On Friday, the launch of Chandrayaan 3 marked the second attempt to send a rover to the lunar surface. We look at what went wrong last time—and why it’s so damn hard to land on the moon.
Researched by: Rachel John & Aarthi Ramnath
About our lead image: This is a Japanese woodblock print by Keisai Eisen, Autumn Moon over Atago Hill (Atagosan no aki no tsuki), from the series Eight Views of Edo, 1846. Credit: Wikiart.
First, a quick history of India’s ‘moon shots’
India’s first rocket launch dates back to 1963 but the Indian Space Research Organisation (ISRO) was only established in 1969. We have been eyeing the moon since 2008—and have launched two lunar missions since.
Chandrayaan 1: The name literally means ‘Moon Craft’ in Sanskrit. And the first mission aimed merely to crash-land a probe on the moon’s surface. The spacecraft launched on October 22, 2008 aboard the India-made Polar Satellite Launch Vehicle rocket. It reached the moon on November 8—and released its Moon Impact Probe on November 14.
A landmark success: Chandrayaan 1 was the first to confirm the presence of water on the moon—thanks to its lunar probe:
Chandrayaan-1, India's first-ever moon probe, was aimed at mapping the lunar surface and determining its mineral composition... While the probe was still active, its NASA-built Moon Mineralogy Mapper (M3) detected wavelengths of light reflected off the surface that indicated the chemical bond between hydrogen and oxygen—the telltale sign of either water or hydroxyl.
The spacecraft’s orbiter made 3,400 orbits of the moon and continued transmitting data until August 29, 2009—when controllers permanently lost communication with it. But it was rediscovered by a powerful earth radar in 2017—still making its rounds about 125 miles (200 kilometres) above the lunar surface. You can see what it looks like below:
Point to note: Chandrayaan’s launch vehicle PSLV has been a great technological success, as well. Since 1993, it has helped launch hundreds of satellites—both Indian and foreign—plus three lunar spacecraft and the Mars orbiter in 2013.
Chandrayaan 2: The logical next step was to land a rover on the moon—and that’s what we tried to do in 2019. Chandrayaan 2 was scheduled to launch in 2011—as a collaboration with Russia—which would provide the moon lander and rover. But the Russian design proved incompatible—and we had to develop our own. It was finally launched on July 22, 2019—and achieved lunar orbit on August 19, 2019.
The plan: The GSLV Mk-III rocket was to deliver a module containing an Orbiter, a Lander named Vikram and a Rover called Pragyan into the Moon’s orbit. Once the Orbiter is circling the moon, the Lander will detach itself and land on the surface. Once there, it will release the Rover which will carry out experiments. The primary aim: study the extent and distribution of water on the moon’s surface and below it.
The failure: At first, everything went to plan. The rocket delivered the module containing an orbiter, lander and rover into the Moon’s orbit. The orbiter was circling the moon as per schedule. But the attempt to deliver Vikram on the surface went terribly wrong—and ISRO lost contact with it right before landing.
What went wrong: Basically, the lander Vikram was equipped with thrusters to make sure that it makes a soft landing on the surface. They act like brakes that are applied at various intervals to slow the lander down, and correct its orientation so it lands on its legs.
One or more of these did not perform as required in the last five minutes due to a software glitch: “At this point, the thrust might have been more than optimal, impacting the lander's orientation. It's like a car losing direction due to sudden braking at high speed.” Translation: it may have hit the brakes a bit too hard. The result: Vikram tilted 410 degrees instead of the planned 55 degrees. It went off trajectory and failed to slow down—and crash-landed on the surface.
Also this: The selected landing site may have been too small.
Say hello to Chandrayaan 3
The third mission launched on Friday—and is expected to achieve lunar orbit by August 24. It is the similar to the previous mission but for some key differences:
- There is no orbiter—which made Chandrayaan 2 a partial success. It continues to send back valuable data that is critical for planning future exploration.
- The new version of the lander—Vikram—is 280 kilograms heavier—and is around the size of a small car. Much of the added weight is due to tweaks aimed at avoiding a repeat of the previous debacle—such as extra fuel, stronger legs etc.
- But it only has four engines instead of the five on its predecessor—to alleviate the added weight.
- The landing site is larger and more carefully mapped.
Key quote to note:
“Instead of a success-based design, ISRO has this time opted for a failure-based design,” said ISRO’s chairman S. Somanath during a July 6 press briefing. That is, for Chandrayaan-3, ISRO has focused on what can fail and how those failures can be prevented. “We looked at sensor failure, engine failure, algorithm failure, calculation failure,” Somanath said.
Here’s a clip of the Friday launch:
Aiming to make history: This will be the first mission to attempt to land a rover on the south pole. Previous rovers—including those of NASA—landed close to the lunar equator—and for a very good reason:
It is easier and safer to land near the equator. The terrain and temperature are more hospitable and conducive for a long and sustained operation of instruments. The surface here is even and smooth, very steep slopes are almost absent, and there are fewer hills or craters. Sunlight is present in abundance, at least on the side facing the earth, thus offering a regular supply of energy to solar-powered instruments.
But precisely because it is still unexplored, the south pole offers great potential for ground-breaking discoveries. There are indications of polar ice—and the freezing temperatures better help preserve traces of the moon’s ancient past. FYI: NASA’s next manned mission to the moon will also land on the moon’s south pole.
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Why moon landings are hard
Three out of the last four landing attempts on the moon—including Chandrayaan-2—have failed. The most recent was in late April—an attempt by a private Japanese startup that was aborted when it lost contact with its lander. This is why soft landings on the moon are hard:
One: The moon has very little atmosphere or gravity compared to say Mars or Venus:
Soft landing on the surface of Mars and Venus was done using parachutes to reduce the speed at the time of fall, but this can’t be done on the moon as it does not have sufficient gravity and has no atmosphere (unlike Mars).
Two: The lander can churn up dust and loose bedrock that blocks its sensors:
Landers could kick up a cloud of dust that blocks sensors from detecting the craters or boulders that a last-minute engine burn might avoid. And the thrust could displace enough lunar matter that the spacecraft lands tilted, a position that could prevent a rover from rolling out safely.
Three: Scientists have to make complicated calculations about a landing sequence that has to be executed in an alien environment:
Simulations on Earth provide incomplete pictures of a preprogrammed process that unfolds autonomously thousands of miles away. The spacecraft must go from a speed of thousands of miles an hour to nearly zero in about 15 minutes. It has to ignite its engines and thrust itself against the direction it is hurtling toward. As it slows, it falls, and more engine burns are needed to keep it from plummeting too fast.
Point to note: China made the only successful attempt in recent years. In 2019, it landed a spacecraft on the far side of the moon—the side that never turns toward Earth—a historic first.
The bottomline: Only three countries have successfully completed a soft landing on the moon—United States, China, and the former Soviet Union. Becoming the fourth will rightly be a reason for great national pride. We plan to explain why at greater length when India nails this achievement in a month. Fingers crossed:)
Reading list
The Scientific American and Space.com have very good overviews of Chandrayaan 3. Indian Express explains why the south pole matters. Space.com has details on Chandrayaan 1. The Hindu explains why this mission means so much to India. Outlook India looks at the challenges of nailing a soft landing.
