It is estimated that 25 tonnes of helium-3, which can be transported by a space shuttle, would be enough to provide electricity for the USA, which uses the largest amount of electricity globally, for one year. It has also been estimated that the Moon holds 1 million tonnes of helium-3, compared to the 10 kilograms available on Earth. Another bonus is that it would be safe to process helium-3, and reactors could be built in the middle of cities.