Water on the Moon?

One of the first things I learned about going to a waterless Moon, was that you had to know a lot about water to get there and back.  And here are some of the most important characteristics of water.

  1. It holds a lot of heat.  So, it makes a good medium for removing body heat from astronauts that are isolated inside a spacesuit.
  2. Like many other materials, it evaporates even when it is frozen.  That process is called “sublimation”.
  3. Gases dissolve in water.  That is a big problem, and I will soon tell you why.

Your body is always getting rid of heat.  If it didn’t, you would literally die.  On the earth, you can get rid of that heat by both conducting heat away to air that is colder than your body and by sweating, cooling by evaporation.  However, there is no air on the Moon, and no place in a spacesuit to collect sweat.  So, the first job of a spacesuit is to keep you cool, especially when you are working hard.

Inside the Apollo Back Pack worn by the astronauts on the Moon, there is a device called a heat exchanger that cools both the air that the astronaut breathes and water that has been running around the body in small tubes.  That heat exchanger is called the “Sublimator”.  It’s original name was the “Porous Plate Water Boiler.”  NASA thought that was too big for a name and not as catchy as they liked.  So, it was changed to “Sublimator”.  However, in fact the Sublimator is more a water boiler than a sublimator.  Yes, there is some amount of sublimation going on inside, but most of the heat is boiled off into the vacuum of space at a boiling temperature of around 32 degrees F.  Lest we get lost, I’ll stop the explanation here.

And then came the first problem.  I had not been out of the Air force and working for Hamilton Standard very long when I was asked to finish writing a specification for the Water Reservoir that provided the water boiled off by the Sublimator.  Well, you don’t want air in the Reservoir because it tends to mess up the action of the Sublimator.  In order to avoid that, the specification said that you had to evacuate the Reservoir before backfilling it with water.  In fact, the specification wanted you to evacuate it to the point of what is called a “hard” vacuum.  And I thought, as a joke really, that there was more air dissolved in the water than was left in the Reservoir after evacuating it.

So, off I went to the Hamilton library, and I looked up the amount of air dissolved in water at sea level conditions.  Much to my surprise, it was a lot of air.  And when you drop the pressure in the Reservoir as you do when using it on the surface of the Moon, it all comes out of solution, just like opening a hot bottle of soda.  That is bad, very bad — but it gets worse.

And in my next BLOG, I will tell you why.  You will learn about how things were done in space, and you will learn a little about office politics.

Water on the Moon? Part 2

There is a sarcastic explanation of the stages of a project which ends in the phrase, “Awards and accolades for the non-participants.” I don’t know its origins, but there is some truth to it.  Soon after discovering this problem of air being dissolved in the reservoir water, my boss told me to write a memo explaining the issue.  I did that, and several weeks later, an engineer from another group wrote an essentially identical memo, but made it thicker by adding copies of technical tables from my library source.  He had nothing to do with the discovery of the problem, but his boss wanted their group to get full credit for having done something they actually did not do.  You would think that someone above them would have the good sense to stop that sort of nonsense.  Unfortunately…

The problem with dissolved gas in the reservoir water was that it kept the water pressure at the Sublimator from dropping to an acceptable level, thus causing water to go through the Sublimator into space without actually boiling.  That prevented the Sublimator from doing its cooling job.

Anyway, it turned out that the water being used to fill the Back Pack Reservoir was indeed saturated with dissolved nitrogen at about three times the atmospheric pressure on the Earth at sea level.  This was done to solve a problem with the source of the water, the water tanks in the Lunar Excursion Module, or LEM as we called it.  No one had considered what it meant to the Back Pack.  And as problems go, it was a show stopper.  However, the problem was solved by placing an orifice in the tubing between the Reservoir and the Sublimator, a pretty simple change.  That lowered the pressure at the Sublimator to an acceptable level.  I am sorry to say that I don’t remember who thought of it.  It wasn’t me, and it certainly was not the guy who wrote the bogus memo. — END



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