Dew Point Analysis for Space Station Freedom

This paper contains a partial review of the requirements and design of the Environmental Control and Life Support System (ECLSS) for Space Station Freedom (SSF); a review of G189A ECLSS computer models developed for different SSF configurations; and some significant computed results from these models showing transient dew point responses during maximum and minimum dew point conditions on board SSF.

SSF operational requirements which pertain to dew point have two major thrusts:

1. 1)
   Quantification of high and low moisture contents allowable in the atmosphere; i.e., dew point within the range of 40°F to 60°F, and relative humidity within the range of 25% to 70%.
2. 2)
   Prohibition of condensation on any interior surfaces (such as the interior pressure shell wall, or cool air/water lines) (1).*

Detailed computational results presented in the paper pertain primarily to the verification of compliance with the first of the two items mentioned above. Further discussions in the paper are devoted to various characteristics or phenomena which affect the second of the two items. While the computed results indicate that the dew points will always be below 58°F, interior condensation is still a valid concern. Analyses of present designs indicate that some internal SSF surfaces will be as cool as the mid 50s; discussions will cover the accommodation of this situation. Discussion topics also include 1) reduction of the presently observed dew point spikes, 2) atmospheric drying due to operation of the Carbon Dioxide Removal Assembly, and 3) the use of ventilation behind the racks, in order to raise various surface temperatures.