The length of travel in space is one of the major limitations of how far humans may travel in the solar system. It is directly related to the level of performance that is available from existing propulsion systems. The performance of propulsion systems also defines the mass of payload that can be transported in space.

Propulsion technologies can be framed in three different categories: "escape propulsion" (from Earth surface to orbit), "in-space propulsion" (in orbit), and "deep space propulsion" (from orbit to outer space). The launch vehicles currently used for "escape propulsion" rely on very mature technologies, but for "in-space" and "deep space" vehicles, there are prospects of significant technological advances. 

Until nowadays, the propulsion types used in launch vehicles to operate the "escape propulsion" region are variations of the chemical propulsion. The technologies used in satellite launch vehicles or spacecrafts operating in "in-space" are mainly chemical propulsion-based, such as in espace propulsion, but research and use of other propulsion types are increasing. The types of propulsion used to operate the "deep-space propulsion" region are variations of the chemical, such as used in escape propulsion and in-space propulsion, non-chemical, like used in-space propulsion, and advanced propulsion