Source: TH
Subject: Science and Technology
Context: Space re-entry has gained attention with advancing human spaceflight missions, especially India’s Gaganyaan programme, which focuses on safely returning astronauts to Earth.
About Space Re-entry:
What is Space Re-entry?
- Space re-entry refers to the process by which a spacecraft or crew capsule returns from orbit and safely passes through Earth’s atmosphere to land on the surface.
What is a Re-entry Corridor?
The re-entry corridor is a narrow, precisely defined atmospheric window through which a spacecraft must enter Earth’s atmosphere to ensure safe return.
- Too shallow (Overshoot): The spacecraft may skip off the atmosphere and return to space.
- Too steep (Undershoot): Extreme heat and deceleration forces can destroy the vehicle or endanger the crew.
Hence, maintaining the correct entry angle is critical for survival.
How Space Re-entry Works?
- De-orbit Burn: The spacecraft turns opposite to its direction of travel and fires engines to reduce orbital velocity, allowing gravity to pull it into the atmosphere.
- Atmospheric Aerobraking: Atmospheric drag converts kinetic energy into heat, slowing the capsule rapidly.
- Thermal Protection: Heat shields protect the capsule using ablation or insulation to withstand temperatures generated during re-entry.
- Controlled Guidance: Semi-ballistic design and attitude control help maintain the vehicle within the re-entry corridor and guide it toward the landing zone.
- Communication Blackout: Ionised plasma forms around the capsule, temporarily blocking radio communication.
- Parachute Deployment & Landing: At lower altitudes, multi-stage parachutes reduce speed for safe splashdown or landing.
What is a Semi-Ballistic Body?
- A semi-ballistic body is a re-entry vehicle that is not fully steerable like an aircraft but is also not completely passive like a falling object.
- By flying at a controlled angle of attack (created through an offset centre of gravity), it generates limited aerodynamic lift in addition to drag.
- This lift allows the capsule to perform small steering corrections, control descent path, and accurately reach a designated landing zone during atmospheric re-entry.
What is a Communication Blackout?
- A communication blackout occurs during re-entry when extreme heat ionises surrounding air, creating a plasma layer around the spacecraft. This plasma sheath blocks or reflects radio signals, temporarily preventing communication between the spacecraft and ground stations.
- Communication resumes once the vehicle slows down and the plasma dissipates at lower altitudes.
How will the Gaganyaan Crew Module Re-enter?
- The Orbital Module consists of a Crew Module (CM) and a Service Module (SM).
- Re-entry begins with a de-orbit burn performed by the SM to reduce orbital velocity.
- After de-orbiting, the Service Module separates and burns up in the atmosphere.
- The Crew Module enters Earth’s atmosphere within a carefully controlled re-entry corridor to avoid overshoot or undershoot.
- Operating as a semi-ballistic body, it performs controlled manoeuvres using thrusters to maintain trajectory.
- A robust thermal protection system shields the module from intense heating.
- At lower altitudes, a three-stage parachute system deploys to reduce speed.
- The capsule finally performs a safe splashdown in the Bay of Bengal, the designated recovery zone for the mission.
