Paving the Way for a Mission to Mars: Nuclear Thermal Propulsion
The landing of NASA’s Perseverance rover on Mars in February of this year prompts the natural follow-up question: when will we get humans on Mars? Before sending astronauts millions of miles into deep space, we have to consider the many factors involved in a mission to Mars, such as the dangers they will face on the journey to the red planet. With current technology, the mission would take around 3 years, with 12 to 18 months of those 3 years spent just traveling to the planet and back.
While traveling through space, astronauts experience microgravity (where they seem to become weightless) and become exposed to cosmic radiation, which can pose serious risks to their health. Astronauts may face vision problems stemming from fluid buildup in the head due to microgravity, or they may develop cancer as a result of being constantly pelted by heavy ions and high-energy protons traveling at nearly the speed of light.
Clearly, there are many complications involved in space travel, but we can minimize the effects of radiation and microgravity by making the journey the quickest and safest it can be. A possible solution lies in nuclear thermal propulsion (NTP), which has already been explored by NASA with the Nuclear Engine for Rocket Vehicle Application (NERVA) program during the 1960s.
The typical rocket uses chemical combustion to generate thrust, as the propellant (consisting of fuel and an oxidizer) reacts inside a combustion chamber to produce hot gases. The rapidly expanding hot gases are ejected at very high speeds from the rocket nozzle to create thrust and propel the rocket forward. Rocket propulsion demonstrates Newton’s Third Law, which states that every action has an equal and opposite reaction; when the high speed gas propellant is ejected from the end of the rocket, the rocket is pushed in the opposite direction. The Merlin engines used by SpaceX provide an example of chemical rocket engines, as they use rocket-grade kerosene as fuel and cryogenic liquid oxygen as the oxidizer.
On the other hand, NTP employs the energy released by the fission of uranium atoms in a nuclear reactor to heat liquid hydrogen to around 2,430℃ and convert it to a gas. The heated hydrogen gas expands and rapidly rushes through the nozzle to generate thrust, propelling the rocket forward. The specific impulse (thrust produced from a specific amount of propellant) of an NTP engine is roughly twice that of chemical rocket engines, which means an NTP rocket can travel farther while using less fuel. This would cut travel times significantly and reduce a flight crew’s exposure to cosmic radiation and microgravity.
Currently, NASA is working with the Department of Energy to explore the feasibility of using low-enriched uranium instead of high-enriched uranium to fuel NTP systems, which would make the endeavor more affordable and manageable due to fewer security regulations. Ultimately, NTP could open the entire solar system to us, allowing us to push the boundaries of space exploration and scientific discovery. The day we see man set foot on Mars may not be too far.