Did you know the US government once had plans to design a spacecraft powered by nuclear reaction?
Humanity may not need a warp drive to go interstellar
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It is not widely known, but the US government spent real money, tested hardware and employed some of the best minds in late 1950s and early 60s to develop an idea called
nuclear pulse propulsion.
Known as Project Orion, the work was classified because the principle was that your engine shoots a series of “nuclear pulse units”—atomic bombs of roughly Hiroshima/Nagasaki power—out the back. Each unit explodes and the shockwave delivers concussive force to an immense, steal pusher plate, which is connected to the most immense shock absorber system that you could imagine.
An Orion propulsion schematic. (Credit: NASA)
The researchers calculated the ship to could reach five percent the speed of light (0.05 c), resulting in roughly a 90-year travel time to Alpha Centauri. The Nuclear Test Ban Treaty of 1963, which forbade nuclear explosions in the atmosphere, and the Outer Space Treaty of 1967, which forbade nuclear explosive devices in space, effectively ended Orion.
In his epic TV series Cosmos, Carl Sagan noted such an engine would be an excellent way to dispose of humanity’s nuclear bombs, but that it would have to be activated far from Earth.
But back when Orion was being funded, amazingly, the plan was to use the nuclear pulse engine even for launching the vessel, in one massive piece, from the surface of Earth. 
Suffice it to say it does not seem likely that we’ll every build a nuclear pulse ship, but it’s something that we already have the technology to build.