A propellant management device (PMD) provides a way to expel propellant in a low-gravity environment. Devices can use surface tension as the primary expulsion device with a combination of baffles, fins, and vanes. The main goal of the PMD is to provide gas-free propellant to the rocket engine.[1]
Concept
editIn the absence of gravity, buoyancy forces do not determine liquid and gas position in a vessel. The positions are primarily driven by surface tension.[2]: 1 The liquids tend to adhere to the walls and leave a gaseous bubble in the center of the vessel.[3]: 2 Propellant management devices (PMDs) are required to provide gas-free operation of the engine.[4]: 1
PMDs are typically unique and specially designed for each mission.[2]: 1
Types
editThere are two groups of PMDs, total communication and control-type. A total communication PMD can acquire propellant from anywhere in the tank.[5]: 3
Total communication PMD
editThere are three types of total communication PMDs: vane, gallery, and pleated-liner.[6]: 3
Vane
editVanes are used when the spacecraft experiences low acceleration and requires low propellant flow rates. Due to their simple mechanical design, they are low cost and highly reliable.[5]: 3 They are typically used in small monopropellant thrusters or to refill another type of PMD: sponges.[5]: 5 Vane length (whether it extends partially up the vessel or to the top) is partially determined by the shape of the tank. Cylindrical tanks require full-length vanes since a portion of the propellant could adhere to the forward tank head. Spherical tanks need full-length vanes in a case by case basis. If the acceleration is lateral, partial-length vanes can work.[5]: 5
A center post can be added to the tank in addition to the side vanes. This provides a direct path for the propellant to the tank outlet.[4]: 4
Control-type PMD
editThere are three types of control-type PMDs: sponge, trough, and trap.[6]: 4
Sponge PMDs are primarily used to provide the engine with propellant needed for ignition, providing the engine with propellant during a specific maneuver, and propellant control in microgravity environments.[2]: 3
References
edit- ^ "DESIGN AND MANUFACTURE OF A LIGHTWEIGHT FUEL TANK ASSEMBLY" (PDF).
- ^ a b c "Propellant Management Device Conceptual Design and Analysis: Sponges" (PDF).
- ^ "Inverted Outflow Ground Testing of Cryogenic Propellant Liquid Acquisition Devices" (PDF).
- ^ a b "Design and Development of a Communications Satellite Propellant Tank" (PDF).
- ^ a b c d "Propellant Management Device Conceptual Design and Analysis: Vanes" (PDF).
- ^ a b "Cryogenic Propellant Management Device, Conceptual Design Study" (PDF).