Mitigation of damage to the International Space Station (ISS) from water dumps

The International Space Station (ISS) and Orbiter dump water overboard. This water is from the ISS condensate system, and from the Orbiter's fuel cell (supply side) and wastewater (urine and condensate) systems. When water is dumped into a vacuum, some of it flashes into a vapor. The expanding vapor bursts the stream into vapor, and small and large liquid/ice particles. The large liquid/ice particles are approximately 2 mm in diameter and have nominal velocities of approximately 31 ft center dot s(-1) (U.S. Lab) and 50 ft center dot s(-1) (Orbiter). As these liquid/ice particles impact, they may cause mechanical damage due to erosion/pitting of sensitive surfaces, including solar array or radiator surfaces. Solar arrays are of particular concern because of the thin optical coatings on the surface of the cells. The thickness of these coatings is 43300 angstrom. Damage to these coatings can cause degradation of the cells' optical characteristics that can potentially reduce performance and shorten the life of the cells. To mitigate damage from water dumps, the characteristics of the water dumps were studied and the results used to develop the constraints needed to mitigate damage to ISS hardware from U.S. Lab and Orbiter water dumps.