India’s space agency, ISRO (Indian Space Research Organisation), has achieved a significant milestone with the successful execution of the orbit reduction manoeuvre for Chandrayaan-3, its third lunar mission. This manoeuvre comes just a day after the lunar orbit insertion, marking a critical step towards its ultimate goal of a soft landing on the Moon.
Orbital Manoeuvres
An orbital manoeuvre is a fundamental aspect of space missions, involving the alteration of a spacecraft’s orbit using propulsion systems. These manoeuvres are vital for adjusting the trajectory, speed, and direction of a spacecraft during its journey through space.
Deep-Space Manoeuvres (DSM)
When spacecraft are far from Earth, such as those in orbits around the Sun, the manoeuvre is referred to as a deep-space manoeuvre (DSM). It is important to note that the assertion of the term “DSM” requires verification within the context of space missions.
Coasting Phase in Orbital Transfers
Following an orbital manoeuvre, particularly during a transfer orbit, spacecraft enter what is known as the coasting phase. During this period, the spacecraft continues its journey without active propulsion, coasting along its new trajectory.
Various Techniques of Orbital Transfer
- Hohmann Transfer Orbit: This technique involves transitioning between circular orbits at different altitudes within the same plane using an elliptical orbit. The Hohmann transfer is commonly used for interplanetary missions due to its energy efficiency.
- Bi-Elliptic Transfer: Unlike the Hohmann transfer, the bi-elliptic transfer uses two half elliptic orbits for the orbit change. Although it may require more time, it has the potential to demand less delta-v (applied change in velocity of each manoeuvre) than the Hohmann transfer.
- Low Energy Transfer: This technique focuses on energy-efficient trajectory for orbit changes, which may take longer but minimizes the usage of fuel. Low energy transfers are ideal for missions with resource constraints.
- Orbital Inclination Change: Altering the orbit’s inclination is achieved by changing the spacecraft’s velocity at the orbital nodes. However, this technique is usually avoided due to the high delta-v required for the manoeuvre.
- Constant-Thrust Trajectory: This method involves a prolonged engine burn with constant thrust, leading to high acceleration over an extended period. Constant-thrust trajectories are utilized in specific missions with unique requirements.
Chandrayaan-3’s Lunar Mission
Returning to India’s Chandrayaan-3 lunar mission, the successful execution of the orbit reduction manoeuvre is a critical step in the spacecraft’s journey towards the Moon. Following the recent lunar orbit insertion, the mission plans to undertake three additional moon-bound manoeuvres by August 17. Once these manoeuvres are completed, the lander and rover will detach from the propulsion module.
Subsequent de-orbiting manoeuvres will then be initiated to prepare for the final moon descent, aiming for a soft landing on August 23. The soft landing is of utmost importance to ensure the safety and success of the lander and rover on the lunar surface.