And that's the rub. We evolved on Earth and life became an active part of shaping the planet. The early Earth would be toxic to most current life. Earth allowed life to take hold, and then life turned around and changed the Earth, a sort of symbiosis if you will. The odds of finding another planet out there where we could just step out of our ship and take a deep breath, bend down and smell the alien flowers, dig our fingernails into alien dirt, and hunt a local beast and roast it over an open fire to dine on are virtually nil.

The reason to find an Earth-like planet is because we want to know about E.T. We want to find the aliens, if there are any. We want to know how common life is, and how normal it is for intelligence to evolve. We want to see an example somewhat analogous to our own past - something that we can relate too. We want to answer some of the most fundamental questions of existence, in other words. We want more than one model to study.

If we ever actually live on Gliese 581c, it will be in artificial habitats. But is such a place a good choice? The moderate temperatures would make running a bio-dome cheaper, and liquid water is also handy. Then again, a planet of that size has a deep gravity well. Even Earth has a rather steep gravity well – getting material to and from the planet's surface is costly in terms of energy. Planets close to stars are also in a bad spot for the cosmic, never-ending, pool game, as comets and asteroids get sucked towards heavy sources of gravity. Earth has a history of violent collisions, but luckily, we have a heavy gravity vacuum in the outer Solar System called Jupiter that helps deflect many of these death-mountains.

This view assumes much. It assumes that future humans will use the same type of cost/benefit analyses that we do. Perhaps asteroid deflection will become standard practice and lift-vehicles so cheap that we don't care about the extra hassle to build colonies on actual planets, when asteroids and other high mineral/low gravity bodies would suffice. Further, it assumes that humans will reach the stars as they are now, in our present form.

I tend to doubt this. We can't imagine that just a single path of technology will develop. The science of biology will also advance, along with propulsion and such. Although this might sound like fiction to most reading this, I have no doubt that we'll be able to simulate the human mind within 100 years or so; Intel claims 50 based mostly on Moore's Law. Our brains are just machines, albeit very complex ones. There is no reason yet known for why we couldn't simulate a brain eventually, like we can simulate a wind-tunnel now. The laws of nature are the same in either case.

We may not have any real reason to keep flesh. Our bodies might become just avatars, replaceable and disposable. We could beam our minds to other bodies and even space probes. In cases like that, it wouldn't matter what the conditions on other planets and space bodies would be, or rather, it wouldn't be near the problem that it would be with our frail human bodies. We could take a “swim” in the oceans of Gliese 851c by being the brain of robotic submersibles. Further in the future, we could probably make some darn good bodies as well, bodies that let us feel the environment by passing sensations to our minds. In other words, we could feel those waters on our skin.

Science fiction-ish, yes, but not impossible or even implausible. Look back to what we were doing 200 years ago and keep in mind that the rate of change is itself accelerating.

Having said all of that, it is also quite feasible to reach the stars using mostly existing technology and envisioning that we humans will stay the flesh and blood short-lived delicate beings that we are right now. The only real hurdle is money. Once we can live in space, we can live at great distance from our Sun. In fact, we shouldn't just wait for breakthroughs. We should be spending massive amounts of money right now to learn to live independently of the Earth.

Nuclear pulse propulsion already seems quite feasible and is based on existing technology. The top speed for such vehicles is predicted to be around 10% light speed. It's so good in fact that it can be used to lift large vehicles right from the ground to space, rather than having to first assemble bigger craft in orbit and such, though we may choose the orbital route anyway to lower pollution. Ironically, it's a decades old technology and is, in its most simple form, very basic: you simply set off nuclear explosions under a pusher plate at the base of your rocket and up you go, faster and faster, accelerating like a normal rocket, except that the tanks of fuel don't burn out nearly as fast, since the fuel has far higher energy densities – more bang in a much smaller package. You keep going faster and faster and faster, analogous to the Energizer Bunny but for pushing-power instead of just electrical current.

We should have stayed on the Moon. A lunar base is a technical challenge, but in terms of actual technology, it's a no-brainier. We could take something like the space station modules, which already recycle water, clean and make air, keep a stable temp and so forth, land them on the Moon, and bury them in the Lunar soil for radiation protection. This would be an expensive massive effort, but entirely doable.

Lunar soil is 40% oxygen by weight, we just have to extract it. Power is a simple matter on the Moon – we could lay out fields and fields of solar panels. One side of the Moon always faces the sun, and there are no clouds to block the free energy. Solar power is expensive, but not at all beyond our tech or requiring something fancy from the mind of Greg Bear or Isaac Asimov. Water might be an issue. They think there are trace amounts of water on the Moon, hiding in the semi-permanent shadows in the larger craters and such. With existing recycling tech, there could be plenty to have a permanent city-sized settlement there, however. To get started, we would probably need to send up many landers loaded with water and other essentials, until an infrastructure is setup to mine the Moon and extract the existing water and oxygen. Long term, we could divert a comet and crash it on the moon and get as much water as we desire. The tech here would be no more difficult than what we would use to stop one from hitting us. If you can deflect something away, you can deflect something at you as well.

The water and minerals in the asteroid fields could easily fill Earth's oceans many times over. Speaking of asteroids, one large heavy asteroid, the kind made of iron and nickel and such, would be worth trillions of dollars in minerals and could singlehandedly change the economy of Earth, vastly affecting the markets. The Lunar gravity well is just 1/6^th of Earth's so doing anything space-esque from the moon is much cheaper, and eventually, the investment in the Moon will pay for itself.

Of course, many think that a cheaper first step, with a guarantee of water, is just to build a settlement on a near Earth asteroid...

Once we get good at mining asteroids and such, we can have self-sufficient space colonies. Reaching other stars then is just a matter of pushing such a colony with enough spare material towards another solar system. Gliese 851c is pretty far away, but other stars are within 40 years or so assuming the nuclear pulse propulsion designed in the late 1950s mentioned above. The colony would reach the next star system and exploit it for minerals, making more space colonies and in turn launching them to other star systems, and so forth. If the gaps become bigger, we simply launch bigger colony ships. With big enough ships, speed doesn't matter as much. Earth is, after all, just a very large colony ship that flies a fixed course around the Sun. Earth also has a finite amount of material – there's no magic here – it just has a heck of a lot of material (though far less than all of the asteroids and comets combined) that we already know how to get at.

There are of course always much more exotic and fantastical ideas out there which could allow us to travel even faster, and these really are further off in the future. Although these aren't required to reach the stars, they would of course make it much more convenient. Here is information about an anti-matter system, and here is information about the Bussard Ramjet. There are also far-out designs for true “Warp drives”, but these rely on exotic forms of energy that we can't yet, nor might we ever, be able to produce. The good news is of course that with a self-sufficient space colony, speed is no longer the essential ingredient. We could take our time, the scenic route.

Will we ever fly around in Bussard ramjets? Personally, I doubt it, but who knows? I do know that if we survive long enough, that zip around we will in some manner. We fly through the air, though we don't do it in vehicles which look like this. To a future human, our designs for a Bussard ramjet would probably look laughable – but that's not the point. In 1,000 years I expect humans to have colonized a decent chunk of the galaxy. If not, we'll most likely be extinct.

If we can put a man on the Moon, why can't we put a man on the moon? -- Larry Niven

The dinosaurs died because they didn't have a space program. -- Larry Niven

I don't think the human race will survive the next thousand years, unless we spread into space. There are too many accidents that can befall life on a single planet. But I'm an optimist. We will reach out to the stars. -- Stephen Hawking

Right now, we aren't doing much. We have a line of telescopes being designed specifically to study the atmospheres of extra-solar planets. This will allow us to pick targets without so much guesswork. We also have some quasi-specific plans to return to the Moon, though I doubt it will happen until another country challenges us directly for Lunar supremacy. We have a replacement for the Space Shuttle planned, which seems to be a simpler and cheaper system. I'm not holding my breath...

--

To summarize, assuming humans go to the stars in their current frail forms, something I personally doubt but something that is of course up for serious debate, speed isn't the ultimate problem. We already have solid, clear ways to achieve significant speeds, taking thousands of years off of the trips. While still long, between 40 and 100 years to the closest stars, these trips are entirely doable if we send cities/colony ships with plenty of extra material, such as small asteroids with hollows in the middle containing life-support habitats.

The real challenge is for humans to learn to “live off the land”, that land being space. To work in space, construct equipment in space, and mine raw materials in space. We can already make crude but capable space habitats, we just need to be able to supply them without going back and forth to mother Earth.

Once the first large ships reach the nearest star, they can either refuel and move on, or, leave some folk behind to establish a permanent presence in that new system, and so forth, star hopping as far as we choose to go. We would of course study “Earth like” planets, but probably wouldn't live on their surfaces permanently if we arrived in flesh-form, as colonies in space are cheaper and safer and since we'd gain nothing by doing so anyway (we couldn't eat the native “plants”, etc.).

And go we must, at least to other parts of our own solar system in the short term, or die we will.

--

Here are some quips about the Orion, a nuclear pulse propulsion rocket designed in 1958:

By using energetic nuclear power, Orion offered both high thrust and high specific impulse — the holy grail of spacecraft propulsion. It offered performance greater than the most advanced conventional or nuclear rocket engines now under study. Cheap interplanetary travel was the goal of the Orion Project. Its supporters felt that it had great potential for space travel, but it lost political approval because of concerns with fallout from its propulsion. The Partial Test Ban Treaty of 1963 is generally acknowledged to have ended the project.

The expense of the fissionable materials required was thought high, until Ted Taylor proved that with the right designs for explosives, the amount of fissionables used on launch was close to constant for every size of Orion from 2,000 tons to 8,000,000 tons. Smaller ships actually use more fissionables, because they cannot use fusion bombs. The launch cost for the largest Orions was 5 cents per pound (11 cent/kg) to Earth orbit in 1958 dollars. In 2005 dollars, the cost would be 32 cents/lb or 70 cents/kg. The larger bombs used more explosives to super-compress the fissionables, reducing fallout. The extra debris from the explosives also serves as additional propulsion mass.

The biggest design above is the "super" Orion design; at 8 million tons, it could easily be a city.[2] In interviews, the designers contemplated the large ship as a possible interstellar ark. This extreme design could be built with materials and techniques that could be obtained in 1958 or were anticipated to be available shortly after. The practical upper limit is likely to be higher with modern materials.

The Orion nuclear pulse rocket design has extremely high performance. Orion nuclear pulse rockets using nuclear fission type pulse units were originally intended for use on interplanetary space flights.

The top cruise velocity that can be achieved by a thermonuclear Orion starship is about 8% to 10% of the speed of light (0.08–0.1c).

	Web useless-knowledge.com