Solar Energy

Space travel requires fuel, and in the Empire and Union the main source of fuel is solar energy. Solar panels are highly efficient, and purification chambers remove impurities from the collected solar (these impurities take the form of Umbra, which is difficult to perceive normally but can be manipulated by some Susceptor). In its more pure state, solar takes on a liquid, highly corrosive form. While this form is almost pure energy and thus can power space ships and faster-than-light travel, it's corrosive nature also makes it a good weapon. Solar gunshots are very dangerous and damaging. They dissolve all sorts of matter, until they eventually evaporate. The best defences involve sacrificial matter for it to eat through (e.g. many layers of ship hull), plasma shields, or special materials designed to absorb light.