I'm attempting to do a term paper about the above title. There are a lot of potential alternatives to chemical rocket launches in the works; some realistic, and some not very. My hope in creating this thread is to gain some insight into what exactly these alternatives are (I'm sure I've missed a couple), which ones are the most promising, and how far ahead in the future these methods might become reality. Answering questions like economic feasibility, commercial practicality, and comparisons concerning the technical reliability of these alternatives will be central to my paper, along with describing each method in basic, conceptual detail. Basically, I want to gain a simple understanding about where our current capabilities in these areas of engineering are going, if it makes any real sense to switch to something new, and which, if any, alternative methods could take the place of chemical space launches. Feel free to post links to interesting sources, or elaborate on whatever personal experience and knowledge you have about this topic. I'm all ears.