ISRO’s Chandrayaan-3 Successfully Launched

Source: The Hindu

Context:

Chandrayaan-3 is India’s second attempt to land a spacecraft on the moon after the unsuccessful landing of Chandrayaan-2’s lander and rover in 2019. If successful, India will become the fourth country to achieve a soft landing on the moon, following the United States, Russia, and China.

How do Space Missions Work?

Rocket and Spacecraft Components:

A space mission consists of two main components: the rocket (or carrier) and the spacecraft (satellite or payload).

The rocket’s primary function is to transport the spacecraft into space, while the spacecraft carries out its mission once in space.

In most missions, the rocket is destroyed after completing its job, while the spacecraft remains operational.

Powered Flight and Launch:

The launch of a spacecraft involves a period of powered flight, where the rocket rises above Earth’s atmosphere and accelerates.

Rockets are powered by a propellant, a combination of fuel and oxidizers, which generate the energy required for lift-off.

The powered flight continues until the rocket’s last stage burns out and the spacecraft separates.

By this point, the spacecraft ideally should have been placed into the intended orbit of the planetary body it is targeting.

Chandrayaan Missions:

Chandrayaan-1:

Chandrayaan-1 was India’s first lunar exploration mission launched on October 22, 2008.

The primary objective was to create a three-dimensional atlas of the Moon and conduct chemical and mineralogical mapping of the lunar surface.

It operated for at least 312 days, making over 3,400 orbits around the Moon.

The mission made significant discoveries related to the presence of water (H2O) and hydroxyl (OH) on the lunar surface, with enhanced abundance towards the polar regions. Ice was also detected in the North Polar region.

Chandrayaan-2:

Chandrayaan-2 aimed to explore the south pole of the Moon and consisted of an Orbiter, Lander, and Rover.

It was launched in July 2019 but encountered partial success.

On September 7, 2019, the lander named Vikram and the rover named Pragyaan crashed on the Moon’s surface.

Despite the setback, the Orbiter performed well and continued to gather data.

It built upon the water discovery of Chandrayaan-1 and found signatures of water at all latitudes.

The Large Area Soft X-Ray Spectrometer (CLASS) on the mission also detected the minor elements chromium and manganese for the first time through remote sensing.

Chandrayaan-3 Mission Objectives:

The main objective of the Chandrayaan-3 mission is to demonstrate India’s technical capabilities and achieve a successful soft landing on the Moon.

A soft landing refers to safely landing a spacecraft on the Moon’s surface at a gentle pace, without human intervention, after traveling through space at high speeds.

Payloads and Scientific Objectives:

The payloads on the lander and rover will be similar to those used in the Chandrayaan-2 mission.

The lander will carry four scientific payloads to study lunar quakes, thermal properties of the lunar surface, changes in plasma near the surface, and perform a passive experiment to measure the distance between Earth and the Moon accurately. One of the payloads will be provided by NASA.

The rover will carry two payloads to study the chemical and mineral composition of the lunar surface, focusing on elements like magnesium, aluminum, and iron in the lunar soil and rocks.

Landing Site and Importance of the South Pole:

The landing site for Chandrayaan-3 will be near the south pole of the Moon, which is the same as the previous  Chandrayaan-2 mission.

The lunar south pole offers challenging conditions but holds promise for deep-space scientific discoveries.

NASA highlights the significance of lunar polar volatiles, which are chemical elements or compounds in a solid state that can melt or evaporate at moderately warm temperatures. Understanding their distribution on the Moon is crucial.

If these volatiles contain elements like hydrogen and oxygen, it could have a profound impact on future deep space exploration and commerce, potentially reducing the need for Earth-based supplies to support human activities in space.

Launch Window and its Precision:

Definition of Launch Window:

A launch window refers to the specific period during which a mission must be launched.

For example, Chandrayaan-3 took off at 2:35 pm, indicating the designated launch window for that mission.

Importance of Precision:

The precise timing of a launch window is crucial for missions that require the spacecraft to approach another spacecraft, a planet, or a specific point in space.

It ensures that the orbits of the spacecraft and the target body overlap at some point in the future.

Illustration with Athletics Race Track:

The European Space Agency (ESA) offers an analogy to explain the concept.

Imagine the Solar System as an athletics race track.

If you want to intercept a runner on the opposite side of the track, you could chase them, but it would require a lot of energy and a long distance to catch up.

However, a more efficient method is to walk across the center of the circular track, reaching the other side at the same time as the runner.

Timing is crucial: arriving too early means waiting, while arriving too late means missing the runner completely and having to wait for another lap.

Curved Paths in Spaceflight:

The analogy demonstrates that straight-line paths do not exist in spaceflight due to the curved paths of celestial bodies.

Planets, including Earth, move in long, curved orbits around the Sun, following circular or elliptical paths.

Calculating the constant movement of Earth and other planetary bodies is essential to determine the shortest and most fuel-efficient path for the spacecraft.

Duration of Lander’s Journey to the Moon:

The journey of the lander to the Moon is expected to take approximately 42 days, with the landing scheduled for August 23 at lunar dawn.

Process and Manoeuvres:

The Chandrayaan-3 mission will be launched into space by the Launch Vehicle Mark-III (LVM-III).

Initially, the spacecraft will be in an orbit around the Earth at an altitude of 179 km.

Through a series of maneuvers, the spacecraft will gradually increase its orbit to escape Earth’s gravity and head towards the Moon.

Upon reaching proximity to the Moon, the spacecraft will need to be captured by the Moon’s gravity.

Orbit Reduction and Descent:

Following capture by the Moon’s gravity, further maneuvers will be conducted to reduce the spacecraft’s orbit to a circular one at 100×100 km.

At this stage, the lander, carrying the rover inside, will separate from the propulsion module and begin its powered descent toward the Moon’s surface.

Lunar Day and Night:

The lander and rover have a mission life of one Lunar day, which lasts for 14 Earth days.

Each Lunar day and night is equivalent to approximately one month (close to 28 Earth days) as the Moon completes one rotation on its axis and one revolution around the Earth.

The extreme drop in temperatures during lunar nights makes it challenging for the lander and rover to survive, which is why they are being landed at dawn.

Reasons for Exploring the Moon:

The Moon is the closest cosmic body to Earth and provides an opportunity for space discovery and documentation.

It serves as a test bed to demonstrate technologies required for future deep-space missions.

Exploring the Moon can stimulate technological advancements, foster global collaborations, and inspire the next generation of explorers and scientists.