I'm wondering if it is possible to make metallic hydrogen. Metallic hydrogen would be a good thing to have because hydrogen is an excellent fuel source, and since it is; under STP, a gas, having it be in a metallic form would be a great way to carry lots of hydrogen, only with less volume in transportation. The way I see it, it would improve efficiency as a fuel/propellant. I was thinking that since the melting point and the freezing point of a substance are essentially equivalent, it might be possible to make hydrogen gas into a metallic form by lowering the temperature of hydrogen gas to its melting point (-259.14°C). If this theory has any flaws in it, please tell me about them.