  
At our present level of technology, using the fastest spacecraft technology we currently posess, the trip to the nearest star would take tens of thousands of years. How do we deal with this problem? There are various methods that have been exhaustively researched, both by speculative authors, and by scientists interested in the future of science and engineering. One solution would be to create a giant starship that contains a self-sustaining ecosystem...a sort of 'bio-ark'. Enclosed by a giant torus or cylinder that is spun to maintain artificial weight, the ark would contain living plants, bodies of water, housing, schools, and whatever else the occupants would need for their journey. Clearly many generations of inhabitants would live out their lives and die before the ark reached its destination. This kind of spacecraft has been called a 'generation' ship. Although vast in scope, far greater in complexity than any engineering project ever undertaken, the technology exists to build and power such a spacecraft. This concept is explored in the Jennifer Lawrence and Chris Pratt movie 'Passengers'. The problem with such a design is that once the crew sets off on their journey, we never see them again! In fact, not even the original crew, or their children, or children's children, will live to witness the arrival. Is it possible to construct a ship that will move fast enough to get us there in the lifetime of the original crew? We can rule out travel faster than the speed of light...in principle, it may be possible, (physics rules out only reaching the speed of light itself, not speeds faster than light); but we have no idea how to achieve this, so for our purposes here we will ignore the possibility. Similarly, it would seem impossible to accelerate an ordinary spacecraft to speeds even approaching that high value. Relativistic physics makes it very clear that as objects such as our spacecraft accelerate to speeds approaching that of light (300,000 km per second), the spacecraft's mass will increase asymptotically towards infinity...requiring that the spacecraft carry more and more fuel as acceleration increases. One calculation puts the amount of fuel needed to accelerate to just one-tenth the speed of light as an amount equal to the mass of the moon...for a payload of about 100 kilograms! Hardly an effective solution! But there may be another way... 
We need not take the fuel with us...it's already out there!A very efficient means of powering a spacecraft would be to compress hydrogen atoms with a powerful magnetic field (or perhaps inundate them with a high-energy laser beam) in order to fuse them into helium. This process, known as nuclear fusion, is what powers the sun. One day soon such a technique will be used to provide power on earth. Interstellar space has been called a vacuum, but in actual fact, it isn't. It's almost a vacuum. The difference is crucial...the hydrogen (and other) atoms that exist thinly throughout space may be enough to provide fuel for a nuclear fusion spacecraft. All that is necessary is for some method of collecting the gas as the craft moves along. The collection device would have to be very large...perhaps as wide as 100 km. Some sort of generated magnetic field acting as a scoop would collect the hydrogen gas and funnel it back to the nuclear engine, where it would undergo fusion. The resulting thrust would be more than enough to accelerate our craft to a high fraction of the speed of light. (And a bonus...the magnetic field technology could also be used to deflect larger dust particles away from our path, as their apparent mass at relativistic speeds might obliterate the craft...but lets not worry about the details!) Sound fantastic? Well, such a craft has been designed, at least in principle. It has been called a 'Bussard Ramjet' after its inventor. Details of its operation can be gleaned from any of the speculative future history stories (science fiction) of Larry Niven...see the 'Resources' page. Other quite feasible solutions have also been proposed, that could be used alone or in combination with the ones above. For example, a 'light sail'...a kilometres-wide ultra-thin sail attached to the spacecraft, which would cause the craft to accelerate due to pressure from sunlight. The acceleration is small, but unlike a rocket where the propulsive force only lasts a short time, the force of sunlight is constant and unending. It is capable of producing considerable acceleration over time...and it's free! I worked out an example of this as an assignment in an astrophysics class in university. This idea would work! Another possibility is a craft which continuously detonates atomic or nuclear devices (bombs)...the pressure wave pushes you forward! This vehicle would need a large shield and some sort of damping device to cushion the shock and block the radiation from the passengers...but design studies have shown that it is feasible. These ideas are not just fanciful suppositions. They represent solid scientific research that has been underway for many decades. Moreover, they have generated ideas that you can explore by reading the works of many authors...who have taken these concepts and created whole worlds based on them. Check out the science fact and fiction references on our 'Resources' page! |