Continuing our series of blog posts on the Gaganyaan mission, we had previously discussed the overall mission profile, development stages, and rigorous testing of the human-rated LVM3 launch vehicle and the Crew Escape System. In this blog, we will delve deeper into the main Orbital Module, which will house three astronauts for a 3-day mission to 400 km Low Earth orbit (LEO) and bring them back safely.
This critical component of the mission not only demonstrates ISRO’s advanced capabilities but also lays the groundwork for future endeavors, including the potential addition of International Docking System Standard (IDSS) compatibility. This would enable docking with the International Space Station (ISS) and future visits to India’s planned Bharatiya Antariksha Station[1]. Join us as we explore the intricacies of the Gaganyaan Orbital Module and its pivotal role in India’s human spaceflight ambitions.
Orbital Module Overview
The Gaganyaan Orbital Module consists of two parts:
- Crew Module (CM)
- Design: The Crew Module, weighing 4520 kg, is designed to carry three astronauts to space and back safely. It provides a habitable space with an Earth-like environment. The module has a double-walled structure: a pressurized metallic inner structure and an unpressurized external structure with a Thermal Protection System (TPS)
- Capabilities:
- Houses crew interfaces, human-centric products, life support systems, avionics, and deceleration systems
- Equipped with displays and control panels for the astronauts to monitor and control the spacecraft.
- Ensures safe re-entry and landing with advanced heat shield technology.
- Service Module (SM)
- Design: The Service Module supports the Crew Module by providing power, propulsion, and other essential services during the mission.
- Capabilities:
- Service Module Propulsion System (SMPS), powered by liquid bi-propellant engines, which performs crucial functions such as orbit-raising maneuvers and the deorbit burn necessary for atmospheric re-entry.
- Contains solar panels, batteries, avionics, deployment mechanisms and other power supply systems.
Together, the Crew Module and Service Module form the 8.2-ton Orbital Module[2].
Below is an image showcasing various subsystems of the Orbital Module:
Credits : Orbital module schematics, NASA spaceflight forum[3]
Testing and Development
The development and testing of the Gaganyaan mission include multiple phases:
1. Service Module Propulsion System demonstration[4]
The propulsion system for the service module is a single bi-propellant system consisting of sixteen 100 Newton thrusters for reaction control system (RCS) and five primary 440 Newton thrust engines, using monomethylhydrazine (MMH) and mixed oxides of nitrogen (MON-3) as the fuel and oxidizer, respectively.
Phase-1 test series on July 19, 2023
The test of the Gaganyaan Service Module Propulsion System (SMPS) was successfully completed by ISRO. Five hot tests totaling 2,750 seconds were conducted as part of the Phase-1 test series. Eight 100 N reaction control system (RCS) thrusters and five 440 Newton liquid apogee motor (LAM) engines were used. The system’s hot testing replicated the operation of the flight-qualified thruster, helium pressurization system, propellant tank feed system, and control components.
The test, which lasted 250 seconds, saw continuous use of RCS thrusters and LAM engines. During the Gaganyaan mission’s ascending phase, the RCS thrusters will ensure precise attitude correction, while the LAM engines will supply the primary propulsive force.
Phase-2 test series on July 20, 2023
A hot test in the final configuration of SMPS was conducted. Sixteen RCS thrusters with 100 Newton thrust and five LAM engines with 440 Newton thrust were used. The hot test simulated the fluid circuit of the SMPS, including the propellant tank feed system, helium pressurization system, flight-qualified thrusters, and control components. The combined performance of SMPS was showcased in the first hot test of the Phase-2 test series. Each 440 Newton thrust engine were also be tested individually for longer duration involving various parameters to gain human-rating certification.
Final test on July 26, 2023
Two more hot tests on the SMPS were successfully conducted by ISRO. The thrusters were run in tandem with the mission profile, both in continuous and pulsed mode. The first hot test, lasting 723.60 seconds, demonstrated the pumping of fuel into the orbital module and the burning of 100 Newton thrusters and LAM engines for calibration. The calibration burn was essential to identify and isolate any non-operational engines. The RCS thrusters and LAM engines operated as anticipated.
The second hot test, lasting 350 seconds, demonstrated how the Orbital Module circularizes to reach the final orbit. The RCS thrusters functioned in pulse mode throughout this test, while the LAM engines ran continuously.
Gaganyaan Mission:
— ISRO (@isro) July 27, 2023
Two more hot tests on the Gaganyaan Service Module Propulsion System were conducted successfully at IPRC/ISRO on July 26, 2023.
Tests were conducted in pulsed and continuous modes necessary for the mission.
Three more hot tests are scheduled to demonstrate… pic.twitter.com/Vn7BrzbpHE
2. Orbiter Module Adapter (OMA) assembly[5]
In 2022, Kineco Kaman Composites became the first private company in India to supply the first OMA. A 4-meter diameter conical structure made of carbon fiber-reinforced plastic was successfully provided. This structure is integrated with the crew escape module and the equipment bay shroud.
3. Evaluation of Thermal Protection Systems(TPS)[6]
Ablative Thermal Protection System (TPS) refers to a type of heat shield used in spacecraft to protect the astronauts from the extreme temperatures experienced during atmospheric reentry. The term “ablative” comes from the process of ablation, which involves the gradual erosion or wearing away of the material due to intense heat and friction.The fore-body region of almost all manned crew modules flown to date uses ablative TPS. Ablative TPS is chosen for its simplicity, reliability, self-regulating nature, and proven flight heritage.
Three candidate TPS materials, Carbon Phenolic (CP) composite, Silica Phenolic (SP) composite, and Medium Density Silica Phenolic (MDSP), were identified for the Gaganyaan mission of ISRO. These materials were evaluated in the Plasma Wind Tunnel facility (6MW capacity) under simulated reentry environments. Tests were conducted at expected peak heat flux and total heat load conditions. The performance of the materials was compared based on thermal response and material surface recession characteristics.
All three TPS materials (two models each) were tested at a cold wall heat flux of 150 W/cm² for a duration of 180 seconds. Post-test, the test model surface was profiled to obtain material surface recession. CP showed the lowest surface recession at 1.8 mm, followed by SP and MDSP.
MDSP and SP exhibited comparable back-wall temperature rise. Due to MDSP’s lower density, it translates to a lower overall TPS weight, giving MDSP an edge over SP TPS. However, MDSP had the highest surface recession, necessitating detailed study of its effect on the aerodynamic configuration of the vehicle. Efforts are now underway to improve MDSP by replacing the glass micro-balloon filler with silica aerogel filler. Additionally, a new graded TPS development has been initiated, combining the erosion resistance of SP with the reduced thermal conductivity and density of the MDSP variant.
4. Crew module testing and integration
Credits : ISRO Gaganyaan test vehicle TV-D1
A series of tests will be carried out by ISRO to ensure the safety of the Crew Module and to prepare for its safe recovery. For the first Integrated Air Drop Test (IADT), the Crew Module will be dropped from an Indian Air Force (IAF) helicopter from a height of around 4-5 km above ground level. After the integrated air drop tests, a series of test vehicle missions, pad abort tests (a trial run for the launch abort system), and two rounds of unmanned flights will be conducted before the manned mission is launched.
Conclusion
Extensive testing and integration have been conducted on the Crew Orbital Module. ISRO is committed to ensuring the safety and success of the Gaganyaan mission through these efforts, though additional testing, certification, and qualifications are still ongoing. The astronauts will be protected throughout their journey by the module’s robust design and advanced systems. For further updates, please follow my blog and the Gaganyaan mission series.