Ship Propulsion: Which to Use? Part 1

The next thing to think about, and possibly the most basic thing needed on a space ship is the propellant. Modern marine ships use a fuel to move their mechanical propeller or paddle wheels. Space crafts use a chemical reaction to push against space and send them in the direction they want to go. The current method is a chemical reaction but gravity assist is used while out in space to speed a ship on its way around planets. Nuclear engines were tried on aircraft during the Cold War but were deemed too dangerous for the crew as there was no way to safely have the crew near that much nuclear radiation for any period of time. NASA is currently working on developing a fusion engine. Such an engine would cut space travel in half and since the main fuel would be hydrogen, the ship could refuel merely by dropping into an upper planetary atmosphere somewhere (or sending a small cargo ship into a lower atmosphere if purer hydrogen was needed). However, current theories say it would still take two years to go to Jupiter and back from Earth.
Solar sails are similar to wind sailing. The thin sheets of metal with a lot of surface area aim towards a light source, like a star, and photons and solar winds propel the ship where the sails are aimed. A problem with these are that the sails can be influenced by gravity fields of passing planets so they need to be monitored and probably adjusted whenever a planet. Moon, or another star is nearby. However. That effect can be used to an advantage for slingshot maneuvers, or gravity assist.
Another possibility that is scientifically possible from current science but still years from usable is antimatter. Antimatter is what powered many ships in the Star Trek series but it would be very difficult to create enough antimatter to move a ship by present technologies. However, scientists believe that areas in space may have huge clusters of natural antimatter so you could always have them stopping at times to refuel. Another problem with antimatter may be that it could be similar to oil in that it takes thousands of years to regenerate. Once a supply is gone, it’s gone. However, little is known about natural antimatter at the moment so use it how you want in your stories.