Nuclear Rockets Could Reach Mars Twice as Fast Compared to Current Methods. The Challenge Lies in the Design of the Reactors

Mars is humanity’s next big destination. NASA plans to launch a crewed mission to the Red Planet sometime in the next decade, though a specific date hasn’t been set. And understandably so—the challenges the space agency must overcome before sending humans to Mars are immense. One of the biggest hurdles is the time it will take to get there.

A trip to Mars will take six to nine months using the current chemical rocket technology. However, developing nuclear thermal propulsion could cut that time in half dramatically. With nuclear thermal rockets, the journey could take just three to four months, reducing the strain on astronauts’ health. In this case, the mission would also require fewer resources.

Nuclear Thermal Propulsion Offers Advantages but Also Presents Significant Challenges

Conventional chemical propulsion systems in today’s rockets rely on a chemical reaction between a light fuel, such as hydrogen, and an oxidizer. When mixed, ignition occurs instantaneously, ejecting the fuel from the nozzle and generating the thrust needed to propel the rocket. This is the technology used by spacecraft.

The strategy proposed by nuclear thermal propulsion (NTP) is quite different. Nuclear fission, a well-known reaction used in nuclear power plants and submarines since the mid-1950s, works by inducing fission reactions in uranium-235. When a uranium-235 nucleus absorbs a neutron, it becomes an unstable uranium-236 nucleus, which splits into two smaller nuclei—typically barium-144 and krypton-89—while emitting two or three neutrons.

The fission used in NTP is essentially the same as in nuclear power plants, but with a key difference: The fuel contains a higher concentration of uranium-235, meaning it has a higher level of enrichment than the fuel rods used in power plants. Additionally, nuclear reactors for propulsion operate at higher temperatures than chemical reactors, making them both more powerful and compact.

In fact, NTP systems have about 10 times the power density of a conventional light-water reactor. Moreover, they have roughly twice the specific impulse of chemical rockets, meaning that, in theory, they could cut the travel time to Mars in half. Interestingly, the government has been funding NTP development programs since the mid-1950s. Since then, researchers have tested dozens of designs. However, a spacecraft’s reactors must deliver a high specific impulse, be as light as possible, be safe, and avoid the use of highly enriched uranium. Most importantly, they must be able to operate reliably throughout the mission.

NASA plans to test a nuclear thermal engine in space in 2027, making this technology potentially critical for the exploration of Mars—and possibly for sending humanity beyond the Red Planet. Time will tell.

More info | The Conversation

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