Protection of Space Hardware During Ground Testing

ISS batteries are designed to operate within a temperature range of 32 to 50°F. In order to maintain batteries within this range, cold ammonia is circulated through their coldplates. During testing, ammonia chiller temperature setpoint is typically set at 20°F and the test room dew-point temperature is typically about 50°F. These operating conditions will result in considerable water condensation on cold surfaces.

In order to minimize water condensation, test hardware is enclosed in a tent within which air dew-point temperature is controlled at 0°F or lower. This is more than adequate to prevent any moisture condensation on batteries.

There is still a problem of moisture trapped within battery enclosure. All batteries are enclosed in a box, which has small openings for electrical wires, pressure equalization during launch, and other mechanical interfaces. Prior to enclosing batteries inside humidity control tent, the battery enclosures are full of moist room air. After batteries are enclosed inside humidity control tent, there may be considerable delay before the moisture inside the enclosures diffuses out and makes them safe to be exposed to cold ammonia. This waiting period is called dry-soak period.

In order to predict dry-soak requirements, a test was planned and carried out at the Kennedy Space Center in parallel with actual hardware testing. This paper describes objectives of this study, dry-soak tests and test data reduction, water vapor diffusion models and model validation, and recommended operating guidelines to ensure no condensation within actively cooled batteries and other actively cooled hardware.