Determining the "most likely" successful propulsion system for interplanetary travel is a complex question and subject to ongoing research and development. Several propulsion technologies have been considered and explored for future interplanetary missions. Here are a few notable ones:
Chemical Rockets: Chemical propulsion systems, such as liquid or solid rocket engines, have been the primary means of propulsion for space exploration thus far. They provide high thrust but are limited in terms of efficiency and specific impulse.
Ion Propulsion: Ion thrusters, also known as electric propulsion, use electromagnetic fields to accelerate ions and generate thrust. While they provide low thrust, they have excellent fuel efficiency and can operate for extended periods. Ion propulsion has been successfully used in missions like NASA's Deep Space 1 and Dawn spacecraft.
Nuclear Propulsion: Nuclear propulsion involves using nuclear reactions, such as nuclear fission or fusion, to generate thrust. These systems have the potential for higher specific impulse and faster travel times. However, nuclear propulsion technologies are still in the experimental stage and face challenges related to safety, radiation, and public perception.
Solar Sails: Solar sails utilize the pressure of sunlight to generate propulsion. They deploy large, lightweight reflective sails to capture the momentum of photons from the Sun. While solar sails provide continuous acceleration without the need for onboard propellant, they are more suitable for long-duration missions rather than rapid interplanetary travel.
Plasma Propulsion: Plasma-based engines, like the Variable Specific Impulse Magnetoplasma Rocket (VASIMR), ionize propellant into plasma and accelerate it using magnetic fields. Plasma propulsion offers high specific impulse and potential for efficient long-duration missions, but it is still under development.
It's important to note that the choice of propulsion system depends on various factors, including mission objectives, travel distances, payload mass, available resources, and technological readiness. Additionally, future advancements and breakthroughs in propulsion systems may introduce new possibilities.
As technology progresses and more research is conducted, we may see a combination of propulsion systems or entirely new concepts emerge to facilitate efficient and faster interplanetary travel.