the Earth and during the phase, only one side (it’s always the same side) is exposed to Earth days of light for 14 days (also called lunar day) and Earth days of dark for 14 days (also called lunar night).

Many areas on the lunar surface are always dark. Scientists have named these areas PSRs (Permanently Shadowed Regions). Therefore, craters in these places are always dark. They are formed when comets or asteroids hit the Moon’s surface. Craters could be a few meters to a few hundred kilometers wide. The moon houses millions of craters all over its surface.

For rovers, solar panels are the only source of power. Therefore, rovers cannot operate or communicate with the Earth at night. Solar panels function only in the presence of sunlight. Due to delicate designs, solar panels need heavy protection during the rover’s launch and landing. The heavy force and vibrations at the time of launch can harm solar panels. A hard landing on the moon could cause panels to break. Therefore, engineers should consider making solar panels stronger so that they can endure rigorous space travel. These panels should have strong protection against potential damages. 

How will rovers survive the lunar night? According to Lingama, rovers must have sunlight-powered rechargeable batteries that will enable the heaters to function during the cold lunar night. Rovers can use a nearby lunar lander to recharge their batteries. For the rovers, the lander functions as a home base, giving them a space to dock and recharge. The rovers find the lander via docking software and after they are docked, can recharge their batteries through wireless charging.

The extreme temperature on the moon’s surface swings heavily between day and night. The temperature can be as high as 127°C in the daytime and drops to -173°C at night. The temperature inside craters can even plummet more coz they never receive sunlight. Scientists have identified the coldest place in the solar system and these are the moon’s poles and the bottom of the Hermite Crater on the moon. The temperate in the Hermite Crater measured on NASA’s Lunar Reconnaissance Orbiter (LRO) is -250°C.

The lunar rovers should have gold paint as it prevents heat transfer by radiation. The mechanism works the same way a thermos flask preserves heat. Rovers can also use a special type of insulation, called aerogel. It is filled with 99.8% of air. Aerogel is lightweight and air is an excellent insulator. Hence, aerogel is an ideal insulator for space missions.

Rovers have heat rejection systems and heaters for temperature control. A thermostat controls heaters by switching them on and off automatically. The heat rejection system uses tubing and a pump to emit heat out into the space. The mechanism is similar to the functioning of an air-con system in cars.

The moon’s surface releases extremely high levels of radiation that can damage the insulation on the lunar rover wires by making it brittle, which may result in short circuits. Therefore, lunar rovers must have radiation-resistant, specially shielded wires. Usually, engineers use a shielded wire with a black plastic wire on its outside, a plaited wire shield underneath and under that, a white insulating material. Wires of different colours extend out from the end.

From the Earth, the moon’s surface looks flat and smooth. However, it is actually diverse. The entire surface comprises flat areas, rocky terrains and deep craters. Therefore, lunar rovers must be designed to climb up craters, maneuver the slopes and overcome odds to explore the diverse terrain. Their design structure must enable them to avoid getting stuck in sand or soft soil.

According to experts, the distance between the Earth and the moon is approximately 384, 000 kilometers and it also makes the mission more complex. Only sophisticated communication software allows for a highly complex command structure and smart decision-making procedures to make the rover’s moments easier on the lunar surface. It is an important and intelligent level of autonomy as even a minor error will prove fatal in the harsh and challenging space environment.

Targeting the moon’s South Pole, known for its unforgiving conditions, is a testimony to India’s high ambition and strong determination. The successful landing of Chandrayan III will be a defining moment in India’s space research and add to its to-date remarkable feats in the field. Given the wide range of its purposes, Chandrayan III is a highly economical project, with a budget of nearly Rs. 610 crores.

Lunar rovers need specially designed wheels that will not sustain any damage in the rugged terrain having sharp rocks and rough, microscopic rocky shards as well.  The rover wheels must have good treads to have tight grips on powdery regions; otherwise, it might have problems driving on a slippery surface. A test drive is performed on an artificial lunar surface. Rover wheels need to ascend and descend the steep slopes of craters and hence, must be designed accordingly. These wheels have long spikes, deep groves or mesh. It is mandatory for drivers to undergo rigorous training to avoid the places where wheels can get stuck. NASA has unveiled a new rover design, DuAxel, which can easily climb steep slopes. It is a two-wheeled vehicle connected by a cable. The design allows the rover to stay stable when travelling on the lunar surface.

The lunar surface has fine dust, which, if gets on a rover’s cameras, the driver cannot see clearly. As a result, the rover could crash. The rover can stop functioning if dust enters its mechanical parts. Engineers are busy finding ways that will repel dust from rovers and astronaut spacesuits. They are working on different projects, which include applying dust-resistant coatings and producing electric charges to keep dust off rovers.

Chandrayan III

Pragyan is the name of the rover for Chandrayan III. In Sanskrit, ‘Pragyan’ means wisdom. The six-wheeled rover is about 1.6 meters in length and 1 metre in width. It will carry in-situ chemical analysis of the moon’s surface during the course of its movement. Laser-Induced Breakdown Spectroscope (LIBS) and Alpha Particle X-ray Spectrometer (APXS) are the two first payloads that will be used to study the lunar surface’s chemical compositions. The first one will be used to analyse the mineralogy of the surface.

This rover can travel up to 500 meters on the surface of the moon and operate for 14 Earth Days (equal to about one lunar day). It does not have the kind of electronic that can withstand frigid lunar temperatures. The lander ‘Vikram’ will be used to deploy ‘Pragyan’ after a successful landing on the lunar surface. The rover module, weighing only 26 kg, will generate 50 watts. Chandrayan II – the 2020 mission was a failure – deployed an orbiter that will be assigned with the task of facilitating rover-earth communication.