Currently, all spacecraft use chemically propelled rockets for launch and most vehicles use such rockets for interplanetary travel. However, to reach Alpha Centauri, the nearest star system, using chemical rockets would take around 165,000 years. However, new technologies such as nuclear fusion rockets, interstellar ramjets, solar sail ships, and antimatter rockets offer the possibility of future interstellar travel.
Humans have yet to perfect nuclear fusion technology, but some are hopeful that in the next ten to twenty years, it will not only become commonplace, but also will be able to be used to propel spacecraft. The energy released by fusing light elements such as helium and deuterium has the potential to power a spacecraft to 10% of the speed of light.
The interstellar ramjet, which utilizes nuclear fusion, is an interesting concept first developed in 1960 by Robert W. Bussard. Instead of carrying fuel for travel, ramjets collect hydrogen atoms in space, fuse them, and expel the final products out the back. Although this concept is appealing because of the lack of need to carry fuel for long-distance journeys, there are certain technical issues associated with building such a spacecraft, including the difficulty in fusing interstellar hydrogen. This makes it unlikely that a ramjet will be built in the near future.
Solar sailships, on the other hand, have already been designed and some are in the process of being built. These sailships intend to use the energy emitted from the sun to propel the spacecraft forward. One solar sailship called Sunjammer was set to launch in 2014. NASA planned on using it to better detect oncoming solar flares. However, after Sunjammer’s contract with NASA was up, NASA pulled the plug due to lack of confidence that the Sunjammer would fulfill NASA's goals. The next date set by NASA to launch this project is around 2018.
Antimatter rockets are by far one of the more farfetched proposals of interstellar propulsion. Although humans have detected antimatter in particle detectors and when cosmic rays strike the atmosphere, there is still the issue of designing a system for storing it. Although antimatter might just be a science fiction dream, should humans achieve such a project, the energy released from antimatter rockets would be enough to theoretically accelerate a spacecraft to near the speed of light.
Sources:
http://earthsky.org/space/alpha-centauri-travel-time#conventional
http://www.forbes.com/sites/eliseackerman/2013/09/29/seven-sci-fi-scenarios-for-interstellar-space-travel-that-could-happen-in-this-century/3/
http://www.sunjammermission.com/AboutSunjammer
http://spacenews.com/42227nasa-nixes-sunjammer-mission-cites-integration-schedule-risk/
http://science.howstuffworks.com/antimatter.htm
http://www.space.com/23084-mars-exploration-nuclear-fusion-rocket.html
Sources:
http://earthsky.org/space/alpha-centauri-travel-time#conventional
http://www.forbes.com/sites/eliseackerman/2013/09/29/seven-sci-fi-scenarios-for-interstellar-space-travel-that-could-happen-in-this-century/3/
http://www.sunjammermission.com/AboutSunjammer
http://spacenews.com/42227nasa-nixes-sunjammer-mission-cites-integration-schedule-risk/
http://science.howstuffworks.com/antimatter.htm
http://www.space.com/23084-mars-exploration-nuclear-fusion-rocket.html
- Siqi Yang
