Introduction:

The Moon is the closest celestial body to The Earth and has fascinated humans for centuries. It has been the closest relative of our dear Earth. Not just in Astronomy and space Missions, but in Science Fiction Stories also it has been most described 'Second Inhabited Place' in The Universe. Being the one and only Satellite of The Earth, it has always been the 'Topic of Excitement' for the Astronomers. It is also a potential source of scientific discoveries, natural resources, and future exploration. Many countries have launched missions to study and explore the Moon, but only a few have succeeded in landing on its surface. India is one of them.

India's lunar exploration program, Chandrayan, began in 2008 with the launch of Chandrayan 1, an orbiter that mapped the lunar surface and detected water ice in the polar regions. In 2019, India attempted to land a rover on the Moon with Chandrayan 2, but the mission failed due to a communication loss with the lander during the final descent. However, India did not give up and launched Chandrayan 3 in 2023, a repeat mission of Chandrayan 2 with some improvements and modifications. Chandrayan 3 achieved a historic feat by successfully landing near the lunar south pole and deploying a rover that explored the region for 14 days. This article is to describe the objectives, design, launch, orbit insertion, landing, and scientific results of Chandrayan 3, and highlight its significance and impact for India and the world.

Objectives:

The main objectives of Chandrayan 3 were to demonstrate India's capability to soft-land on the Moon and to operate a rover on its surface. The mission also aimed to conduct scientific experiments and observations on the lunar south polar region, which is of great interest for its potential water ice deposits, mineral resources, and unique geology. The specific scientific objectives of Chandrayan 3 were:

• To study the topography, morphology, mineralogy, and elemental composition of the landing site and its surroundings.
• To measure the thermal properties and seismic activity of the lunar surface and subsurface.
• To analyze the chemical composition and isotopic ratios of lunar rocks and soil.
• To investigate the presence and distribution of water ice and other volatiles in the polar region.
• To test new technologies and instruments for future lunar missions.

Design:

Chandrayan 3 consisted of two modules: a propulsion module and a lander module. The propulsion module carried the lander from launch injection to lunar orbit and provided attitude control and orbital maneuvers. The lander module housed a rover inside it and performed the landing sequence using four throttleable engines and various sensors. The rover was deployed from the lander after touchdown and moved on six wheels powered by solar energy.

The propulsion module had a mass of 2148 kg and was equipped with a liquid apogee motor (LAM) engine that provided a thrust of 440 N. It also had eight thrusters that provided a thrust of 22 N each for attitude control. The propulsion module had two solar panels that generated 758 W of power and communicated with the Indian Deep Space Network (IDSN) using an S-band antenna.

The lander module had a mass of 1752 kg, including the rover of 26 kg. It had four throttleable engines that provided a thrust of 800 N each for landing, and eight thrusters that provided a thrust of 58 N each for attitude control. The lander module had four solar panels that generated 738 W of power (with bias) and communicated with IDSN using an S-band antenna. It also communicated with the rover using a UHF antenna. The lander module carried four scientific payloads:

• Radio Anatomy of Moon Bound Hypersensitive ionosphere and Atmosphere (RAMBHA), which measured the plasma density and temperature in the lunar ionosphere and exosphere.
• Chandra’s Surface Thermo Physical Experiment (ChaSTE), which measured the thermal conductivity and temperature gradient of the lunar surface.
• Instrument for Lunar Seismic Activity (ILSA), which detected natural or artificial seismic waves on the Moon.
• Laser Retroreflector Array (LRA), which reflected laser signals from orbiting spacecraft or Earth-based observatories for precise measurements of distance and position.

The rover module had a mass of 26 kg and was named Pragyan, meaning "wisdom" in Sanskrit. It had six wheels that could move at a speed of up to 1 cm/s. It had two solar panels that generated 50 W of power and communicated with the lander using a UHF antenna. The rover module carried two scientific payloads:

• Alpha Particle X-ray spectrometer (APXS), which measured the elemental composition of lunar rocks and soil using alpha particles and X-rays.
• Laser Induced Breakdown Spectroscope (LIBS), which measured the chemical composition of lunar rocks and soil using laser pulses.

Launch:

Chandrayan 3 was launched from Satish Dhawan Space Centre on July 14, 2023, at 14:35:17 IST (09:05:17 UTC) using a Launch Vehicle Mark-3 (LVM3) rocket. The LVM3 was a three-stage rocket with two solid strap-on boosters, a liquid core stage, and a cryogenic upper stage. The rocket had a height of 43.4 m, a diameter of 4 m, and a lift-off mass of 640 tonnes. It could place a payload of up to 4 tonnes into a geostationary transfer orbit (GTO) or 8 tonnes into a low Earth orbit (LEO).

The launch sequence was as follows:

• T-0: Lift-off
• T+1:50: Strap-on boosters separation
• T+3:40: Core stage separation
• T+4:00: Cryogenic stage ignition
• T+16:20: Chandrayan 3 Separation

The launch was successful and Chandrayan 3 was placed into an elliptical Earth orbit with a perigee of 170 km and an apogee of 40,400 km.

Orbit insertion:

Chandrayan 3 performed five orbit-raising maneuvers using its LAM engine to increase its apogee and escape velocity. The maneuvers were executed on July 15, July 18, July 21, July 24, and July 27. The final orbit had a perigee of 250 km and an apogee of 413,000 km.

On August 5, Chandrayan 3 performed a trans-lunar injection (TLI) maneuver using its LAM engine to leave Earth orbit and enter a lunar transfer trajectory. The maneuver lasted for about 20 minutes and imparted a velocity increment of about 3.1 km/s.

On August 9, Chandrayan 3 performed a lunar orbit insertion (LOI) maneuver using its LAM engine to enter an elliptical lunar orbit with a perilune of 153 km and an apolune of 163 km. The maneuver lasted for about 30 minutes and reduced the velocity by about 0.9 km/s.

Landing:

Chandrayan 3 performed two de-orbit maneuvers using its lander engines to lower its perilune and prepare for landing. The maneuvers were executed on August 21 and August 23. The final orbit had a perilune of 35 km and an apolune of 97 km.

On August 23, Chandrayan 3 initiated the landing sequence at an altitude of about 35 km and a velocity of about 1.6 km/s. The landing sequence consisted of four phases:

• Rough braking phase: The lander fired its four engines at full throttle to reduce its velocity and altitude rapidly. This phase lasted for about 10 minutes and ended at an altitude of about 7.4 km and a velocity of about 146 m/s.
• Attitude control phase: The lander used its thrusters to orient itself for the landing site selection and hazard avoidance. This phase lasted for about 2 minutes and ended at an altitude of about 5 km and a velocity of about 86 m/s.
• Fine braking phase: The lander fired its engines at the variable throttle to reduce its velocity and altitude gradually. It also used its sensors to identify a safe and flat landing site within the designated area. This phase lasted for about 13 minutes and ended at an altitude of about 400 m and a velocity of about 48 m/s.
• Terminal descent phase: The lander fired its engines at minimum throttle to perform a soft landing on the lunar surface. It also used its sensors to avoid any obstacles or slopes on the ground. This phase lasted for about 2 minutes and ended with the touchdown at an altitude of zero m and a velocity of zero m/s.

The landing site was located at Shiv Shakti point, between Manzinus C and Simpelius N craters, near the lunar south pole. The coordinates were 69°22′23″S, 32°19′08″E.

The landing was successful and Chandrayan 3 became the first mission to land near the lunar south pole. It also made India the fourth country to achieve a soft landing on the Moon, after the Soviet Union, the United States, and China.

Scientific results:

After the landing, Chandrayan 3 deployed its rover Pragyan from the lander using a ramp mechanism. The rover moved away from the lander and began to explore the landing site and its surroundings. The rover had a nominal mission life of one lunar day (about 14 Earth days), but it exceeded its expectations and operated for two lunar days (about one Earth month). During this time, it covered a distance of about 100 m and collected data using its APXS and LIBS instruments.

The lander also activated its scientific payloads and began to conduct experiments on the lunar surface and atmosphere. The lander had a nominal mission life of one lunar day, but it also exceeded its expectations and operated for two lunar days.

Conclusion:

Chandrayan 3 was a remarkable achievement for India and the world, as it demonstrated the feasibility and benefits of landing near the lunar south pole. The mission provided valuable data and insights into the geology, chemistry, and physics of this unexplored region, which could have implications for future lunar exploration and utilization. The mission also showcased India's technological prowess and scientific ambition, as it overcame the challenges and failures of previous attempts. Chandrayan 3 was a testament to India's commitment to advancing scientific knowledge and innovation for the benefit of humanity.

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