Stars use different fuel than reactors. To fuse simple hydrogen, four nuclei have to collide at once. This is so unlikely that it requires a very large mass of fuel to sustain a reaction: at least the size of the Earth, according to one article I saw.<p>It&#x27;s entirely possible to burn deuterium in small reactors but there&#x27;s only about 1&#x2F;2500 as much deuterium as hydrogen.<p>(Perhaps some unthinkably advanced civilization could figure out how to get energy from hydrogen fusion in a small reactor, but you did specify &quot;our current understanding of physics.&quot;)