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. Water dumped from either the ISS or Orbiter is a possible source of damage. When water is dumped into a vacuum, some of it flashes into a vapor. The expanding vapor bursts the liquid 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 Wsec (U.S. Lab) and 50 Wsec (Orbiter). As these liquid/ice particles impact, they can 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 in the range of 1300 to 44000 angstroms. Damage to these coatings can cause degradation of the cells optical characteristics. To mitigate damage from water dumps, the characteristics of the water dumps were studied and an impact code was used to study damage to sensitive surfaces. The results were used to develop the constraints needed to mitigate damage to ISS hardware from Orbiter and U.S. Lab dumps.