Well, if not impossible, then extremely difficult, expensive and time-consuming. Rocket boffins at the 44th Joint Propulsion Conference in Hartford, Connecticut believe that it would be nearly impossible to reach the stars within a human lifetime, as reported in Wired:
The major problem is that propulsion — shooting mass backwards to go forwards — requires large amounts of both time and fuel
…
Even the most theoretically efficient type of propulsion, an imaginary engine powered by antimatter, would still require decades to reach Alpha Centauri, according to Robert Frisbee, group leader in the Advanced Propulsion Technology Group within NASA’s Jet Propulsion Laboratory.
And then there’s the issue of fuel. It would take at least the current energy output of the entire world to send a probe to the nearest star, according to Brice N. Cassenti, an associate professor with the Department of Engineering and Science at Rensselaer Polytechnic Institute. That’s a generous figure: More likely, Cassenti says, it would be as much as 100 times that.
It’s tempting to cite Clarke’s First Law and point out the number of times in history when esteemed scientists have claimed that something is impossible until it is actually accomplished.
However what is really being said by Professors Cassenti et al is that travelling to nearby stars is merely massively expensive in terms of time and energy, to the point of being infeasible.
There are a couple of points I can think of that might be relevant to the discussion of the possibility of interstellar space travel:
1: Increased longevity – if people live longer they may change their perceptions as to what constitutes a worthwhile scientific endeavour. Waiting several decades before we receive any useful scientific information about other solar systems may be unacceptable now, but if engineered negligible senescence is achieved then that perspective might change.
2: Increased wealth – as the global economy increases in size and people (hopefully) become richer the vast amounts of investment needed to travel between the stars will become less of a barrier.
3: As Professor Cassenti says: “We just can’t extract the resources from the Earth … They just don’t exist. We would need to mine the outer planets.” Presumably after exploring and developing the solar system we would be in a better position to launch an interstellar mission – a case of learning to walk before we run.
4: If you were aiming for a one-way unmanned interstellar mission then it is likely that the ongoing miniaturisation of space technology, as exemplified by developments in micro-spacecraft described here, might help reduce the mass of any interstellar probe to the point that it becomes a cheaper prospect.
Dr Robert Frisbee describes what might be entailed by an interstellar spacecraft:
Frisbee’s design calls for a long, needle-like spaceship with each component stacked in line to keep radiation from the engines from harming sensitive equipment or people.
At the rocket end, a large superconducting magnet would direct the stream of particles created by annihilating hydrogen and antihydrogen. A regular nozzle could not be used, even if made of exotic materials, because it could not withstand exposure to the high-energy particles, Frisbee said. A heavy shield would protect the rest of the ship from the radiation produced by the reaction.
So the general conclusion seems to be that interstellar travel is hideously expensive, time-consuming and technically challenging, but hopefully just short of being impossible, as Dr Frisbee points out:
“It’s always science fiction until someone goes out and does it”
I remain of the same opinion – as soon as earth itself has become a somewhat despicable backwater, when the top asteroids and the jovian system have been thoroughly explored, when the moon and mars are losing their frontier appeal and become stifling and suburbanite, when venus is looked into as a topic of terraforming, when probes are moving through the outer planets atmospheres and among the KBO’s and into the cometary halo, when you can see on the earth’s night sky the moving dots of solar-orbiting solarplexes and habitat clusters – then the first slow travels to the nearest stars may start. And they wont be intentional – habitats may slowly spiral outward over decades and consecutively drift beyond orbits into long cold spirals out into the thousands and eventually ten thousands of AE hopping from comet to comet, mining the odd interstellar plutoid. These voyages could well take thousands of years, and be totally dissimilar to the rushed phallic penetration of the void by “thin needle like” vessels. Moving in the solar system is epic. Moving through interstellar space is of a completely different order we have no metaphors for as a collective humanity.
And then to think most SF writers in the 1950s were predicting colonies on alpha centauri in the early 20th century. For me the solar system is enough fun and adventure to last me at least a thousand years.
What if they extend human lifetime.
If we were to send frozen embryos, then a human lifetime become irrelevant, mass is very small
and hence speeds can be high without bankrupting Earth’s energy account. Also, travel times don’t necessarily have to be in 40 or 60 years. They can be about 2,000 years. The purpose of such a mission would be to “purchase insurance” for humanity against the possibility of extinction from self-replicating technology.
I have done a fairly extensive write-up of such a mission. It can be seen and discussed at:
http://www.peregrinus-interstellar.net/index.php?option=com_kunena&Itemid=85&func=showcat&catid=9