And Project Orion is old nuclear pulse tech. The current state of the art thought on that kind of thing is slighty less crude than dropping fission bombs behind a big shield.

I think that once a habitable planet is 99.9% confirmed instead of 90% confirmed, there will be an unprecedented international cooperation in order to build a probe that can get there at .1-.25c.

It's an interesting time to be a human.

Before I came here, I did my own brief (and likely inaccurate) calculations:

Distance to Gliese 581 g: 21 light years Speed of Helios 2 (fastest manmade object in space) = ~ 241350 km/h Time for Helos 2 to reach Gliese 581g ~= 93 907 years

I couldn't help but think of Carl Sagan's "Pale Blue Dot". 93 thousand years is an awful long time. I'm glad I'm wrong.

But the Helios probes aren't constantly accelerating.