Even if we don't assume a basic science breakthrough like hyperspace, warp drive or time travel, we still need at least big engineering paradigm shifts to get to even "not laughable" concepts. Fun sci-fi premises though the previous answers are, they are basically laughable.

To go meta for a minute, the early history of space exploration was all waterfall planning. It was a miracle of OCD design that more things didn't go wrong.

But basic reliability theory tells you that architectural approach just won't work for the interstellar scale of engineering. If you don't know what reliability theory is, here's a kindergarten example: if 2 components each need to work for a system to work, and each has a 0.9 probability of working, then the probability of the series working is 0.9*0.9 = 0.81. With probability 0.18, one will fail. With probability 0.01 both will fail. The more things that have to go right for a system to work right, the more fragile the system becomes. Even if your component reliability is 99%, a critical path of about 70 pieces brings chain reliability below 50%.

This is why movies like Ocean's 11 or The Italian Job seem fundamentally unrealistic from an engineering point of view. This is why Rube Goldberg machines are funny: we intuitively recognize how delicate they are.

Every distant space colonization idea I've read about has such an absurdly long chain of things that have to go right for the whole thing to go right. Their reliability is terrible even on paper.

So my criticism is basically identical to Ian Malcolm's in Jurassic Park: there are far too many ways to go wrong.

You need system architectures that fix this problem: ways to build reliable systems out of unreliable pieces. There are two basic ways to do it:

1. Redundancy: build a lot of such things that try to make it work in parallel. Different architectures, many instances of each architecture etc. This is the lean startup model: make each experiment so cheap that you can "spray and pray"... if enough entrepreneurs are working on enough interesting problems, a few hits will create enough economic growth to make the whole sector as a whole turn a positive ROI. This is unfeasible for space stuff because there is no realistic way to bring the cost of each instance down to lean startup levels. But just as a note, NASA DID try what you might call "agile space" through the 90s.
2. Get there horizontally: the question makes it sound like this a single "mission." That's a poor way to think about it. Rather than building a single wobbly Jenga tower 2 million blocks high, you build a pyramid. By the time the top reaches 10 feet, the bottom will have spread out to be 100 sq ft. It is stable all the time. You keep the angle of the pyramid safe by building out horizontally as you try to raise its height. For space, "horizontal" may be a lot better. What do I mean by that? You completely colonize the moon and make the process of going back and forth as routine as a bus trip. Make it civilizational muscle memory. Done? Do the same for the whole solar system. Once the whole Solar System has shrunk from "impossibly scary" to "backyard" suddenly Alpha Centauri starts to look a lot more accessible.

One way to understand the distinction is this: vertical strategies attempt to plant a human civilizational "seed" somewhere else (for THAT, I just prefer transmitting the human genome by radio all over, along with some civilizational history, and hope some aliens are smart enough to do the rest).

Horizontal strategies will attempt to grow civilization itself, and envelop those target zones. First with an interplanetary Internet that then grows into an Interstellar Internet. Then it "thickens" into a materials/logistics supply chain. Finally, it is robust enough that we can travel along it.
The first step to "horizontal" grow-the-infrastructure strategies is already being considered: an Interplanetary Internet:

http://www.spaceref.com/news/vie...

And oh yeah, somewhere along the way, we will have to build stable clanking replicators:

http://en.wikipedia.org/wiki/Cla...

By the time the first humans get to Base Pluto, we should have one going there.

Hod Lipson at Cornell has gotten us started.

Back around 2003 when there were furious debates about whether the Moon was a meaningful stepping stone on the way to Mars, many old-school space technologists were furious that effort was being invested in going back to the Moon. I disagree with that program for other reasons, but the critics of the Moon as a stepping stone don't get this basic premise of horizontal engineering. The Moon was one delicate achievement in the 60s-70s. It needs to become a robust achievement before Mars can be meaningfully tackled. The "verticalists" would rather do one delicate Mars run to prove a point than build out a space-based civilization more slowly.

But all this is just happy speculation on my part. Basically, my doom-and-gloom prediction is that none of this has even the remotest chance of happening. We are going to fail at a much more basic challenge: keeping civilization functioning here on Earth. Collapsonomics looms.

For the record: my claim to credibility here is that my PhD (NASA sponsored) was partly about coordinating spacecraft formations that act as interferometric telescopes to find terrestrial exosolar planets. It feels kinda weird that I paid the rent for a few years doing something so surreal.

I almost ended up working at JPL on this sort of thing, but couldn't continue to suspend disbelief. The nice thing is, if I am wrong, I'll be dead before anyone finds out.