Frozen hydrogen is the solid form of the common gas hydrogen. Scientists are interested in frozen hydrogen because it may be a potential fuel source which is more powerful than existing fuel sources. Already, liquid hydrogen has found a niche in the rocket fuel market. Currently, frozen hydrogen is still in the experimental phase and has no practical applications.
If frozen hydrogen is found to be a viable fuel source, scientists and engineers believe the potential power generated from liquid hydrogen would rival, if not far surpass, that of fuels currently in use. The advantage of frozen hydrogen is in its potential energy, per pound. Scientists at NASA believe that if it could be put to practical use, launches could occur with a mere 20 percent of the fuel weight currently required to achieve orbit. This also has the potential of allowing larger, heavier payloads and saving billions of dollars.
Freezing hydrogen is no simple task. In order to achieve frozen hydrogen, the gas must be cooled to very low temperatures. Liquid hydrogen, cooled to 14 kelvins (-435 Fahrenheit, -224 Celsius), is dropped onto liquid helium, and cooled to 4 kelvins (-452 Fahrenheit, -233 Celsius). The colder medium of the liquid helium causes the liquid hydrogen to freeze and float on top of the helium. It is when used together that both the hydrogen and helium have the potential ability to be used as a fuel source.
The energy to achieve propulsion comes after the helium and hydrogen is transferred to, and reheated in, the rocket’s engine. Physics tells us that as things cool, atoms begin to move slower and as things heat up, atoms speed up. In this case, once heated, the atoms would begin to move very rapidly and get even hotter. This also would produce massive amounts of energy, which would then be funneled out of the engine at an extremely high rate of speed, causing propulsion.
Some may be confused with what the difference is between frozen hydrogen and metallic hydrogen. The main difference is the form. Frozen hydrogen is a solid. Metallic hydrogen can, theoretically, be a gas, liquid or solid, although usually it is a gas or liquid. Metallic hydrogen is so named because when hydrogen is subjected to extreme pressure, it can display metallic properties. Because it is much more dense than ordinary hydrogen, it also has the potential of being a huge source of energy.