As you already know, hydrogen is unique among fluids for a number of reasons. I like to introduce one of these key differences from the historical perspective:

In 1932, Werner Heisenberg won the Nobel Prize in physics “for the creation of quantum mechanics, the application of which has, inter alia, led to the discovery of the allotropic forms of hydrogen.” These allotropic forms of hydrogen called orthohydrogen and parahydrogen exist due to parity between the nuclear spin and rotational spin function for the hydrogen molecule. Orthohydrogen is a higher energy triplet restricted to odd rotational energy levels (J = 1,3,5…) and parahydrogen is a lower … » More …

Jim Lovell is famously quoted for saying, “There’s one whole side of that spacecraft missing” after a routine collapse of the liquid oxygen tank ullage volume caused an explosion that infamously rocked Apollo 13. While the explosion was the result of an overpowered motor switch, the ensuing disaster underscores the importance of ullage volume collapse.

Ullage is defined as the volume of vapor above a liquid in a sealed storage tank. Ullage volume collapse is the process of stirring the contents of a cryogenic liquid tank to reduce pressure. That sentence alone should give pause to those of you who have taken thermodynamics.

Not head … » More …