Well I can take a shot at it... When a liquid is stored at high pressure it has a much higher boiling point, and the closer the temperature is to the boiling point, the more will evaporate. But in a tank like this, any vapor released will simply raise the pressure even higher, which will raise the boiling point even higher, so that the tank reaches equilibrium and the pressure stops going up. So, to build up a really large amount of pressure, t/space is heating the fuel a lot before they light the engine. When they light it, the fuel will go into the combustion chamber due to the pressure without needing pumps. They aren't heating it _that_ much - not enough for it to spontaneously ignite if exposed to air. Leaving a bucket of gasoline out in the sun for a few hours in the hours won't make it explode, but it'll make it hotter. I don't see any reference to 'superheating' the fuel.<br /><br />As the engine burns more fuel, the pressure in the tanks drop and the boiling point drops because of it, releasing even more vapor and so keeping the tanks pressurized enough to keep the engines working. Of course you'll still have to have some loss in pressure, so perhaps they keep heating the fuel as the engine works. Maybe they’re even running a fluid through the engine bell nozzle to keep it cool and then transferring some of that heat to the fuel tanks by directing the fluid there. However, it’s not as if they're releasing blueprints or anything, so I can’t be expected to know all of the details.