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How does water spray behave in Low Earth Orbit (LEO), from the side exposed to the Sun to the side in Earth's shadow? Could it be used as means of augmenting atmospheric drag and deorbiting defunct spacecraft and debris from LEO faster than their orbits would naturally decay?

The only mention of drag augmentation as means of active debris removal that seem to be under consideration for the moment are the use of gossamer drag augmentation structures and deployable sails, or expanding foams, e.g. as mentioned in ESA's Active Removal of Space Debris: Expanding foam application for active debris removal (PDF):

The core idea of this method is to increase the area-to-mass ratio of these objects such that the atmospheric drag can cause their natural re-entry, thus “cleaning up” different regions in the near-Earth space. The drag augmentation system proposed does not require any docking system and just an uncontrolled re-entry can follow, thus it seems a short-term application free from the usual technological issues of these debris removal systems.

Venerable idea, but what about the other way around? Instead of increasing the area-to-mass ratio of space junk, would it be feasible to increase local atmospheric density by means of spraying water ahead of their orbits, while perhaps at the same time using such spraying as means of maintaining orbit (propulsion for orbital reboost) of the "drag augmentation device"?

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    $\begingroup$ Wouldn't the low pressure of the atmosphere push the boiling point of water very low? I believe that even at cold temperatures the vapor pressure would be higher than the atmospheric pressure (thus any water would boil). I think this rules out "snow", but I think the rest of your idea has merit. Source I found $\endgroup$
    – Jack
    May 15, 2014 at 20:50
  • $\begingroup$ @Jack Depends on the exhaust temperature and density (mass internal pressure). External pressure would be below water's triple point, but not necessarily for the whole mass. Still, neglect that "snow" in the title, it's just a fun title that I liked, but the point is in increasing local atmospheric pressure (where local is in orbit, so not local to some point above the surface of the Earth). For that, I doubt it matters so much what state the water is in, even if it's split into atomic hydrogen and oxygen gas by UV. The cloud should still be in orbit, just expanding with time, losing density. $\endgroup$
    – TildalWave
    May 15, 2014 at 20:59
  • $\begingroup$ There was an experiment with water ballast released at a height of about 100 to 167 km. Over 50 years ago using a test of the Saturn I rocket. See Wikipedia and a project report. $\endgroup$
    – Uwe
    Apr 23, 2018 at 21:05

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Edgar Andreas made a nice chart for water sublimation in a vacuum at various temperatures:

enter image description here

At 270 K it looks like a square centimeter of water ice surface sublimates 100 grams per hour. A typical snow flake masses 3 milligrams. Unless the snowflakes were cryogenic, they'd quickly sublimate

Root square mean speed of water molecules at 270 K would be ~.618 km/s (if my arithmetic's right). The water vapor cloud would quickly dissipate.

O2 has a higher molar weight than H20. At 270 K it's root square mean speed would be about .46 km/s

Better yet would be CO2. Root square mean speed at 270 K would be .4 km/s.

But it seems to me all these would dissipate too quickly to intercept and bring down much orbital debris.

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Based on your comment stating you're question is irrespective of if the water is liquid/snow etc. I'd suggest reading about tungsten dust.

Tungsten dust has been proposed as a solution to this problem, in fact you can even read the patent for it. The general concept is to release a collection of tungsten dust into a specific orbit to more quickly de-orbit craft in that region of space. The downsides are pretty major though, since the dust itself will de-orbit it will potentially pass through other regions of space; it will also cause a significant increase in drag in ALL objects that fly through it so you might end up de-orbiting a spacecraft that shouldn't be de-orbited. On the plus side though, since the particles are very small they have a reasonably low ballistic coefficient so they will only stay in orbit for a short period of time. I remember discussing this with a colleague and for Envisats orbit the lifetime of the dust was only about 8 years.

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  • $\begingroup$ Yikes!!!!!!!!!! $\endgroup$
    – uhoh
    Apr 24, 2018 at 1:07
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Water cools rapidly in a vacuum to its boiling point at the ambient pressure. STS-1 attempted to dispose of waste water by venting it into space. It froze, forming a fair sized mass on the side of the shuttle.

Water jetted into a vacuum will form pellets with a size that depends on the jet diameter, velocity and probably also water temperature forming a cloud of 'sleet'. It would sublimate, but could last long enough to interact with solid debris.

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  • $\begingroup$ Do you have a reference to back up your assertion that the waste water dump on STS-1 "froze, forming a fair sized mass on the side of the shuttle?" Cause it's not mentioned in the post flight mission report, which states "Supply and waste water dumps were accomplished with no problems." $\endgroup$
    – Organic Marble
    Apr 23, 2018 at 19:33

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