Artists concept of a Bimodal Nuclear Thermal Rocket in Low Earth Orbit. Credit: NASA

In the past four decades, NASA and other space agencies from around the world have accomplished some amazing feats. Together, they have sent manned missions to the Moon, explored Mars, mapped Venus and Mercury, conducted surveys and captured breathtaking images of the Outer Solar System. However, looking ahead to the next generation of exploration and the more-distant frontiers that remain to be explored, it is clear that new ideas need to be put forward of how to quickly and efficiently reach those destinations.

Basically, this means finding ways to power rockets that are more fuel and cost-effective while still providing the necessary power to get crews, rovers and orbiters to their far-flung destinations. In this respect, NASA has been taking a good look at nuclear fission as a possible means of propulsion.

In fact, according to presentation made by Doctor Michael G. Houts of the NASA Marshall Space Flight Center back in October of 2014, nuclear power and propulsion have the potential to be game changing technologies for space exploration.

As the Marshall Space Flight Centers manager of nuclear thermal research, Dr. Houts is well versed in the benefits it has to offer space exploration. According to the presentation he and fellow staffers made, a fission reactor can be used in a rocket design to create Nuclear Thermal Propulsion (NTP). In an NTP rocket, uranium or deuterium reactions are used to heat liquid hydrogen inside a reactor, turning it into ionized hydrogen gas (plasma), which is then channeled through a rocket nozzle to generate thrust.

NASA design for a Nuclear Engine for Rocket Vehicle Application (NERVA). Image Credit: NASA

A second possible method, known as Nuclear Electric Propulsion (NEC), involves the same basic reactor converted its heat and energy into electrical energy which then powers an electrical engine. In both cases, the rocket relies on nuclear fission to generates propulsion rather than chemical propellants, which has been the mainstay of NASA and all other space agencies to date.

Compared to this traditional form of propulsion, both NTP and NEC offers a number of advantages. The first and most obvious is the virtually unlimited energy density it offers compared to rocket fuel. At a steady state, a fission reactor produces an average of 2.5 neutrons per reaction. However, it would only take a single neutron to cause a subsequent fission and produce a chain reaction and provide constant power.

In fact, according to the report, an NTP rocket could generate 200 kWt of power using a single kilogram of uranium for a period of 13 years which works out of to a fuel efficiency rating of about 45 grams per 1000 MW-hr.

In addition, a nuclear-powered engine could also provide superior thrust relative to the amount of propellant used. This is what is known as specific impulse, which is measured either in terms of kilo-newtons per second per kilogram (kNs/kg) or in the amount of seconds the rocket can continually fire. This would cut the total amount of propellent needed, thus cutting launch weight and the cost of individual missions. And a more powerful nuclear engine would mean reduced trip times, another cost-cutting measure.

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Exploring the Universe with Nuclear Power