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Thermal Nuclear Rocket Propulsion Explained


In late 1960s, early 1970s, nuclear thermal rockets were fully developed and tested under programs such as the Nuclear Engine for Rocket Vehicle Application or NERVA. This program was just one of the two categories that studied nuclear propulsion. In this project, they developed a solid core reactor based on Uranium, Zirconium carbide-graphite matrix.
There were four main configurations tested with increased thrust levels. The largest NERVA derived engine produced approximately 112.1 kN of thrust. The fuel element was a complex mix of Gadolinium Oxide (Gd2O3) and Uranium oxide (UO2) particles distributed along a Tungsten matrix. Each fuel element was hexagonal in shape with 19 coolant passages. A total of 564 fuel elements and 241 tie tube were used with a total mass of 2,645 kg, containing 36.8 kg of U-235. It delivered a thermal power of 555 MW. To contain the reactor core, a thick radial reflector wall of 14.7 cm with control drums were used.
Just like in conventional rocket engines, the nozzle is cooled by hydrogen that comes in through the inlet valve. It is then transported upwards to the outside of the reactor towards turbo-pumps that increase its pressure. At the same time, a second flow of hydrogen is pumped into the tie tubes which further increases temperature and pressure.
This flow is added to flow number one and is directed towards a second set to turbo-pumps. In this last phase, hydrogen goes back to the core passing through the fuel elements where it experiences the largest increase in temperature. From 367 K to 2,794 K with a mass flow of 12.68 kg/s.
A quick comparison with the average flow rate of the Falcon 9 rocket at 2,496 kg/s makes it easy to understand why nuclear is the best choice for space travel, not lifting large payloads into space.

Sources
NASA
5 hazards of human space flight
https://www.nasa.gov/hrp/5-hazards-of...
WIKI
Health threats from cosmic rays
https://en.wikipedia.org/wiki/Health_...
Sievert
https://en.wikipedia.org/wiki/Sievert...
Specific impulse
https://en.wikipedia.org/wiki/Specifi...
Web Archive
Plastics to help protect astronauts in space
https://web.archive.org/web/201003232...
Nuclear propulsion for space
https://www.osti.gov/includes/opennet...



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