Chandrayaan-3: India’s South-Pole Landing and Its Systems

Chandrayaan-2 reached the Moon in 2019 but its lander did not land safely. Chandrayaan-3 was the second try at the hard part.

What were the three goals?

• Landing: show a safe and soft landing on the Moon.
• Roving: show a rover moving on the surface.
• Science: run experiments on the spot.

ISRO planned for one lunar day of work. That is about 14 Earth days.

What went wrong with Chandrayaan-2?

NASA says ISRO lost contact with the Chandrayaan-2 lander shortly before touchdown. That was on 7 September 2019, India time. It aimed at a site about 600 km from the pole.

Why a landing near the south pole?

The main reason is possible water ice. Scientists suspect it hides in permanently shadowed areas near the poles. The Sun never reaches the floors of such areas, so they stay extremely cold.

• The ice: NASA says a team saw definite evidence of water ice on the Moon’s surface in 2018. At the south pole, most of that ice sits in craters.
• What the site is: the prime site lay near 69.4 degrees south. That is a high southern latitude, but not the pole itself.
• What was new: the lander gave a first on-the-spot soil temperature profile for this region. The rover’s laser tool confirmed sulphur there. Neither result is about ice.

How did the journey go in dates?

The rocket lifted off on 14 July 2023 at 14:35 IST (Indian Standard Time). It flew from the second launch pad at Sriharikota. The lander touched down on 23 August 2023. The rover rolled out on 24 August.

Four countries have done it: the Soviet Union, the United States, China and India. A soft landing means the craft touches down in one piece. A crash landing does not count.

Who was first?

• Soviet Union: Luna 9 made the first survivable landing, on 3 February 1966.
• United States: Surveyor 1 made the first true soft landing, on 2 June 1966.
• China: Chang’e-4 landed in the Von Karman crater on 3 January 2019.
• India: Chandrayaan-3 landed on 23 August 2023.

NASA gives the first two dates. It also dates the Chang’e-4 landing.

Apollo 11 put humans on the Moon on 20 July 1969, US time. That crewed landing is a separate story.

What did the Prime Minister say?

On 26 August 2023 he told the ISRO team that India had become the fourth country to touch the Moon’s surface.

Was Japan’s try a landing?

Only partly. Japan’s SLIM landed on 20 January 2024. JAXA says it ended tilted and could not make power. So it is not counted here as a full success.

Was India first at the south pole?

Not clearly. ISRO’s wording is that the soft landing was near the south polar region. This lesson says no more than that.

It flew up on a rocket, raised its orbit step by step, and then sent the lander down. The craft was made of three parts that worked as a team.

What were the three modules?

• Propulsion module: 2,148 kg. It carried the lander to a 100 km circular polar orbit.
• Lander module: 1,752 kg, including the 26 kg rover. Its name is Vikram.
• Rover: 26 kg. Its name is Pragyan.
• Total: about 3,900 kg.

The propulsion module also carried one science payload, SHAPE (Spectro-polarimetry of HAbitable Planet Earth). It studies Earth in near-infrared light.

How did the orbit grow?

It grew in steps, like a slow spiral outward. ISRO raised the orbit again and again.

• 15 July: 41,762 by 173 km.
• 1 August: the craft left Earth for the Moon, at 288 by 369,328 km.
• 5 August: it entered lunar orbit at 164 by 18,074 km.
• 16 August: a near-circle of 153 by 163 km.

When did the lander split off?

Vikram separated from the propulsion module on 17 August 2023. On 20 August the orbit was 25 by 134 km. ISRO then expected powered descent around 17:45 IST on 23 August.

It slowed with throttleable engines and used sensors and cameras to pick a safe spot. The final minutes are the hard part. Vikram had to slow from orbital speed to almost nothing.

What hardware did it have?

• Engines: four throttleable engines of 800 N each.
• Thrusters: eight of 58 N each.
• Sensors: laser and radio altimeters and a laser Doppler velocimeter.
• Cameras: cameras that spot hazards and steer around them.

Throttleable means the thrust can be turned up or down in flight. That lets the lander slow gently.

What were the touchdown limits?

• Vertical speed: 2 m/s or less.
• Sideways speed: 0.5 m/s or less.
• Slope: 12 degrees or less.

ISRO tested the system on a helicopter for the cold run. It used a tower crane for the hot run.

Where was the target?

The prime site was a box of 4 km by 2.4 km. Its centre was at 69.367621 S and 32.348126 E. That is about 69.37 S and 32.35 E. The lander touched down on the evening of 23 August 2023.

Did the rover talk to Earth?

No. The rover talked only to the lander. Chandrayaan-2’s orbiter stood by as a backup link.

Each module had its own tools. Together they studied the surface, the plasma above it and Earth.

What did the lander carry?

• RAMBHA-LP (Radio Anatomy of Moon Bound Hypersensitive ionosphere and Atmosphere, Langmuir Probe): a probe that studies the plasma near the surface.
• ChaSTE (Chandra’s Surface Thermophysical Experiment): a probe that measures how heat moves through the top soil.
• ILSA (Instrument for Lunar Seismic Activity): a tool that senses ground shaking.
• LRA (Laser Retroreflector Array): a NASA reflector for laser ranging.

What did the rover carry?

• LIBS (Laser Induced Breakdown Spectroscope): a laser tool that finds which elements a rock holds.
• APXS (Alpha Particle X-ray Spectrometer): an X-ray tool that looks for magnesium, aluminium, silicon, potassium, calcium, titanium and iron.

How does ChaSTE work?

Its probe can reach 10 cm below the surface. It has 10 temperature sensors along its length. That gives a vertical profile of heat.

Why did the rover matter?

The rover could test ground that the lander could not reach.

It found sulphur and other elements, and it recorded soil temperatures near the pole. The results arrived in the days after landing. Later studies added more.

What did the first week show?

• 27 August: ChaSTE sent the first temperature profile for the lunar south pole.
• 28 August: the rover’s LIBS confirmed sulphur.
• 30 August: APXS found minor elements in the soil.

ISRO credits the sulphur result to the rover’s LIBS tool.

How far did the rover travel?

ISRO’s release of 23 August 2024 says the rover covered about 101 m. The data are open to researchers on ISRO’s portal.

Did it land inside a crater?

Yes, a buried one. A study by PRL and ISRO scientists found the site sits inside an old crater. It is about 160 km wide and 4.4 km deep. Layers of debris have worn it down.

Where is the site compared with the big basin?

It sits about 350 km from the rim of the South Pole-Aitken basin.

• South Pole-Aitken basin: the largest and oldest basin on the Moon.
• Distance: the site lies about 350 km from the basin rim.
• Ejecta: the basin added about 1,400 m of material. Eleven other basins added about 580 m.

Is the site near the pole?

Fairly near, but not at it. NASA says it is about 600 km from the pole. Its Lunar Reconnaissance Orbiter imaged the site four days after landing. The bright halo is where the rocket plume hit the regolith.

The lander and rover worked about one lunar day. Then came a hop, a long sleep and a quiet second career.

What was the hop?

On 2 September 2023 Vikram fired its engines again. It rose about 50 cm and landed nearby. It used its leftover fuel. ISRO calls this a key skill for future sample-return missions.

What did the hop teach?

The engine blast stripped the top few centimetres of loose dust. ChaSTE measured that change. The top 2 to 6 cm of soil is sticky and full of holes. It can act like a thermal blanket.

Did the craft wake up again?

No wake-up has been reported.

• 4 September 2023: ISRO put the lander and rover in sleep mode.
• About 22 September: the Sun was due to return. ISRO said it was trying to reach them.
• Outcome: the ISRO pages read give no sign of a reply.

What did the lander’s mirror do?

It is meant to serve as a fixed laser marker near the pole for decades. The LRA has eight small corner reflectors and weighs about 20 g. NASA’s Lunar Reconnaissance Orbiter (LRO) bounced a laser off it on 12 December 2023. ### What happened to the propulsion module?

It moved from lunar orbit back to Earth orbit. The first move was on 9 October 2023. It left the Moon’s pull in November 2023. SHAPE carries on watching Earth.

Success brought names, a new national day and a bigger plan.

What is the Shiv Shakti point?

On 26 August 2023 the Prime Minister named the lander’s spot Shiv Shakti Point. He named the Chandrayaan-2 spot Tiranga Point. A Cabinet resolution also lists both names. The US names gazetteer lists the landing site as Statio Shiv Shakti.

What is National Space Day?

The Government named 23 August as National Space Day to honour the landing. The first one was held on 23 August 2024. The theme was “Touching Lives while Touching the Moon: India’s Space Saga”.

What is Chandrayaan-4?

On 18 September 2024 the Union Cabinet approved it. It is a technology demonstration mission. The craft must land, collect samples and return to Earth.

• Cost: Rs 2,104.06 crore.
• Time: 36 months from approval.
• Rockets: two launches of the LVM3 rocket.
• Bigger plan: an Indian landing on the Moon by 2040.

One news report describes it as a remote testing centre at VSSC in Thiruvananthapuram. UPSC asked about this centre. The ISRO pages read say little about it.

What does the report say it is?

A news report quotes S. Somanath, then director of the Vikram Sarabhai Space Centre (VSSC). He said ISRO built a Virtual Launch Control Centre there, in Thiruvananthapuram. It lets teams test rocket systems at Sriharikota from far away.

Why was it built?

To cut travel during the Covid-19 pandemic. ISRO wanted fewer people to travel to Sriharikota. The real launch control centre stays in the Mission Control building at Sriharikota. Its systems are copied at VSSC.

Did it launch Chandrayaan-3?

Not as far as the sources show. No ISRO page read describes its role in the Chandrayaan-3 launch. The report does not mention that mission. It supports only a role in remote testing.

What do we know about nearby events?

PSLV-C49 lifted off on 7 November 2020. Business Standard called it ISRO’s first launch since the lockdown. ISRO’s page gives a lift-off time of 1511 IST.

UPSC asked about Chandrayaan-3 in the 2023 Mains. This card gives the wording, an outline and the traps.

What did the past paper ask?

How could you answer it?

• Task: a safe, soft landing on the Moon.
• Countries: the Soviet Union, the United States, China and India.
• Subsystems: propulsion module, lander module and rover, with their payloads.
• Centre: remote testing of rocket systems from VSSC.

What are the traps?

1. Dates. Launch 14 July 2023. Landing 23 August 2023.
2. Hop. 2 September 2023, about 50 cm.
3. Masses. 2,148 kg, 1,752 kg and 26 kg. The total is about 3,900 kg.
4. Names. Shiv Shakti is Chandrayaan-3. Tiranga is Chandrayaan-2.
5. Rank. Fourth country to touch the Moon, per the Prime Minister.
6. Crater. About 160 km wide, 4.4 km deep.
7. Sleep. Sleep mode began by 4 September, not 2 September.