Sound familiar? It should, although, technically, it is nonsense. A parsec is a distance, not a speed or time. Given the speed of the Millennium Falcon – making 0.5 past light speed – the imagined magnitude of this feat seems reasonable. Being able to travel 18 parsecs, about 60 light-years or 555 trillion kilometers in a time that isn’t greater than the age of the Earth, would make our foray into space much easier. Since there are no Millennium Falcons at our disposal, we must wait and further develop our technology.
One of the constraints on space travel is the time that astronauts have to spend exposed to all the nasty stuff in space. This includes debris, interstellar gas, cosmic radiation, and a whole host of other hazards. It would be really beneficial, to the astronauts and humanity as a whole, to be able to travel to our nearest planetary neighbours or distant stars, for that matter, in a reasonable amount of time. What is a reasonable amount of time, you ask? Well, how about 40 years? Imagine you’re in your 1970s space minivan for four decades with the kids, and then their kids are asking you “Are we there yet?”
So, why would it be beneficial? What do we have to gain by moving quickly through space? The thrill of adventure and the unknown – going boldly where no one has gone before – is an alluring prospect for travel in deep space. But this justification, by itself, is not a sufficient reason. Additional reasons include Earth’s growing industrial economies which will require new supplies of minerals and energy to sustain their growth. The solar system is full of resources, including metals and solar energy that can be used to power factories, offices, and homes. Efficient delivery of raw materials to factories on Earth requires that ships carrying this cargo can travel quickly to be able to keep up with increasing demand to sustain Earth’s growing population. Furthermore, colonies on other planets would also relieve the burden on Earth’s resources to sustain a huge population. This would help solve the problem of over-population, which is a real threat to the social order, sustainable growth, and environmental protection in some countries today.
Many theoretical methods of space propulsion take advantage of crazy space-bending equations to accelerate ships to near the speed of light. Better yet, the idea of wormholes would allow ships to instantaneously travel to any point in the universe, or any time. The requirements for these propulsion systems? Massive amounts of energy – the total solar output to date would not be enough – or “negative” energy, which has yet to be proven to exist.
But let’s be more practical here. What could we achieve? The propulsion systems currently available can be divided into passive and active systems. Passive systems include using either gravity or the solar wind to propel the craft out of the solar system. Active systems include using on-board fuel and rocket systems to propel the craft.
Active systems must carry their own weight, plus the weight of fuel, which, depending on the type of system employed, could add significant weight to the craft and reduce the thrust-to-weight ratio. However, these systems generally are more powerful (provide more instantaneous thrust to the vehicles themselves) and have much greater acceleration. This would make reaching the next star a less time-consuming journey. Conventional chemical rockets are probably the cheapest and least complicated system to build – just lots of fuel and go boom. However, there’s not much bang for your buck there, meaning that, even though alternative systems may be more complicated and expensive, they could potentially deliver more power for a longer period of time instead of just one big push. Also, rockets would be hard to refuel. There are no refueling stations on the way, so you would have to conserve your fuel and use it only when you need it. Systems such as ion or plasma propulsion make use of ionized or hot gases expelled at high speeds behind the ship. Even though the mass of fuel is small, conservation of momentum means that forces is directly delivered to a ship and can be sustained over a long period of time. However, these engines are currently small scale and only produce about 1/1000 of a Newton of thrust. For large ships travelling long distances, the thrust will have to be increased by several orders of magnitude before it could be installed.
Some passive systems rely on a slow steady push from a stream of charged particles from the sun, or the solar wind. The push doesn’t amount to much but, over time, the push results in the craft achieving a significant speed. It would be like blowing breaths at a sailboat on the other side of the lake and expecting it to move. In the absence of other forces it would move, but very slowly at first and then gradually build up speed over time. Other passive systems include rocketing the craft on a trajectory towards Jupiter or Saturn. The craft would enter into a hyperbolic orbit around the planet and then be ejected into interstellar space at velocities greater than the escape velocity of the sun. The Voyager probes, now 17 billion kilometers out, used this method to reach the outer solar system. Although the probes have been travelling for 40 years, they are still only about 1/4000th the distance to the nearest extra-solar star, Proxima Centauri. Still, these systems will take a longer time to achieve their maximum velocity and that will inevitably add time to the journey.
One practical system was called the “Orion” project by NASA. This project basically called for a spacecraft that could be scaled from something about the size of DWE, to something else about the size of campus. It relies on the detonation of nuclear devices behind the craft. The blast directed towards a steel pusher plate that transfers force, acts to ease the impulse to prevent injury to the crew, and limits the amount of radiation exposure to the rest of the ship. The predicted speeds approach 0.1 c, about 30,000 km/s. With these kinds of speeds it would be possible to reach the nearest star in 44 years. However, to reach the next cluster of stars with potentially habitable planets (found by the Kepler telescope to be about 100-1000 light-years from Earth) it still might take on the order of 1,000 to 10,000 years. This is still significant in terms of time and is an unrealistic scale to justify sending a ship into interstellar space.
It will be exciting to see what else engineers come up with in the next couple of years. Inevitably, our future is in space, and it will require propulsion systems better than we currently have. This is an exciting opportunity to advance scientific knowledge and apply it to a field of engineering that lies outside most of the public view. It is also an opportunity to fulfill the hopes of people on Earth of a better future by providing more resources to our economies, more living space, and, hopefully, a higher standard of living for everyone. The challenge of taking on this project and succeeding will also fulfill the dreams of people since the start of the space race, and inspire future generations of explorers to keep pushing the boundaries of human exploration.
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