Editing Fission-fragment rocket (section)

== Design considerations ==

In traditional [[nuclear thermal rocket]] and related designs, the nuclear energy is generated in some form of [[nuclear reactor|reactor]] and used to heat a working fluid to generate thrust. This limits the designs to temperatures that allow the reactor to remain whole, although clever design can increase this critical temperature into the tens of thousands of degrees. A rocket engine's efficiency is strongly related to the temperature of the exhausted working fluid, and in the case of the most [[Nuclear lightbulb|advanced gas-core engines]], it corresponds to a [[specific impulse]] of about 7000&nbsp;s.

The temperature of a conventional reactor design is the average temperature of the fuel, the vast majority of which is not reacting at any given instant. The atoms undergoing fission are at a temperature of millions of degrees, which is then spread out into the surrounding fuel, resulting in an overall temperature of a few thousand.

By physically arranging the fuel into very thin layers or particles, the fragments of a nuclear reaction can escape from the surface. Since they will be [[ionized]] due to the high energy of the reaction, they can then be handled [[magnet]]ically and channeled to produce thrust.  Numerous technological challenges still remain, however.