An invention is a unique device, method or process. It could be something completely new and never seen before or an improvement on an existing product. Often these technologies can be disruptive innovations which completely change the market place, taking the performance of a product onto a new paradigm of thought. The automobile or motor car for example, was an incremental technology changer, because it did not result in a major disruption to the market place which was dominated by the horse-drawn carriage. But once mass production of cars took off in the early 1900s and their performance involved significant reductions in journey times, the technology transitioned to a game-chaning innovation. This is an example of a technology that was not immediately disruptive, but with its introduction and further investment, it soon became one. It is what you might call, revolutionary. Those products which do not dramatically affect the market place are known as evolutionary, and they merely add incremental improvements to a technology over time.

One of the greatest inventors in history was the Italian Renaissance man Leonardo da Vinci who lived between 1452 and 1519. Among his many accomplishments were his many engineering innovations. This included designs for a bridge, diving suit, cannon, large cross bows tanks, submarine, and designs for various flying machines including a hang glider, parachute and something that resembles a helicopter. Leonardo clearly had some understanding for the basic laws of momentum, centripetal force, friction and the aerodynamics of aerofoils. He used an extensive knowledge of engineering, including pertaining to gears, pulleys, cantilevers and hydraulics. Despite all Leonardo’s genius, it would not have been possible to successfully construct some of the machines of his imagination, simply because the technology and physics knowledge did not yet exist. From the perspective of many people in his time, Leonardo’s inventions would have seemed fanciful and not something that would ever be a part of any plausible future. To the minds of us today, his inventions were prophetic, future looking, realistic and credible in principle. Opinions are relative when viewed through the lens of history.

Today, many people spend their time designing vessels what could someday travel to other stars. How will history view these attempts? We know that space travel is possible, and indeed we have sent spacecraft to the furthest reaches of our solar system. Many of the technological advances made today take us that little bit further, faster and sooner. They are evolutionary technologies (e.g. chemical propulsion) although some can now been seen as revolutionary (e.g. electric propulsion).

Today, eager minds, young and old, imagine what the future spacecraft will be like, the ones that we can definitely call revolutionary, and the ones we can especially call disruptive. Is it possible that we can conceive of “da Vinci machines” that will take us to the Stars in decades, years, months, weeks or even days? From all we have learned about the laws of physics and its application to technology, we can at least answer this question with a positive: Yes, it does appear possible at some point in the future.

The British Interplanetary Society Project Daedalus study of the 1970s was essentially a proof of existence theorem, to show that interstellar travel was feasible in theory. In general, many agree that the team succeeded in this aim. One of the key elements of the design was the need to carry Deuterium and Helium-3 fuel, and due to the scarcity of Helium-3 this necessitated mining the material from the gas giants. This was suggestive of the need for a solar system wide economy and so the first launch date was pushed out quite extensively. In order to build large Starships (Daedalus was approximately 53,000 tonnes) you need large space infrastructure in place and in particular cheap and reliable access to Earth Orbit. The Project Daedalus Study Group expected that this would plausibly come about between the years 2200-2250. Given that the Daedalus probe was to take around half a century to get to its stellar target of Barnard’s star, the first Starship would not be arriving at a distance star system until around the year 2300.  Can we do better?

When I initiated the Project Icarus study I placed a design constraint on the mission of mainly fusion based propulsion. Internal to the team this was interpreted to mean that approximately 80-90 percent of the thrust generation of the mission should come from fusion reactions, although the remainder could be augmented from alternative propulsion systems. This was done not because it was the view of the team that fusion was the best way, but mainly to facilitate a design constraint so that the problem would be tractable within a finite duration of the project. In addition, it was thought important to maintain continuity with the original Daedalus project, which was also fusion driven. Given the advances in science and technology over the last few decades what would we do differently?

One of the obvious goals for the design team is to shrink the mass. This includes the enormous 50,000 tonnes of fuel, 450 tonnes of payload, and 2220 tonnes structure mass. The team are looking at typical payload masses of around 150 tonnes and typical propellant masses of around 20,000-25,000 tonnes. Because Helium-3 raises obvious acquisition issues, the team are also looking at alternative reaction combinations such as Deuterium-Tritium, Deuterium-Deuterium, and even options like Proton-Boron. However the design turns out, it is likely that the Project Icarus design will have some resemblance to the original Project Daedalus Study but also have some marked differences. No need for that old vacuum tube electronic technology for example, although the need for an Artificial Intelligence based system is still thought to be high.

One of the clear distinguishing characteristics between the two projects (Daedalus and Icarus) is the need for deceleration. At the outset of Project Icarus the team had a discussion about projections for future deep space astronomical platforms. It was soon realised that by the time we actually launch a Starship, we will likely know where we are going and what is there, before we ignite the engine. The resolution of telescopes will be so good that we will be able to resolve atmospheric compositions and perhaps even detect orbiting Moons around the planets in the target system. There is unlikely to be any surprises, at least on a planetary scale. For this reason, in order to justify the cost and effort of the Starship endeavour, flying through the stellar system in a matter of days was seen to be inadequate and it was determined that atmospheric penetrators and the boots of atmospheric landers needed to be placed directly onto these most interesting of worlds. Hence for Project Icarus deceleration is the name of the game. To achieve this the team are looking at the use of Magnetic sail systems (MagSails), rearward deployed sail systems (Medusa Sails) and of course reverse engine thrust.

Nuclear fusion propulsion is just one of the methods for getting to the stars. The many others include antimatter or exotic solutions like space drives and warp drives. Some propose to go the way of propellantless solutions and to fly by the “wind” of the Sun using solar sails or converging the solar energy into laser powered systems using large Fresnel lenses. Who is to say which one of these concepts that we dream up will be the actual blue print for how the first interstellar missions are conducted? On the other hand, it may be the case that they are all form a part of our future, each performing their own role, optimised for their specific purpose, payload and destination. None of our efforts would have been wasted, it would have been time well spent preparing the way of the Starship for our future interstellar generations.

When Leonardo da Vinci considered flight, he didn’t just think of one machine, but he considered many methods, be it parachute, glider or helicopter. He observed that there were forces of nature, and although he did not understand by what rules they were governed, he set out to find ways to tame them and mimic nature for good use. One wonders how he would have approached the problem of designing a Starship if he existed in our times? Would he have focussed on only one method? No, the evidence is that he sought multiple solutions for a problem and it is likely that he would have been looking hard at ways to master the solar wind, tame the atom, or collide the anti-protons, to produce energy for the Starship. Although the Starships we design today may not appear ready for the existing markets and the technology they require not sufficiently mature, it is possible that we are in the position of Leonardo all those centuries ago, who conceived of machines that were centuries ahead of his time. In this respect, we are all then students of the Renaissance.

“When once you have tasted flight, you will forever walk the earth with your eyes turned skywards, for there you have been and there you will always long to return”.

Leonardo da Vinci