The awesome 100 Year Starship (100YSS) initiative by DARPA and NASA proposes to send people to the stars by the year 2100 — a huge challenge that will require bold, visionary, out-of-the-box thinking. One possible solution is mind-uploading — what could give rise to highly versatile and resilient software-based astronauts and their e-crews. And at the same time, the development of the requisite technologies could result in important spinoffs in neuroscience, computer science, and longevity — perhaps even including indefinite life extension.
There are major challenges. "Using current propulsion technology, travel to a nearby star (such as our closest star system, Alpha Centauri, at 4.37 light years from the Sun, which also has a a planet with about the mass of the Earth orbiting it) would take close to 100,000 years," according to Icarus Interstellar, which has teamed with the Dorothy Jemison Foundation for Excellence and the Foundation for Enterprise Development to manage the project.
"To make the trip on timescales of a human lifetime, the rocket needs to travel much faster than current probes, at least 5% the speed of light. … It's actually physically impossible to do this using chemical rockets, since you'd need more fuel than exists in the known universe," Icarus Interstellar points out.
So the Icarus team has chosen a fusion-based propulsion design for Project Icarus, offering a million times more energy compared to chemical reactions. It would be evolved from their Daedalus design.
This propulsion technology is not yet well developed, and there are serious problems, such as the need for heavy neutron shields and risks of interstellar dust impacts, equivalent to small nuclear explosions on the craft's skin, as the Icarus team states.
Although Einstein's fundamental speed-of-light limit seems solid, ways to work around it were also proposed by physicists at the recent 100 Year Starship Symposium.