A Russian spacecraft will travel to the moon for the first time in nearly half a century. A Soyuz rocket launched Luna-25, a moderately sized autonomous lander, into Earth's orbit early on Friday (11 August) morning from a remote spaceport in Russia's far eastern region.
Approximately 80 minutes after launch, Luna-25's trajectory was altered to direct it towards the moon.
It will then endeavour to land on the moon's surface as early as August 21, two days ahead of India's Chandrayaan-3, which is also scheduled to land in the same vicinity — the moon's south polar region.
This has caused many Indians to question why the Russian moon lander, which was launched nearly four weeks after the Chandrayaan-3 mission, could conceivably reach the lunar surface days before Chandrayaan-3.
Indian Space Research Organisation's (ISRO's) heaviest rocket, Launch Vehicle Mark-3, launched Chandrayaan-3 from Sriharikota as its two solid strap-on boosters exhaled orange smoke, guiding it through its brief but majestic vertical ascent.
After more than 28 days and a number of orbital manoeuvres, the propulsion module has been deposited in an orbit around the Moon.
Despite the fact that the travel time may seem reasonable given the distance between the Earth and the Moon, it is essential to remember that many previous missions have completed this journey in less time.
For example, China's Chang'e 2, launched in 2010, and its follow-up mission to the lunar surface, Chang'e 3, both covered the distance between the Earth and the Moon in four days.
In less than four days, the Apollo-11 command module Columbia, transporting three astronauts, reached the Moon.
Luna-25 would not be the first Russian mission to the Moon to follow the shorter route. Luna-1, the first unmanned mission to reach the Moon's vicinity, completed the voyage in just 36 hours.
The straightforward explanation is that ISRO, unlike the Russians, Chinese, and Americans, lacks a rocket potent enough to propel Chandrayaan-3 directly to the Moon.
Apollo missions, including Apollo 11, utilised a direct trajectory known as Translunar Injection (TLI). The Saturn V rocket propelled the Apollo spacecraft into Earth orbit before anything else.
From that point on, a forceful engine burn was executed to propel the spacecraft directly towards the Moon. A single six-minute discharge of the Saturn rocket's third stage directed the spacecraft towards the LTT, simulating a slingshot effect.
This direct route enabled the Apollo missions of NASA to reach the lunar surface relatively swiftly, in a matter of days.
The Russian Luna-25 would employ a similar methodology. However, Chandrayaan-3 follows a very different trajectory.
The mission utilised a series of Earth orbits and engine burns to enhance the spacecraft's velocity and position it for a lunar insertion.
After its launch on 14 July, the spacecraft first entered an initial Earth orbit and then performed specific engine burns to transition to a trajectory that intersects the Moon's orbit. A second engine burn was then performed to place the spacecraft into lunar orbit.
ISRO's multi-step strategy for the Chandrayaan and Mangalyaan missions necessitates additional time but permits the use of relatively less potent launch vehicles.
LVM-3 is a competent launch vehicle, but it lacks the power and payload capacity of the Saturn V used for Apollo missions and the Soyuz rockets used by the Soviet Union and now Russia.
ISRO opted for a more gradual trajectory to optimise the mission within the limitations of the launch vehicle.
ISRO has utilised the gravity of the Earth and Moon to circumvent the limitations.
When passing through the closest point of an elliptical orbit around the Earth, a spacecraft will be travelling at its maximum speed. This location is known as the perigee.
The opposite point in the orbit is the apogee, where the spacecraft is farthest from the Earth and travelling at its slowest speed.
Due to variations in the Earth's gravitational pull, the speed varies at various points along the orbit. The closer a spacecraft is to Earth, the stronger its gravitational influence and the faster it will travel.
Each time the spacecraft reaches the perigee, or point of maximum speed, the onboard engines are activated to increase its speed, propelling it into an orbit that is higher and more elongated.
With each discharge of the onboard propulsion system, the spacecraft continues to spiral outward in ever-expanding ellipses.
Eventually, as it continues its journey, it attains the required escape velocity to flee Earth's gravity. At this juncture, the spacecraft's orbit will expand, enabling it to set a course for the moon.
This is the strategy ISRO has employed for the Chandrayaan missions.
Chandrayaan-3's entry into the LTT was precisely timed to coincide with the moon's position in its own orbit. This strategic scheduling allowed the module to reach the vicinity of the Moon's orbit precisely when the Moon was in that region.
Once the module reached this location, the onboard propulsion system was used to execute a precise manoeuvre. This manoeuvre, known as lunar orbit insertion, is intended to slow down the module.
The moon's gravitational field then drew the module into a stable orbit around the moon. This successful lunar insertion marked the conclusion of the critical phase required to place the spacecraft in lunar orbit.
After escaping the Earth's gravity and entering lunar orbit, the module is presently orbiting the moon.
ISRO is presently lowering the module's orbit around the Moon in order to bring it closer to the lunar surface. When it reaches a 100 km circular orbit around the Moon, the propulsion module will separate from the lander, which will proceed towards the lunar surface.
Chandrayaan-3 entered lunar orbit on August 5 and is scheduled to touch down on August 23, requiring more than 18 days to travel from its initial lunar orbit to the cratered surface.
In contrast, Luna-25 is scheduled to enter lunar orbit on August 16 and attempt a landing on August 21, completing the voyage from orbit to the surface of the Moon in five days.
Similar to its voyage from Earth's orbit to lunar orbit, the Russian spacecraft's path from lunar orbit to the lunar surface will be more direct. ISRO will execute orbit reduction manoeuvres to position the module for landing by progressively lowering its orbit.
The Luna-25 mission would beat Chandrayaan-3 in the quest to land near the lunar south pole if it successfully landed on August 21.
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