**NASA to Develop First Nuclear-Powered Spacecraft for 2028 Mars Mission**

This week, NASA Administrator Jared Isaacman announced a groundbreaking initiative: the agency will develop the first nuclear-powered spacecraft designed for interplanetary travel. This pioneering vessel is slated for a 2028 launch, with Mars as its primary destination.

Here are a few options, each with a slightly different emphasis, while maintaining the core meaning and journalistic tone:

**Option 1 (Focus on broader impact):**

> The Space Reactor-1 (SR1) Freedom mission is poised to achieve far more than simply reaching Mars. Should this ambitious project succeed, it would represent the culmination of over six decades of persistent, often challenging, research and failed endeavors in nuclear propulsion, ultimately promising to revolutionize the very nature of interplanetary space travel.

**Option 2 (Focus on historical context):**

> After more than 60 years of ambitious experiments and numerous setbacks in nuclear propulsion, the Space Reactor-1 (SR1) Freedom mission stands at a pivotal juncture. While its immediate objective is Mars, the true scope of SR1 Freedom extends far beyond, carrying the potential to fundamentally transform humanity’s ability to traverse the solar system.

**Option 3 (Concise and direct):**

> Known as Space Reactor-1 (SR1) Freedom, this mission’s ambitions transcend its proposed journey to Mars. A successful outcome would not only cap over six decades of diverse experiments and persistent challenges in nuclear propulsion, but it could also fundamentally redefine the future of interplanetary space travel.

A cutting-edge nuclear electric propulsion (NEP) system is slated to power the upcoming spacecraft, a technology NASA extols as offering “an extraordinary capability for efficient mass transport in deep space.” This groundbreaking engine, however, prompts key questions for space exploration: What exactly is nuclear electric propulsion, and how does its operational principle fundamentally differ from the nuclear power applications utilized in earlier space missions?

The ambitious pursuit of nuclear-powered spacecraft has historically been underpinned by groundbreaking concepts. Among the most prominent is Project Orion, a 1950s endeavor that envisioned propulsion via the shockwaves generated by a rapid series of nuclear detonations behind a spacecraft. Decades later, in the 1970s, the British Interplanetary Society’s Project Daedalus offered an alternative vision, proposing the use of nuclear fusion-powered engines for interstellar travel.

NASA’s groundbreaking SR-1 Freedom concept proposes a sophisticated propulsion system powered by a nuclear fission reactor. This reactor, a compact adaptation of the same technology that energizes cities across Earth, would generate the vital electricity required to operate an advanced ion engine.

While terrestrial nuclear power often conjures images of massive reactors, NASA missions have, for decades, harnessed a distinct form of nuclear energy in space: radioisotope thermoelectric generators, or RTGs. These enduring power sources have been critical for powering numerous deep-space probes far from the sun’s reach.

However, as the SR-1 Freedom spacecraft prepares to utilize a different, more dynamic system – nuclear electric propulsion (NEP) – a crucial distinction emerges. What fundamentally separates these long-serving RTGs from the cutting-edge nuclear electric propulsion system poised to drive this next generation of space exploration?

Radioisotope Thermoelectric Generators (RTGs) are critical power systems for spacecraft, generating electricity by harnessing the heat released during the radioactive decay of plutonium-238. A defining characteristic of this particular isotope is its half-life of nearly 88 years, meaning that approximately half of its original quantity will have undergone decay within that timeframe. This exceptional longevity and consistent energy output enable RTGs to reliably power missions across the solar system for decades, far surpassing the operational limits of other energy sources.

NASA’s deep involvement with nuclear power for space missions dates back almost to the very beginning of the Space Age itself. During the 1960s, the agency established and funded the groundbreaking Systems for Nuclear Auxiliary Power (SNAP) project. As its title suggested, SNAP was dedicated to leveraging nuclear-derived energy sources to power spacecraft and instruments. According to NASA’s records, the first deployment of this technology occurred in 1961 with the SNAP-3 mission, which featured an RTG aboard.

In the nascent era of space exploration, the SNAP-3 Radioisotope Thermoelectric Generator (RTG) offered a glimpse into the technology’s humble beginnings, producing a modest 2.5 watts of electrical power from its 96-gram plutonium-238 core. This early 1960s innovation, however, marked merely the genesis of a power system that would become indispensable for deep-space missions.

Since then, RTGs have dramatically advanced, powering some of humanity’s most ambitious interplanetary voyages. These robust generators have propelled iconic spacecraft like Pioneer 10 and 11, and Voyager 1 and 2 on their epic journeys to the outer reaches of our solar system. They were also critical for the New Horizons probe’s historic flyby of Pluto and beyond, powered the pioneering Viking 1 and 2 Mars landers, and continue to provide vital energy for the Red Planet’s most advanced robotic explorers, Curiosity and Perseverance.

The critical need for Radioisotope Thermoelectric Generators (RTGs) was starkly underscored by the challenges faced by Curiosity and Perseverance’s predecessors: the Mars Exploration Rovers, Spirit and Opportunity. These earlier missions relied solely on solar power, a dependency that ultimately proved costly. As pervasive Martian dust gradually accumulated on their solar arrays, the rovers’ power output steadily diminished, revealing a significant limitation of purely solar-powered operations on the Red Planet.

The 1960s, a decade of profound technological advancement, also heralded the advent of electric propulsion — an innovation now more commonly known as the ion engine. At its core, this sophisticated thrust system operates by first ionizing atoms of a gaseous propellant, typically noble gases such as xenon or krypton. Once ionized, these charged particles are then powerfully accelerated and expelled through a specialized nozzle, generating the precise, sustained thrust required for space travel.

The critical process of accelerating these ions can be achieved through two distinct methods. One prominent technique involves the strategic application of electromagnetic fields to induce a phenomenon dubbed the “Hall effect,” which then drives the ions forward.

Another distinct approach utilizes the **gridded ion thruster**. In this system, positively charged ions are first introduced into a ‘discharge chamber,’ where they are subsequently drawn towards a negatively charged grid. An applied voltage then powerfully accelerates these ions through small apertures in the grid, propelling them outwards through a nozzle. The operation of this type of ion engine is famously marked by a distinctive, soft blue glow.

For missions venturing through the inner reaches of our solar system, a critical technology is Solar Electric Propulsion (SEP). This innovative system utilizes expansive solar arrays to generate electricity, which is then employed to ionize propellants, thereby creating the necessary thrust. What might surprise many, however, is the modest output of this sophisticated propulsion: a typical SEP system generates less than a single pound of thrust.

While the Space Launch System (SLS) will unleash an immense 8.8 million pounds of thrust to propel the Artemis 2 mission toward the Moon, Solar Electric Propulsion (SEP) operates on an entirely different, yet highly effective, principle. Though SEP generates only a fractional amount of thrust at any given moment, its continuous and additive nature allows momentum to build steadily over time. This sustained acceleration eventually drives spacecraft to remarkable velocities, often exceeding 200,000 miles (320,000 kilometers) per hour—long after a conventional chemical rocket would have exhausted its fuel supply.

Solar Electric Propulsion (SEP) technology boasts a storied history in space, having powered Earth-orbiting missions since the 1960s. Its true frontier, however, was unlocked in 1998 with NASA’s Deep Space 1, marking the first interplanetary application of SEP.

Since that pioneering journey, the technology has proven exceptionally effective, propelling landmark missions such as the European Space Agency’s SMART-1 to the Moon, NASA’s Dawn spacecraft during its extensive exploration of Ceres and Vesta in the Asteroid Belt, and the DART mission, which famously impacted the binary asteroid Didymos and Dimorphos in 2022.

For deep-space exploration, transitioning from solar to nuclear power offers two compelling advantages.

Firstly, nuclear power dramatically simplifies the deployment and operation of ion engines, particularly in the distant outer solar system where sunlight is too faint to effectively power solar arrays. This allows missions to utilize highly efficient propulsion systems far from the sun’s energy.

Secondly, and critically for ambitious missions, nuclear systems generate a vastly superior amount of power. They can produce between one and two orders of magnitude more energy than conventional Solar Electric Propulsion (SEP) systems. This substantial increase in power directly translates to significantly greater thrust capabilities and the capacity to carry much heavier payloads, thereby expanding the scope and potential of deep-space endeavors.

For more demanding operations, Radioisotope Thermoelectric Generators (RTGs) simply cannot provide sufficient power. This necessitates that Nuclear Electric Propulsion (NEP) systems instead rely on a fission reactor. Within this setup, the intense heat generated by the reactor is efficiently converted into electricity. This electrical power then serves to ionize, or electrically charge, the propellant gases, preparing them for use in the ion engine.

Powering the SR-1 Freedom will be a 20-kilowatt fission reactor, fueled by a precise combination of low-enriched uranium and uranium dioxide. Crucially, this compact power source is designed for placement at the extreme end of an extended boom. This strategic engineering choice is paramount for safety, establishing a vital standoff distance to shield the spacecraft’s sensitive systems and any potential crew from the reactor’s operational radiation.

In SEP, a large fraction of a spacecraft’s total area is devoted to solar arrays. With NEP those solar arrays are switched out for heat exchange fins to radiate away some of the excess heat from the reactor and prevent the spacecraft’s components from melting.

It’s worth noting that there is a third variation of the nuclear engine, which is nuclear thermal propulsion, in which the energy produced by a fission reactor heats a propellant, causing it to expand and burst through a nozzle, producing thrust like a more conventional rocket.

Safety is, of course, of paramount importance when sending nuclear material into space, and people are very often scared of the word ‘nuclear’.

In 1997, controversy engulfed the launch of the joint NASA/European Space Agency Cassini–Huygens mission to Saturn. It carried on board three RTGs carrying 73 pounds (33 kilograms) of plutonium-238 between the two probes.

The mission’s environmental impact study suggested that there was a 1 in 1,400 chance of an accident during blast-off, and 1 in 476 chance during the flight through Earth’s atmosphere, which could spread radioactive material not just across Florida, from where Cassini–Huygens launched, but across the entire globe depending upon the altitude at which an accident happened. This led to serious concerns from some quarters, with science popularizer Michio Kaku among the leaders of the protests demanding the launch be scrubbed, but Cassini–Huygens’ went ahead without a hitch, as have all the subsequent RTG missions.

Care is of course taken in ensuring that should an accident occur, the radioactive material is protected as well as can be. The risk is minimized by packaging that radioactive material inside extremely durable graphite blocks bolstered by a layer of iridium and surrounded by an aeroshell to protect the RTG should it undergo an atmospheric re-entry.

Though this does not provide an absolute guarantee, one would imagine that any fission reactor launched into space would require similar safety protocols. Indeed, there are very stringent regulatory constraints, both in the United States and internationally, regarding sending nuclear material into space.

There’s also the issue that nuclear fission is a highly toxic process. It involves splitting the atom, producing radioactive waste as well as energy. By using fission reactors in space, we are essentially sending little packets of toxic waste across the solar system, which could in the future prove dangerous for any astronauts that encounter them, or any biospheres that may exist on other planets or moons, such as Mars or Europa, should one of these toxic parcels crash land there.

This isn’t the first time that NASA has toyed with using nuclear electric propulsion. In 1965 the agency launched the SNAP-10A mission, which was the first and so far only time that nuclear electric propulsion has been successfully deployed. It was also the first time that a nuclear reactor was launched into space. That reactor operated just fine for 43 three days before developing a fault and shutting down, according to the U.S. Department of Energy.

However, in the 61 years since SNAP-10A, there have been no further missions successfully demonstrating nuclear electric propulsion, but there have been many attempts to do so. NASA’s most recent project was DRACO, the Demonstration Rocket for Agile Cislunar Operations, in conjunction with DARPA, Lockheed Martin and BWX Technologies.

Alas, the DRACO program was paused in January 2025 because of technical and regulatory challenges, before being cancelled outright that summer when it was left off the proposed 2026 federal budget. DARPA claimed that the costs of the program no longer matched the benefits, given that ordinary launch costs were coming down.

Now, however, NASA seems to have changed their tune with their renewed interest in nuclear electric propulsion. There is certainly a strong case that using nuclear power is vital if we are to launch more regular interplanetary missions and send astronauts and massive payloads to Mars or elsewhere.

Yet time is certainly against NASA launching the mission in 2028 as planned, and it remains to be seen whether, after more than sixty years of trying, NASA can finally get the technology to work. If they do, then the increased efficiency and power that it can bring to electric propulsion engines could transform space travel, whether it be taking astronauts to Mars or driving scientific missions to the outer solar system.