Pellet Injection for Fusion Engines

Currently i’m having some fun playing around with hydrogen gas gun configurations but I am not investigating them for the usual application. Instead, I am looking at them for the potential of delivering an inertial confinement fusion pellet into a reaction target chamber within a fusion engine. The pellets of thermonuclear fuel have to be accelerated at high velocity into the target chamber so that a bank of lasers can then fire at them to initiate the fusion reaction. This must happen many times per second in what is known as pulse repetition frequency.

The initial concept for a single gas gun design is shown below and it includes many pistons acting in sequence to supply the injection barrel. It is a bit like a giant machine gun.

This is for the application to the large interstellar Pegasus spacecraft I have been designing as a part of Project Icarus. With a pulse frequency of 1,000 Hz, and an injection length of 1 m the pellet would have to be injected with a velocity of 1 km/s which is credible. Lowering the pulse frequency results in a lower injection velocity requirement. Increasing the injection length increases the velocity requirement.

In the current setup I am using a 72 mg pellet which has an energy of 36 J or a power of 36 kW. But here is the thing, this is on a spacecraft that has four parallel thrust engines, so you need four of this units operating simultaneously. Each unit has 100 pistons They are positioned onto a large rotating 10 m disc where the units are aligned with the pellet injection line to the target chamber of each reaction chamber. The whole system has an associated moment of inertia 1.25 million kgm2, kinetic energy 0.422 MJ and a power requirement of around 5.275 kW.

The calculations are suggesting that the quantity of hydrogen and oxygen gas required to operate these would be too excessive. It also requires an assumption of an unrealistic high efficiency of operation with negligible energy losses. For these reasons for the particular design I am looking at they may not be appropriate. But it sure is a lot of fun attempting to do engineering design on the application of existing machines to envisaged ones. After all, this is how the future is made.

Fusion Propulsion for Exploring the Solar System & Beyond

Fusion propulsion for exploring the solar system and beyond (openaccessgovernment.org)

Dr Kelvin F Long, Aerospace Engineer and Astrophysicist, leads the Interstellar Research Centre, a division of Stellar Engines Ltd. He argues that fusion propulsion will enable the full exploration of the solar system and beyond

Beginning from the last century with the first orbital satellites placed into space, humanity explored all of the planets of our solar system using robotic probes. This includes the launch of the Voyager 1 and 2 probes in 1977 which are now far outside of the solar system and headed out into interstellar space. It is feasible that in the future we may construct probes that can go much faster and further.

The maturation of advanced propulsion technology is also required for human crewed missions beyond the Moon, such as to the red planet Mars. One of the main hazards for astronauts in space is overexposure to space radiation in the event of a solar flare, as well as loss of bone density in a microgravity environment. Yet this cannot be achieved with existing technology and requires a new propulsion paradigm with a high-energy capability. This is possible with fusion reactions, the same physics mechanism that powers the Sun.

Laboratory fusion

Any fusion facility must demonstrate thermonuclear ignition of hydrogen and helium nuclides. This is typically set by the Lawson criteria which demands that the product of the number density, confinement time, and plasma temperature exceeds some minimum value.

n France, work is underway on the construction of the International Thermonuclear Experimental Reactor (ITER), which is based on magnetic tokamak technology. Its goal is to produce a net energy gain of 10 as measured by the ratio of 500 MW energy output to 50 MW energy absorbed for 100s of seconds, but it is generated from a 300 MW electrical supply.

The Joint European Torus (JET) has operated at the Culham Centre for Fusion Energy in Oxfordshire, England, since 1983. In 1991, it performed the first-ever experiments with deuterium-tritium fuels in a laboratory and then, in 1997, broke records by achieving a gain of around 0.67, with an input power of 24 MW producing an output of 16.1 MW (21.7 MJ). After upgrade work to align JET technologically with ITER, in 2021, it went on to produce 12 MW (59 MJ) in a 5 s pulse. Yet it takes a total power requirement of 500 MW to run JET.

JET was closed down in 2023 and is moving towards full decommission by 2040, although not before breaking its record and achieving 69 MJ in 2024 with 0.2 milligrams of DT fuel. Culham does still operate the Mega Ampere Spherical Tokamak (MAST) experiment. This is also supported by other facilities like the Central Laser Facility (CLF) at the Rutherford Appleton Laboratory near Oxford, which conducts innovative fusion-related experiments on its Vulcan laser, which is the highest-intensity focussed laser in the world at 1021 W/cm2.

The prospects for fusion on Earth significantly increased in 2022 when the U.S. National Ignition Facility (NIF) achieved thermonuclear ignition in a laboratory in what some have described as a “Kitty Hawk” moment for fusion energy. This was using 192 Nd: glass laser beams frequency tripled from infrared light to ultraviolet so as to reduce laser-plasma instabilities, and compress a DT target using inertial confinement fusion (ICF) for a fraction of a second, producing a net energy gain of 1.5, using an input energy of 2.05 MJ and an output energy of 3.08 MJ and the actual wall plug energy was 300 MW. In 2024, they went even further and achieved a gain of 2.4, demonstrating further progress with 5.2 MJ laser energy delivered to the target. We are inching our way towards controlled fusion, although optical lasers have a very low efficiency at <1%.

First Light Fusion was established in the UK in 2011 and is pursuing an innovative type of ICF. The method involves the electromagnetic acceleration of a metal projectile at 10s km/s into a fusion target embedded within a cube, where spherical cavities help to focus the shock waves of the incoming projectile energy to implode the capsule to 100s km/s for fusion ignition. The idea takes its inspiration from a pistol shrimp claw. It has recently conducted experiments on the Sandia National Laboratory Z-machine to demonstrate a record 1.85 TPa pressure for an 80 TW shot.

Established in 2009, UK-based Tokamak Energy operates the ST40 high-field compact spherical tokamak. Although its main interest is electricity for a national grid, by the 2030s, it is considering alternative applications for its High-Temperature Superconductor (HTS) technology, including space.

Fusion propulsion

Once fusion on Earth has been successfully achieved and is regularly supplying energy to a national grid, the application to space technology will be the next obvious step. One option is to use Diode Pumped Solid State Lasers (DPSSL) which are based on semiconductor technology and may have a driver efficiency of 6-12% and may even approach 20% in the future. These were also proposed for use in Mars missions such as the Vista concept design also developed by NIF scientists.

Also in the U.S., RocketStar, founded in 2014, has invented a FireStar fusion drive, a fusion-enhanced space thruster. This is achieved by injecting boron into the thruster exhaust, which then collides with high-speed protons produced from a H2O-fueled pulsed plasma. They claim that once the boron decays, 11B →3α, this results in a 50% thrust augmentation.

The Direct Fusion Drive (DFD) is a concept that has been under development by the Princeton Plasma Physics Laboratory since around 2001.

It uses a magnetic confinement torus heating method inside of a linear solenoidal coil and a radio frequency antenna to heat a D3He fuel to plasma conditions and fusion ignition. They plan to use it to carry a 1 tonne payload to Pluto in a trip time of four years or, Saturn’s Moon Titan in around 2.6 and six months, or a crewed mission to Mars in around four months.

Helicity Space is a company founded in 2018 with the goal to catalyse humanity’s spacefaring ambitions for fast, sustainable and safe applications. Their Helicity Drive design utilises magneto-inertial fusion method to confine, heat and compress the plasma. Applications include a round-trip journey to Mars in under four months carrying a 450 tonnes payload.

Pulsar Fusion was founded in 2011 and is developing a compact Direct Fusion Drive (DFD) engine to be operational by 2027 and may achieve a velocity of 223 km/s for use in missions to Mars using D3He fuel. The DFD aims to carry a 1 tonnes payload to Pluto in a trip time of four years with an orbital test by 2027.

This author has been examining the possibility of a 1,000 AU mission, called SunVoyager, to facilitate an astronomical telescope at the outer reaches of our Solar System driven by an ICF engine. An even more ambitious design by this author is for an interstellar mission in a robotic spacecraft concept called Pegasus; the vehicle is illustrated in Figures 1 and 2. It would carry a 150 tonnes payload to 4.3 light years in a trip time of order 100 years.

For any companies pursuing fusion research, they have to demonstrate experimental credibility if they are to avoid being accused of practising “voodoo fusion” as some have claimed without showing verifiable results which prove fusion reactions have occurred, but also that they can exceed the Lawson criteria to give a positive energy gain. This will be an important criterion for any would-be investors. Indeed, in June 2024, a fusion energy start-up, Xcimer Energy, announced they had raised $100 million to build a prototype laser-driven inertial fusion facility based on the results of NIF. These are exciting times.

Economic vision for the UK

In 2023, the UK Government published a policy paper titled Towards Fusion Energy 2023, which built on from the earlier 2021 fusion energy strategy. The report noted the importance of the UK looking to the future to maintain its position and set a goal to prove the commercial viability of fusion by constructing a prototype fusion power plant that delivers net energy.

In addition, it is to build a world-leading fusion industry that supports different technologies which can be exported in subsequent decades and, therefore, contribute to the UK economy. An overall focus seems to be on the maturation of a fusion-based industry by the 2030s through a combination of private and public sector partnerships.

The UK Government has also stated that it wants to create a world-class space nation from its existing base of around 45,000 people. This includes supporting UK business, research, and innovation to enable us to collaborate with international partners in space activities and then seek out new competitive opportunities that contribute to economic growth and strengthen our national defence. In real terms, this means an ambition to move from the current 5% share of the global space sector with £17.5 billion domestic revenue to a nation that has a 10% share by around 2030.

A sure way to achieve that is to build on the UK’s already highly skilled aerospace and nuclear industry and put significant resources into the development of commercial power reactors for Earth and future colonies on the Moon and Mars. Yet after that comes the application of advanced space propulsion. The nation that becomes an early adopter of this technology will surely garner a significant advantage in the development of any off-world economic development.

Such a reality will only come to fruition when policymakers can see into a future beyond their own lifetime, one where our nation is serving a vital purpose in the exploration of space.

To ensure long-term growth, we must adopt a strategic vision that surpasses existing problems and paradigms if we are to receive the benefits of new and innovative technological developments as they mature into the market. Investing in fusion today, including fusion propulsion, is one way to help facilitate such a vision.

Pegasus Interstellar Probe

In 2009 I initiated Project Icarus, an effort to design an interstellar rendezvous probe as an exercise in the application of extreme aerospace engineering. Over the years this has led to dozens of peer reviewed publications by members of the team. Recently we have began the process of bringing the project to a final close. We held our close-out symposium in September 2023 and we are now busy finishing up the final papers.

My own work, has focussed on a particular design called Pegasus, which is a four-engine parallel thrust system carrying a 150 tons science payload to orbit around one of the exoplanets of Centauri A/B. Travelling at a cruise velocity of 0.046c or 13,680 km/s it reaches the destination target in a trip time of just under 100 years.

Orthographic Depiction of the Pegasus Interstellar Spacecraft Concept Design

Designing fusion engines is difficult and as a team we have spent many hours thinking about the problem, on a project that has endured for 15 years. Although this is a purely theoretical exercise, we have been using our engineering and physics skills to produce concepts for machines that may one day become feasible. This has required a combination of existing technology integrated into near-future technology, through a process of extrapolation from current technology trends.

The Pegasus, uses an inertial confinement fusion engine driven by high energy laser beams. The fuel capsules are pretty big at 72 milli-grams and they are detonated at a frequency of 1,000 Hz. This produces a mass flow rate of 0.288 kg/s, thrust of 2.65 MN, jet power 12.21 TW and a specific power of 2.45 MW/kg. As I said, designing fusion engines for deep space exploration is hard and challenging.

Four Parallel Thrust Engines of the Pegasus Interstellar Spacecraft

The laser requirements for the propulsion system is 145 MJ operating with an efficiency of 36% and a peak power of 903,427 TW, with 50 separate beamlines firing down onto the target. Yet this is for an assumed energy gain of 23, which is not great but perhaps what might be expected from a commercial ground reactor that supplies energy to a national electrical grid. However, for this study I have assumed worst case conditions and I could have assumed much higher energy gains in order to get the total mass down. For example a Mars study called Vista previously assumed an energy gain of 1500. But I would just rather start from the bottom line definition and then allow others to improve on the model.

I have also been costing the probe, which includes the design and development phase, construction and production phase and the mission utilisation phase. Currently its coming in at around $150 Billion. The biggest factor in the Capital Expenditure Model (Capex) is the acquisition costs of obtaining helium-3 such as from gas giant mining, since the Pegasus requires 43,300 tons of Deuterium-Helium-3 fuel in equimolar mixture. I have also costed a program to lead up to the launch of Pegasus, to include lower energy flights into the Solar System with increasing reach and velocity. The total program is currently coming it at around $300 Billion, over a timespan of around 150 years. That is $2 Billion per year or $20 Billion per decade - smaller than the current NASA budget.

Pegasus Scientific Payload with Autonomous Artificial Intelligence Capability

The payload would be controlled by an artificial intelligence computer, and it would also carry an on-board self-repair factory and spare parts using large robotic arms similar to what is currently on the ISS. Once it arrived at the local planetary system it would deploy dozens of smaller spacecraft to include orbiters, atmospheric penetrators, surface landers and rovers, to permit a full scientific reconnaissance of the planetary system and all celestial objects. All of the papers for the project should be submitted to the Journal of the British Interplanetary Society during October/November 2024 so look out for their release in 2025. The key papers pertaining to Pegasus includes:

  1. Project Icarus: The Pegasus Spacecraft Concept Design ICF Propulsion for an Interstellar Rendezvous Mission.

  2. Project Icarus: The Pegasus Spacecraft Concept Design Engineering Systems Description.

  3. Project Icarus: Strategic Roadmap Conclusions of the Starship Design Study.

Think of all the benefits that would come from the development of such a spacecraft. If humanity was to pull its resources and work towards such a visionary goal as interstellar spaceflight. How constructive would be the application of our energies and how creative would be the utilisation of our intellectual capacity as a species in search of knowledge.

The Pegasus is more than just an engineering machine. It represents hope itself. Hope that humanity can grow wings and become something greater than the quagmire of despair it has currently become as conflicts rage around the world. Think of all the jobs it would create. Consider all of the new technology spin-offs that would result from the construction of such a machine. How transformative those technologies could be on the human condition. The visionary inspiration that it would cause. The enhancement of our educational standards as young people found careers that would enable them to contribute to such an exciting initiative.

A Single Engine for the Pegasus Interstellar Spacecraft Concept Design

It is initiatives like this which I think is the solution to humanity’s problems. Nations need to find ways of co-operating together on large scale endeavours that can bring massive benefit to the contemporaneous society but also help to secure a prosperous future. This doesn’t just apply to space, but to exploration of the oceans, or inside the Earth, or the microbes under a microscope, or finding cures for diseases. Big project problems being attacked by the world’s best scientists working in co-operation as a common humanity.

History has often depicted a great hero on a horse coming to save a people. In England this is King Arthur, a leader in post-Roman Britain in battles against the Anglo-Saxons during the 5th and 6th centuries. There is also Queen Boudica of the ancient Iceni tribe who led an uprising against the conquering forces of the Roman empire around AD 60. A large statue of her stands on the banks of the River Thames in London today so British people never forget the value of their freedom and the boot of oppression and tyranny.

Pegasus had a rider too, his name was Bellerophon from ancient Greek mythology. He was the slayer of monsters and he killed the Chimera in the Illiad, the epic written by Homer about the battle of Troy. It was Bellerophon that captured and tamed the winged horse Pegasus. That is a metaphor for us in the current times, that in order to become a great civilization among the stars we must capture and tame the starship Pegasus. We must learn how to design it, and then to one day build it. This takes great perseverance, many years of effort and a degree of co-operation currently lacking from our world. I continue to hope that one day humanity will grow up and finally learn to take flight among the stars. For then we will be creating our own mythology as we embark on epic journeys in the Cosmos and beyond.

Pegasus Parallel Thrust Engines Lighting up under Acceleration

Pegasus arrives at Some Distant Exoplanets in Search of the Unknown



World Ship Studies

In some recent studies I have been looking at World Ships. These are massive vessels 10 to the power of 11 to 10 to the power of 12 tons travelling at 1,500 km/s (0.5%c) to reach the nearest stars in 1,000 years or less. They carry 1 million people at the start of the journey and allow for growth of that population.

The design concepts were to be propelled by 1,024 engines based on inertial confinement fusion (ICF) systems and this requires a staggering 170 TJ driver energy assuming an optimistic 25% wall plug efficiency of any lasers. ICF works on the principle of many laser beams hitting a fusion fuel target and leading to a symmetrical implosion and compression of a central hot spot region that leads to thermonuclear ignition and energy gain. The individual pellets in the design are 230 grams each of TN fuel along with 2.43 kg/shot of expellant propellant for thrust augmentation, all detonated at 100 Hz pulse frequency.

The first paper was published and examines population demographics, power supply requirements for the habitats and spin gravity to contain the atmosphere and regolith. It focussed on the issue of the sort of demographic population one would need in such a large vessel and how this links to the demographic models used on Earth within our individual nation state economies. The issue of demographics would be a critical one for a world ship that was operating over many centuries and many generations of people.

The humans that left Earth at launch would never see the new target home world. The humans that arrived at the target home world would never have seen Earth. The ones that are a part of the majority of the journey would never have seen either other than on computer screens and perhaps through large on-board telescopes.

The second paper focused on the propulsion system to be adopted and went into some detail on the calculations. These studies were based on earlier papers from Bond/Martin in 1984 which utilised external nuclear pulse propulsion and seeks to advance concepts to the next stage. Its not easy to push such a large vessel and requires a thrust of 978 GN.

It also gave a form of design review discuss on the many issues that would need to be worked on if such a project was to be taken to the next level of fidelity. It is the hope of this author that indeed others would one day pick up the design studies and continue them further forward.

The concept of a world ship is a rather romantic one carrying millions of people at a time on a journey to the distant worlds. In reality this may not be the manner in which the stars are settled by future humans. There are other routes such as sending banks of embryos, the transport of information through some quantum entangled states of matter, or even the development of faster than light drives. However, it is always fun to first see what the bottom line engineering requirements are likely to be.

K. F. Long, Population Demographics & Other Issues for the Massive Ra World Ship Model - Part 1, JBIS, 76(11), 262 - 272, 2024.

K. F. Long, Inertial Confinement Fusion Propulsion for the Massive Ra World Ship Model - Part 2, JBIS, Submitted, February 2024.

Interstellar Wormholes

With the recent box office film ‘interstellar’ many people are excited about the prospects of wormholes as a means for interstellar transport. These have been depicted in other television programs, such as in the Star Trek: Deep Space Nine universe. Although there is currently no evidence that such exotic objects exists in nature, it is possible that they could be artificially created, perhaps from versions of higher dimensional string theory and engineering of the fundamental space-time foam.  Wormhole research is today an exciting subject with dozens of papers published in peer reviewed journals every year, but it is worthwhile to be reminded of its origins and it starts from a surprising place.


In 1915 Albert Einstein published his General Theory of Relativity, his description of gravity that neatly defines how objects will attract one another and affect the space and time around them. Many years later the American physicist John Wheeler would coin the phrase “space tells matter how to move, and matter tells space how to curve”. Einstein described gravity as a manifestation of space-time curvature.  General Relativity is a continuous field theory in contrast to the particle theory of matter.

Einstein was also involved in the development of quantum mechanics, the theory that described sub-atomic particles. But he was not entirely happy with its inherent uncertainties and probabilistic character. So in 1935 he worked with Nathan Rosen to produce a field theory for electrons, using General Relativity. His paper was titled “The Particle Problem in the General Theory of Relativity” (Phys.Rev, 48, 73, 1935). They were investigating the possibility of an atomistic theory of matter and electricity which, while excluding singularities of the field, makes use of no other variables other than the metric of the general relativity and the potential of the Maxwell theory. In essence, they asserted that the most natural elementary charged particle was found to be one of zero mass.

In the end, what they produced was something quite unusual. They started with the equations for a spherically symmetric mass distribution, typically used for black holes and known as the Schwarzschild solution, and performed what is known as a co-ordinate transformation to remove the region containing the curvature singularity. The solution was a mathematical representation of physical space by a space of two asymptotically flat sheets (negative infinity to positive infinity) connected by a bridge or a Schwarzschild wormhole with a ‘throat’.

Now admittedly, this was not a traversable wormhole, for that we had to await the arrival of physicists John Wheeler in the 1950s and Kip Thorne in the 1980s. In 1987, at the encouragement of Carl Sagan for his novel “Contact” (later a feature film) Thorne and his colleague Michael Morris, were able to construct a metric to describe a spherically symmetric and static wormhole with a proper circumference with the co-ordinate decreasing from negative infinity to a minimum value where the throat was located and then increasing form the throat to positive infinity. This solution has the distinctive feature of being horizon-less. The Thorne and Morris paper titled "Wormholes in Spacetime and their use for Interstellar Travel: A Tool for Teaching General Relativity" (American Journal of Physics, Volume 56, issue 5, May 1988). This paper really helped to establish wormhole research as an exciting pursuit of academic enquiry.

Since then many papers have been published, an indeed astronomical surveys have been conducted to examine the deep stars in search of natural wormholes, none have yet been identified. It is important to remember the origin of a field, and although the Einstein-Rosen Bridge was not a traversable wormhole, and it wasn't the author’s intention to produce one, they did produce the first mathematical attempt at a wormhole solution, and they should be remembered for that. It just goes to show, that often in science, you can produce something quite unexpected.



Warping to the Stars

Warping to the Stars

Like many, I have been inspired and thrilled by the stories of Star Trek. The creation of Gene Rodenberry was a wonderful contribution to our society and culture. I recently came across an old book in the shop window of a store and purchased it straight away. The book was titled “The Making of Star Trek, The book on how to write for TV!”, by Stephen E.Whitfield and Gene Roddenberry. It was published by Ballantine books in 1968 – the same year that the Stanley Kubrick and Arthur C Clarke “2001: A Space Odyssey” came out. What with all this and Project Apollo happening, the late 1960s does seems to have been the year to have witnessed history. 

In this book, one finds the story of how Roddenberry tried to market his idea for a new type of television science fiction show.  It is clear from reading it that Roddenberry was very much concerned for humankind and in the spirit of Clarke’s positive optimism, he was trying to steer us down a different path. In this book we find out many wonderful things about the origins of Star Trek, including that the U.S.S Enterprise was originally called the U.S.S Yorktown and that Captain James T.Kirk was originally called Captain Robert T.April. He was described as being “mid-thirties, an unusually strong and colourful personality, the commander of the cruiser”.

The time period that Star Trek was said to be set was sometime between 1995 and 2995, close enough to our times for our continuing cast to be people like us, but far enough into the future for galaxy travel to be fully established. The Starship specifications were given as cruiser class, gross mass 190,000 tons, crew department 203 persons, propulsion drive space warp, and range 18 years at light year velocity, registry Earth United Spaceship. The nature of the mission was galactic exploration and investigation and the mission duration was around 5 years. Reading these words today, we see that what Roddenberry was doing was laying the foundations for many future visions of what Starships would be like.

What I found absolutely fascinating reading this book however, was the process by which they actually came up with the U.S.S Enterprise design. Roddenberry met with the art department and in the summer of 1964 the design of the Starship was finalised. The art directors included Pato Guzman and Matt Jefferies.

Roddenberry’s instructions to the team on how to design the U.S.S Enterprise were clear: “We’re a hundred and fifty or maybe two hundred years from now. Out in deep space, on the equivalent of a cruise-size spaceship. We don’t know what the motive power is, but I don’t want to see any trails or fire. No streaks of smoke, no jet intakes, rocket exhaust, or anything like that. We’re not going to Mars, or any of that sort of limited thing. It will be like a deep-space exploration vessel, operating throughout our galaxy. We’ll be going to stars and planets that nobody has named yet”. He then got up and, as he started for the door, turned and said, “I don’t care how you do it, but make it look like it’s got power”.

According to Jefferies, the Enterprise design was arrived at by a process of elimination and the design even involved the Sales department, production office and Harvey Lynn from the Rand Corporation. The various iterations produce many sheets of drawings – I wonder what happened to those treasures? The book shows some of the earlier concepts the team had come up with.

 

Today, many of the public take interstellar travel for granted, because Star Trek makes it look so easily with their warp drives and antimatter powered reactions. But for those of us who try to compute the problem of real Starship designs, we know the truth – that it is in fact extremely difficult. Whether you are sending a probe via fusion propulsion, laser driven sails or other means, the velocities, powers, energies are unreasonably high from the standpoint of today’s technology. But, it is the dream of travelling to other stars through programs like Star Trek which keeps our candles burning late into the night as we calculate away at the problems. In time, I am sure we will prevail.


There is an element of developing warp drive theory however that is usually neglected and I think it is now time to raise it – the implications to the Fermi Paradox. This is the calculation performed by the Italian physicists Enrico Fermi around 1950 that given the number of stars in the galaxy, their average distance, spectral type, age and how long it takes for a civilization to grow – intelligent extraterrestrials should be here by now, yet we don’t see any. Over the years there have been many proposed solutions to the Fermi paradox. In 2002 Stephen Webb published a collection of them in his book titled "If the Universe is Teeming with Aliens...where is Everybody? Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life".

Webb, Stephen, “If the Universe is Teeming with Aliens…Where is Everybody? Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life”, Paxis.One of the ways to address this is to ask if interstellar travel was even feasible in theory. Although the British Interplanetary Society, Project Daedalus proved that it was. If you can design on paper a machine like Daedalus at the outset of the space age, what could you do in two or three centuries from now? But even then travel times across the galaxy would be quite slow. The average distance between stars is around 5 light years, the Milky Way is 1,000 light years thick and 100,000 light years in diameter. Travelling at around ten percent of the speed of light the transit times for these distances would be 50 years, 10,000 years and 1 million years respectively. These are still quite long and the probability of encountering another intelligent species from one of the 100-400 billion stars in our galaxy may be low. But what if you have a warp drive?

The warp drive would permit arbitrarily large multiple equivalents of the speed of light to be surpassed, so that you could reach distances in the galaxy fairly quickly. Just like Project Daedalus had addressed whether interstellar travel was feasible as an attack on the Fermi Paradox problem, so the warp drive is yet another question – is arbitrarily large speeds possible, exceeding even the speed of light? If it was, then our neighbourhood should be crowded by alien equivalents of the first Vulcan mission that landed on Earth in the Star Trek Universe.

To my mind, if we can show in the laboratory that warp drive is feasible in theory as a proof of principle, and yet we don’t discover intelligent species outside of the Earth’s biosphere, of the many solutions to the Fermi paradox, perhaps there are only two remaining. The first would be some variation on the Zoo hypothesis, and the second is that we are indeed alone on this pale blue dot called Earth. Take your pick what sort of a Universe you would rather exist in?