The biggest problem facing man's exploration of space, and traveling to even our closest planets like Mars, is the amount of time it takes. So any form of propulsion that makes those times shorter is very important, and interesting to NASA.
Space is daunting and the time it takes to travel anywhere makes it highly questionable when it comes to manned missions to places like Mars. Currently, it can take anywhere from 150 to 300 days for any unmanned mission to complete the trip from Earth to Mars, depending on orbital alignment at the time of launch.
However, some promising new research at the University of Washington has researchers theorizing that we could make the trip to Mars and back in 30 days, which would, needless to say, shave a lot of time off of a round trip to the planet thereby making it more feasible for manned missions.
The university is working on a fusion-powered spacecraft that uses a system they describe as a "unique manipulation of nuclear fusion". Researchers are pretty tight-lipped when it comes to any specific details about their propulsion system, but they have said that it involves "a type of plasma that is encased in its own magnetic field", which apparently can be compressed in order to create nuclear fusion.
So far, their research has proved to be so promising that NASA has offered a second round of funding so that they can continue to work on the propulsion system.