Propulsion aspects of transportation

Propulsion factors have a major influence on the characteristics of transportation systems and their economics, and advances in transportation have been keyed to advances in propulsion technology. Propulsion concepts conceived in the past 30 years have completely revolutionized air, land, and sea transportation,The turbojet engine, the diesel-electric locomotive, and the nuclear submarine are each uniquely suited to their applications and it is difficult to conceive of new systems which would offer significant advantages for current conditions. However, as new transportation concepts are developed, new propulsion requirements are arising and these may be served best by new propulsion concepts. Research on improved batteries, fuel cells, thermionics, and new types of heat enghtes may lead to propulsion systems uniquely suited to future transportation systems; in addition, rapid transfer of advanced aircraft engine technology to other transportation modes can be expected.