propellant management device

In the absence of gravity, buoyancy forces do not determine liquid and gas position in a vessel. The positions are primarily driven by surface tension.{{cite web|url=http://www.northropgrumman.com/Capabilities/PropellantTanks/Documents/technicalPapers/AIAA93-1970.pdf|title=Propellant Management Device Conceptual Design and Analysis: Sponges}}{{rp|1}} The liquids tend to adhere to the walls and leave a gaseous bubble in the center of the vessel.{{cite web|url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140016830.pdf|title=Inverted Outflow Ground Testing of Cryogenic Propellant Liquid Acquisition Devices}}{{rp|2}} Propellant management devices (PMDs) are required to provide gas-free operation of the engine.{{cite web|url=http://www.northropgrumman.com/Capabilities/PropellantTanks/Documents/technicalPapers/AIAA95-2529.pdf|title=Design and Development of a Communications Satellite Propellant Tank}}{{rp|1}}

PMDs are typically unique and specially designed for each mission.{{rp|1}}

There are two groups of PMDs, total communication and control-type. A total communication PMD can acquire propellant from anywhere in the tank.{{rp|3}}

There are three types of total communication PMDs: vane, gallery, and pleated-liner.{{cite web|url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110000503.pdf|title=Cryogenic Propellant Management Device, Conceptual Design Study}}{{rp|3}}

Vanes 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.{{cite web|url=http://www.pmdtechnology.com/pdfs/AIAA91-2172.pdf|title=Propellant Management Device Conceptual Design and Analysis: Vanes}}{{rp|3}} They are typically used in small monopropellant thrusters or to refill another type of PMD: sponges.{{rp|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.{{rp|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.{{rp|4}}

There are three types of control-type PMDs: sponge, trough, and trap.{{rp|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.{{rp|3}}

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Category:Rocket propulsion