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Chandrayaan-3: India’s Foothold on the Moon

By Gurbir Dated: July 18, 2024 Leave a Comment

A version of this article first appeared on Spacewatch.Global in June 2024

A Political Imperative

On Friday, 23rd August 2023, moments after confirming the successful soft landing of the Vikram lander with the words “we are on the Moon,” ISRO Chairman Somnath invited Indian Prime Minister Modi to speak. Unlike September 2019, during the unsuccessful Chandrayaan-2 lander mission, Modi was not in Bangalore but in South Africa, attending a BRICS meeting. This mission, a product of national political and financial commitment, attracted international acclaim. 

With one eye on the vast national and international audience and the other on the upcoming general election in 2024, the Prime Minister spoke for ten minutes. Politics and politicians play a more critical role in facilitating space missions than the scientists and engineers who realise them. When Apollo 11 astronauts Neil Armstrong and Buzz Aldrin took humanity’s first steps on another world, they received a live telephone call from President Nixon from the White House, which they shared live on TV around the world. Whereas Apollo 11’s success was a goal set in response to the USSR’s spectacular success in placing the first human in Earth orbit on 12th April 1961, India’s Chandrayaan-3 success was in response to its regional competitor, China.

India’s first official announcement to go to the Moon came on 15th August 2003. This announcement was not driven by the urge for scientific exploration but more likely a response to China’s announcement in January of the same year that they would launch a mission to the Moon. Ultimately, India reached the Moon on 8th November 2008 with Chandrayaan-1, a year after Chang’e 1, the first Chinese lunar mission, arrived in lunar orbit on 5th November 2007. Reflecting the geopolitical rivalry of the USA and USSR during the Cold War, India and China continue that silent rivalry today. China has achieved several remarkable successes in space (human spaceflight, landing a rover on Mars, lunar sample return, and now a continuously inhabited space station). With its larger economy and centralised political structure, China has rapidly grown in its space capabilities, now second only to the USA. The gap between India and China is exemplified by one metric: In 2023, ISRO missed breaking its all-time high of seven launches in one year, whereas China achieved a new high of 67.

It is not only international politics that influence how ISRO operates but national politics as well. The ISRO website uses English and Hindi, but individual centres may prefer a local language. For over a decade, India has had an Official Language Implementation Committee promoting using Hindi as an official language across all ISRO centres. This remains a challenge given that surprisingly large populations across India do not speak Hindi. As in medicine, science, and information technology, English is the world’s default language for the space industry.

The success of Chandrayaan-3 has demonstrated ISRO’s technological competence and is likely to secure the two key ingredients to accelerate India’s space program: increased political and financial commitment. Propelled by Chandrayaan-3’s success and motivated by China’s ongoing achievements, India will pursue more ambitious space missions. India’s delayed human spaceflight program is on target for the first flight of an Indian astronaut on board an Indian launch vehicle from India by 2025. Motivated by this success, India will likely announce missions for a lunar sample return, Martian rover, Venus orbiter, and exoplanet hunter, and develop more powerful and reusable launch vehicles.

Lessons from Chandraayan-2

Credit: ISRO

Chandrayaan-2, weighing almost 4 tons, was launched in July 2019 using a new LVM-3 rocket. It arrived in lunar orbit on 20th August, and the lander separated on 2nd September; however, the landing attempt was unsuccessful. The Chandrayaan-2 orbiter is now five years into its planned 7.5-year operational life, returning the highest resolution images of the lunar surface among the seven operational spacecraft currently in lunar orbit. Images for identifying potential landing sites for the Chandrayaan-3 lander came from the Chandrayaan-2 orbiter. Whilst the Chandrayaan-3 lander communicated directly with Earth during descent and on the surface, the Chandrayaan-2 orbiter served as a redundant communication relay for the lander in 2019. The Chandrayaan-3 orbiter, which ISRO refers to as the Propulsion Module, did not have this relay capability.

The Chandrayaan-2 Failure Analysis Committee (FAC) findings highlighted concerns with the inadequacy of data on the spacecraft’s attitude, altitude, and velocities during the powered descent. The report pointed to the need for (i) a larger landing target and finer engine thrust controls and (ii) more precise and frequent data on horizontal and vertical velocities, as well as altitude during the powered descent. Chandrayaan-3 would need to know, with higher precision, its location, altitude, and attitude at all times during the powered descent phase. Recommendations included more efficient hazard-avoiding algorithms with built-in redundancy, especially during the fine braking, hovering, and final touchdown phases. As a result, Chandrayaan-3 became ISRO’s spacecraft with the most built-in redundancy to date. The additional instruments which facilitated these recommendations included laser and radio frequency-based altimeters, laser Doppler and horizontal camera velocimeters, laser gyro-based inertial referencing, and accelerometers. The fifth non-throttleable engine in Chandrayaan-2 was removed altogether, reducing the dust kicked up at landing. The four throttleable engines were reconfigured to allow changes of thrust in increments of 10% rather than 20%. The attitude correction rate was also enhanced from 10°/s for Chandrayaan-2 to 25°/s for Chandrayaan-3.

With so many modifications, ISRO planned and conducted a series of experiments to test the new configuration. An Indian Air Force helicopter supported an Integrated Cold Test where navigation sensors were flown over an ISRO-created lunar landscape in the Chitradurga district, about 300 km northwest of Bangalore. India’s vast launch centre at Sriharikota was used to conduct an Integrated Hot Test, which involved the lander hanging from a crane to test propulsion, navigation, guidance, and the updated flight software. Despite the numerous simulations and physical testing, the space environment, which includes near vacuum, extreme variations in temperature, and one-sixth gravity in the vicinity of the Moon, cannot be duplicated on Earth.

The lander mass was increased to 1,726 kg (from Chandrayaan-2 lander’s 1,471 kg), most of this was in fuel. The additional fuel would allow for longer hover periods to avoid hazards and identify the most optimal landing target. The landing zone also increased from 500 m by 500 m to 2,400 m by 4,000 m. In February 2019, a landing simulation for the Chandrayaan-2 lander resulted in some damage to the lander’s legs. As an additional contingency, Chandrayaan-3 lander legs were reinforced to support the eventuality of a harder landing, which also increased the lander’s mass. A series of lander drop tests were conducted to ensure a safe landing with a vertical speed of up to 2 m/s, a horizontal speed of up to 5 m/s, and landing on a slope of up to 12 degrees. Other subtle changes included increasing battery capacity, data transmission capacity during powered descent, solar cells, and enhancing reaction wheels.

ISRO chose to meet the commercial request from OneWeb to launch its satellite in October 2022 and again in March 2023. In the absence of this delay, Chandrayaan-3 would have been launched much earlier. With multiple hardware and software enhancements and rigorous testing, almost three years later, ISRO, with greater confidence, launched Chandrayaan-3 on 14th July 2023.

What Next

Lunar landers and rovers from the USA, USSR, and China survived the lunar night using a Radioisotope Thermoelectric Generator (RTG). The first use of an RTG in space was an experimental navigation satellite placed into Earth orbit by the US Navy in 1961. It used 96 g of Plutonium 238 to demonstrate an alternative, independent power supply. The heat was converted to electricity to power onboard instruments and used for temperature control while the spacecraft was in the Earth’s shadow. During the early 1960s, solar cells had very low efficiency compared to today. International sanctions following India’s first nuclear test in 1974 restricted India’s access to nuclear materials, preventing it from developing RTG technology. Since 2016, India has become a member of the Missile Technology Control Regime, and in 2023 signed the US-led Artemis Accords. Free of the restrictions of the past, India is now developing nuclear power sources for use in space.

As expected, neither Chandrayaan-3’s lander nor the rover survived the ultra-low temperature of a lunar night. The mission ended less than two weeks after the touchdown. Prior to launch, the rover was tested to a temperature of -145°C, but since it could only communicate with Earth via the lander, it is impossible to say if it survived the lunar night.

India is now working on both a Radioisotope Thermoelectric Generator (RTG) and a technologically simpler device based on a radioisotope source, a Radioisotope Heater Unit (RHU). The RHUs are incapable of providing electricity—only heat. They are used in environments other than space, including geographically remote locations on Earth (oceans, polar regions, unattended lighthouses, autonomous vehicles). ISRO tested its first RHU in the Chandrayaan-3 Propulsion Module, and RTG technology will likely follow. ISRO is expected to test a 5W RHU in a Technology Demonstrator Satellite.

ISRO has not formally announced the next mission to the Moon, but it is probably a sample return. This is not only because it follows in the footsteps of the Chinese Lunar Sample Return but also because for any space agency to grow, it must evolve. The scientists and engineers at ISRO will have enjoyed the success of the Chandrayaan-3 lander but will need to add to their experience by taking on the technologically ambitious challenge of sample return. Currently, the early design phase is likely to involve two launches. The first launch will include a Propulsion Module to get to the Moon, a Descent Module for the lunar landing, and an Ascent Module to take the samples back up to lunar orbit. The second launch vehicle, probably a GSLV Mk-2, will carry another propulsion module to the Moon and back and a Transfer Module that will dock with the ascent module in lunar orbit, transfer the samples, and return to Earth for re-entry. Where on Earth it will land has not been finalised. Perhaps mainland India, the Indian Ocean, or the Australian Outback.

Credit: ISRO

Long-term and sustainable exploration and exploitation of the Moon have become a geopolitical target for many nations in this and the coming decade. Just as in the 17th century, European countries competed with each other to acquire new lands in Africa, Asia, and the Americas, and in Antarctica in the 20th century, so today, countries worried about being left behind are committing political and financial resources to establish a foothold on the Moon. A base on the Moon will also be a stepping stone to exploring Mars and beyond. The two countries with concrete plans for sending humans to the Moon are China and the USA. India has stated that it wants to send people to the Moon. It has joined the US-led Artemis Accords instead of partnering with the Chinese and Russian program called the International Lunar Research Programme. Apart from the potential for an Indian astronaut to visit the International Space Station, these new partnerships might provide India with access to the technologies it needs to accelerate and fulfil its growing lunar ambitions.

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Episode 111 – Chandrayaan-3

By Gurbir Dated: November 30, 2023 1 Comment

Project Director P Veeramuthuvel, Associate Project Director: Kalpana Kalahasti  and ISRO Chairman: S. Somanath
Project Director P Veeramuthuvel, Associate Project Director: Kalpana Kalahasti and ISRO Chairman: S. Somanath

Traditionally an ISRO live stream event ends with a few short speeches from the ISRO chairman and several of the key personnel associated with the mission. On 23 August 2023, following the successful soft landing of Chandrayaan-3 lander, this tradition played out as normal. But this time, along with chairman Somanath on the stage was the Chandrayaan-3 Associate Project Director, Kalpana Kalahasti. Although ISRO has many female scientists, engineers and managers, this was the first time (to my knowledge) for a woman to make it to the stage during the live stream.

A qualified communications engineer, Kalapana Kalahasti has worked on several mission including the 2013 Earth observation satellite called SARAL, jointly with the French Space Agency CNES.

She was assigned as the Associate Project Director for Chandrayaan-3 in 2019 following the unsuccessful Chandrayaan-2 landing attempt. In this conversation she recalls her journey with ISRO from 1999 when she joined as a radar engineer based at Sriharikota.

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India to build a Space Station – Bharatiya Antariksha Station

By Gurbir Dated: October 31, 2023 Leave a Comment

Credit: Office of the Prime minister of India

On October 17th 2023, the Indian Prime Minister voiced India’s intentions to build a space station by 2035 and to send the first Indian crewed flight to the Moon by 2040. The formal announcement by the Press Bureau of India (text below) followed an in-person presentation to the Prime Minister by the ISRO chairman – S Somanath. The intention to establish an Indian space station was first announced in 2019 by the then ISRO chairman, K Sivan. Although this announcement is more formal and official, it is not much more than a press release. As significant as this public political undertaking, coming from the office of the prime minister is, there is no formal commitment of the funding to go with it. Yet. This is not unusual. India does not always employ a formal, structured long-term approach, like that for example of China’s rolling five-year plans. India’s journey towards a space station and eventually crewed flight to the surface of the Moon may be a little erratic and may even include a few cul-de-sac, it will get there.

The objectives and target dates for grand national programmes, for example USA’s Apollo programme of the 1960s, are usually determined by geopolitical rivalries. Then it was the USSR then but now it is the rapid growth of China’s space programme that motivated the USA’s Artemis to return to the Moon by 2025. The impetus for India’s date for the “first Indian to the Moon by 2040” is also China which has its target date for its first crewed mission to the lunar surface by 2030. In practice I suspect India will push that 1940 date to 1947 – the centenary of Indian independence.

The prime minister’s decision came on the back of the success of the lunar Chandrayaan-3 mission and the many-years-delayed launch of India’s first solar observatory, Aditya-L1. ISRO is also expected to undertake an uncrewed in-flight abort test on 21st of October 2021 of its crew module. This is one of the several tests towards India’s first crewed flight, known as the Gaganyaan mission. Targeted for 2025, the Gaganyaan mission will take a crew (nominally of three – but I will reckon it will be two) on probably a 24 hour flight to low Earth orbit.

The announcement, unhelpfully refers to a the HLVM-3 – the human rated LVM-3. This is unfortunate and so soon after ISRO, earlier this year, appeared to have settled on a naming convention of LVM-3 instead of of GSLV-3.


Prime Minister reviews readiness of Gaganyaan Mission

Indian Space Station to be set up by 2035

India to send Man to Moon by 2040

India to undertake missions to Venus and Mars
Posted On: 17 OCT 2023 1:53PM by PIB Delhi
Prime Minister Shri Narendra Modi chaired a high-level meeting to assess progress of India’s Gaganyaan Mission and to outline the future of India’s space exploration endeavours.

The Department of Space presented a comprehensive overview of the Gaganyaan Mission, including various technologies developed so far such as human-rated launch vehicles and system qualification. It was noted that around 20 major tests, including 3 uncrewed missions of the Human Rated Launch Vehicle (HLVM3) are planned. First demonstration flight of the Crew Escape System Test Vehicle is scheduled on 21 October. The meeting evaluated the mission’s readiness, affirming its launch in 2025.

Building on the success of the Indian space initiatives, including the recent Chandrayan-3  and Aditya L1 Missions, Prime Minister directed that India should now aim for new and ambitious goals, including setting up ‘Bharatiya Antariksha Station’ (Indian Space Station) by 2035 and sending first Indian to the Moon by 2040.

To realize this Vision, the Department of Space will develop a roadmap for Moon exploration. This will encompass a series of Chandrayaan missions, the development of a Next Generation Launch Vehicle (NGLV), construction of a new launch pad, setting up human-centric Laboratories and associated technologies.

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Birth of the Indian Space Research Organisation

By Gurbir Dated: July 6, 2022 Leave a Comment


This article was first published in the May 2022 edition of the British Interplanetary Society publication – Space Chronicles.


Three weeks after its extraordinarily ambitious mission, the crew of Apollo 11 splashed down in the North Pacific, and the Indian Space research Organisation (ISRO) came into being on 15 August 1969. At that time, it was still operating under the Department of Atomic Energy, where its predecessor, the Indian National Committee for Space Research (INCOSPAR), was founded in 1962. In the same year that the Apollo programme in the USA ended, India established the Department of Space in 1972 and brought ISRO under its management. This is the ISRO that has designed, built, launched and operates the 50-plus spacecraft of the 3500 operating in space today.

Today, its space assets provide services to its security forces, but it did not start that way. India’s space programme is probably the only national space programme that began with plans only for economic and societal development. Space programmes in the USA, USSR, China and elsewhere arose to serve a national security imperative. ISRO has met many of its original objectives for more than half a century. India’s assets in space provide services for communication, television, navigation and Earth observation. For scientific research, India has Astrosat, a space telescope in Earth orbit, Chandrayaan-2 in lunar orbit and since 2014, a spacecraft in Martian orbit. Some of India’s spacecraft provide services for the international community, including remote sensing, search & rescue and navigation for civil aviation.

One objective explicitly ruled out by its first charismatic chairman, Vikram Sarabhai, in 1969 was a human spaceflight. In 2018, India’s Prime Minister announced a new goal. Called Gaganyaan, its task is to place an Indian crew in low Earth orbit using an Indian launch vehicle launched from Indian soil by 2022. A variety of issues, especially the global pandemic, have ensured that the timeline will not be met, but the programme remains active. In January 2022, S. Somanath was appointed as Chairman. As Russia’s space activities diminish, opportunities will arise for others, and India is well placed to exploit them.  

ISRO will ramp up activities that will include the launch of OneWeb’s satellites, the inaugural flight of its Small Satellite Launch Vehicle, the second test flight of its reusable space plane, the third mission to the moon complete with a lander and a rover and a launch abort test for its Gaganyaan programme. I expect ISRO to make a significant announcement on 15th August 2022.

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