How did the Indian spacecraft survive the harsh cold on the dark side of the Moon?

India's Chandrayaan-3 spacecraft is on track to become the first scientific instrument to successfully survive the cold lunar night without heating.

After a groundbreaking two-week mission, India's lander and rover vehicles have gone into sleep mode in the cold darkness of the Moon's south polar region.

India has completed its mission to land and conduct scientific research at the south pole of the Moon. (Photo: ISRO).

However, whether they can "wake up" when the Sun shines at the end of this lunar month is still a big question mark.

Surviving the Cold Shadow of the Moon

According to the Indian Space Research Organisation (ISRO), neither the Vikram lander nor the Pragyan rover of the Chandrayaan-3 mission are equipped with conventional heating equipment for missions to the Moon.

This is an extremely risky decision, as temperatures near the Moon's poles can drop to as low as -253⁰C, colder than some planets like Pluto.

The most common heating system on spacecraft is called a radioisotope heater unit (RHU), which works by passively radiating heat to keep onboard hardware running stably for long periods of time without "freezing up."

Schematic diagram of a radioactive isotope heater. (Photo: Wikipedia).

Most commonly, RHUs used in space missions will convert heat generated from the natural decay of radioactive isotopes of plutonium or polonium into electrical energy.

This process would eventually warm the spacecraft's equipment, or simply help it survive the very cold temperatures.

It is known that both halves of the Moon will experience 2 weeks of sunlight, followed by 2 weeks of darkness.

The closer to the poles, the more extreme the temperatures, due to the influence of tilt and orbit, causing only the highest mountain peaks to be illuminated by the Sun.

For this reason, RHUs were used early in lunar landing missions from the 1970s.

slim chance of survival

Surviving on the dark side of the Moon will be the next challenge for the Chandrayaan-3 spacecraft. (Photo: NASA).

Historically, no device has ever survived the 'cold winter' on the Moon without a heater. The widespread use of RHUs made them a standard for space vehicles before they were deployed.

Lunokhod 1 (1970), Russia's first lunar probe, traveled more than 10 km in 10 months. This was achieved thanks to the ability to maintain temperature and power provided by a polonium-210 radioisotope heater.

Previously, the Apollo 11 (1969) lunar landing also used 34 grams of plutonium-238 to generate heat. Chang'e-3 (2013), a Chinese probe, also has similar mechanisms to protect the system from harsh lunar nights.

The mission's Yutu rover survived the first night but lost the ability to move after the second. Meanwhile, its successor, Yutu-2 (2018), was more successful, waking up every sunrise to continue its mission.

The Russian Luna-25 lunar lander launched on August 11 was also equipped with this heating system. Unfortunately, the vehicle encountered a problem during landing and could not complete the journey.

A simulated image of the Vikram lander and Pragyan rover of the Chandrayaan-3 mission. (Image: ISRO).

ISRO has not publicly discussed why radioisotope heating systems were not installed on Chandrayaan-3's Vikram lander and Pragyan rover. However, it has acknowledged that the duo will have to rely heavily on luck to survive the cold night.

"If it fails to wake up, the Chandrayaan-3 lander will remain there as India's lunar ambassador ," ISRO said in a statement. Still, the mission has been hailed by the media as India's "greatest scientific feat."

On the bright side, it is true that both instruments of the Chandrayaan-3 mission have successfully completed their scientific objectives in what is sure to become a "hot spot" for human space exploration in the coming decade.

According to ISRO, the mission's rover traveled more than 100 meters on the lunar surface, performing many important tasks such as chemical analysis, thermal mapping of the top surface of the regolith layer, as well as plasma measurements.

Chandrayaan-3's scientific instruments also confirmed the presence of sulfur, iron, oxygen and many other elements on the Moon.

The Pragyan lander and Vikram rover are scheduled to resume operations on September 22, which is also the next sunrise phase on the dark side of the Moon.

If it can do this, Chandrayaan-3 will set a new record, becoming the first scientific instrument to successfully survive the cold lunar night without heating equipment.