Nuclear Fusion

Nuclear fusion is the most common form of large-scale energy production in human space, and is nearly ubiquitous on civilian spaceships. The most common form of fusion is Deuterium-Helium 3 fusion, which supplanted Deuterium-Tritium fusion in the late 24th Century. Proton-Boron fusion is also in use, but is less common and more expensive than traditional methods.
The main alternative to fusion power is antimatter power, which is notably used to power human wormhole gates. However, due to strict regulations by the United Leagues of Earth and other governments, it is illegal for antimatter power to be used by private individuals or organisations in space, or at all within a habitable world's atmosphere. Thus fusion remains the dominant method of power generation in human space.