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Nuclear Thermal Propulsion 
A good way to start for Space Exploration
A good way to start for Space Exploration
Let’s start with propulsion in general!
The word is derived from Latin words: pro meaning before or forwards & pellere meaning to drive. Propulsion means to push forward or drive an object forward. A propulsion system is a machine that produces thrust to push an object forward
The word is derived from Latin words: pro meaning before or forwards & pellere meaning to drive. Propulsion means to push forward or drive an object forward. A propulsion system is a machine that produces thrust to push an object forward
On airplanes, thrust is usually generated through some application of Newton's third law of action and reaction 
A nuclear thermal rocket (NTR) is a type of thermal rocket where the heat from a nuclear reaction, often nuclear fission, replaces the chemical energy of the propellants in a chemical rocket.
In an NTR, a working fluid, usually liquid hydrogen, is heated to a high temperature in a nuclear reactor and then expands through a rocket nozzle to create thrust
NTRs have been proposed as a spacecraft propulsion technology, with the earliest ground tests occurring in 1955. The US maintained an NTR development program through 1973, when it was shut down to focus on Space Shuttle development.
So basically, the NTR derives its energy from fission of Uranium-235 atoms contained within fuel elements that comprise the engine’s reactor core. 
As far back as the 1940s, it was recognized that energy from nuclear fission could be used to power spacecraft by heating a working fluid such as hydrogen and provide thrust to the rocket via expansion of the propellant through a rocket nozzle.
the nuclear rocket could shorten travel times dramatically!
And there's another big benefit. The thrust of a nuclear rocket could allow missions when Earth and Mars aren't perfectly aligned. Right now, if you miss your window, you have to wait another two years, but a nuclear rocket could give you the thrust to deal with flight delays
