Explained: Why Russia's Luna-25 may reach Moon's South Pole before Chandrayaan-3

Luna-25, Russia’s first Moon landing spacecraft in nearly half a century, will take off for a journey to the lunar south pole on August 11 in what has been termed a ‘race with India to the far side of the Moon’. Its goal will be to carry out scientific observations and tests on the lunar surface and its environment. Even as the world speculates whether Russia will beat India to become the first nation to land a rover on the Moon’s south pole, experts say that the Russian mission may closely coincide with, or even slightly precede, Chandrayaan-3’s touchdown on the Moon. But all similarities end there as there exists a gulf of difference between the two voyages.

Chandrayaan-3 vs Luna-25

According to Russian space agency Roscosmos, the Luna-25 is likely to reach the Moon in five days and remain five to seven days in lunar orbit before descending to one of its designated landing sites -- one of two possible spots near the pole. The Luna-25 mission will be on the Moon for a year and will carry out many scientific experiments and observations.

In contrast, India’s Chandrayaan-3 mission, launched on July 14, is due to land on the Moon’s south pole on August 23 -- a whole one and a quarter months after takeoff from Sriharikota. The Chandrayaan-3 mission, with its limited time of only two weeks, will focus on specific experiments on the Moon.

Luna-25 is expected to reach the Moon between August 21 and August 23. India’s Chandrayaan-3, too, is scheduled to land on the Moon’s south pole around August 23-24. But Roscosmos confirms that the two missions will not clash with each other as they plan to land in different locations.

Purpose of Luna-25 Mission

Luna-25 will try to make a soft landing very carefully on the bottom part of the Moon, similar to Chandrayaan-3. The spaceship wants to study the substance on the Moon’s surface, along with the environment surrounding the Moon. One of its primary tasks will be to collect and study the rocky layer of the surface (regolith), exospheric dust and particles and the gases surrounding the Moon (plasma). 

For a year, the Luna-25 lander will study exospheric dust and particles or the small pieces of matter found in the Moon’s atmosphere to learn more about their origin and composition.

The lander has four legs with landing rockets and fuel tanks. Up top, there is a compartment with solar panels, communication gear, computers and most of the scientific tools. It weighs around 800 kg without fuel and is expected to have about 950 kg of fuel when it launches. 

The lander also has a 1.6-metre-long Lunar  Robotic Arm (LRA, or Lunar Manipulator Complex) that scoops up stuff from the Moon’s surface up to a foot deep (20-30 cm).

The LRA has a tool and scooper to hold nearly 175 cubic cm of material. The tool looks like a 4.7 cm-long tube with a tiny 1.25 cm hole. Up-down, left-right, bend-at-elbow and twist-at-wrist -- these are the four directions in which the arm moves. With a 5.5 kg weight, the arm uses about 30W (similar to a regular light bulb) with a bit more power for stronger movements (50W).

Luna-25 Has 8 Scientific Tools

1) ADRON-LR: This device will measure the gamma rays and neutrons (tiny particles that make up the centre of atoms) coming from the surface of the Moon. Gamma rays are high-energy rays that come from really small particles, like when atoms change. They are important because they can help us learn about things that are hard to see, like what the Moon’s surface is made of and how it behaves.

2) ARIES-L: This device will measure the charged particles and neutrals in the atmosphere of the Moon. ‘Neutrals’ refers to small particles in the Moon’s atmosphere that are not charged, like neutral atoms or molecules.

3) LIS-TV-RPM: This device will measure the water and OH (a type of oxygen) on the surface of the Moon. ‘OH’ refers to a molecule made up of one oxygen atom and one hydrogen atom bonded together. It is often found in substances like water and plays a role in understanding the Moon’s surface.

4) LASMA-LR: This device will measure the composition of the regolith (the loose material on the surface of the Moon) by using laser ablation to vaporize small samples. ‘Laser ablation’ is a process in which a powerful laser beam is used to remove or vaporize tiny bits of material from a surface. In this case, it helps scientists study and analyse the composition of small samples from the Moon’s surface.

5) PML Detector: This device will measure the dust in the atmosphere of the Moon.

6) STS-L: This device will take panoramic and local images of the Moon.

7) THERMO-L: This device will measure the thermal properties of the regolith.

8) Laser Retro-reflector Panel: This panel will reflect laser beams back to Earth, which will be used to measure the distance between the Moon and Earth. The speed at which data will be transmitted from the lander back to Earth is 4 Mbits/sec.

Luna-25’s actual landing site is at 69.545 S, 43.544 E, which is north of the Boguslavsky crater, while the reserve landing site is at 68.773 S and 21.21 E, or the south-west of the Manzini crater. 

Both the sites are within 15 x 30 km landing ellipses. This means both the possible landing sites for the Luna-25 lander are within a 15-kilometre-wide and 30-kilometre-long area, offering the lander scope to land safely at the intended location.

Why Chandrayaan-3 is Delayed

So, why does it take Chandrayaan-3 several weeks to get to the bumpy surface of the Moon? Firstly, ISRO cannot send Chandrayaan-3 directly to the Moon since it does not have a powerful rocket. Besides, to save costs, India is using the most economical technique.

Luna-25 is on a fast track to the Moon. One, a very powerful rocket puts it into Earth’s orbit. Two, they use a strong engine burn known as the Trans-Lunar Injection (TLI) to shoot it straight towards the Moon on a route called the Lunar Transfer Trajectory (LTT), similar to a speedy slingshot. This fast road takes only a few days for the spacecraft to reach Moon.

The author of this article is a Defence and Aerospace analyst based in Bengaluru