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The pursuit of nuclear fusion, a concept promising virtually limitless and clean energy, has captivated brilliant minds globally for decades. Mimicking the power generation within stars on Earth represents a revolutionary leap in energy technology. However, while the terrestrial realization of nuclear fusion power remains years away, harnessing this potent energy source in the vacuum of space presents a potentially nearer-term prospect, especially for advanced space propulsion systems. Such technology could propel spacecraft to astonishing velocities, potentially reaching 500,000 miles (805,000 kilometers) per hour, surpassing even the speed records set by NASA’s Parker Solar Probe.
Sunbird: A Nuclear Fusion Rocket Concept
British startup Pulsar Fusion, backed by funding from the UK Space Agency, has introduced Sunbird, an innovative space rocket design. Sunbird is envisioned to rendezvous with orbiting spacecraft, attach, and then transport them to their destinations at unprecedented speeds using nuclear fusion propulsion.
Richard Dinan, Pulsar Fusion’s founder and CEO, emphasizes the inherent suitability of space for fusion processes. “Performing fusion on Earth is inherently challenging,” Dinan stated. “Fusion reactions naturally occur in space, devoid of atmospheric interference. Space is a considerably more logical and appropriate environment for fusion, aligning with its natural inclination.”
Currently, Sunbird remains in early developmental phases and faces substantial engineering hurdles. Nevertheless, Pulsar Fusion aims to achieve the groundbreaking feat of fusion in orbit by 2027. Should this rocket become operational, it holds the potential to halve travel durations for missions, such as journeys to Mars.
Minimal Fuel Requirements
Nuclear fusion fundamentally differs from nuclear fission, the process powering contemporary nuclear plants. Fission involves splitting heavy, radioactive elements like uranium, releasing energy to generate electricity.
Conversely, fusion entails fusing light elements, such as hydrogen, into heavier ones under extreme temperature and pressure. Dinan elucidates, “Stars, like our sun, are essentially fusion reactors. They transmute hydrogen into helium, and upon their demise, they forge the heavier elements constituting the universe. Hydrogen and helium constitute the majority of the universe; all other elements originate from stellar fusion.”
Fusion is highly desirable due to its energy yield, four times greater than fission and a million times greater than fossil fuels. Unlike fission, fusion circumvents the need for hazardous radioactive materials. Fusion reactors would utilize deuterium and tritium, heavy hydrogen isotopes, consuming minimal fuel quantities and producing no hazardous waste.
However, initiating fusion necessitates substantial energy input to replicate stellar core conditions: immense temperature and pressure, coupled with effective confinement to sustain the reaction. A primary challenge on Earth has been achieving a net positive energy gain from fusion, consistently producing more energy than consumed.
Focus on Propulsion, Not Power Generation
Dinan clarifies that the focus of Sunbird is not terrestrial power generation, which simplifies the technological demands. The objective shifts to achieving a higher exhaust velocity for propulsion.
Nuclear fusion reactions occur within plasma, a superheated, electrically charged gas. Similar to terrestrial reactor designs, Sunbird would employ powerful magnets to heat plasma, creating conditions for fuel fusion. However, contrasting with Earth-bound circular reactors, Sunbird adopts a linear configuration. This design intentionally releases particles to generate thrust for spacecraft propulsion.
Furthermore, Sunbird will not generate neutrons, a byproduct used for heat generation in terrestrial reactors. Instead, it will utilize helium-3, a more costly fuel, to produce protons. These protons serve as “nuclear exhaust,” providing propulsion.
Dinan acknowledges that the Sunbird approach would be expensive and unsuitable for energy production on Earth. However, because energy generation is not the primary aim, the process tolerates inefficiencies and higher costs. The value proposition lies in reduced fuel expenses, decreased spacecraft mass, and significantly faster transit times.
Reducing Travel Time
Dinan draws an analogy between Sunbirds and city bike-sharing systems. “We envision launching them into space, with charging stations for docking and servicing,” he explains. “Spacecraft would dock, deactivate their conventional engines, and utilize nuclear fusion for the majority of their journey. Ideally, stations would be positioned near Mars and in low Earth orbit, enabling Sunbirds to shuttle between destinations efficiently.”
Upcoming Demonstrations
Orbit demonstrations for certain Sunbird components are planned for the current year. “These are essentially circuit board tests in space to validate functionality, albeit without actual fusion. This step is crucial,” Dinan states. “Subsequently, in 2027, a partial Sunbird prototype will be launched into orbit to verify the underlying physics align with computational models. This initial in-orbit demonstration aims to achieve fusion in space, potentially positioning Pulsar as the pioneering company to accomplish this milestone.”
This prototype is budgeted at approximately $70 million. It will be a “linear fusion experiment” to validate the concept, rather than a fully functional Sunbird. Dinan anticipates the first operational Sunbird within four to five years, contingent upon securing necessary funding.
Initial applications for Sunbirds will focus on satellite deployment in orbit. However, their transformative potential lies in interplanetary missions. Pulsar Fusion outlines potential missions, including delivering substantial cargo to Mars in under six months, deploying probes to Jupiter or Saturn in two to four years (significantly faster than NASA’s Europa Clipper mission), and asteroid mining expeditions with round trips reduced from three years to one or two.
Other organizations are also pursuing nuclear fusion engines for space propulsion. Helicity Space, based in Pasadena, secured investment from Lockheed Martin in 2024. General Atomics and NASA are collaborating on a fission-based nuclear reactor for space testing in 2027, intended as a more efficient propulsion solution for crewed Mars missions.
Fusion Propulsion Potential
Aaron Knoll, a plasma propulsion expert at Imperial College London (unaffiliated with Pulsar Fusion), emphasizes the substantial potential of fusion power for spacecraft propulsion. “While terrestrial fusion energy viability is still some years away, space propulsion applications can precede it,” he notes.
Knoll explains that terrestrial power generation necessitates energy output exceeding input. However, for spacecraft propulsion, any energy output from fusion is beneficial, even if less than the input. The combined energy from external sources and fusion reactions enhances thrust and propulsion efficiency.
However, Knoll acknowledges significant technical obstacles in realizing fusion technology in space. “Current terrestrial fusion reactor designs are large and heavy, requiring extensive support infrastructure,” he points out. “Miniaturizing and lightening these systems poses a considerable engineering challenge.”
Bhuvana Srinivasan, an Aeronautics & Astronautics professor at the University of Washington (also independent of Pulsar), affirms the promise of nuclear fusion propulsion for spaceflight. “It would be transformative even for lunar missions, enabling deployment of entire lunar bases in single missions,” she states. “If successful, it would dramatically outperform existing propulsion technologies, not just incrementally.” She also highlights the challenges of miniaturization and weight reduction, more critical for space applications than terrestrial energy.
Srinivasan concludes that unlocking fusion propulsion would revolutionize both human and uncrewed space missions, facilitating resource acquisition, such as helium-3, from the Moon. “A lunar base, potentially leveraging helium-3 reserves, could become a strategic launchpad for deep space exploration,” she suggests.
“Exploring planets, moons, and distant solar systems is fundamental to human curiosity and exploration, potentially yielding substantial financial and societal benefits yet to be fully realized.”