The molecular mass of H2O (s) is around 18 g/mol. The molecular mass of H2 (g) is roughly 4 g/mol. When the average molar mass of a gas within a container is less than the average molar mass of the sum surrounding partial pressures, it does not impart force on its surroundings. From a theoretical standpoint, both of these gases are lighter than the surrounding air, however ice is more dense than water vapour obviously, and does not adhere to the fundamental gas laws, so hydrogen gas would be lighter to transport. I have no idea what the theoretically safe maximum pressure of hydrogen would be but I'd still bet hydrogen. In space engineers, gases don't have mass (Hydrogen, oxygen etc). 1kg of ice uses 0.37L of space. Because you're using a transport ship, I'm gonna assume it's a large ship for the rest of this. A large hydrogen tank weighs 8161.6kg and its contents are weightless. It has a gas capacity of 5 million litres. The O2/H2 Generator weighs 2587.0kg and has a capacity of 4000L.…

Even with hydrogen, the tank weight is quite small compared to the content weight. For some examples, you can look here (you may need to do some math to get the actual numbers): http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19750004950.pdf You are right that the heat loss is less of a problem for larger tanks, but structural integrity, especially when facing the aerodynamic forces of launch, becomes a larger problem. Transporting liquid hydrogen to the moon is probably not a good option. Apart from the high tank volume and weight (compared to other fluids) it also boils away very quickly under thermal radiation. On a path to the moon, the spaceship has to coast for several days, all the while losing fuel. This usually works the following way: The tank is kept at a certain pressure. If this pressure is exceeded, a valve opens to vent some gas. This way the liquid is constantly boiling: If a bit of heat enters the tank, a bit of hydrogen evaporates and escapes through the valv…

o2h2 gens are too slow. It takes many to fuel even a couple thrusters, and it's assumed you'll need 100% thruster uptime with no buffer depletion risks in a dogfight. The small grid gens might as well be useless, they make like 20 liters of H2 a second when even the smallest thrusters use hundreds. Really the only thing you can do is place tanks as close to dead center inside your craft as you can, so the enemy has to shoot through everything else to reach them. Adding too much armor in a fighter is obviously pretty counterproductive. As far as sizing goes, for a fighter craft operating outside of a grav well, take your largest set of directional thrusters on the craft (usually your rear main burn thrusters), figure out their consumption rate of hydrogen at a 100% burn, and budget for about 2 to 3 minutes of burn. I figure if you need more than 3 minutes of continuous burn in hard maneuvers, you've either already won and can coast back to base, or have overstayed your fighter's welcome…

Let's do some quick math. Air has a density of about 1.3 g/L and hydrogen has a density of about 0.09 g/L. The best case for lifting force would be storing the hydrogen at the same pressure as the surrounding air. This means that every L of hydrogen can displace 1.21 g of air, reducing the density of the aircraft. The amount of air displaced by the aircraft (and therefore the buoyancy) would not change, but the density of the aircraft in that space would decrease. This would decrease the lift needed, but let's see by how much. The greatest amount of free volume in an aircraft (that isn't part of the pressurized section of the fuselage) is the fuel tanks. An A380 has a fuel capacity of about 323,000 L. If we consider filling half of that with hydrogen, this would result in a total reduction of about 190 kg. An A380 has a max takeoff weight of 575,000 kg. This change would help but would be very small compared to the total lift needed. As David Richerby points out, hydrogen needed as f…

In order to store hydrogen in large quantities, it is first necessary to create an economical technology for its production. Natural combustible gas is stored in huge natural gas storage facilities. Therefore, first of all, these storage facilities will be used for hydrogen storage. Small storage facilities are needed for liquid hydrogen. To select a material, it is necessary to analyze the correlation between the reaction material + liquid hydrogen and the mechanical properties of the material.

1 liter AT WHAT PRESSURE? One liter of gas could be stored in a thin plastic bag at atmospheric pressure.

Tankers hauling helium, nitrogen, hydrogen and some other gases are shipped as cryogenic liquids. The gas is chilled to -200F or colder, at which point it will liquefy. The tanker is an MC 338 spec, and is a giant vacuum bottle. Since the gases are matter and therefore have mass the tanker gets heavier as it’s loaded. The tanker in the post is an MC 331 and does not haul cryogenic liquid gases.

One issue is that you use an LPG cylinder to store liquid petroleum gas (propane or butane), because their boiling points are high enough that you can keep them liquid under pressure at common temperatures. You can’t do that with hydrogen at anything like the same pressure, its boiling point is way too low, so you’d only have a cylinder of compressed gas, which would contain much less mass. Then you need to remember that hydrogen will diffuse through things really well, so a cylinder, valve and regulator designed for LPG will leak really badly with hydrogen. Quite how you’d be intending to fill an LPG cylinder with hydrogen in the first place is something I’m not quite getting, but you’d do better to talk to an industrial gas supplier on how to store and transport hydrogen.