Fusion rocket

A fusion rocket is a theoretical design for a rocket driven by fusion power which 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 current capabilities, and the construction of rockets much larger and more complex than any current spacecraft. A smaller and lighter fusion reactor might be possible in the future when more sophisticated methods have been devised to control magnetic confinement and prevent plasma instabilities. Fusion power could provide a lighter and more compact alternative.

For space flight, the main advantage of fusion would be the very high specific impulse, and the main disadvantage the (likely) large mass of the reactor. However, a fusion rocket may produce less radiation than a fission rocket, reducing the mass needed for shielding. The surest way of building a fusion rocket with current technology is to use hydrogen bombs as proposed in Project Orion, but such a 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 possible in space in theory. An alternate approach would be electrical (e.g. ion) propulsion with electric power generation via fusion power instead of direct thrust.

Many spacecraft propulsion methods such as ion thrusters require an input of electric power to run but are highly efficient. In some cases their maximum thrust is limited by the amount of power that can be generated (for example, a mass driver). An electric generator that ran on fusion power could be installed purely to drive such a ship. One disadvantage is that conventional electricity production requires a low-temperature energy sink, which is difficult (i.e. heavy) in a spacecraft. Direct conversion of the kinetic energy of the fusion products into electricity is in principle possible and would mitigate this problem.

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