Is there any realistic prospect of interstellar travel on the horizon before I grow old and die?

NO
not by human hand

The technology is within our grasp to get there, surviving the harsh environment of space is another story.

why would anyone want to travel to a star?? You couldn't live there.

why would anyone want to travel to a star?? You couldn't live there.
not on the star itself but you could on one of it's solid planets if it has any.

Is it possible, yes.

Is it probable, no.

We're up around 1/10,000 the speed of light for an unmanned craft. We can barely keep a manned space station in low Earth orbit viable even with resupply every month or so. 'Perhaps' a man on Mars by the last quarter of this century.

That's depressing news - unless I live a lot longer.

Maybe if we could invent a spaceship with an on-board community, that is not afraid to live all their lives traveling to another star, with no hope of comming back or even getting to the star. Thats why I say "cummunity", because there would have to be generations in the spaceship in order to achieve this.

just randomly speaking here

Maybe if we could invent a spaceship with an on-board community, that is not afraid to live all their lives traveling to another star, with no hope of comming back or even getting to the star. Thats why I say "cummunity", because there would have to be generations in the spaceship in order to achieve this.

just randomly speaking here

Good idea. However, one of the biggest problems of long term space travel is long term exposure to radiation for humans. The development of the craft would have to protect all aboard from this harsh environment yet still unto itself, not harm those aboard from the materials required for such protection.

Is there any realistic prospect of interstellar travel on the horizon before I grow old and die?How old are you? If you're a teenager like so many of our members, and if you dodge the major causes of death during your youth (road accidents are in the top three everywhere, even in Africa), you have a very good chance of living almost to the end of this century, and a not insignificant chance of seeing the next one.

As others have pointed out, the technology to launch an interstellar ship is within our grasp. However, as has been inferred, that ship, powered by that technology, will take a couple of millennia to reach the nearest star.

So we have three choices:Send an unmanned probe. Even with the lightspeed lag, we can still exchange telemetry with it to receive any interesting data it gathers along the way and to alter its commands. When it finally gets close to the next star it will send back some really nice close-up shots to our distant descendants. It will never take more than a couple of years for a radio message to reach us. This is an attractive choice because it is far cheaper and safer than a manned voyage. But it will be difficult to rouse the interest of the taxpaying public to fund something they won't live to see to fruition; these are the people who don't even care about the heat wave they're bequeathing to their own great-grandchildren. Still, it could easily be funded as a vanity project out of pocket change by Bill Gates or even a far less multi- millionaire. Send a generation starship. Hard sci-fi writers have thought this one to death. It will require a crew of several hundred people and it will need to be a genuine city with all the resources and culture of a city, to ensure that when their 400th-generation descendants get there they will still be civilized, high-tech modern humans. That means it will be collossal, something built in orbit probably by hollowing out an asteroid. The materials and the great gobs of fuel will require great gobs of money, a project that only one of the largest governments could tackle. Remaining so close to home will allow a large bandwidth of communication despite the lightspeed lag, so that will help maintain both our interest, and their feeling of still being Earthmen. Unfortunately when they arrive the odds are really small that the star will have a planet on which they can establish a colony, even with bubble cities. So volunteers for this mission will be real one-percenters, people who just want to get the hell off of this planet, the people who 200 years ago would have set out for the Klondike. Those people aren't the kind who build smoothly running communities. This desciption contains a plethora of reasons why this choice won't be the one taken. Do nothing. The payoff from the first two choices is minimal, and so long-term that it will be hard to get anyone but Mr. Bannon and a few others like him to vote for the project. Technology will improve. Without hoping for sci-fi to become real and yield a Warp Drive, Star Gate or Worm Hole, even within the limits of Einsteinian physics we should be able to develop ships that can travel faster than the one we could build today. Somewhere on SciForums I either did the math or saw it done, and it's conceivable that using the principles we've already mastered, we could get a spacecraft to Alpha Centauri within John's lifetime, assuming he's nowhere near my age. Powered by a Bussard ramjet, a moon-sized solar sail, or something like that which now only exists in sci-fi stories but the science is valid. However, I still don't see any way that it could be manned. That would just make it too frelling big for anybody to come up with the funding. Whatever it is, it would pass the primitive rocket we launched in 2007 like it was standing still, making anyone who paid for that one feel a little silly.There's something else to be said for waiting: Many things in the universe provide a lot more joy as dreams than as reality. There may very well be life out there somewhere, even intelligent life, but there's no reason to expect it to be nearby. How are we going to feel if we've explored an ever-wider assortment of the nearest stars, and we find that there's nothing there? We all know in the rational side of our minds that this is extreeeeeemely likely.

Now that would truly be a disappointment of cosmic proportions. Frankly I'm not sure I want to be around to experience it. :( Fortunately, since I'll be lucky to live another 25 years, I won't have to worry about that. :)

What else are you going to explore? Frankly, I am probably closer to your age than a teenager's.

There's something else to be said for waiting: Many things in the universe provide a lot more joy as dreams than as reality. There may very well be life out there.

letts ad a 4th option
You already stated that sending a probe is cheaper then a mannend mission,
how abouth we build a verry good space telescope capable to not only detect planets but to also fotograph their surface I doubt we will ever be able to make one big enough to read the small letters of the centurion newspaper but we could make one good enough to tell how much % is covered in water and if there seems to be vegetation, rising Co2 levels artificial gasses etc.

somewhere, even intelligent life, but there's no reason to expect it to be nearby

well maybe not as far as you would think neanderthales where pretty intiligent changes are if aliens stay out humanity will get bored and revive them a intiligent species like most proberly their going to terraform mars before they colonise a other planet that already has living conditions.

you can do it astrally. it's hard to fly to another star with a spaceship but in a few hundred years it's possible. don't worry about dying from old age, you'll just be reborn.

It's simple, all humans alive will become one, they can then build starships and move throughout the galaxy, oh wait we've got women nevermind :P

It's simple, all humans alive will become one, they can then build starships and move throughout the galaxy, oh wait we've got women nevermind :P

huh?

There are many theories about over coming limtations of velocity but the space program has begun a decent pattern that likely will last for the next 10 to 15 years.

The only hope for a renewed space program lies now in the corporate sector.

There's something else to be said for waiting: Many things in the universe provide a lot more joy as dreams than as reality. There may very well be life out there somewhere, even intelligent life, but there's no reason to expect it to be nearby. How are we going to feel if we've explored an ever-wider assortment of the nearest stars, and we find that there's nothing there? We all know in the rational side of our minds that this is extreeeeeemely likely.

Or how about this, we get lucky and find intellegent life on alpha centauri. We send our little blinking lite probe over to establish communications; and the xenophobic monstrosities that live there blow it out of the sky and declare jihad on our asses. They capture one of our ships, deduce the location of earth, and send hypervelocity missles down on all population centers.

Or, as you said, all nearby stars may be deserted. Perhaps we could soup up our radio telescopes to the point they could pick up normal TV/radio broadcasts from nearby stars? As it stands they can't.

Is there any realistic prospect of interstellar travel on the horizon before I grow old and die?

First you have to kill off all the "debunkers" who keep labeling productive lines of research as "pseudoscience." Then the progress of science will accelerate and we will have star travel in a reasonable time.

Or how about this, we get lucky and find intellegent life on alpha centauri. We send our little blinking lite probe over to establish communications; and the xenophobic monstrosities that live there blow it out of the sky and declare jihad on our asses. They capture one of our ships, deduce the location of earth, and send hypervelocity missles down on all population centers.A civilization that advanced will have discovered electromagnetic communication technology way, way more than two years ago, so we will have already been picking up their radio waves across the short distance. The whole reason for SETI is that we haven't intercepted any radio waves from planets orbiting stars close enough to us that they would have been easily detected.

There could be a civilization there that has advanced to where ours was as recently as 200 years ago. But if they haven't yet developed electronics, they're not going anywhere. If our best scientists had discovered an alien starship in 1807, figured out a little of the physics, used it to design an entire new toolset, learned how to use that to decipher some more of the physics, applied that new physics to the design of even more advanced tools, etc. for at least ten iterations of incremental reverse engineering until they really understood how the thing worked, how many years would that have taken? And how many more before they could build one of their own? Meanwhile the aliens are improving their own technology so the weapons we develop using their obsolete stuff will seem pretty primitive and easy to intercept.

An advanced technology will have already betrayed its existence to us. A more primitive one won't be able to do us much damage. I think that particular fear is groundless.

An advanced technology will have already betrayed its existence to us. A more primitive one won't be able to do us much damage. I think that particular fear is groundless.
Sure, sure. Keep saying that. Until you find yourself hip deep in alien kinetic weapons.

But seriously, it may well be that the period of heavy emanations of radio and TV signals is brief. As we move towards cable and internet based methods of mass communication; our emanations will no doubt decrease. In a hundred years, who knows? This pattern may be common.

Our own prescrambled digital transmissions look like noise. Even when you can detect the framing the rest looks like garble.

You would think that there would always be commercial broadcasting and amateur radio in the bands where we see them on Earth. If it were possible for our radiotelescopes to sort out nonterrestrial signals around 100 MHz, for example, I believe that we're much more likely to get strong, recognizable voice signals. We're simply not listening on bands that Earth uses that way.

But seriously, it may well be that the period of heavy emanations of radio and TV signals is brief. As we move towards cable and internet based methods of mass communication; our emanations will no doubt decrease. In a hundred years, who knows? This pattern may be common.If their civilization is advanced enough to be able to come and conquer us, then surely they already have populations living on more than one planet. They have to be using wireless communication.Our own prescrambled digital transmissions look like noise. Even when you can detect the framing the rest looks like garble.But the framing is all anybody needs to know that we're here.You would think that there would always be commercial broadcasting and amateur radio in the bands where we see them on Earth. If it were possible for our radiotelescopes to sort out nonterrestrial signals around 100 MHz, for example, I believe that we're much more likely to get strong, recognizable voice signals. We're simply not listening on bands that Earth uses that way.All those resources going into SETI and they're not looking for somebody else's "I Love Lucy"?

It just seems to me that any civilization which is A. advanced enough to do us harm, and B. close enough to come over here and do it, will already know we're here. We've been broadcasting radio signals for a century, so that means they've covered a hundred-LY sphere within this galaxy. Star Trek makes it seem like you have to be practically in orbit around somebody else's planet before you can detect their radio emissions. Surely those other guys have SETI programs too!

On a vaguely related note, I remember the first Robert L. Forward story I read. Intelligent life had evolved on a neutron star, and because of the physics they were microscopic and their metabolic rate was something like a billion times faster than ours. We arrived in their neighborhood during their stone age, and they perceived our EM emissions as flashes of light. They responded by "lighting a fire" and using a blanket to send flashes of light back at us, sort of like smoke signals. Our scientists went crazy when they analyzed the signal and discovered that the frequency was irregular and each individual pulse was a mess that looked hand-made. Of course while we were sitting there looking, their species went through a few hundred generations, developed civilization and space travel, largely motivated by the knowledge that we were out there.

Two things need to happen before we even contemplate intersellar operations...

a.) Much cheaper means of bringing bulk cargo and people to orbit.
b.) Much better power sources for spacecraft.

If we find a method for launch that can dramatically improve on chemical propulsion systems or, perhaps more radically, do away with chemical propulsion altogether, access to space would ideally be cheaper. This would mean that whatever goes up no longer needs to be ultra-high-tech in construction, cheaper, bulkier, more robust parts can be sent up. If we can develop better power plants for intrasolar travel (either by not being afraid of fission reactors or developing fusion-based systems), we could utilize more economical propulsion methods that drastically minimize travel time between planets. These systems may be able to utilize constant-thrust trajectories that can accomplish such trip times as less than 24 hours to get from earth's surface to the moon's, a week to get to mars, a few weeks to get to jupiter or saturn and their moons.

I can't help but think that solving these two problems might make spaceflight feasable enough that SOME economic gain may come from spaceflight, driving such developements as maybe interstellar travel.

Man on alpha-centauri in this century? No way, not without another space-race, and it'd have to be a fast-paced one at that. Like if earth was due to just suddenly blow up in 2099 or something.

Disclaimer: I'm just a dreaming aerospace-engineering student with no industry experience, so I might be thinking way too optimistically :D

I would think that another type of math and engineering will be needed in order to travel to another solar system. The current scientific views seem to say that we won't be able to travel through our galaxy but if another genius like Einstien comes along and changes the way we look at math than anything could be possible at anytime. We can still use telescopes to find other planets that could sustain life for the time being so hen the time is right we will have a destination to travel to.

Sure I believe we'll see it happen before the death part interplays. There's steps to reaching the stars the first step is free energy. And I think we'll see that soon, at least in another decade. After the first step is done anything is possible.
Well almost anything.

Much cheaper means of bringing bulk cargo and people to orbit.I'm a big fan of the Space Elevator. "Hard" sci-fi writers--real scientists who try to make their fiction plausible--seem to be telling us that this idea is practical. We might be able to start planning the project right now without any advances in science and engineering. The biggest problem is undoubtedly security: How can we protect a project that large, with such a huge, international staff, from the next gaggle of religious wackos? And of course the second problem is economic. There is still a huge contingent of humanity who don't want us "wasting" resources on space flight. Perhaps if we give them all jobs building the elevator they'll shut up. I'm sure most of them would at least be qualified to clean the latrines or even run the commissary. :)Much better power sources for spacecraft.How much nuclear fuel would a craft have to carry in order to maintain one-gee acceleration for half the trip and one-gee deceleration for the other half? That would get a ship to Alpha Centauri within the crew's working lifetime, and--without doing the math--maybe even home again. Alternately, what fraction of c must a ship attain before it starts sucking up enough interstellar hydrogen to fire up a Bussard ramjet? Would that reduce the size of the nuclear fuel tank to something manageable and get the ship there while the crew is still alive?I can't help but think that solving these two problems might make spaceflight feasable enough that SOME economic gain may come from spaceflight, driving such developments as maybe interstellar travel.It's difficult to envision the economic gain from spaceflight. People want an ROI in their own lifetime and Americans want it in this fiscal quarter. Within that time frame we can't bring back exotic cultural artifacts and solutions to our philosophical questions from the nearest civilized planet, much less send even the wealthiest vacationers to their beach resorts. We probably can't even bring back animal and plant life that quickly from the nearest planet that has it to create new medicines or just introduce more lovable invasive species to our gardens and waterways. We can't even start a viable, self-supporting colony on the nearest uninhabited planet with a vaguely compatible environment, which would be Mars. Don't even think about the cost-effectiveness of shipping minerals home, even if we find fifty-carat tsavorites lying on the ground on Titan.Man on alpha-centauri in this century? No way, not without another space-race, and it'd have to be a fast-paced one at that. Like if earth was due to just suddenly blow up in 2099 or something.Earth is destined to lose a frighteningly large part of its most heavily developed real estate sometime around 2099 due to a rise in sea level, and we can't even get people out of their SUVs. The best we can do is hold a huge multinational party with a lot of popular entertainers, and the most influential celebrity we can get to host it is Al Gore.Disclaimer: I'm just a dreaming aerospace-engineering student with no industry experience, so I might be thinking way too optimisticallyI don't think industry is your problem, it's sociology. :)I would think that another type of math and engineering will be needed in order to travel to another solar system. The current scientific views seem to say that we won't be able to travel through our galaxy but if another genius like Einstien comes along and changes the way we look at math than anything could be possible at anytime.The 19th century was the century of chemistry. Nothing we've learned about chemistry since then has really turned science upside down. Similarly, the 20th century was the century of physics. It's not looking like string theory and electrons communicating over long distances and all the next generation of discoveries are going to turn physics upside down like subatomic particles, relativity and the Heisenberg Principle did. People who make it their business to think about such things tell us that this will be the century of biology and that we'll probably have to go to the stars with the physics we've got. Einstein didn't change the way we looked at physics (not math), so much as he developed a theory that explained puzzling new observed data. Where's the puzzling new observed data to inspire the next quantum leap--or Quantum Theory? It's all in biology. Obviously they can all be wrong. :)Sure I believe we'll see it happen before the death part interplays. There's steps to reaching the stars the first step is free energy. And I think we'll see that soon, at least in another decade. After the first step is done anything is possible. Well almost anything.Free energy in ten years? Don't tell that to the SUV owners! Don't forget that every time we think we've found an inexhaustible new supply of something we simply increase our consumption of it by several orders of magnitude until we prove that it was finite after all. Land to expand into, fossil fuels, oceans to fish, places to dump trash. Even utopianist Gene Roddenberry acknowledged this when Captain Picard discovered that "hyperspace" is not an inexhaustible resource.

I'm a big fan of the Space Elevator. "Hard" sci-fi writers--real scientists who try to make their fiction plausible--seem to be telling us that this idea is practical. We might be able to start planning the project right now without any advances in science and engineering. The biggest problem is undoubtedly security: How can we protect a project that large, with such a huge, international staff, from the next gaggle of religious wackos?

You know, I've given this thought, and it makes me wonder just how big a spool 30,000 miles of nano-tube cable really is. Would it fit onto one rocket? Ten? A thousand? If a space elevator could be made with very few rockets, then perhaps rebuilding an elevator after some kind of attack would be fairly straightforward and cheap? Just put the rockets up there, latch one end of the cable to the rock that needs to be at geosync orbit, and dangle the new earth-bound end back down the the ground to be captured and locked back in place. Seems pretty straightforward, but who knows, maybe it will be so vulnerable like this that they can't get cargo off the ground before the cable succumbs to micro meteorites, eco-terrorists with planes, etc. etc.

How much nuclear fuel would a craft have to carry in order to maintain one-gee acceleration for half the trip and one-gee deceleration for the other half? That would get a ship to Alpha Centauri within the crew's working lifetime, and--without doing the math--maybe even home again.

You know, I'm pretty sure that even with travel between planets in this solar system, constant 1-gee trips like this arn't possible using nuclear reactors, but I might be wrong there. To do that between stars might take the use of antimatter. I read a concept for such a space ship on orionsarm.com where the ship needed not picograms, not grams, but TONS of antimatter. It also used a big piece of ice on the front as a micro-meteorite shield. What I guess would most likely happen is we send a probe that can use nuclear power or a small quantity of antimatter to nudge it on a course to a nearby star with a trip time in... perhaps a hundred years? But then again, the probe would have reliability issues, it might not work after that much time drifting in a cold, hard vacuum subject to background radiation and the inevitable impacts from little, fast-moving things.

Don't forget that every time we think we've found an inexhaustible new supply of something we simply increase our consumption of it by several orders of magnitude until we prove that it was finite after all. Land to expand into, fossil fuels, oceans to fish, places to dump trash. Even utopianist Gene Roddenberry acknowledged this when Captain Picard discovered that "hyperspace" is not an inexhaustible resource.

Thought this was funny, because the first cars were not intended to solve an energy problem, they were called horse-less carriages for a reason. Horses shit! Everywhere! They need to be cleaned, they need stalls, they need their droppings picked off the street to prevent disease spreading, etc. etc. But the car, put a fuel into it, and let it run, you can drive the hell out of it without killing something, and it leaves no disease-spreading substance in the middle of cities. Ironically, cars were seen as an environmental SOLUTION! How times have changed... I know that's off topic, but I just thought it was interesting.

Thought this was funny, because the first cars were not intended to solve an energy problem, they were called horse-less carriages for a reason. Horses shit! Everywhere! They need to be cleaned, they need stalls, they need their droppings picked off the street to prevent disease spreading, etc. etc. But the car, put a fuel into it, and let it run, you can drive the hell out of it without killing something, and it leaves no disease-spreading substance in the middle of cities. Ironically, cars were seen as an environmental SOLUTION! How times have changed... I know that's off topic, but I just thought it was interesting.Well it is on topic because it shows that when we first dabble in a promising new technology there is often a down side that we just can't see. Horseless carriages were not even envisioned as traveling faster than horses, whose maximum utility speed I suppose is at best 7mph (12kph). At least one U.S. jurisdiction, 100 years ago, had an ordinance that every horseless carriage had to be preceded by a man on foot carrying a lantern.

Is there any realistic prospect of interstellar travel on the horizon before I grow old and die?

No , sorry John .... that is not possible .....

The closest star to the sun is Proxima Centauri ( in Alpha Centauri) 4.225 light years away = 1.295 parsec (PC) which is the lenght unit used in astronomy ....

Voyager 1 used 27 years ( september 2004 ) to travel 4,6 x 10 in minus 4 PC ..... which means it will take thousands and thousands and thousands ....please go on ........and thousands of years to reach Proxima Centauri ...........

Studies of health of astronauts indicate that cosmic radiation causes :
Cataract of your eyes
Cancer/leukemia
Death of brain cells (which do not regenerate) = demented astronauts in space .....:p

Lack of gravity will cause loss of musclemass ( astronauts -who were in space for a long period - had to be carried !! away from their landing shuttle on earth )
Lack of gravity will cause loss of bone mass (osteoporosis) .........

I´m sorry John ........ just NOT possible .....:( :m:

Another dark horse , is the expanding universe ( Hubble´s law ) , saying that the stars of the universe are RACING AWAY from each other ....making the distance between stars greater and greater .........

The closest star to the sun is Proxima Centauri ( in Alpha Centauri) 4.225 light years away = 1.295 parsec (PC). Voyager 1 used 27 years to travel 4.6x10^-4 PC, which means it will take thousands and thousands and thousands and thousands of years to reach Proxima Centauri.Just about eleven thousand, to be precise. But no one has answered my earlier question. How much nuclear fuel would be required to accelerate constantly at one gee during the first half of the trip, then decelerate during the second half? That would make the trip several orders of magnitude faster than Voyager and I think it would shorten it to fit into a single lifetime.Studies of health of astronauts indicate that cosmic radiation causes: Cataracts of your eyes, Cancer/leukemia, Death of brain cells (which do not regenerate)Even if they did regenerate their contents will be lost. Clearly an interstellar ship will need to be far more massive than the orbital craft we're accustomed to. The whole thing needs the kind of shielding you'd put around a nuclear reactor--especially since it would seem to need a nuclear reactor as a power source anyway. Even if it doesn't have to be a city-sized generation starship in which an entire stand-alone culture can fluorish for millennia, it still has to be big enough for the crew to endure a few decades on board. Private quarters, a gym, a hydroponic garden, etc. Shielding from cosmic rays is just one more of the engineering requirements for the project. Obviously this ship will be built in orbit and never land anywhere.Lack of gravity will cause loss of musclemass ( astronauts -who were in space for a long period - had to be carried !! away from their landing shuttle on earth ) Lack of gravity will cause loss of bone mass (osteoporosis).Thus my stipulation of constant one-gee acceleration. The other "hard" sci-fi way to resolve this (i.e., without inventing artificial gravity) is to spin the ship and use centrifugal force as gravity. This suggests building the ship as a ring instead of the usual torpedo-shaped rocket, so people won't get dizzy from their heads and feet spinning at greatly different speeds. We don't even notice it on our spinning "craft" so it's obviously practical.I´m sorry John,just NOT possibleSo do you think there's an energy technology that can keep the ship accelerating for years after it reaches escape velocity? If so, how long do you think it would take to build that ship? Including the space elevator needed to work on it? Will John at least live to see it launch?Another dark horse , is the expanding universe ( Hubble´s law ) , saying that the stars of the universe are RACING AWAY from each other, making the distance between stars greater and greater.Even if the voyage really does take ten thousand years, we'll barely notice the magnitude of the expansion. It may require a tiny correction in the navigational computer.

Just about eleven thousand, to be precise. .

No, it's about 80,000 years to Proxima give or take a couple thousand. That's to the nearest star and there is no reason to consider it a viable destination. The nearest star systems that are thought to have stable rocky planets are 10 to 12 light years away. And stable doesn't necessarliy mean earth-like.

Fraggle ...
You allways think sound and study your object before answering ...
even rarer , you actually have a sense of moral ...:) and I allways like reading your posts .... this time you are in over your head .......

It will simply NOT happen in our time ....!!!!!!!!!!


27 years x 1.295 PC/ 4,6 x 10 in minus 4 PC = 76000 years ....I think .....

Fraggle ... there is NO way this can be acomplished in less than a few hundreds years - just to get the technology and get the necessary items in space to build the spaceship would take that time ..at least at the rate technology known today will allow it ...........

No man without a deathwish would like to be an astronaut on this ship ......
There is radiation penetrating all known man-made shields out there.........
Cosmogenic neutrons can have significantly higher energy than neutron radiation found in reactors .......

But no one has answered my earlier question. How much nuclear fuel would be required to accelerate constantly at one gee during the first half of the trip, then decelerate during the second half?
You need to specify the specific impulse (Isp).
A quick check through Google gives figure anywhere between 850 seconds to 5000 seconds - that's a huge variation!

You need to specify the specific impulse (Isp).
A quick check through Google gives figure anywhere between 850 seconds to 5000 seconds - that's a huge variation!

Wow I wouldn't want to be in that ship. You end up looking like an egg yolk after your body goes flying into the inner wall of the ship during the deceleration process.

But no one has answered my earlier question. How much nuclear fuel would be required to accelerate constantly at one gee during the first half of the trip, then decelerate during the second half?

That's a tough one, considering one would have to take into account the efficiency and size of the propulsion units.

Shielding from cosmic rays is just one more of the engineering requirements for the project.

Probably one of the most difficult problems to solve as much of the radiation simply penetrates most materials, over time, if not right away. So far, the best solutions I've seen are with rigolith. Mining an asteroid for the elements and fuel and leaving a hollow shell might be just the ticket.

Obviously this ship will be built in orbit and never land anywhere.

Agreed, and with very good shuttles that can land and take-off planets easily and safely.

The other "hard" sci-fi way to resolve this (i.e., without inventing artificial gravity) is to spin the ship and use centrifugal force as gravity.

That hasn't been a popular solution as many tests have shown this method is quite hard on the human body in that much of the ship's "gravity" will vary from place to place.

27 years x 1.295 PC/ 4,6 x 10 in minus 4 PC = 76000 years ....I think .....Yes, you guys are right. I should know better than to do a calculation like that in my head. Nonetheless I was barely off by an order of magnitude. We all agree that we clearly can't send people to the stars with Voyager's propulsion system. A generation starship considerably smaller than the smallest nation-state, probably no larger than necessary to carry the minimum gene pool of 600 humans in moderate comfort, set adrift for more years than civilization has existed, unlikely to encounter any external stimuli that might enrich their local culture, that gives new meaning to the term "long shot."Fraggle ... there is NO way this can be acomplished in less than a few hundreds years - just to get the technology and get the necessary items in space to build the spaceship would take that time ..at least at the rate technology known today will allow it.That's okay, there's no way it was going to happen in my lifetime anyway. Somebody will have to break the news to John, it was his question. My question is, how long will it take to develop a spacecraft that can travel to the nearest extrasolar planet, pick up souvenirs, and come back within the lifetime of the people who paid for it? In a couple of hundred years we'll have AIs that we can trust the mission to, if there's really no way to send people out into those cosmic rays.No man without a deathwish would like to be an astronaut on this ship. There is radiation penetrating all known man-made shields out there. Cosmogenic neutrons can have significantly higher energy than neutron radiation found in reactors.Somewhere between the size of a planet with an atmosphere and a magnetic field, and the size of the space shuttle, there is a size for a spacecraft that will protect its occupants against the radiation that we're shielded from here on earth.Wow I wouldn't want to be in that ship. You end up looking like an egg yolk after your body goes flying into the inner wall of the ship during the deceleration process.You start decelerating at the halfway point and decelerate at one gee.That's a tough one, considering one would have to take into account the efficiency and size of the propulsion units.Surely somebody can do a back-of-the-envelope calculation and guess how practical it is to build a ship that can carry enough nuclear fuel to accelerate at one gee until it gets halfway to the nearest promising extrasolar planet.

Actually--and check my arithmetic again--it looks like the ship will have reached a large fraction of c after just one year. Time dilation will make the rest of the trip go by pretty quickly for the crew. So the question remains: Can a ship the size of an asteroid carry enough fuel to accelerate it to that speed? Or at some point do we power up the Bussard ramjet?

Wow I wouldn't want to be in that ship. You end up looking like an egg yolk after your body goes flying into the inner wall of the ship during the deceleration process.

No, that's the specific impulse from the power plant (measured in seconds) not the trip time...

anybody believe in a starwisp (http://en.wikipedia.org/wiki/Starwisp) variant for the relative near (lifetime) future?

anybody believe in a starwisp (http://en.wikipedia.org/wiki/Starwisp) variant for the relative near (lifetime) future?Ah, Robert L. Forward, my favorite "hard" sci fi author. He thought up the most fantastic ideas and they were all scrupulously scientific. I sure miss him.

The starwisp looks like a concept whose problems will be easier to solve with nanotech. So maybe our younger members will live to see it.

Once it gets to .2c, could it fire up a nano-Bussard ramjet and just consume that interstellar hydrogen? Until the Galactic Federation pays us a visit and tells us to stop using up their finite resource? :)

a ship only weigting 1.8kg, that afther intial costs (the power beam station) could be manufactored in bulk ad a price class of only thousands of dollars per ship, whill the grocely expensive power beam station can perform other tasks in between launches, would seem like today's future considering our trend for miniaturisation, alternative energy production methodes, etc.
It's this way people think nowdays forget gigatons heavy multitrilion ships. With large enough energy station and funding these things could be developed and build in a lifetime.