Chandrayaan-3 (CH-3) is currently on an ambitious journey to reach the moon, with the objective of achieving a soft landing, exploring the lunar surface, and collecting invaluable scientific data. This mission is a technological challenge undertaken by India, led by ISRO.

As the attention turns towards the approach and landing of CH-3 on the moon, it is the right time to reflect on the making of CH-3. The spacecraft is the result of a collaborative effort, involving a vast array of experts from nearly all ISRO centres and contributions from external partners. This article aims to shed light on these efforts and provide readers with a glimpse of the CH-3 endeavour.

A spacecraft carries payloads or scientific instruments in space. When it revolves Earth or a celestial body, it is referred to as a satellite – an artificial one. CH-3 consists of a lander, designed to gently touch down on the moon's surface, and a rover, ready to explore the lunar terrain upon the lander's successful landing. To propel the lander and rover towards the moon, CH-3 relies on a propulsion module (PM).

Space is an unforgiving environment, characterized by high vacuum and ionizing radiation. Due to the lack of possibilities for in-situ repairs, the development of space missions demands meticulous planning, design, testing, analysis, and review. It is a true example of "rocket science" that necessitates a multi-disciplinary team of domain experts working hand in hand with project execution teams, to tailor solutions for each specific mission.

The major ISRO Centres/units involved in the design, development, testing and realization of the CH-3 mission include

The U R Rao Satellite Centre (URSC) serves as the lead centre for conceptualizing, designing, developing, testing realizing, and operationalizing satellites. Experts at URSC meticulously design, test, and certify the spacecraft's structure. Further, to ensure the spacecraft's survival in extreme temperature variations in space, thermal engineering experts maintain the temperature of different parts within specified limits, using various sensors for monitoring. The thermal protection system for CH-3 is contributed by URSC and Vikram Sarabhai Space Centre (VSSC). Various mechanisms required for payload systems, Rover ramp deployment, antenna deployment, etc and the development of Lander’s legs were carried out at URSC, while pyro systems for deployment were provided by VSSC. These elements collectively form the mechanical subsystems of the spacecraft.

The electronic subsystems of the satellite, are powered by energy generated by solar panels and stored in batteries. Power system engineers at URSC estimate and provide suitable power generation and distribution systems. VSSC provided solar panel substrates for CH-3. Communication engineers design, test, and deliver sophisticated communication subsystems, which serve as the link between various modules of CH-3 and the ground station.

The satellite's orientation in space is determined by sensors such as sun sensors, star sensors, laser-based altimeters and velocimeters, which were provided by Laboratory for Electro-optics Systems (LEOS). Space Applications Centre (SAC) provided the CH-3 Lander Imager cameras, Ka-band altimeter, hazard avoidance sensors and Rover imagers along with their data processors.

Inertial elements such as wheels, accelerometers, and gyroscopes, which provide attitude and velocity information as well as correction of attitude errors, were delivered by ISRO Inertial Systems Unit (IISU).

Further, all these systems are controlled and monitored by an onboard computer. Engineers with expertise in Control electronics and Digital electronics sub-systems contribute to the Attitude & Orbit Control Systems, Onboard Computers and different software catering to Navigation, Guidance & Control, base band telemetry, telecommand, data handling and storage functions.

Once the spacecraft is deployed by the Launch Vehicle, it is the responsibility of tracking and mission engineers to ensure on-orbit operations. Tracking expertise is offered initially by SDSC-SHAR, Sriharikota and later by ISRO Tracking and Command Network, ISTRAC, Bengaluru. In interplanetary missions such as the Mars Orbiter Mission (MOM), Chandrayaan – 2(CH-2) or Chandrayaan -3(CH-3), they occupy the driving seats during orbit insertion or final landing phases.

Once placed into the orbit, the satellite experiences a constant drag and drifts towards the earth or celestial body that it orbits. The propulsion system is used for restoring the satellite to its orbit. Propulsion engineers offer dedicated modules for the purpose, along with the propellants. While the Liquid Propulsion Systems Centre (LPSC), Valiamala offers the engines, thrusters, and valves with associated electronics, LPSC, Bengaluru realizes the propulsion system comprising propellant tanks, control components and sensors. The engines and thrusters are all tested at the dedicated facilities at ISRO Propulsion Complex (IPRC), Mahendragiri.

For CH-3, the integrated hot test with propulsion, sensors, Navigation, Guidance & Control and flight software was conducted at SDSC-SHAR, Sriharikota. National Remote Sensing Centre (NRSC), Hyderabad supported the ground-testing of on-board sensors with references and aerial imaging. The Indian Air Force provided helicopter for the integrated sensors and navigation testing called the Integrated Cold Test at Chitradurga.

Several Lander drop tests with different touch down conditions, simulating the lunar environment, were conducted at URSC. The mechanical hardware was mainly provided by Hindustan Aeronautics Limited (HAL), with the Titanium Tanks delivered by Bharat Heavy Electricals Limited (BHEL). Further, a large number of private firms have also contributed to CH-3, in terms of mechanical and electronic fabrication. Those contributed to mechanical systems include DUCOM Aerospace, Smart Technologies, Artha Technologies, Multi Teck Engineering Solutions SLN CNC Tech, Southern Electronics, Systems control technology solutions, Avasarala Technologies while those for electronic systems include Ananth Technologies, Centum Electronics, Data Patterns, Kaynes, Keltron, Newtech Solutions, etc.

The integration and testing of each subsystem is conducted rigorously to ensure functionality and reliability. Dedicated teams of engineers work on Assembly, Integration, Testing and Checkout of subsystems to create a fully functional spacecraft, ready to be integrated with the launch vehicle. These activities for CH-3 were undertaken at URSC.

A major step taken was incorporating the learnings from the unsuccessful landing of Chandrayaan-2 mission in 2019. In Ch-2, certain unexpected variations in performances of the Lander module eventually resulted in higher velocities at touchdown, which was beyond the designed capability of the Lander’s legs, resulting in a hard landing.

Chandrayaan-3 has been made more robust by making hardware as well as software improvements in Lander, with the capabilities to autonomously handle wider range of dispersion, improvements in sensors, software and propulsion systems, full level redundancies in addition to exhaustive simulations and additional tests being conducted towards ensuring a higher degree of ruggedness in the lander.

Throughout the CH-3 realisation across different stages, expert committees from academia and ISRO meticulously reviewed test results, observations, and non-compliances, and offered necessary guidelines to proceed as-is, repair, or replace components.

Former Experts who have served in ISRO have immensely contributed to CH-3. Former chairmen Dr. K Radhakrishnan, Shri A S Kiran Kumar and Dr. Sivan reviewed the overall configuration as members of the ISRO level Apex committee. Shri AS Kiran Kumar serves as the Chair of Apex Science Board and Contingency Operations Review Committee for the entire duration of CH-3.

A committee of experts headed by Dr. V Koteswara Rao guided and oversaw special tests on the lander such as integrated cold test, integrated hot test, lander leg hot test etc. This committee is comprised of scientists who served ISRO in the related fields of expertise. Along with them, the directors /eminent senior scientists from institutions like National Aerospace Laboratory (NAL), Aeronautical Development Agency (ADA), National Institute of Advanced Studies (NIAS), Inter-University Centre for Astronomy and Astrophysics (IUCAA), Indian Institute of Astrophysics (IIA), Raman Research Institute (RRI), Tata Institute of Fundamental Research (TIFR), Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Indian Institute of Geomagnetism (IIG), Aryabhatta Research Institute of Observational Sciences (ARIES) and National Geophysical Research Institute(NGRI), and academicians from University of Hyderabad, IIT Kharagpur, Indian Institute of Science (IISc), IIT-Madras, IIT-Bombay, IISER-Kolkata, Ashoka University, IIT-BHU, and Manipal Academy of Higher Education (MAHE) have contributed in reviewing the configuration, test results, contingency plans, operations, science outcomes etc. during National Panel of Experts for appraisal.

Women scientists/engineers have been contributing to each of the ISRO Programmes. Specifically, over 100 women staff have played a direct significant role in conceptualising, designing, realising, testing and executing of CH-3. Specifically, they have taken lead roles in

As CH-3 approaches its landing on the moon's surface, the entire team, comprising experts from various domains, shall become humble spectators during the final moments of landing. The lander shall be granted autonomy to execute commands, as the minimum two-way communication delay between the moon and Earth is unbearably long. The mission team shall take on the role of commentators during this critical phase, and any observations or anomalies shall be addressed collectively by expert committees, designers, fabricators, reliability experts, and mission engineers.

It is evident that a mission like CH-3 requires organized, dedicated and cumulative efforts, supplemented with a thorough and open review mechanism –the spirit of which is collectively referred to as ‘ISRO culture’. Anyone, irrespective of organizational hierarchy, can put forth a technical argument that warrants a detailed discussion before proceeding further. No member of the team, including its leader, is greater than the team. Team leaders need not and cannot be an expert in all the disciplines but the leader ensures to bring the best in each. Anyone who notices an anomaly, even if the person noticing it is directly responsible for it, brings it to the notice of the teams and is highly appreciated. Discussions and remedies need not demand formal meetings; they can happen over tea or lunch tables.

It is this ‘ISRO culture’ that has yielded the greatest rewards and CH-3 imbibes it in its entirety.