Jeff Watson (Scientific editor)

The dream of sending humans to the Red Planet, a fixture of science fiction for over a century, is now edging decisively into the realm of engineering reality, and the key to unlocking this next giant leap for humankind appears to be a return to a powerful and controversial technology: nuclear propulsion. While traditional chemical rockets, the workhorses of space exploration since its inception, successfully carried astronauts to the Moon, they are fundamentally ill-suited for the immense distance and duration of a Mars mission. The journey using current technology would take approximately seven to nine months each way, exposing crews to dangerous levels of cosmic radiation, inducing severe physiological deconditioning like muscle atrophy and bone loss, and requiring an enormous amount of consumables. The limitations of chemical propulsion are stark; these engines are powerful but incredibly inefficient, like a dragster that burns all its fuel in a spectacular, short burst. For a sustained journey to Mars, a more efficient, enduring engine is required. This is where nuclear-powered rockets, specifically Nuclear Thermal Propulsion (NTP) and the more advanced Nuclear Electric Propulsion (NEP), enter the picture, promising to cut transit times in half and revolutionize deep space travel.

The fundamental advantage of nuclear propulsion lies in its exceptional efficiency, measured in specific impulse (Isp)—the rocket equivalent of miles per gallon. Chemical rockets have a relatively low Isp because they are limited by the energy stored in the chemical bonds of their propellants. Nuclear Thermal Propulsion (NTP) operates on a different principle, using a fission reactor to heat a lightweight propellant like liquid hydrogen to extremely high temperatures, which is then expelled through a nozzle to create thrust. This process generates roughly twice the Isp of the best chemical engines. In practical terms, an NTP system could reduce the transit time to Mars to about 100-120 days. Dr. Anita Sharma, lead propulsion engineer at the NASA-led Artemis program, explains, “The reduction in transit time isn’t just about convenience; it’s a massive risk mitigation strategy. Shorter travel times mean less exposure to deep-space radiation, reduced consumable requirements, and a lower probability of critical system failures over the long haul. It fundamentally changes the safety calculus for a crewed Mars mission.” This faster transit is crucial for astronaut health, as it minimizes their time outside the protective magnetic field of Earth.

Beyond NTP, an even more efficient, though less thrust-powerful, technology is on the horizon: Nuclear Electric Propulsion (NEP). Instead of using reactor heat directly, NEP systems use a nuclear reactor to generate electricity, which then powers an ion or plasma thruster. These thrusters eject particles at velocities orders of magnitude higher than chemical or NTP rockets, resulting in an exceptionally high Isp. While NEP engines produce a very gentle, continuous thrust over long periods, they are incredibly fuel-efficient. This makes them ideal for cargo missions or, in a hybrid system, for the long-duration phases of a crewed journey. Dr. Ken Bowersox, Associate Administrator for NASA’s Space Operations Mission Directorate, recently stated, “We see a future where nuclear electric propulsion becomes the cargo ship of the solar system, slowly but surely moving the heavy infrastructure—habitats, supplies, return vehicles—into position ahead of the crew. This ‘pre-positioning’ strategy is essential for a sustainable Mars campaign.” The development of high-power NEP systems is a primary goal for agencies looking to establish a permanent presence beyond Earth orbit.

The current momentum behind nuclear rocketry is palpable. After decades of research that began with projects like NASA’s NERVA (Nuclear Engine for Rocket Vehicle Application) in the 1960s and 70s, which successfully ground-tested reactors but never flew, we are witnessing a renaissance. The United States government, through NASA and the Defense Advanced Research Projects Agency (DARPA), has launched the DRACO (Demonstration Rocket for Agile Cislunar Operations) program, with the explicit goal of demonstrating a fission-powered NTP system in space by 2027. This public-sector push is being mirrored by significant private investment. Companies like Ultra Safe Nuclear Corporation and Lockheed Martin are developing their own NTP designs, while others are focusing on small fission reactors to provide surface power on the Moon and Mars, a complementary technology that shares many of the same core challenges and solutions as propulsion reactors. The international landscape is also shifting; China has publicly declared its intention to develop nuclear-powered spacecraft, and Russia has claimed tests of nuclear systems for space, underscoring the strategic nature of this technology.

However, the path to launching a nuclear reactor into space is fraught with immense technical and safety challenges. The foremost concern for the public and regulators is the issue of safety, particularly during launch. The primary technical hurdle is ensuring that the nuclear reactor remains completely inert and intact during launch, in the event of a catastrophic failure on the launch pad or during ascent. Engineers address this by designing the reactor fuel to withstand extreme impacts and temperatures without releasing radioactive material. Modern NTP designs use Low-Enriched Uranium (LEU) fuel, which is less potent than the weapons-grade Highly Enriched Uranium (HEU) used in the NERVA program, reducing proliferation concerns. Furthermore, the reactor would only be activated once the spacecraft is in a safe, stable orbit high above Earth. Dr. Elena Petrova, a nuclear safety expert with the European Space Agency, emphasizes, “The containment and safety protocols we are developing are incredibly robust. The reactor core is designed to be a sealed unit that can survive re-entry and impact without breaching. We are treating safety not as an afterthought, but as the foundational principle of the entire design process.” Beyond launch safety, engineers are grappling with the challenges of managing extreme heat in the vacuum of space, developing materials that can withstand the blistering temperatures and neutron flux inside the reactor, and integrating these complex systems into a reliable spacecraft.

The geopolitical and regulatory landscape is as complex as the engineering. The use of nuclear material in space is governed by a web of international treaties and oversight bodies, primarily the United Nations Office for Outer Space Affairs (UNOOSA) and national nuclear regulatory agencies like the U.S. Nuclear Regulatory Commission (NRC). Any launch of a nuclear-powered spacecraft will require rigorous review and approval to ensure it complies with the Principle of Peaceful Use and does not pose an unacceptable risk to people or the environment. Gaining public acceptance is another critical hurdle. The word “nuclear” inevitably evokes memories of disasters like Chernobyl and Fukushima. Proponents argue that the context is entirely different—a space reactor is minuscule compared to a terrestrial power plant and operates in a remote environment. A sustained public education campaign will be essential to distinguish the controlled, contained risk of a space-based fission system from the catastrophic failures of ground-based power generation.

Looking beyond the initial Mars missions, the potential applications of nuclear propulsion are profound. The true promise of nuclear-powered rockets extends far beyond Mars, offering the capability to make the entire solar system accessible. While a chemical rocket might take a decade to reach the outer planets, a robust NEP or advanced NTP system could cut that journey time to a fraction, enabling sophisticated orbital missions around Jupiter’s moons like Europa or Saturn’s Titan. It could facilitate the establishment of a permanent cislunar economy, with efficient transport between Earth and the Moon. It is, in essence, the enabling technology for humanity to transition from being a planet-bound species to a truly spacefaring civilization. As SpaceX founder Elon Musk, whose Starship vehicle is often cited as a potential crew carrier for such missions, has noted, “To become a multi-planetary species, we need to master new forms of propulsion. Chemical rockets are a great start, but the stars will require something more potent. Nuclear is the obvious next step on that ladder.”

In conclusion, on this day, September 9, 2025, the answer to whether astronauts could travel to Mars on nuclear-powered rockets is a resounding and increasingly confident “yes, and soon.” The technological pieces are falling into place, driven by concerted international effort and private innovation. The journey will not be simple, and the challenges of safety, regulation, and public perception remain significant. Yet, the imperative is clear. The development of nuclear propulsion is no longer a speculative endeavor but a strategic necessity for the future of human space exploration. It represents the difference between a daring, one-off sprint to Mars and the beginning of a sustainable, enduring human presence in deep space. The nuclear torch, first lit in mid-20th-century laboratories, is now being carefully forged into the engine that may very well carry the first humans to the Red Planet within the next two decades.