Gaganyaan Service Module Propulsion System

Gaganyaan Service Module Propulsion System

Why in News? 

Recently, ISRO conducted two hot‑fire tests in July 2025 for the Gaganyaan Service Module Propulsion System (SMPS) at Mahendragiri. These tests ran smoothly, validating the engines and thrusters under real‑world conditions. This success marks a key step toward crewed spaceflight with Gaganyaan.

Key Highlights of Gaganyaan Service Module Propulsion System

• The Indian Space Research Organisation conducted two successful hot tests of the Service Module Propulsion System (SMPS) on July 3, 2025 at the ISRO Propulsion Complex (IPRC) in Mahendragiri, Tamil Nadu.
• The two hot tests had a clear objective—to verify the real-time behavior of the propulsion system’s engines and thrusters. 
• The first hot test ran for a total of 30 seconds, while the second was significantly longer, lasting 100 seconds.
• ISRO engineers simulated flight-like conditions for both tests. This included matching pressure, temperature, and vacuum levels expected in actual mission scenarios. 
• The hot tests successfully demonstrated coordinated firing of multiple engines and thrusters. 
• During the tests, engineers used high-fidelity sensors and real-time telemetry systems to capture data.

What is Service Module Propulsion System (SMPS)?

• About: The Service Module Propulsion System is the engine-based control system that powers the spacecraft’s key orbital movements. 

• It was built to guide and adjust the Gaganyaan crew module while in space. 

• • • The propulsion system is placed inside the Service Module, located beneath the Crew Module in the spacecraft structure.
    • ISRO’s Liquid Propulsion Systems Centre is responsible for building the Service Module Propulsion System.

• Purpose: The propulsion system serves multiple roles in India’s first human spaceflight project. 

• The system helps change the spacecraft’s direction while it remains in Earth’s orbit.

• It helps the crew module enter and exit the orbit safely. 

• It also performs fine-tuned control during the descent back to Earth. 

• It also provides stability and orientation during docking or undocking in future missions.

Design and Components of the Service Module Propulsion System

• Main Engine Configuration: The heart of the propulsion system lies in its main engines. ISRO engineers have included five engines, each producing 440 Newtons of thrust. These engines help perform key maneuvers such as orbital insertion and deorbit burns. 

• Reaction Control Thrusters: In addition to the main engines, the propulsion system includes reaction control thrusters. These small thrusters are responsible for adjusting the spacecraft’s orientation or attitude. ISRO integrated sixteen thrusters, and each one can deliver a 100 Newton thrust level. They become active during critical moments, such as when aligning the spacecraft for reentry.

• Fuel and Propellant: The propulsion system uses hypergolic propellants. This means the fuel and oxidizer ignite instantly when they meet. The fuel used is Monomethylhydrazine (MMH). The oxidizer is Mixed Oxides of Nitrogen (MON-3). This combination is stable and well-suited for long-term storage in space. 

• Propellant Storage: Engineers have arranged the fuel tanks in a balanced configuration within the service module. The design includes two fuel tanks and two oxidizer tanks. These tanks are placed symmetrically to maintain stability during flight. The tanks are built with titanium alloys, chosen for their light weight and strength. 

• Thermal and Structural Design: The structure of the service module has heat shields and insulation to protect fuel lines and engine nozzles. The system is mounted on vibration-damping structures to prevent mechanical stress from affecting performance.

• Redundancy: The SMPS was designed with multiple layers of redundancy. If one engine or thruster fails, others can take over. This fail-safe design increases mission reliability. 

Operational Mechanism of the Gaganyaan Service Module Propulsion System

• Activation: The propulsion system becomes operational after the launch vehicle separates the Gaganyaan module from the final stage of the rocket. At this point, the crew module and service module enter low Earth orbit, approximately at 400 km altitude. The SMPS activates immediately after separation and takes over the responsibility of controlling the spacecraft’s movements in space.

• Orbital Insertion: Once in orbit, the spacecraft might need slight adjustments to reach the desired altitude and orientation. The SMPS handles these orbital correction tasks by using its 440 Newton engines. These engines fire in brief intervals to either raise or lower the spacecraft’s orbit.

• Attitude Control: Throughout the mission, the spacecraft must maintain proper orientation. The propulsion system achieves this using 100 Newton reaction control thrusters. These thrusters provide accurate directional control during orbital movement.

• Power and Thermal Management: While in space, the propulsion system must operate in extreme temperatures, which can swing from minus 150°C to plus 120°C depending on solar exposure. The SMPS includes thermal insulation and heating elements to regulate engine and fuel temperatures.

• Reentry Preparation: When the mission reaches its final phase, the SMPS takes on its most critical role—deorbiting the spacecraft. The propulsion system performs a long-duration engine burn using its main engines to reduce the spacecraft’s velocity. 

Why the Service Module Propulsion System Matters for India?

• Indigenous Space Engineering: The SMPS is an entirely Indian-built propulsion system, designed and developed by the Indian Space Research Organisation (ISRO). It reflects years of focused effort to build space hardware within the country. Before 2018, most of India’s human spaceflight planning was still on paper. The approval of Gaganyaan in 2018 marked the beginning of serious investment in indigenous crewed space capabilities.

• Safety in Human Spaceflight: The main purpose of the propulsion system is to ensure that astronauts return home safely. Once the Gaganyaan module reaches orbit, the launch vehicle steps aside, and the propulsion system takes over. The system adjusts the spacecraft’s path, maintains direction, and performs the crucial deorbit burn for reentry. The SMPS is central to creating a trusted path back from space. 

• India’s Long-Term Space Goals: India aims to set up long-term human presence in space. This includes planned space station modules, deep-space missions, and lunar exploration programs. For instance, the same engine principles can support future missions where orbit transfer or docking maneuvers are needed.