A key issue with replacing conventional jet fuel is that the alternatives just don’t offer the same range, performance and economics. A lot of this has to do with energy density. If we think of a fully electric aircraft as an example, batteries quite simply offer only a fraction of the energy per unit of weight when compared to conventional fuel.
When we think about energy density, the true hero today is nuclear power. But we’re already worried about keeping nuclear reactors safe in powerplants that are located firmly on the ground, so is it realistic to believe we’d ever use them to power aircraft? And how would that work.
A brief history
For sure, the history here does not look promising. Both the United States and Russia considered designs for nuclear powered military aircraft, such as the Convair X-6, Convair NX-2 and the Tupolev 119, but none of these aircraft ever flew. These aircraft all intended to use heat produced from a nuclear reaction rather than the burning of jet fuel to generate thrust. With nuclear power, aircraft could have exceptional range, which made them interesting for applications like ultra-long-range bombers.
While none of the aircraft concepts mentioned ever took to the skies, several aircraft have been flown with nuclear reactors onboard for testing, but without them powering the aircraft itself; the Convair NB-36H in the United States and the An-22PLO and Tupolev 95LAL in the Soviet Union. Ground runs of nuclear-powered jet engines were conducted in the United States by General Electric as part of a series of tests know as Heat Transfer Reactor Experiment (HTRE) series. The primary reason for these programs not working out for the military was one of safety. How to avoid a nuclear catastrophe in case one crashes?
So, technical or financial feasibility aside, if the military didn’t believe nuclear power could even be safe for use in their aircraft, where safety may not be as high of a concern as with civilian aircraft, how could nuclear power ever be safe in commercial airliners? It’s not surprising that the idea has been basically dead for decades.
But what about nuclear fusion?
Using nuclear fission does not appear like something that’d ever be viable for commercial aircraft. However, there’s that other more elusive form of nuclear power: nuclear fusion. While work on building a net-positive (that is to say, a reactor that produces more energy than it consumes) nuclear fusion reactor seemed elusive for decades until the Lawrence Livermore National Laboratory (LLNL) announced it had the achieved this in in December 2022 at their National Ignition Facility.
While most attention in the nuclear fusion space has gone towards experiments using large nuclear fusion reactors such as the National Ignition Facility and ITER which would be entirely unsuitable for aviation use, other companies believe that compact reactors can be built. This includes Lockheed Martin’s infamous and secretive Skunkwork’s division, which has been working to develop a compact fusion reactor. While compact is a relative term as it’d still be the size of a shipping container, they believe that very large aircraft could be made to fit this type of reactor. The power this reactor would be able to generate would allow such an aircraft to have virtually unlimited range.
Another player in this space is Avalanche Energy. While they do not specifically call out use cases, their focus is on developing “micro fusion power packs” for which they claim the uses would be “nearly limitless”, which in concept sound like the sort of thing one could fit in an airplane. A competing company, Electric Fusion Systems, believes they will be able to develop a reactor the size of a suitcase. In all, for 2022 the Fusion Industry Association listed over 30 private companies working to develop a wide variety of different fusion reactors, several of which focus on compact designs.
Does that mean with all this development going on and the recent success at LLNL that soon we’ll have nuclear fusion reactors powering the world around us, including aircraft using compact fusion reactors? Opinions on this are extremely varied. The achievement by LLNL was a scientific success but by no means demonstrated a practical or means of generating electricity just yet. Let alone that this results in the successful development of a fusion power source that could be fitted on an airplane as the LLNL National Ignition Facility is huge. And timeline estimates from companies in the nuclear fusion space around when they may deliver solutions are notoriously inaccurate. Indeed, since first announcing their plans in 2014, Lockheed Martin appears to have fallen behind significantly on their timeline sketched at that time, with seemingly little news in recent years at all.
So, there’s good reason to not be overly optimistic here, but not everyone is a skeptic. In a December 2022 interview, Mona Ghassemi, associate professor and director of the ZEROES (Zero Emission, Realization of Optimized Energy Systems) Lab at the University of Texas at Dallas, is optimistic about the potential of compact fusion reactors powering widebody aircraft if advances in this space come sooner than the development of improved battery systems.
Overall, it still seems like nuclear fusion powered aircraft is an extremely unlikely scenario. But nuclear fission we probably shouldn’t rule out just yet. And even if we don’t ever see this used in civilian airliners, we may still see these reactors used for a different kind of flight: space travel.