|MadSci Network: Astronomy|
Erin: That is an interesting question indeed. I like the fact that you are interested in creating a scenario of plausibility in your science fiction writing, but certainly don't let the accomplishments to date sway you from dreaming up completely new technologies and propulsion systems. I will tell you about a few ideas concerning interstellar travel and then I will tell you about semi-realistic technologies to approach that, and then some partially theoretical, approaches. First of all, one would have to know where the "Earth-like" planet to which you were travelling was. It matters to some point if it is located at a relatively close star like Alpha Centauri (4.5 light years), or a more distant star, such as Capella (In the constellation Taurus). One has to appreciate the massive distances involved in interstellar travel too. The distance to the nearest star (Not the Sun) is about five light years, which is orders of magnitude further than Pluto, which we have yet to send a spacecraft to. Assuming you sent a probe from Earth today, using standard methods of acceleration, getting it to a speed somewhere around 30,000 miles an hour, it would take about 150,000 years to reach the nearest star. So, obviously, liquid (rocket) propulsion is not going to be an effective, nor plausible means of stellar travel. As for the fuel supply, it is certainly not practical to carry the amounts of hydrogen and oxygen necessary to provide the propulsion, and at some point, it is rate limiting with regard to most of your power is necessary to accelerate your fuel supply. So, letís discuss other technologies. A technology that NASA is currently employing that is more efficient than rocket propulsion, but not suitable for short term duration flights is ion drive. The process is essentially like spraying charged gas atoms out the back of the craft like a rocket, but they provide very little push, about the force of a piece of paper on your hand, but the efficiency is much higher and the engines run continuously, so the effect is cumulative, so in theory it is plausible to carry large stocks of (Xenon) in this case, and presumably get to another solar system, perhaps an order of magnitude or two quicker than standard propulsion... There are two other technologies being explored for propulsion, and both of these utilize ejection of some matter, (energy) from the craft and utilize Newton's 3rd law to propel the craft. They are anti-matter drives and nuclear drives. A nuclear drive works much like an ion drive, except the material being ejected is neutrons (Which have no charge), and are produced in massive quantities from nuclear reactions. Another variation is the use of a nuclear drive as a small controlled nuclear explosion, with the force of the blast directed towards space. I know little of antimatter drives, which is why I included an URL for you to browse, but essentially antimatter (antiprotons) when they encounter matter (normal protons, hydrogen), they annihilate each other with the release of large amounts of energy, so antimatter is a very efficient(energy dense)method of storing fuel. There are certainly physical limits to the velocities one can attain with these physical drives, and to the limit of the technology is relativity. Simply put, that ubiquitous equation E=MC^2, means that as you go faster and faster (apply more energy E), the equation has to balance since C, the speed of light is constant, so the mass M has to increase... Basically, it says that as you approach the speed of light (Obviously really fast, about 3 x 10^8 meters per second) your mass approaches infinity. With this in mind, any of these technologies are limited in upper speed, by various things, and mostly my physics. To make them 'practical' a suspended animation of people involved would have to be undertaken, or a community could live on the spacecraft for multiple generations and the great...great...great... grandchildren could visit the surface of a planet in a new solar system. There are 'warp' technologies too, that people have conceived of, and there are lots of references that illustrate this much better than I and I will list them at the end, but the basic concept is that if you compress space-time in front of you and expand it behind you, you will travel these large distances in short periods of time relative to you... I do not have the space here to explain curved space, strings, or space time, but again, some of the references at the end of this should help. Essentially, this massive e-mail is telling you that we have only ourselves landed a human on another object a few times, and it was only 367,000 km away (The Moon). So, anything of which you can conceive is great, let your imagination race. Great question, there are tons of possibilities. -Matt- http://www.nasa.gov http://antimatter.phys.psu.edu/ The Physics Of Star Trek, Lawrence M. Krauss. A Brief History Of Time, Stephen Hawking. At Home In The Universe, Stuart Kauffman. The Edge Of The Unknown, James Trefil Gravity, George Gamow, Scientific American March 1961, pp.94 Time And The Space Traveller, George Allen & Unwin, (1971)
Try the links in the MadSci Library for more information on Astronomy.