A common design uses controlled nuclear fusion — for example, the **Daedalus** and **Icarus** concepts developed by the British Interplanetary Society - wikipedia 
These rely on pellet-based fusion reactions (often deuterium–helium-3) ignited behind magnetic nozzles to generate high thrust.
- **Advantages:** High efficiency and achievable within known physics. - **Challenges:** Requires massive fuel stores and stable long-term fusion systems.