'Need Bigger Rockets': Ex-DRDO Chief On How & Why Luna-25 Overtook Chandrayaan-3

Despite launching about a month before Russia's Luna-25 mission, ISRO's Chandrayaan-3 mission might land on the Moon after its competitor (if everything goes well for the former). Russian space agency Roscosmos launched the Luna-25 mission on August 10 from the Vostochny Cosmodrome whereas ISRO's Chandrayaan-3 lifted off on July 14 from Sriharikota. However, the Soyuz-2.1b launch vehicle, which is more powerful, sent Luna-25 directly into a lunar trajectory as opposed to Chandrayaan-3 which was launched using the LVM3 rocket. 

As for the landing, Roscosmos has set the landing date on August 21 whereas ISRO says the Vikram lander will touch down on the Moon on August 23. Notably, both dates can get extended in case any anomaly arises or the landing sites are unsuitable. 

Russia has launched its lunar mission for the first time in 47 years since Luna-24 in August 1976. The latest mission comprises a lander weighing 1750 kg (800 kg dry mass + 950 kg propellant) which will operate for one year on the Lunar South Pole. The Vikram lander will also touchdown on the South Pole but will be operational for only 14 Earth days (one lunar day). But unlike Luna-25, Vikram (weighing 1,752 kg)  is carrying a 26-kg rover which will work in tandem with the lander to explore the characteristics of the Moon. 

We need a bigger launch vehicle: Dr. Pillai

While speaking to Republic TV, former DRDO Director Dr. AS Pillai stressed on the need for bigger rockets that could send heavier payloads to orbit and cut the travel time for missions like Chandrayaan-3. 

"We need to do more in launch vehicle development to make bigger launch vehicles so we can put maximum payload in the orbit. When you do that, you also get the capability to go faster. Today Russia has gone faster (with Luna-25). So we have to do that fast, we need a bigger launch vehicle," Dr. Pillai said. 

(Luna 25 mission profile; Image: Roscosmos/X/@katlinegrey)

The Luna-25 lander entered the lunar orbit on August 16, just six days after the launch as the Soyuz rocket injected it directly into a lunar trajectory. Chandrayaan-3, on the other hand, entered the lunar orbit on August 5 after making five elliptical orbits of the Earth and five of the Moon before entering a near-circular orbit. Although this path is considered more efficient since it requires less fuel. 

(Chandrayaan-3 mission profile; Image: ISRO)

Soyuz provides extra thrust to Russia's lunar ambitions

The Soyuz rocket's Fregat upper stage played a crucial role in sending Luna-25 right into the lunar orbit. The Fregat stage of the Soyuz-2.1b greatly enhances the rocket's capacity as it can alone deliver a 3,500 kg payload in geostationary orbit in one of its configurations. On the other hand, the three-stage LVM3 rocket, ISRO's heaviest, is capable of delivering 8,000 kg to a low-Earth orbit and 4,000 kg to a geostationary orbit. 

Dr. Pillai said that ISRO is working toward building boosters that rely more on cryogenic fuel which provides more thrust during launches. "We are going further on the semi-cryogenic booster. We want to make a powerful booster so that in future (there) will be a large launch vehicle to put maximum payload in low-Earth orbit as well as the geo-transfer orbit," he said.