![]() My wife had a veterinary conference and I tagged along because, well, Boston is just a really cool city to visit. Although I’d worked on the preparations for that launch and had participated in the flight readiness review at the engine project level, I was actually in Boston when it launched. It was a mission to Space Station and the orbiter was Atlantis. STS-104 was a Space Shuttle mission that launched in July 2001. And, specifically, this is the background that you need to understand the curious case of STS-104. When dealing with cryogenics, you have to think in terms of these topsy-turvy situations where things “boil” at four hundred degrees below zero and, in a rocket engine where we produce very high pressure situations, that boiling point in terms of temperature can be entirely situational or, above a certain pressure point, completely go away. ![]() So, what does all this supposing have to do with rocket engines? Well, it has to do with thinking about the cryogenic fluids that we use for propellants. Kitchen stoves on this hypothetical, high-pressure planet would be using some serious energy just to make a bit of pasta for dinner. That’s 300 degrees higher than what we’re used to on Earth. Suppose that our atmospheric pressure was 1000 pounds per square inch (as opposed to our pleasant 14.7 psi on the surface of Earth), then our water wouldn’t boil until it reached well over 500 degrees Fahrenheit. In that case, we’d still have a general sense of water, steam, and ice, but our transition from liquid to gaseous would occur at a higher temperature. Now, let’s suppose that rather than a hot planet, we lived on a planet with much higher atmospheric pressure (again, with everything else pretty much like it is on Earth). And making solid water would require chilling even further, roughly to 270 degrees below “normal.” If this was our world, then we probably wouldn’t have three separate words like “ice, water, steam.” We would likely instead talk in terms of “solid H2O, liquid H2O, and gaseous H2O.” The only way that we could get liquid water would be to chill some of the gaseous stuff down far below “normal” ambient temperatures, down below its boiling point. All of the H2O that we would know of in our everyday lives would be gaseous. ![]() Please ignore, for a moment at least, all of the other issues arising from such a scenario and imagine what our sense of “water” would be. On our planet, at typical, habitable temperatures and given our atmospheric pressure at the surface where we live, water is liquid and the other states – gaseous and solid – are generated from there as deviations from “normal conditions.” And that’s good since we otherwise wouldn’t exist as a species and, more importantly, nobody at all would be reading this blog.īut let’s suppose that we lived on a planet where the typical ambient temperature was, say, 300 degrees Fahrenheit, but everything else was mostly the same. We have three different words for three different states of the same chemical stuff: H2O, two atoms of hydrogen bound to a single atom of oxygen. And, of course, we know that steam is water made hot enough to boil and become gaseous. Our language has been made to fit our experience, but we all know, of course, that ice is just frozen water. That’s why we have two different words.” That’s right. Okay, but what about ice? “Yes,” you say, “but ice is ice and water is water. In fact, if you think about the word “liquid” just for a couple of moments, you probably had an image of water in your head. To start this post, I want you to think a little bit about water.
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