The Environmental and Control and Life Support System (ECLSS), located in Node 3 of the International Space Station (ISS), was designed to support up to six crew members. The Oxygen Generator Assembly (OGA) within the ECLSS electrolyzes water to produce oxygen and hydrogen; the oxygen is delivered to the cabin atmosphere and the hydrogen is vented overboard. The system required a positive displacement pump to continuously circulate de-ionized water though the system’s electrolysis cell stack.
Among the challenges for the pump design were the exposure to high vibration loads during launch, the poor lubricating properties and low viscosity of the de-ionized water, and the ultra-high reliability demanded by this application. As expected, the project also came with stringent quality and documentation requirements.
A fixed-clearance ceramic spur gear configuration was chosen for the design. The selection was based on its simplicity and the relative availability of equipment needed to grind the precise gear-tooth profile in the ceramic material. The pump gears are carried on shafts constructed of Stellite 6b which in turn are supported by silicon-carbide bearings. Stainless steel housings support the internal components, provide for mounting, and accommodate fluid interconnect.
The pump is delivered by Cascon as a precision cleaned item, ready for mating with the customer’s drive motor, integration into the OGA, and transport to the ISS. The Oxygen Generator Assembly and the Cascon supplied pump have been in successful operation since 2007. Cascon also supplies pumps used in the Water Processor Assembly on the ISS.
This ECLSS NASA Fact sheet provides an overview of the system.
Fluid: Deionized Water
Pump Technology: Spur Gear
Drive: Customer BLDC Motor
Number of flow circuits: 1
Rated flow: 5 lpm (1.3 gpm)
Rated pressure rise: 275 kPa (40 psi)
Input power: 50 W
Spacecraft launch vibration and shock loads