A 2010 U.S. paper examined an unusual idea for spacecraft propulsion: using nuclear fusion. Fusion releases energy by combining tiny atomic nuclei.
The idea wasn’t aimed primarily at aircraft or interstellar travel. The paper identified large satellites and distant space missions as possible applications. The promise is propulsion more powerful than conventional electric engines used in space. But major challenges remain.
Fewer Particles, Less Heavy Shielding
The paper was written by the Defense Intelligence Agency, part of the U.S. Department of Defense. It surveys existing knowledge about fusion-powered spacecraft propulsion; it doesn’t describe an engine that has been built and tested.
Among other things, it focuses on fuels such as hydrogen and boron. Fusion using these fuels could produce fewer neutrons, particles that can damage an engine. Fewer neutrons could reduce the need for heavy shielding. In space, lighter shielding could make a propulsion system easier to build.
A Powerful Engine for Satellites
The paper identifies large communications satellites as a possible early application. It also describes potential uses on missions to Mars and beyond. According to the paper, large satellites that need powerful propulsion could spur development of the concept in the coming decades.
The proposed system is unlike an aircraft engine. It could use energy from fusion to power an electric or plasma engine. Plasma is an extremely hot gas whose particles carry an electric charge. The paper suggests that such a system could propel spacecraft more powerfully than conventional electric propulsion systems used in space.
A Long Way From Operation
To produce energy, the fuel must be brought to a state where fusion begins. The hot material must then be kept in place without making the system too heavy. Large amounts of energy also need to be transferred, and the fuel must be stored.
The challenges don’t end with building the engine. Engineers would need to find a way to integrate it into a spacecraft, launch the craft, and operate the system in space.
What Remains Unknown
It’s not yet known whether fusion can be sustained over time or whether a system light and powerful enough can be built. The paper doesn’t say when the technology might become practical.
