A fusion rocket is a theoretical design for a rocket powered by a fusion power that could provide efficient and long term acceleration in space without the need to carry a large fuel supply. The design relies on the development of fusion power technology beyond the current capabilities, and the construction of much larger and more complex rockets than any current spacecraft. A smaller, lighter fusion reactor could be possible in the future when more sophisticated methods have been designed to control magnetic confinement and prevent plasma instabilities. Inertial fusion could provide a lighter and more compact alternative, such as a fusion engine based on a FRC.
For spaceflight, the main advantage of fusion would be the very high specific thrust, and the main disadvantage of the (probably) large reactor mass. However, a fusion rocket can produce less radiation than a fission rocket, reducing the mass needed to shield. The safest way to build a fusion rocket with current technology is to use hydrogen bombs as proposed in the Orion Project, but that spacecraft would also be massive and the Partial Nuclear Test Ban Treaty prohibits the use of nuclear bombs. Therefore, the use of nuclear bombs to propel rockets on Earth is problematic, but it is possible in space in theory. An alternative approach would be electric (eg, ionic) propulsion with electric power generation through the fusion power instead of direct thrust.