 Fusion power could be used in interstellar space where solar energy is not available.Research into nuclear fusion started in the early part of the 20th century.In 1920 the British physicist Francis William Aston discovered that the total mass equivalent of four hydrogen atoms are heavier than the total mass of one helium atom (He-4), which implied that net energy can be released by combining hydrogen atoms together to form helium, and provided the first hints of a mechanism by which stars could produce energy in the quantities being measured.