Imagine landing in a place where no one has ever set foot before. A place where the sun never rises and the temperature is always below freezing. A place where water ice and other treasures are hidden beneath the dust. That’s exactly what Chandrayaan-3 is aiming to do by landing on the lunar south pole. Chandrayaan-3: India’s third lunar mission. What is it, why it’s important, and how does it work? Read on to find out everything about Chandrayaan-3. So, buckle up and get ready for a journey to the moon!
What is Chandrayaan-3?
Chandrayaan-3 is a follow-on mission to Chandrayaan-2, which was launched in July 2019 and had the goal of putting a rover on the lunar South Pole. Unfortunately, Chandrayaan-2’s lander and rover crashed on the moon’s surface. It motivated ISRO (Indian Space Research Organisation) to plan another mission that would demonstrate its capability of landing safely and roving on the lunar surface. Chandrayaan-3 blasted off from the launchpad on 14th July 2023 at 14:35 pm and consists of two main components: a Lander (Vikram) and a Rover (Pragyan) module. Vikram is designed to accomplish a soft landing at a predetermined location on the moon and deploy the rover. Pragyan is a six-wheeled robotic vehicle that will conduct chemical analyses of the lunar surface and carry various scientific instruments for experiments. They will communicate with each other through a UHF antenna, and with the earth through an S-band antenna. The lander will also have a laser retroreflector array that will reflect laser pulses from orbiting spacecraft or ground stations. Chandrayaan-3 does not have an orbiter module as Chandrayaan-2 did. Instead, it will use the orbiter from Chandrayaan-2, which is still functioning well in its orbit around the moon. The orbiter will act as a relay station between the lander/rover and the earth station. The orbiter will also continue to perform its scientific observations of the moon using its eight payloads.
How is Chandrayaan 3 different from Chandrayaan 2?
- Tech Stacks: Although they look vastly similar, their tech stacks are very different. Ch2(left) was comprised of an Orbiter, Lander(Vikram) and Rover(Pragyan). The orbiter is meant to deliver the payload and orbit the lunar surface, where it is performing invaluable research to this day with its vast array of scientific instruments. Ch3(right) also has a Lander and Rover named likewise due to the previous mission’s partial success and similar design. However, in place of an orbiter, Ch3 has a propulsion module, which carries it to the moon. The propulsion module has a single instrument, SHAPE (Spectro Polarimetry HAbitable Planet Earth) which uses spectroscopy to study the atmosphere of Earth. This will help scientists to understand the nature of reflected light from habitable exoplanets.
-
Lander Hazard Detection and Avoidance Cameras(LHDAC) What appears through telescopes as a vast, smooth plain is deceitful. The moon’s surface is riddled with craters and plenty of slopes. Ch3 has 2 Hazard Detection and Avoidance Cameras, as compared to only 1 on Ch2. They analyse the lunar surface for a safe spot to land, avoiding any boulders, craters or uneven slopes.
-
Larger Fuel Tank and removal of central Engine ISRO has ditched the Central Engine design which is suspected to be one of the causes of the failed landing of Ch2. The lander of the CY2 had four engines surrounding a fifth central engine to deal with the dust plume during landing. The surface of the Moon is covered with powdery lunar soil called “regolith”. Regolith is notorious for being highly abrasive and electrostatically charged which damages sensors and other equipment. Simulations have shown that the four engines would kick up a dust plume that would cover the lander, severely hampering its abilities. Hence, ISRO added this fifth engine at the last minute on Ch2 to prevent dust from settling on the lander. Now, ISRO feels that the blowback isn’t such a problem, and has ditched the central engine. Instead, it has four thrusters on the corners of the lander of Ch3, which provide better stability and control.
-
Insane Communication system As an upgrade from Ch2, Ch3 has an insane number of TTC(Telemetry, Tracking and Command) antennae. These are used to transmit the position, velocity and other important parameters to ground stations of IDSN(Indian Deep Space Network). These antennae help in orbit determination and navigation. They make use of the S-band frequency range (2-4 GHz) with a receiver and exciter.
-
Laser Doppler VelociMeter(LDVM) The LDVM is a cutting-edge technology that ISRO has developed exclusively for Ch3. It works like a radar that uses a laser instead of radio waves. It sends out a laser beam and measures how much the beam changes its frequency when it bounces back from the lunar surface. This change is called the Doppler shift, it tells the LDVM how fast the lander is moving relative to the surface. The LDVM also calculates how long it takes for the beam to return, which gives the distance between the lander and the surface. The LDVM can do this with high precision, up to 0.1 m in distance and 0.1 m/s in velocity. It can also operate over a long range, from 30 km to 2 m above the surface.
-
Landing Site There’s been a slight change in the landing site, it will attempt to land at the near-polar location of 69.33425. This is just 100km east of the Ch2 intended landing site. The location was chosen to provide abundant sunlight, good communication with the earth and the presence of water ice, which is of high scientific interest. Further, the Ch2 orbiter has already photographed the landing location with its OHRC(Orbital High-Resolution Camera). The permissible landing area has been expanded to provide higher flexibility in selecting an exact landing location by the lander.
-
Improved Landing Software Contrary to popular belief, scientists do not control the lander as it descends onto the lunar surface. It is done so by its autonomous landing software, a glitch in which led to the failed soft landing attempt of Ch2. The new version for Ch3 has been improved with the lessons learned from Ch2. This is a failure-based algorithm, which tries to correct the lander’s trajectory from any failures that crop up.
-
Improved plethora of Scientific instruments on Lander
- ILSA(Instrument for Lunar Seismic Activity)
- CHaSTE(CHandra’s Surface Thermophysical Experiment)
- APXS (Alpha Particle X-Ray Spectrometer)
Why is Chandrayaan-3 important?
Chandrayaan-3 is important for several reasons. Firstly, it is a matter of national pride and prestige for India to achieve a successful landing on the moon, especially after the setback of Chandrayaan-2. Secondly, it will contribute to the scientific knowledge and understanding of the moon, which is still largely unexplored and mysterious. It will help us learn more about the origin and evolution of the moon. Thirdly, Chandrayaan-3 will pave the way for future lunar missions by India and other countries, such as Gaganyaan (India’s first manned space mission), Artemis (NASA’s program to return humans to the moon) etc.
How does it work?
Chandrayaan-3 works by following a series of steps that involve launching, orbiting, landing, roving, and communicating. Let me explain each step in detail.
Launching
Chandrayaan-3 was launched by GSLV Mk III (Geosynchronous Satellite Launch Vehicle Mark III), which is India’s most powerful rocket. It can carry up to 10 tonnes of payload into a low earth orbit or 4 tonnes into a geostationary transfer orbit. GSLV Mk III has three stages: two solid rocket boosters (S200), one liquid core stage (L110), and one cryogenic upper stage (C25). The cryogenic stage uses liquid hydrogen as fuel and liquid oxygen as oxidizers, which are more efficient than conventional propellants.
Orbiting
After launch, Chandrayaan-3 will enter into an elliptical orbit around the earth, with a perigee (closest point) of about 170 km and an apogee (farthest point) of about 40,000 km. It will then perform a series of orbit-raising manoeuvres using its propulsion module, which has a liquid engine and four thrusters that can each generate 800N of thrust. These manoeuvres will gradually increase the apogee of the orbit until it reaches the vicinity of the moon’s orbit, which is about 384,000 km from the Earth. Once Chandrayaan-3 reaches the moon’s orbit, it will perform a lunar orbit insertion manoeuvre using its propulsion module. This manoeuvre will slow down the spacecraft and place it into an elliptical orbit around the moon, with a perilune (closest point) of about 100 km and an apolune (farthest point) of about 18,000 km. It will then perform a series of orbit-lowering manoeuvres using its propulsion module, which will reduce the perilune and apolune of the orbit until it reaches a circular orbit of about 100 km.
Landing
The landing phase of Chandrayaan-3 is the most critical and challenging part of the mission. It involves separating the lander module from the propulsion module, initiating a powered descent towards the lunar surface, avoiding obstacles and hazards on the way, and achieving a soft landing at a suitable site. The landing site for Chandrayaan-3 is close to the south pole of the moon, which is of great scientific interest and has never been explored before by any other mission. The landing sequence will start when Chandrayaan-3 is about 30 km above the lunar surface. The lander module will detach from the propulsion module and orient itself towards the landing site using its Reaction Control System (RCS), which consists of eight thrusters. It will then fire its four throttleable engines to initiate a rough braking phase, which will reduce its velocity from about 1.6 km/s to about 100 m/s. During this phase, the lander will use its onboard sensors and cameras to detect its altitude, velocity, attitude, and position. The rough braking phase will end when Chandrayaan-3 is about 7.4 km above the lunar surface. The lander module will then enter into a fine braking phase, which will further reduce its velocity from about 100 m/s to about 2 m/s. During this phase, the lander will use its onboard sensors and cameras to detect its altitude, velocity, attitude, position, and terrain features. It will also use its Hazard Detection and Avoidance System (HDA), which consists of a LASer Altimeter(LASA) and Hazard Detection Camera. The HDA system will scan the landing site for any obstacles or hazards, such as craters, boulders, slopes, etc., and select a safe spot for landing. The fine braking phase will end when Chandrayaan-3 is about 400 m above the lunar surface. The lander module will then enter into a terminal descent phase, which will bring it to a hover mode at an altitude of about 10 m. During this phase, the lander will use its onboard sensors and cameras to fine-tune its position and attitude for landing. It will also use its throttleable engines to control its vertical and horizontal velocities. The terminal descent phase will end when Chandrayaan-3 touches down on the lunar surface with a velocity of less than 5 m/s. The lander module will then shut down its engines and thrusters. From a height of three metres, the craft will fall to the ground with a thud.
Roving
The roving phase of Chandrayaan-3 is the most exciting and rewarding part of the mission. It involves deploying the rover module(Pragyan) from the lander module, driving it on the lunar surface, conducting scientific experiments and observations, and sending back data and images to Earth. Pragyan is a six-wheeled robotic vehicle that weighs about 27 kg and can travel up to 500 m from the lander. It has two solar panels to generate power and two antennas to communicate with the lander.
The roving sequence will start once Vikram lands successfully on the lunar surface. The lander module will open a ramp on one side and release the rover module onto it. The rover module will then drive down the ramp and onto the lunar soil. It will then start exploring its surroundings using its onboard sensors and cameras. It will also use its robotic arm to collect samples of lunar soil and rocks. The rover will also carry four scientific instruments to perform various analyses and measurements. They are:
- Alpha Particle X-Ray Spectrometer (APXS): This instrument will derive the chemical composition and infer the mineralogical composition of the lunar surface. This will help us identify the elements and minerals that are present on the moon and how they vary across different regions.
- Chandra’s Surface Thermophysical Experiment (ChaSTE): ChaSTE will measure the thermal conductivity and temperature of the lunar surface. This will help us understand how the moon loses heat and how it affects its geology and evolution.
- Instrument for Lunar Seismic Activity (ILSA): ILSA measures the seismicity around the landing site. This will help us detect any moonquakes or impacts that might reveal the internal structure and dynamics of the moon. It employs a MEMS(Micro Electro Mechanical Systems) based design to ‘feel’ moonquakes.
- Laser-Induced Breakdown Spectroscope (LIBS): This instrument will determine the elemental composition of lunar soil and rocks around the landing site. This will help us study the diversity and distribution of elements on the moon and how they relate to its origin and history. The rover will operate for at least 14 Earth days, which is equivalent to one lunar day. During this time, it will send back data and images to the lander, which will relay them to the Chandrayaan-2 orbiter, which will transmit them to the Earth station. The rover will also receive commands from the Earth station through the same route.
Expected Goals
Chandrayaan-3’s expected outcomes are:
- To achieve a successful landing and roving on the moon
- To collect and transmit data and images from the lunar surface Chandrayaan-3 hopes to achieve a successful landing and roving on the moon. This will be a historic achievement for India and a milestone for ISRO. It will also showcase India’s technological prowess and innovation in space exploration. It will also pave the way for future lunar missions by India, such as Gaganyaan (India’s first manned space mission) and Shukrayaan(India’s unmanned mission to Venus). It also hopes to collect and transmit data and images from the lunar surface. This will be a valuable contribution to the scientific community and the public. It will also enrich our knowledge and understanding of the moon, which is still largely unknown and mysterious. It will also help us answer some of the fundamental questions about the moon, such as: How did the moon form and evolve? What is the composition and structure of the moon? Where are the sources and distribution of water ice and other volatiles on the moon? How does the moon interact with the sun and other celestial bodies? What are the potential resources and opportunities for human exploration and settlement on the moon? The Challenges The total budget of Chandrayaan-3 is estimated to be around Rs 615 crore (equivalent to US$90 million in 2023). This is a relatively low budget compared to other lunar missions, such as NASA’s Artemis program, which has a budget of US$28 billion for the period of 2021-2025. Therefore, Chandrayaan-3 has to achieve its objectives with minimal expenditure and maximum output. The lunar environment is unpredictable and hostile. It has extreme variations in temperature, gravity, terrain, illumination, and atmosphere. It also has various hazards and obstacles, such as craters, boulders, slopes, dust, shadows, etc. It also has various disturbances and interferences, such as solar flares, cosmic rays, meteoroids, etc. Therefore, Chandrayaan-3 has to deal with these uncertainties and ensure its safe landing.
Why explore the moon at all?
The moon is not only a fascinating celestial body but also a potential treasure trove of resources and opportunities for human exploration and settlement. Some of the resources and opportunities that the moon offers are-
- Water ice: Water ice is one of the most valuable resources on the moon, as it can be used for drinking, agriculture, hygiene, cooling, and manufacturing. It can also be split into hydrogen and oxygen, which can be used as rocket fuel or as breathable air. Water ice is mainly found in Permanently Shadowed Regions (PSRs) near the lunar poles, where temperatures are below 110 K. These regions are estimated to contain up to 600 million metric tons of water ice. Chandrayaan-3 will explore some of these regions and confirm the presence and distribution of water ice on the lunar surface.
- Helium-3: Helium-3 is a rare isotope of helium that has potential applications in nuclear fusion, a clean and powerful source of energy. Helium-3 is scarce on Earth, but abundant on the moon, where it is implanted by the solar wind. The lunar regolith (soil) is estimated to contain about one part per million of helium-3, which amounts to about one million metric tons 2. Chandrayaan-3 will measure the concentration and depth of helium-3 in the lunar regolith using its alpha particle X-ray spectrometer (APXS).
- Rare Earth Elements: Rare Earth Elements (REEs) are a group of 17 elements that have unique physical and chemical properties. They are used in various high-tech applications, such as electronics, magnets, lasers, batteries, catalysts, etc. REEs are scarce and unevenly distributed on Earth, but relatively abundant and accessible on the moon. The lunar regolith is estimated to contain about 0.01% of REEs by weight. Chandrayaan-3 will determine the composition and mineralogy of the lunar regolith using its Laser-Induced Breakdown Spectroscopy (LIBS).
- Lunar soil: Lunar soil is a fine-grained mixture of rock fragments, minerals, glass, and organic compounds. It has various uses, such as construction material, radiation shielding, thermal insulation, etc. It can also be processed into metals, ceramics, glass, or bricks using various techniques. Lunar soil is abundant and ubiquitous on the moon. Chandrayaan-3 will collect samples of lunar soil using its robotic arm and analyze them using its scientific instruments.
- Solar energy: Solar energy is an abundant source of energy on the moon. The lunar day lasts for about 14 Earth days, during which the sun shines continuously on the lunar surface. Solar panels can be deployed to capture this energy and convert it into electricity or heat. Solar energy can be used to power various systems and devices on the moon, such as rovers, habitats, factories, etc. It can also be transmitted to Earth via microwave or laser beams. Chandrayaan-3 will use solar panels to generate power for its lander and rover modules. By exploiting these resources and opportunities, humans can establish a permanent presence on the moon and use it as a base for further exploration of the solar system and beyond.
What went wrong earlier?
So, what exactly went wrong with Chandrayaan-2? Here is a detailed technical description of what happened:
- The final descent phase of Vikram started at 1:38 am IST on September 7, 2019, when it was about 30 km above the lunar surface. It was supposed to last for about 15 minutes and consist of four sub-phases: rough braking, camera coast phase, fine braking, and soft landing.
- The rough braking sub-phase lasted for about 10 minutes and reduced Vikram’s velocity from about 1.6 km/s to about 140 m/s. This sub-phase was executed as planned and Vikram performed nominally. The fine braking sub-phase lasted for about 3 minutes and reduced Vikram’s velocity from about 140 m/s to about 60 m/s. During this sub-phase, Vikram used its four throttleable engines to perform a further deceleration. It also used its onboard sensors and cameras to detect its altitude, velocity, attitude, position, and terrain features. It also used its hazard detection and avoidance (HDA) system to scan the landing site for any obstacles or hazards, such as craters, boulders, slopes, etc., and select a safe spot for landing. This sub-phase was executed as planned and Vikram performed nominally.
- In the camera coasting phase, which lasted for 38 sec, things started going wrong. Here, Vikram held a 50deg attitude and held its camera towards the ground to determine its landing side. Here, it stopped making changes to its attitude. Since the engines were transitioning from a high to lower thrust regime, they produced more thrust than estimated(0.6m/s more). Although the error was pretty small, it was added and accumulated over 38 sec. This caused Vikram to gain altitude rather than lose it. It couldn’t do anything, since its attitude was locked in the cam coasting phase. As it exits the camera coasting phase, it is hundreds of meters off its targeted trajectory.
- It then started chasing the ideal point where it was supposed to land and became inverted. The rotation was limited by the software, which only allowed a 10deg/sec turn. Hence, it crashes headfirst into the lunar surface.
It was a heartbreaking moment for ISRO and India, as well as for space enthusiasts around the world. However, ISRO did not give up and tried to locate and communicate with Vikram using various methods, such as sending radio signals from IDSN (Indian Deep Space Network) etc. It also analyzed data from Chandrayaan-2’s orbiter to understand what went wrong. As a result, the max turn rate on Chandrayaan-3 was increased to 25deg/sec, along with better software.
Future prospects?
Chandrayaan-3 is a remarkable achievement for India and a testament to the country’s scientific prowess and ambition. The mission has demonstrated India’s capability to land softly on the lunar surface and conduct scientific experiments with the lander and rover modules. Chandrayaan-3 has also paved the way for future lunar exploration missions, such as the Lunar Polar Exploration Mission (LPEM), which will aim to land near the lunar south pole and drill for water ice. As Indians, we can be proud of our space agency and its accomplishments. We can also contribute to the success of Chandrayaan-3 and other space missions by supporting ISRO’s initiatives, spreading awareness about the benefits of space exploration, and inspiring the next generation of scientists and engineers. We can also participate in citizen science projects, such as Moon Mappers, which allows anyone to help map the lunar surface and identify features of interest Chandrayaan-3 is not just a mission, but a vision. A vision of exploring the unknown, expanding our horizons, and enhancing our knowledge. A vision of making India a global leader in space science and technology. A vision of inspiring humanity to reach for the stars.