Solar Electric Propulsion

Solar Electric Propulsion (SEP) is a combination of solar power as an energy source, and electric propulsion as an drive engine.

SEP is more mass effective and cost effective compared to most Nuclear Electric Propulsion (NEP) proposals for the inner solar system. However, electric propulsion is not very interesting for crewed missions, due to the high mass requirements and long travel times. Chemical propulsion has been used for most missions instead. SEP might be useful for cargo transfer to and from Mars, although the practical difficulty of landing materials carried by SEP make it less attractive. Chemical propulsion vehicle are configured in such a way that they can carry out aerobraking, which can significantly reduce the deltaV requirements of an orbital transfer, while aerobraking is difficult to devise for SEP vehicles.

SEP is basically a fuel saving device. If fuel in Earth orbit is very cheap, many of the benefits of SEP disappear. The development or orbital fuel transfer and the expected advent of much lower cost transportation to Earth orbit will reduce the interest of SEP compared to chemical propulsion.