Pay-Off of Nuclear Thermal Systems
The principal advantages of a nuclear system in the overall scope of the mission are sufficient to project manned missions that employ this type of propulsion. Besides reducing the cost of this type of space mission, nuclear propulsion systems also have advantages for the crew in terms of time and of health.
The nuclear propulsion system is a cost effective alternative in comparison to the chemical propulsion system, because power derived from the former system is greater than the one derived from the latter. Also, less mass is wasted by a nuclear rocket than by chemical one. This means that more of the mass that composes the nuclear rocket can be reused than of the chemical one. The reuse of most of the components of a rocket of this type make its use in space exploration economically viable.
For the crew, the use of a nuclear propulsion system means a minimized time in exposure to microgravity, solar flares, ambient space radiation, and a greater portion of the mission spent on the target planet.
In terms of the crew, the nuclear rocket minimizes exposure to microgravity. Microgravity or zero gravity, which occurs during the transfer time between one planetary orbit to another, causes no considerable damage to electronic components of a space craft, but in prolonged periods of time can result very detrimental for the health of the crew members. The absence of gravity causes the loss of calcium from the bones and the loss of muscle tissue. This leads to a crew that is incapable to carry out the tasks necessary for its survival. The minimum exposure to this phenomenon, which results from the use of a nuclear propulsion system, provides mission designers with a high degree of confidence that the crew will be capable to carry out mission tasks both during the transfer orbit and during the exploration of the destination planet.
Also, exposure to solar flares and ambient space radiation is minimized and the health hazards to the crew are consequently decreased. Besides decreasing the exposure of the crew to these types of radiation and energy, the exposure of the electronic components of the vehicle is also decreased. The electronic components, which might not be as shielded as the crew, might be easily damaged with minimum exposure to high energy radiation. This possible damage, which can not be fixed in space, can lead to the abortion of the mission and to the return to Earth before the mission site is reached.
The other main pay off of the use of a nuclear rocket for the propulsion of a space mission is the increased time spent at the actual mission site in comparison to the transit time. In the case of a manned mission to Mars, this means that the crew would have more time to explore the surface of the planet and less time in the transfer orbit between the Earth and Mars. The planet can be more thoroughly explored before both the Earth and Mars are in position for the return transfer orbit.