[afreak]

Keep in mind that at best it would take maybe 1,000 years with current technology to get there with a probe or human-supporting ship. It would be highly unpopular however as it involves exploding nuclear bombs behind the craft to get it there that fast--that and it would probably cost trillions to build the thing.

[sehugg]

There's a $100 million effort to develop tiny spacecraft that are accelerated to 10%-20% the speed of light with ground-based lasers: https://en.wikipedia.org/wiki/Breakthrough_Starshot

[gene-h]

Today at 2:55 EST Philip Lubin, who is involved with the Starshot project, will present some work on the study he is doing for NASA investigating the feasibility of this.

You can watch it live here: http://livestream.com/viewnow/NIAC2016

[MOARDONGZPLZ]

The craziest thing to me is that if we sent a generational spaceship there that was expected to take 1,000 years, it seems likely that better technology would allow the next generation of spaceships to get there much faster. So by the time the 1,000 year spaceship arrived, there would already be people there!

[nerfhammer]

This is a known paradox, I forget what it's called though. The concept is that it's arguable that any long-term space travel is pointless because there will always be a faster ship surpassing it as the originating civilization improves its technology, and so on for that faster ship. So, it's irrational to ever launch anything...

[uptown]

Apple has adopted a similar philosophy with their MacBook Pro line of computers.

[mkhalil]

I haven't laughed so much in days. Thank you.

[ChristianBundy]

This is known as the incessant obsolescence postulate: http://arxiv.org/abs/1101.1066

[kamaal]

>>This is a known paradox >>So, it's irrational to ever launch anything...

That faster ship just won't appear out of the blue.

You need to launch slower ones to get to the faster ones.

Its like the original inventor of the car opting not to build it because someday there would be a Ferrari.

[cgriswald]

Improving the speed of a 1000-year ship may only require improvements in propulsion or structure (lighter ships). There are nearby incentives to create better propulsion and structure. We do not necessarily have to launch a 1000-year ship to create a 500-year ship.

[7Z7]

But you don't have to send your people 1000 years away.

[cnp]

Yup -- This is precisely the answer to the question, so it thus remains an unresolvable paradox.

[mikeash]

Seems like you'd reach a point where it becomes worth it even with continuous improvement. If the speed of light really is a speed limit, then you'll get to a point where the maximum theoretical improvement is still some small amount. If there's a way to go faster than light, then you'll get to a point where it only takes two seconds to get to your destination.

[dmurray]

Even without the speed limit, you can expect to reach this point. Let's say your technology gets 10% faster every 25-year generation, you should launch a 200-year trip but not a 250-year one. We'll probably keep improving at that pace or better for a few iterations at least, but eventually space travel will be a stable technology, speed improvements will be rare and incremental, and 1000-year journeys will be justified.

[mikeash]

Right, barring time travel, once you can make the voyage at all, you'll always reach a point where it makes sense to depart on it. If you invent technology that takes a million years to arrive, then you have a maximum deadline of a million years. Past that point, even instantaneous travel won't be worth waiting for, if your goal is simply to get there as early as possible.

[jackcosgrove]

> So, it's irrational to ever launch anything...

Sounds like the interstellar version of Zeno's paradox.

[utku_karatas2]

On a tangent with this topic, you guys should treat yourselves with a short sci-fi story named "The road not taken".

[semi-extrinsic]

I just finished reading the entire novel series that Turtledove spun out of that short story concept. It's really good, well-researched and imaginative.

[gengkev]

But technology that would be able to send spaceships significantly faster would probably cost significantly more, so it might not be worth pursuing given the cost.

[phkahler]

Moore's law never stopped anyone from making chips with current technology.

[maerF0x0]

Or maybe they'd rendezvous and bring them "up to speed" so to speak ?

[platz]

it would be better to just 'seed' the tiny starshot spacecraft with human embryos that could litter the planet and then develop on arrival.

[jcoffland]

Right because human babies let alone embryos do so well on their own.

[platz]

that's why we also send self-replicating nanobots along with them.

[jdmichal]

See James P. Hogan's Voyage from Yesteryear. It involves a post-scarcity civilization seeded in much the way you suggest.

https://en.wikipedia.org/wiki/Voyage_from_Yesteryear

[ju-st]

Adults from later, faster spacecrafts could raise the babies.

[bdamm]

Why wouldn't they just bring their own? Or make some?

[platz]

we'll also send send self-replicating nanobots

[flukus]

If you're limiting it to generational ships then there isn't much improvement to be made, we can still only accelerate at ~1G. The only variable is how long that acceleration can be maintained.

[scotty79]

It was a theme it this cartoon: https://en.wikipedia.org/wiki/Once_Upon_a_Time..._Space

[lifeformed]

Maybe there could be a kind of factory-ship that was built to be self-improving, so during those 1000 years it would improve itself and increase it's speed.

[mrfusion]

After we build the laser it might not cost that much more just to keep a constant stream of these guys going to the planet relaying their information back along the stream. Effectively giving us a streaming feed of what's happening on the planet.

A single probe in orbit could obviously do this but with this idea there's no way to slow down.

[aminok]

There's a way to slow down:

http://www.lunarsail.com/LightSail/rit-1.pdf

>The lightsail is built in two sections, an outer doughtnut- shaped ring, and an inner circular section 30 km in diameter. This 30 km payload section of the sail has a mass of 71 metric tons, including a science payload of 26 metric tons. The remaining, ring-shaped "decel" stage has the mass of 714 metric tons, or ten times the smaller payload "stage". The central payload section of the sail is detached from the larger stage and turned around so that its reflecting surface faces the reflecting surface of the ring-shaped portion (see Fig. 4). At a time 4.3 years earlier, the laser power from the solar system was upgraded to 26 TW (there are 37 years to get ready for this increase in power). The stronger laser beam travels across the space to the larger ring sail. The increased power raises the acceleration of the ring sail to 0.2 m/s2 , and it continues to gain speed. The light reflected from the ring sail is focused onto the smaller sail, now some distance behind. The light rebounds from the 30-km sail, giving it a momentum push opposite to its velocity, and slowing it down. Since the smaller sail is 1/10 the mass of the larger one, its deceleration rate is 2.0 m/s2 , or 0.2 g. The light flux on the smaller sail has increased considerably, but it is only two-thirds of the maximum light flux that the sail can handle.

[leftandright]

This is from the same people who announced the "Breakthrough Message", an open competiton with a $1 million dollar prize pool, whose details were "to be announced soon". [1]

The press release was made in July 2015, and there has been no communication about it since then. I'm not sure how seriously to take this group.

[1] http://www.breakthroughinitiatives.org/Initiative/2

[VikingCoder]

Also, https://en.wikipedia.org/wiki/Starwisp

0.20 c

[Roboprog]

Unless "The Moties" send one here, first :-)

Yet another comment plugging a story involving some novel interplanetary travel (this one involving a species from a red dwarf): https://en.wikipedia.org/wiki/The_Mote_in_God%27s_Eye

[mrfusion]

This should be the top comment! Not the guy poo pooing on the idea of checking out this planet.

[afreak]

(ignore what I said here)

[malz]

Also at 10% the speed of light the probe zips by the planet in a fraction of a second. There's no slowing down in this scenario.

[sevenless]

You can slow down - just that the probe won't remain intact. But perhaps that isn't necessary for the probe to be useful. We can also use these space probes to do geological and atmospheric surveys of the planet when they arrive.

Simply: we slam the probe into the planet, a few milliseconds after it transmits the final images. One gram going at 20% of the speed of light has kinetic energy that bears comparison to the Hiroshima bomb.

At a steep angle of entry, the huge entry glow will give a reading of the atmospheric molecular makeup. And if we can ionize some of the crust, massive space telescopes can get a spectroscopic measurement of the composition, four light years away.

[onion2k]

Let's hope any alien race living there doesn't have the same idea and send a few probes to smash in to Earth.

[sevenless]

That would be like Christopher Columbus, mid-Atlantic crossing, encountering a gunpowder-equipped Mayan navy going off to conquer Europe. Not likely.

[saiya-jin]

now that's a way to say Hi to a foreign species! there isn't high chance this wouldn't be considered as an act of hostility, and if they would check our history of our current world, they would probably just decide to erase this dangerous species from the face of the universe for greater common good.

[sevenless]

I think we both know humanity's interstellar destiny is to become the murderous alien invaders we've faced down in so many movies.

[elektropionir]

There are ideas for slowing them down and even returning them back to Earth, at least in principle:

http://www.centauri-dreams.org/?p=31913

Nothing that could be implemented in any foreseeable future though.

[mrfusion]

Could they carry mini solar sails to slow down? Solar parachutes if you will.

Or if we sent them in single file several seconds apart they could each relay what they see to the ones behind them and then back to us. Effective oh giving us a long exposure.

[zeven7]

The laser is only on each device for 10 minutes. And there are 1,000 of them. So the hope is that at laest 1 in 1,000 will make it.

[dingbat]

if even a tiny fraction of those 1000 tiny probes hit that planet at 20% of speed of light, could that pose a problem? it sounds like a shotgun approach, not so figuratively, using pellets loaded with plutonium.

[jessriedel]

The probes would each be only a few grams, so they'd have about 10^13 J of relativistic kinetic energy, or a half kilotons of TNT equivalent. This can be compared with the 15 kilotons for the (small, by modern standard) Little Boy atomic bomb. So it's probably noticeable for any inhabitants in the area, depending on how the energy is dissipated in the atmosphere, but still quite small on the scale of a planet.

[mikeash]

It should be noted that meteors explode with Hiroshima-like force fairly regularly within Earth's atmosphere, on the order of once a decade or so. It happens high up enough that nobody notices beyond an occasional light show. The meteor explosion which hurt a bunch of people in Chelyabinsk a few years back was about 500 kilotons.

[kamaal]

>>So it's probably noticeable for any inhabitants in the area

An intelligent civilization with a 1000 year head start whose presence was just proven by device that arrived at 10% the speed of light would pretty much scare any government on earth.

I would assume it would scare the aliens there too.

[antiffan]

This is the coolest project I've heard about in a while. Thanks for sharing!

[ourmandave]

I wonder what it would be like to be the Nth generation of guys-that-left-in-2016 finally arriving and be greeted by the descendants of the FTL guys that arrived 800 years before you.

[zrail]

This is the plot of at least one Star Trek: Enterprise episode.

[Grishnakh]

Which one? I Netflix'ed my way through that whole show a couple years ago and didn't see any like that.

It does sound a little bit like "Space Seed" from TOS though, except I don't remember that ship having a particular destination. There was another TOS episode where they find a stray asteroid that turns out to actually be a generation ship inside. And there was some TNG episode where they find a ship with some 20th-century Earthers in cryogenic storage because they had just died of medical ailments. But I don't remember any ENT episodes like this, just some talk about "slow" Earth ships traveling at only Warp 1.5 or so, so that people lived their whole lives on them while on long-term trading missions (their helmsman came from one of these ships).

[MeetTheCryo]

I'm pretty sure you're wrong and it was an episode of 'The Next Generation, although I've no idea what the title of the episode was... [0]

[0] I've watched the episode only once (I'm not a Trekkie :) ), but if I remember correctly a synopsis of the plot was that decades (at least...) ago an automated ship containing Klingons in cryogenic suspension was launched to colonise a distant planet; in the time following the launch of that ship, the Federation reached and colonised that planet using faster ships, unaware that the Klingon ship was on the way...

The crew of the Enterprise [D] has to try to figure out how to stop the Klingon ship from introducing the Federation colonists on the planet to the magic of orbital bombardment (a casus belli) without destroying the Klingon ship (a casus belli).

[InclinedPlane]

I think you're mixing up some details of that episode. The closest episode I can think of that matches that is "The Ensigns of Command", which involves a colony of humans that were isolated and underdeveloped due to interference from the planet's radiation. The colony was on a planet that technically belonged to the "Sheliak", a mysterious race the Federation had limited contact with, but who had decided to begin colonizing the planet and gave the Federation a short time span to remove the humans before they would eradicate them.

[MeetTheCryo]

I looked it up, and the title of the episode was "The Emissary" [S2E20] (although, yes, either I remembered a few details incorrectly or the Wikipedia synopsis of the plot is incomplete).

[blakeyrat]

... are you sure?

There's one episode where they visit a colony established decades previous by a warp 1 or warp 2 ship, but they don't beat the colonists to the planet.

[ygjb-dupe]

no shortage of fiction covering that scenario...

[gnaritas]

Since we're pretty sure FTL is pure fiction and not possible in reality, that likely won't be an issue. Just because we don't know everything, doesn't mean we don't know anything.

[dbingham]

We are, by no means, sure of that. There are numerous theoretical possibilities that fit current theory. Not least of which is the Alcubierre Drive: https://en.wikipedia.org/wiki/Alcubierre_drive

[gnaritas]

Mathmatically compatible with GR (which is known to be incomplete) doesn't mean possible in reality, in fact, read your own source, it makes that clear..

> Although the metric proposed by Alcubierre is mathematically valid (in that the proposal is consistent with the Einstein field equations), it may not be physically meaningful, in which case a drive will not be possible.

That drive is nothing more than speculative science fiction.

[nsxwolf]

Are there really numerous possibilities? I know about Alcubierre, what are the others?

[adrianm]

Alcubierre's drive is a solution to Einstein's field equations which simply means the math checks out in theory for warp drive.

The resulting practical problem is that the energy requirements necessary for the solution are far greater than what we can feasibly achieve now or in the future (exotic matter's existence notwithstanding).

But the fact that a physicist was able to derive this metric (energy requirements aside) is significant. Given the history of science, I would not discount the possibility that someone else will come along in the future with another solution which lowers the energy requirements to something feasible. But we can't predict this.

But isn't it amazing that the math checks out at all? I find it inspiring...

[dbingham]

I'm not so sure the energy requirements are all that high. Alcubierre suggested that the sort of exotic matter needed would actually be fairly easy to create. NASA's been running experiments hoping to measure it with inconclusive results:

https://en.wikipedia.org/wiki/Alcubierre_drive#Experiments

> In 2012, a NASA laboratory announced that they had constructed an interferometer that they claim will detect the spatial distortions produced by the expanding and contracting spacetime of the Alcubierre metric. The work has been described in Warp Field Mechanics 101, a NASA paper by Harold Sonny White.[5][6] Alcubierre has expressed skepticism about the experiment, saying "from my understanding there is no way it can be done, probably not for centuries if at all".

> In 2013, the Jet Propulsion Laboratory published results of a 19.6-second warp field from early Alcubierre-drive tests under vacuum conditions.[33] Results have been reported as "inconclusive".[34]

[dbingham]

Wormholes are another. There's some debate whether or not the idea of creatable wormholes really exists in our physical models. But the idea of existing shortcuts through space time certainly does.

[gnaritas]

Wormholes aren't known to exist; they're theoretical implications of some math, not known things. It's entirely possible they don't exist at all.

[pilom]

No, but if we leave today with a trip time of 1000 years and in 100 years we invent a way to travel .2c, then the people on the ship with the new tech will arrive in 120 years instead of 1000. Don't need FTL tech to make generation ships a silly prospect.

[Grishnakh]

The other thing you guys are missing is relativistic time dilation: get the ship moving fast enough and time will pass more slowly inside the ship than outside. The ship may take a century or two to get to the destination, but only a few years will have passed for the travelers.

[aetherson]

You have to go really, really fast to get 100:1 time dilation (like, 99.99% c) -- probably fast enough to make interstellar travel hazardous in a "collide with a hydrogen atom, it hurts" kind of way.

Also, the energies involved are absurd.

[cgriswald]

They will still arrive after the faster ship.

[stincity]

Pretty sure? I'm pretty sure we don't know near enough to make any type of guess on that.

[gnaritas]

Your mistaken, and this opinion is what the second sentence was for; just because we don't know everything doesn't mean we don't know anything. FTL is likely not physically possible. That's not to say it's impossible, just that it's not likely given the vast number of things we do know about physics.

[Bluestrike2]

Maybe you'd get a nice little tech upgrade when you got there. And I'd hope that we'd at least develop some form of suspended animation to make things bearable.

[naravara]

To be honest, assuming, you get there safely I'd rather be in suspected animation on the slow ship than the fast one. I'd get all the heroism and send-offs of a pioneer, I'd have my name etched on a monument somewhere, I'd have the thrill of exploring something totally new. All that, except when I arrive all the brutal, dangerous, boring work of establishing a self-sufficient biome will already be done and I can jump immediately into the "boldly go where no one has gone before" part.

[loader]

They'd just get picked up along the way.

[raverbashing]

Well, they can stop at the spaceship on their way back and then... I don't know

[dTal]

It's not quite that bad. Have you heard of fission-fragment rockets? Highly feasible, and travel times to Alpha Centauri on the order of decades, not millennia. Baffles me that no one talks about them.

https://en.wikipedia.org/wiki/Fission-fragment_rocket

[greglindahl]

Someone mentioned them in this discussion ~30 minutes before you posted.

[dTal]

Where? I'm ctrl-f-ing here and seeing nothing older than my comment.

[greglindahl]

OK, the previous ref was for nuclear pulse propulsion, which I'm sure you consider completely different.

[dTal]

They are extremely different. One is a highly impractical idea from the 1940s, and the other is a relatively recent and promising design that continues to be refined.

[m_mueller]

What's exactly impractical about a nuclear pulse drive - conventionally launched and activated outside the atmosphere? We know how to build that stuff safely to account for launch failures, it has been done with RTGs many times already.

[DominikR]

Actually the 1000 year number comes from Project Orion in the 1940ties and 50ties.

https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...

An updated design from the 80ties calculated a time of 100 years:

https://en.wikipedia.org/wiki/Project_Longshot

And a nuclear fusion design is calculated to achieve 12% of light speed, thereby reducing time to reach the fourth nearest sun system in 46 years.

https://en.wikipedia.org/wiki/Project_Daedalus

So there are concepts that could make unmanned interstellar travel possible, even within a humans life span, it's just that it costs so much and the incentive is pretty low compared to the incentive countries had for getting objects into space. (primarily military incentives - get spy satellites and nuclear warheads into space to not fall back behind adversaries)

I believe that given a strong enough incentive humans could do it, no matter what current consensus is telling us.

Humans set out to work on reaching outer space without even having a design on how this could be achieved and we did it anyway.

[Trufa]

At current rates, it would be 137 thousand years.

http://www.ucolick.org/~mountain/AAA/aaawiki/doku.php?id=how...

[jnicholasp]

50ties - Fifty-ties -- Fifties - 50s / 50's

[DominikR]

Thanks, English is not my native language. So what is correct, 50s or 50's?

[jnicholasp]

Yeah, I figured, no worries. Your English is excellent, apart from this little oddity. Either way to put the 's' is fine, really, but I think with the apostrophe (50's) is more common.

[DominikR]

Thanks a lot! Very kind of you.

[pjmlp]

Yeah, I smiled when I read "Just over four light-years" as if just around the corner kind of thing.

It might be just around the corner in space travel time, but those are quite a few light years still.

[TheLarch]

Also no one knows how to shield a spaceship from the interstellar medium https://en.wikipedia.org/wiki/Interstellar_travel#Interstell... over such distance.

[beefman]

Fission fragment rockets are well within current technology and can achieve delta-vs of 0.1c at reasonable payload fractions, getting us there in ~ 40yr.

Edit: Nuclear pulse propulsion is good for about half that (80yr, not 1000).

[the_rosentotter]

How does it slow down?

[dogma1138]

It doesn't hence its going to be used for flyby missions and not orbit/capture missions.

Many missions to the outer planets are flybys since we can't have enough fuel to actually slow down.

[solotronics]

just curious but how would you even capture any usable signals when passing a planet at 20% lightspeed?

[dogma1138]

Well if you think about it we are capturing useful signals that move at relativistic speeds all the time.

Many galaxies we see are moving at very high speeds due to the expansion of the universe hence the doppler shift and we can take both optical and radio images of them.

I'm not an RF/Optical engineer but I would think that it would be possible to capture and send some data back to earth even its minimal it's still might be better than nothing / what we can get from earth/our solar system, at the end we only might have to account for the doppler shift.

IIRC there have been also other tricks like deploying very large sails and using them as drag chutes or using some mechanical trickery and deploying a very small probe by literally like having it on some pendulum and some other weird stuff so you would transfer most of the momentum it has to the probe and you'll release it with considerably less momentum than the rest of the spacecraft.

[dougk16]

The planet itself could slow the probe down quite rapidly. ;)

[omginternets]

Would it be possible to drop a payload that would enter orbit?

[outworlder]

The payload would need to slow down to be captured by the planet just the same. Normally you could try aerobraking and the like, but we are talking about relativistic speeds here.

[paulvs]

To get better closeup pictures, if possible, aim the probe for the planet and live stream picture home all the way to impact.

Although I'm not sure these probes are at all steerable, either autonomously or remotely.

[messe]

Highly unlikely, the mass of the probes will be on the order of several grams at most, and, depending on the trajectory relative to the planet, steering could require an equally impractical amount of fuel as slowing down would.

[garaetjjte]

Livestream at 20% of light speed?

[jcoffland]

There may not be any significant atmosphere for aerobraking. This likely would not be known until long after the probe arrived.

[Bluestrike2]

We'd also have limited knowledge of the system itself. Without more accurate data about its objects and their orbits, it'd be almost impossible to plan out orbit insertions even assuming we come up with a means of slowing a probe from relativistic speeds.

Even if your probe had the computing power to run orbital mechanics calculations, there's no guarantee that it'd be in a position to actually make it work when it got there. Of course, that's ignoring the mass constraints involved.

But that doesn't discount the value of even 'just' flyby missions. The scientific benefit would be, literally, incalculable. And the data could help with followup missions, assuming we develop a drive system that could get there and slow down.

[pilom]

The StarShot probes are going to be about a gram. Not much weight to make a primary probe AND a payload.

[baq]

slowing down from that kind of velocity is serious business. you're talking about braking from 75000km/s to ~8km/s and not blowing up in a spectacular explosion.

[cloverich]

I just died laughing. I'm reading all the inspiring comments on how we actually could get there, and could totally see myself being on an engineering team that builds this thing, and 100 billion dollars later you ask that question and we all go: "Oh... oh crap." On a constructive note -- does anyone have a list / book of generally smart people getting sidelined by such things?

[irremediable]

There's a book called It Looked Good On Paper full of things a bit like that, albeit on a smaller scale.

[seizethecheese]

This comment left me flabbergasted. Great thinking.

What about orbiting the planet and using the lasers when the craft is orbiting towards us in blasts to slow it down gradually?

[danielweber]

Magsails would work.

[LeifCarrotson]

If you're going to use magsails to slow it down, why not use a magsail to get it there? The trip is basically symmetrical.

I suppose it's possible that the laser could produce a much more stable and precise trajectory, while a magsail would just slow it's descent towards or accelerate it away from the sun. But I think it's more likely to be a case of the materials science and energy density being in favor of the laser method over sails.

What if we used lasers to send a fleet of laser ships with powerful one-time-use chemical lasers, then the front set of laser ships fired the same kind of beam back at the rearmost ship to to slow it down?

[ingenter]

> If you're going to use magsails to slow it down, why not use a magsail to get it there? The trip is basically symmetrical.

If you launch a strong magnet in interstellar space, it will slow down relatively to plasma by deflecting charged particles.

In order to speed up, you need to spend energy.

The symmetry is broken between accelerating and slowing down relatively to interstellar plasma (Edit: or solar wind).

[LeifCarrotson]

Ah, I had neglected the effects of interstellar plasma.

I assumed the magsail operated in a similar fashion to a solar sail, depending on the solar wind. If the destination's solar wind was sufficient to slow us down, I expected that the Sun's solar wind would be sufficient to speed us up.

Thanks for the explanation!

[defen]

Imagine the political implications of choosing who will go onto that ship, as well (assuming the intent is to colonize the world and fill it up with humans)

[dTal]

Telephone sanitisers.

[oslavonik]

A poet.

[sandebert]

This is a (likely) reference to Contact (1997), with Jodie Foster.

Some celestial event. No - no words. No words to describe it. Poetry! They should've sent a poet. So beautiful. So beautiful... I had no idea.

[ianai]

Only the richest, elites. I say we ship them immediately! /s

Let's get real, they wouldn't go anyway. It's too good for them here where they have people to do things for them.

[tzs]

> Only the richest, elites.

Would they actually want to go? If we are talking about a 1000 year voyage, and not assuming a major breakthrough in cryogenics or longevity, signing up for that trip means you are going to spend the rest of your life on that ship, mostly outside but near our solar system.

I don't see that being particularly enticing to rich elites.

I don't remember were I read this so cannot properly give credit, but I saw an interesting variation on the generation ship.

The conventional approach is to send a large crew, whose job is to operate the ship, reproduce, and raise their kids to take their place, generation after generation until the ship arrives and they become colonists.

The variation would be to start with a much smaller crew and large collection of frozen embryos. You make use of the embryos when you arrive to build up the population to full colony size.

The advantage of this approach is that since there are fewer people during the trip, you have more capacity for supplies. You can better equip the ship to deal with unforeseen problems.

For instance, suppose taking the embryo approach, you can get it down to a crew of 6. You'll have 12 when the crew is overlapping with their kids. Call it 18 if the crew's parents have not yet died when the crew has their kids.

Suppose each crew member needs 3000 calories per day. Then on a 1000 year voyage, you need 18 people x 3000 calories/person/day x 365.2422 days/year x 1000 years = 19.7 billion calories.

I have a protein bar by my desk at the moment. It is 190 calories, and is about 125 mm x 30m x 20mm = 75000 mm^3. So, 19.7 billion calories x 1 bar/190 calories x 75000 mm^3/bar gives a volume of 7.8 x 10^12 mm^3. Stored in a cubic storage container, this would require a container with an interior length, width, and height of 19.8 m.

The "small active crew, everyone else a frozen embryo" generation ship could start out with enough food on board to last the entire voyage, and so would not need to raise food onboard. That alone should greatly simplify things, and greatly improve the chances of making it. Of course they probably would still grow food, but now it would be for added variety and flavor, not a necessity.

(I'm not going to do the calculation to see if they could start with enough water for the whole trip. Water is very bulky and we use a lot of it, so my totally uneducated guess is that it would take too much space. However, I believe that efficient water recycling in a closed environment is something we know how to do very well, and so water should not be a problem).

[flogic]

The problem is that these people are going to be living out their entire lives on the ship. While you can maintain genetic viability by supplementing from frozen stock. Maintaining a viable culture and a society that the caretakers will actually want to live in is another thing. Forcing anyone to live a culturally and socially impoverished life is cruel.

I would suspect you would want to have at least 10-20 people in each 5 year age bracket. Then people will have a fighting chance at developing their own social lives and maybe even their own culture.

[notahacker]

That's a lot of generations of inbreeding before the approx three descendant females of childbearing age get to unfreeze the embryos and start widening the gene pool though, assuming they're up for the task of being the surrogate mother for dozens of other people's kids...

tbh I think storing enough food for the journey is going to be the least of all problems

[tzs]

You could do a mix of crew replacement by breeding and crew replacement by reviving frozen embryos to keep the genetic diversity up.

Or maybe an all female crew that does crew replacement either using frozen sperm or frozen embryos, and selects for female replacements.

When the ship arrives and it is time to start the colony, I don't think you'd try to grow to thousands of people quickly. I think you'd want to go slow early to make sure you understand your new environment. Maybe 12 years out, the crew switches from 1:1 replacement to 3:1. Sticking with 6 as the main crew, plus possibly up to 6 of the crew's parents still alive, plus 18 kids. I think you'd want to spend a few years based on the ship studying the planet and conducting research expeditions to figure out if the planet really is suitable for colonization and figure out dangers that unmanned probes and study from Earth may have missed. When that is done, the kids should be 18 or so, and you can start the colony with them and with their grandparents, with the main crew staying with the ship to provide support. That would give 18-24 people on planet attempting to live there, but not needing to be self-supporting yet because of the ship.

In a few years, the colony population should start naturally growing. If the babies do OK, people can be encouraged to have bigger families, with one or two per family being from the frozen embryos and the rest produced the old fashioned way.

> tbh I think storing enough food for the journey is going to be the least of all problems

Yeah, there will be a lot of problems.

Many of the hard ones will not even be technical. For instance, you'd want to have some way to stop from happening something that happened to a colony in Larry Niven's "Known Space" universe. When the colony ship arrived the crew decided to set up the colony so that the crew was the ruling class and the colonists essentially serfs.

The ship in that Niven story wasn't a generation ship. Crew and colonists were cryogenically suspended for the trip, with the crew being automatically revived when the ship arrived. I supposed one advantage of the traditional generation ship is that it has some protection against that scenario because during the trip everyone is crew.

[mrfusion]

There's no reason they have to wait to arrive to start using the embryos.

[m_mueller]

I think you're conflating a few things here:

1.) A probe and a human spaceship are vastly different problems. Since all a probe really needs is electricity to sustain itself, you could get away with a tiny payload and some long lasting radioactive energy source, light sails or even sending the energy from earth's orbit. Such a thing would be either slow and cheap or fast (a few percent of light speed) and expensive, but not both at the same time and I doubt it would be in the trillion dollar range whatever you do.

2.) I completely agree that sending humans would currently not be feasible within a single nation's budget and the technology for that is still at the very least decades out (cryogenics, EM shielding, better propulsion systems, using mass from cheaper solar system bodies than earth etc.).

3.) 1000 years is what we'd need with conventional current technology. The theoretical limit for a nuclear impulse propulsion drive is 20% of light speed if you want to break or 40% for a fly-by.

[gene-h]

Well using laser propulsion, we might be able to get a very lightweight probe up to 1/4 c using technology that isn't too far off.[0]

Coincidentally, the group working on this will be presenting some of their most recent work on this at 2:55 EST today. You can watch that live here[2].

[0] http://www.deepspace.ucsb.edu/projects/directed-energy-inter... [1]https://www.nasa.gov/sites/default/files/atoms/files/2016_sy... [2]http://livestream.com/viewnow/NIAC2016

[ams6110]

Don't forget that halfway there you have to turn it around and start slowing down.

[mikro2nd]

The bigger deal is, How do you deal with the ablation problem at those speeds? Given the likely density of H in interstellar space, erosion is your primary problem.

[nsxwolf]

Add the Broussard ramscoop, magnetically deflect the atoms into an accelerator and expel them to add to your propulsion.

[kilroy123]

What about a solar sail mixed[1] with, ion engine[2] and nuclear powered[3]? With all those things combined, you would constantly be accelerating for many years.

[1] http://www.planetary.org/explore/projects/lightsail-solar-sa... [2] http://www.nasa.gov/centers/glenn/about/fs21grc.html [3] https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...

[boxy310]

I'm interested in NASA's work on the Alcubierre drive [1]. Still likely to require much more energy than we'll be able to produce in the near future, but 100 years ago we were just getting a firm handle on the basic mechanics of flight.

[1] http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/2011001...

[krastanov]

The Alcubierre drive is just a solution to the equations of general relativity that most probably can not be achieved in practice. Sure, maybe one day we will have drives like that, but we do not have any idea currently that even remotely resembles a warp drive permitted by the laws of nature.

[openasocket]

That would require us to create matter with a negative energy density, which has never been detected and is likely impossible.

[gnaritas]

Still fiction; it relies on magic, i.e. things not known to actually exist.

[naasking]

Magic operates in ways we don't understand. I think we understand negative energy density, we just don't know if it's possible in reality.

[gnaritas]

> Magic operates in ways we don't understand.

Witches would disagree. :)

> I think we understand negative energy density, we just don't know if it's possible in reality.

Exactly as in magic. When you propose things are possible if only X material with some magical property necessary for thing to work, that's speculative fiction. Especially when those constructs only make sense mathematically. Math isn't physics, but physics is math, there's an important implication there.

[c3534l]

According to Niel DeGrasse Tyson, you could send a tiny, pocket-sized payload and get it there in only a few decades. So if we just want a couple snapshots and not the sort of thing we typically send to orbit planets, it could be done in a reasonable amount of time.

[ams6110]

Why would it be unpopular? On the scale of the space involved, any "pollution" would be literally inconsequential.

On the cost, I agree and think we have much bigger fish to fry on our own planet than to spend huge sums to discover what is in all likelihood a barren rock.

[mikeash]

Frying every piece of electronics on the ground below the ship when you fire it up, and every satellite visible above the horizon, would be bad PR.

You could potentially boost it far away from Earth by more conventional means before turning on the nukes, but suddenly it becomes a far larger and more difficult thing.

[Grishnakh]

Oh please.

Any interstellar ship like this is not going to be built on Earth's surface, it's going to be constructed in space somewhere. Building a craft that large on the surface is far more difficult than just assembling it in zero-g from components, since the stresses of leaving the gravity well through the atmosphere on a large object are huge.

[mikeash]

The point is, not only does it need to be built in space, but it needs to be built (or moved) pretty far away from Earth before you light it up. You can't just build it in Earth orbit. And even that would be well beyond modern capabilities. A ground-launched Orion could be built now, but constructing an interstellar ship in solar orbit will require a lot more work on space access.

[Grishnakh]

A ground-launched Orion could be built now, but it'd make a mess when it launches, and it'd probably be much too small for a useful interstellar mission anyway, because of that scaling problem I mentioned. The stresses are just too high, and it's pointless because you don't need a ship that rugged in space, only for transiting planetary atmospheres.

I don't think we have the capability now to build a sufficiently large ship on the ground anyway, even if we decided to say "screw it, we don't care if it's wasteful to massively overbuild this thing"; our materials science probably isn't up to the task. So we need to learn to build things in space anyway.

No, we don't really have this capability right now. But we need to assume we'll have it when we need it, and we need to work towards it, and not try any kind of missions requiring it until we do. Thinking about interstellar missions right now is really putting the cart before the horse; we haven't even gotten manned missions beyond the Moon, and even those were pretty simple (walk around, hit some golf balls, drive a rover around), not anything involving real work such as building a habitat or serious excavation or mining.

This is why I think all this talk about going to Mars is silly too; we need to be concentrating on closer things, like near-Earth asteroid retrieval and prospecting, and building a Moon base, and figuring out how to mine materials and build larger ships offworld. We need a bigger ship to go to Mars, not some little tin can that you can stick on top of a rocket; something the size of the ISS would be good, because the crew will have to be trapped in it for months, and they need stuff for landing on the surface and doing real work there. You can't do all that with something the size of the lunar modules we launched on the Saturn V.

[tokai]

Just build it in space.

[Chris2048]

Maybe wait for space elevators?

[Merad]

Didn't Project Orion determine that it's theoretically feasible to accelerate to not-insignificant fractions of c using NPP? If your journey could average even 0.05c, you can potentially make it within a human lifespan.

[pc86]

I thought the issues were:

  - navigation at any non-trivial fraction of *c* (not running into something that would obliterate the vessel)
  - slowing down and actually arriving where you wanted to and not overshooting it or stopping .5 LY away

[marcosdumay]

About slowing down, it's pretty predictable. The idea is even to run the ship in constant acceleration.

I don't think you'll want to actually navigate that ship. It's a point and go task. But if needed, you rotate the ship and keep accelerating. But I have no idea on how much you'd be able to fix your route after you discovered it is wrong.

I think the main issues are how do we make a ship where people can live for decades? And how do we launch it from the ground?

[dghughes]

I think speed is only one part of it you'd be dead from radiation over such a long period of time unless you were surrounded by lead.

[Nadya]

Proxima Centauri is 4ly away. New Horizons (the Pluto Probe) was travelling at 15.73km/second (just over 34,000/mph)

You're looking at closer to 75,000 years - not 1,000 years - to reach Proxima Centauri.

E:

Did actual maths. Closer to 75,000 not 100,000.

[simplemath]

This whole conversation reminds me of Europeans who have never been to the states thinking of flying over for a week, renting a car and visiting the Florida Keys, Times Square, the grand Canyon and Disneyland.

At 34k MPH it would take 75 Millenia to reach our literal stellar next door neighbor.

Makes the blood boil how vast and empty space really is, when you think about it

[Nadya]

As you mention - comprehending how large/small countries are is tough for some people. Planet-size differences even more so. Many probably don't realize how big the sun is! Then you have to comprehend that on a galactic scale - our sun is really, really tiny [0].

We exist on a tiny spec of dust; inside of a solar system that is no larger than a tiny spec of dust; inside of a galaxy that is no larger than a tiny spec of dust; inside a supercluster that is only a tiny spec of dust.

[0] http://i.imgur.com/DUzDo3k.gifv

[sevensor]

Every time I try to comprehend the sun as it actually is -- its size and composition -- I end up completely boggled and unnerved. A vast and uncaring ball of plasma, mostly hydrogen, supporting billions of years of fusion reactions, so big that the orbit of the planet I live on causes only the slightest wobble in its position; it's no wonder the ancients worshiped the sun. There's nothing about it I can begin to grasp except by analogy.

[hexagonc]

I'll just leave this here for you. . .

https://upload.wikimedia.org/wikipedia/commons/d/d0/Comparis...

[simplemath]

Ill just leave THIS here for you

https://www.youtube.com/watch?v=QgNDao7m41M

[macintux]

I did some rough estimation on a map recently and decided that driving from Seattle to Miami was only slightly shorter than from Paris to China.

This is a bloody big country.

[Retric]

New Horizons is a traditional design with chemical propultion. Ion drives should hit ~5.5x that speed fairly easily. (http://www.extremetech.com/extreme/144296-nasas-next-ion-dri...)

A larger issue is RTG's are not useful on a very long long timescale.

ITER style fusion is likely the best power source for such missions and should hit ~1-10% of light speed fairly easily. But, building something that large is a major issue.

On the upside, we have already gone 18.1 light hours, 4.2 light years is not an unreasonable jump.

[Nadya]

~5.5x that speed is still about 13,636~ years. Much better but still not very realistic....

18.1 lighthours is 3/4ths of 1 lightday. Which is 1/1533 of 4.2 lightyears or in other words: 0.06% of the way there. Going the remaining 99.94% is a massive jump!

[cheez]

Can you link to more information?

[afreak]

Not the best link but here's something to chew on:

http://www.universetoday.com/15403/how-long-would-it-take-to...

>However, despite these advantages in fuel-efficiency and specific impulse, the most sophisticated NTP concept has a maximum specific impulse of 5000 seconds (50 kN·s/kg). Using nuclear engines driven by fission or fusion, NASA scientists estimate it would could take a spaceship only 90 days to get to Mars when the planet was at “opposition” – i.e. as close as 55,000,000 km from Earth.

> But adjusted for a one-way journey to Proxima Centauri, a nuclear rocket would still take centuries to accelerate to the point where it was flying a fraction of the speed of light. It would then require several decades of travel time, followed by many more centuries of deceleration before reaching it destination. All told, were still talking about 1000 years before it reaches its destination. Good for interplanetary missions, not so good for interstellar ones.

There's talk of other drive systems being able to pull it off but this is the only one that actually has been tested but never built to scale.

[boxy310]

He's probably thinking of Freeman Dyson's Project Orion: https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...

[Cozumel]

http://breakthroughinitiatives.org/Initiative/3 http://www.spaceflightinsider.com/missions/stephen-hawking-r...

It says the probe would be able to get there in about 20 years, travelling at 20% the speed of light, that's around 37,200mps.

There's going to be a relativistic effect, I think 20 years from our perspective will be slightly shorter from the probes point of view?

[brazzledazzle]

I'm reminded of the books Illium and Olympos by Dan Simmons.

[civilian]

I've read them--- how and why are you reminded of them by this story?

[brazzledazzle]

I was referring to the comment I replied to.

[fapjacks]

<Obligatory flamewar-starting "Em Drive" comment>