Development of a Contaminant Insensitive Sublimator

Sublimators have been used for heat rejection for a variety of space applications including the Apollo Lunar Module and the Extravehicular Mobility Unit (EMU). Sublimators are excellent candidates for heat rejection devices on future vehicles like the Crew Exploration Vehicle (CEV), the Lunar Surface Access Module (LSAM), and future spacesuits. One of the drawbacks of previous designs was sensitivity to contamination in the feedwater. Undissolved contaminants can be removed with filters, but dissolved contaminants would be left in the pores of the porous plates in which the feedwater freezes and sublimates. These contaminants build up and clog the relatively small pores (~3–6 μm), thereby blocking the flow of the feedwater, reducing the available area for freezing and sublimation, and degrading the performance of the sublimator. For the X-38 program, a new sublimator design was developed by NASA-JSC that is less sensitive to contaminants. It separates the control point from the sublimation point, thereby allowing a larger pore size media (~350 μm) to be used where the freezing and sublimation occur. The larger pores do not clog as easily, making the sublimator less sensitive to contaminants. This paper describes the Contaminant Insensitive Sublimator, which improves upon the JSC X-38 design by (a) reducing its mass, (b) improving the heat rejection performance, and (c) improving manufacturability. Thermal analysis and design changes are presented, along with fabrication and test results of a sub-scale “mini-sublimator.”