The design of a propulsion module typically includes several key components and structural features tailored to its mission and propulsion type. Based on various sources, here are the main aspects of propulsion module design:
Structural and Configuration Design
- The propulsion module often has a conical or cylindrical shape to accommodate propellant tanks and support structures efficiently. For example, a propulsion module designed for a sample return mission was conical with propellant tanks attached externally and helium gas bottles inside. It had dimensions such as 1300 mm height, 2000 mm bottom diameter, and 1200 mm top diameter, designed to withstand inertia loads up to 13 g axial acceleration and 5 g lateral acceleration
- The module includes interfaces for attachment to the reentry or service module and payload adapters.
Propellant and Tanks
- Propellant tanks are sized based on the required propellant mass and volume. For example, a boost module might carry around 20,700 kg of propellant split between two tanks (N2O4 and Aerozine 50), with volumes around 17.4 m³ total and tank pressures designed for efficient feed to the engine
- Gas bottles (e.g., helium) are included for pressurization of the propellant tanks and feed lines.
Propulsion System
- The propulsion system may include main engines (e.g., dual engines providing thrust of about 2 tons each) and smaller thrusters for attitude control.
- Engines can be chemical (e.g., hydrazine monopropellant thrusters, bipropellant engines) or electric (e.g., ion or Hall thrusters) depending on mission requirements
- Some modules incorporate modular propulsion units with standard interfaces to allow on-orbit refueling and upgrades, such as AFRL’s MODPROP system, which uses non-toxic propellants and modular thrusters for flexibility and rapid integration
Additional Systems and Features
- The exterior of the propulsion module may carry deployable solar panels, communication antennas, sensors (star trackers), and avionics for flight control and navigation
- Propulsion modules are designed to be expendable or reusable depending on mission design. For example, some modules are intended to separate and impact a target surface after use, while others remain attached or are refueled on orbit
In summary, the propulsion module design integrates structural support, propellant storage, propulsion engines, and auxiliary systems into a compact, robust module tailored for the spacecraft’s mission profile, with considerations for modularity, refueling, and system redundancy where applicable. This design approach supports efficient propulsion, spacecraft maneuvering, and mission adaptability.
