Let’s imagine that the Artemis astronauts had a train-style toilet that dumped into space. Actually, we don’t have to imagine that; Apollo and Artemis both vented urine to vacuum. Videos show a coruscating rush of glittery ice crystals flying away from the craft.
ISTM that the mean temperature of such ice in sunlight in high Earth orbit will be significantly above whatever is needed to drive sublimation. So what would the lifespan of these icy shards be? Minutes? Hours? Days?
Suppose I dropped a cubic meter of water ice in high Earth orbit: would it last a year?
Scale is clearly a factor here; a cubic kilometer of ice would perhaps last quite some time, outgassing furiously. Does anyone have an inkling as to how to relate volume to longevity?
Well, at the extreme, comets are “a cubic kilometer or so of ice”, and they can generally survive several passes through the inner solar system (for a few months each time, but part of that is generally closer to the Sun than the Earth is).
True, and/but they have varying amounts of dust that probably affects the sublimation rates.
Focusing on the smaller end of the scale, how would I estimate the lifespan of a cubic meter of ice? There’s the solar flux on the surface (roughly a kilowatt per m^2), and Google informs me that the sublimation rate is exponentially dependent on the ice temperature, ranging from essentially zero at 173K to 9mm/hr at 273K.
I’m not sure how to meaningfully estimate what the temperature of ice in Earth orbit is, though. It does seem as though a standard refrigerator ice cube wouldn’t last a day, though.