Chandrayaan-3 vs Luna-25 has been touted as a race to the lunar South Pole. However, it’s not a competition between India and Russia to see who will land first. Indian lunar lander Chandrayaan-3 was launched on July 14 and has been in lunar orbit since August 5. It is currently lowering its orbit in preparation for a landing attempt scheduled for August 23.
For Russia, this marks a return to the Moon. The last lunar mission of the Soviet era, dubbed Luna-24, took place in 1976. Luna-25 was launched on August 10, and due to its more direct trajectory to the Moon, it might attempt a landing on August 21.
Vikram and Pragyan Need the Sun
The key factor for successful lunar landing is the timing of the solar trajectory. Sun needs to rise over the respective impact points to provide energy to the vehicles on the surface. Both Luna-25 and Chandrayaan-3 are in lunar polar orbits. Chandrayaan-3 is targeting a landing site (ref.) where the sun will rise on this area at the beginning of August 21. This means that the illumination for the Vikram lander and the Pragyan rover will be optimal on August 23.
Luna-25 is targeting the Boguslawsky crater. As this region is further to the east, the sun will rise on this site on August 20. This implies that Luna-25 might have a chance to land earlier. However, it will depend on Luna-25’s lunar orbit and the plan of Roscosmos.
Vikram and Pragyan are solar-powered and have a mission duration of about one lunar day, roughly 14 Earth days. On the other hand, Luna-25 is equipped with a radioisotope thermoelectric generator (RTG) that will provide the necessary heat and energy to keep the lander operational for at least a year. Therefore, the timing of landing at the start of the lunar day might not be a priority.
Landing on the Moon Isn’t Easy
Moon is at the center of renewed global interest and is being visited by a fleet of spacecraft from various countries. Currently, only China has successfully landed on the Moon in this century with the Chang’e 3, 4, and 5 missions. However, unlike the Chinese missions, the attempts by India and Russia aim for a closer proximity to the lunar South Pole.
Russia hasn’t landed on the Moon since the Soviet era. Russia’s last interplanetary mission, Fobos-Grunt, aimed at collecting samples from Mars‘ moon Phobos, but it failed to leave Earth‘s orbit in 2011. The Luna-25 mission has been delayed for over a decade, and engineers had to make modifications to the landing navigation system during the advanced stages of vehicle development.
As for India, the country aims to join the exclusive club of nations that have achieved lunar landing. This would be an extraordinary feat alongside the Mangalyaan mission, which entered Mars’ orbit in 2014. The Indian Space Research Organization (ISRO) claims to have learned from the unsuccessful landing attempt of the Chandrayaan-2 spacecraft in 2019. Landing cannot be taken for granted for either of the two missions, for various reasons. Certainly, India and Russia’s efforts will be closely followed worldwide.
Will They Actually Land at the South Pole ?
Landing at the South Pole is the focal point of both missions. The entire world is eager for concrete evidence of trapped water ice in those regions. This is because water could be used as propellant or to provide vital sustenance materials for lunar habitats.
Both Chandrayaan-3 and Luna-25 aim to land further south than any previous lunar landing, respectively at 69 and 72 degrees south of the equator. These sites are not truly polar but will undoubtedly provide new insights. Landing near the equator is also known to be favorable for various technical reasons, including illumination, communications, and easier terrain for navigation.
“Neither of these is a polar location, but rather high-latitude positions” says Clive Neal, a lunar exploration expert at the University of Notre Dame in Indiana. “We’ve never visited such southerly high-latitude places before. So from a scientific standpoint, these landers will provide data from new positions on the Moon”.
Characteristics of the Spacecraft
The two landers have similar masses. Luna-25 weighs 1,750 kg at liftoff, with slightly over half of that being propellant, Chandrayaan-3 weighs 1,752 kg, including a 26 kg rover named Pragyan. A significant portion of Vikram’s mass is propellant for landing. Luna 25 carries eight scientific instruments, including the Lunar Manipulator Complex (LMK) capable of digging lunar regolith, and the Alpha-particle X-ray spectrometer (ADRON-LR) for ice detection.
Meanwhile, Vikram will make the most of its day in the sun. It carries four scientific payloads, one of which will insert a thermal probe into the lunar soil to a depth of about 10 centimeters and take temperature readings of the regolith during the lunar day. Pragyan will carry the Laser-Induced Breakdown Spectroscope (LIBS) and the Alpha Particle X-ray Spectrometer (APXS) to study the regolith.
A notable aspect of these missions is international cooperation, which is usually a strong feature of space endeavors. However, Russia has been largely isolated internationally since its invasion of Ukraine in February 2022. This has disrupted the involvement of the European Space Agency (ESA) in the Luna-25, 26, and 27 missions. It has also delayed the launch of the Rosalind Franklin rover of the ExoMars program. India, on the other hand, is planning a joint mission with Japan called the Lunar Polar Exploration mission (LUPEX), to be launched later in the decade. The country has also joined the Artemis agreements with NASA.