I love the whole "it's only 20 years if you travel at 20% of the speed of light!" part. It makes it sound so close. But you're not going to snap your fingers and jump right to 20% of the speed of light from one second to the next. That's 6,114,064.6 standard Earth g-forces! You'd be much better off having a slow, steady acceleration all the way there and a slow, steady acceleration all the way back. Unless I did the math wrong, you'd need to maintain about 0.38 m/s^2 (yeah, I rounded - I'm not the one sending the craft) the entire trip.
The interstellar space probe concept mission they are referencing is this one by Philip Lubin. The scheme has the 70 gigawatt launching lasers accelerating a tiny wafer thin probe to 20% c in 10 minutes, which is about 10,000 gees. A tiny wafer thin structure can handle that. And no, there is no slowing down. These things fly through the target system at 0.20 c, and keep on going.