The Breakthrough Starshot project has a
realistic plan for humans to have a spacecraft inside another solar system in 20-30 years. Their idea is to make a swarm of tiny vehicles. They would be thrown into space somehow and propelled onward using a lightsail. Power for the lightsail doesn't need to be stored on the ship. These ones would get little power from the sun. The light would come from a massive laser on earth. The physicists figure they can achieve speeds of 1/5 the speed of light or 60,000 km/s.
Each ship would have a mass of a gram or two. It would be a couple of cm in size but have a light sail that folds out to an area of 4m x 4m.
There are a lot of challenges: powering a computer for 30 years; recording, storing and transmitting photographs and video; cosmic rays; dissipating waste heat and impacts with space debris.
Ultimately, after all that journey, the craft would spend about two days travelling the distance of the earth's orbit.
If you want a ship that can
take up orbit around the next star, that will take 100-150 years.
