> The actual suitability of this kind of planet to support water and Earth-like life is a matter of intense but mostly theoretical debate. Major concerns that count against the presence of life are related to the closeness of the star. For example gravitational forces probably lock the same side of the planet in perpetual daylight, while the other side is in perpetual night. The planet's atmosphere might also slowly be evaporating or have more complex chemistry than Earth’s due to stronger ultraviolet and X-ray radiation, especially during the first billion years of the star’s life. However, none of the arguments has been proven conclusively and they are unlikely to be settled without direct observational evidence and characterisation of the planet’s atmosphere. Similar factors apply to the planets recently found around TRAPPIST-1.
This was a good one: https://www.reddit.com/r/WritingPrompts/comments/35mgnn/wp_a...
They'd likely have radically different definitions of poles. One hot enough to melt lead, one cold enough to freeze C02.
It's a Sci-fi book about life on Proxima Centauri and includes the idea you mentioned.
(Also a really good read!)
I have this annoying habit of impulsively buying books recommended on HN. Never been disappointed by one though. So thanks! :).
Well, in a certain sense the West Pole and East Pole would exist in the manner you describe, but the behavior is not similar to that of the north and south poles. The stars will still rotate around the north-south axis, and east-west still won't affect that. It's not obvious that both phenomena should be called "poles".
Note that "north - south" poles already refers to two distinct phenomena, the axis of rotation and the axis of the magnetic field (these happen to be closely-enough aligned on Earth that the latter has historically been used as a proxy for the former, though this is by no means a universal feature of all planets.) The axis of orientation to the sun, for a tidelocked planet, seems no less plausibly described as "poles".
People always make use of local geographic features when describing directions; river communities use "upstream" and "downstream" and island communities use "inland" (away from the sea). Those aren't termed poles (even though "inland" is defined by reference to a line perpendicular to the ground!), and while I agree that the axis of orientation to the sun is more pole-like than they are, it's still different enough that I don't see that it would necessarily be referred to in the same terms.
Sure, and that's why the axis-to-the-star probably wouldn't define "north" and "south" poles, but not a reason it doesn't make sense to call that the points where the surface intersects that axis through the planet "poles".
Having thought a bit more, I tend to think it's unlikely that both axes would be significant to the same people (and therefore that they are particularly unlikely to share terminology):
- One important aspect of east-west historically is that east is sunrise and west is sunset. This wouldn't matter to anyone on Tidelocked World, but it corresponds pretty well to the idea of having a Day Pole and a Night Pole. The Day Pole would be apparent to anyone who lived in an area where the sun was visible, and the Night Pole would be totally unapparent to everyone else; it is significant only in that the Day Pole is on the opposite side of the world.
- Historically, north is cold and south is hot. This would apply, I believe, only to the day side of Tidelocked World. It reinforces the idea of a Day Pole while doing nothing for the Night Pole (everything beyond the terminator should (?) be equally cold).
- North and south are also defined by reference to the stars, which rotate around the polar axis (this is the origin of the word "pole", and would definitively rule out a Sun Pole if "poles" had to be defined that way, which they don't). This would be apparent to everyone living in the night, but probably not to anyone in the day.
If you believe all that, then we have the sun as a navigational aid that guides us toward the hottest part of the world, and the stars as a navigational aid to indicate the North and South Poles, but no concept of a Night Pole, because that concept is useless on the night side and there are no local indicators for where it is. Day people would be likely to refer to "sunward" and "darkward" in the manner of islanders, and night people would likely refer to "north" and "south", but day people would be unlikely to recognize "north" and "south", and night people would be unlikely to recognize "lightward".
I don't think so. Winds, diffusion, conduction, refraction probably come into play.
It does occur to me that the Night Pole might be revealed by the shadow of the planet, if it has a moon.
Think of the industrial applications! You'd have early metalworks near the hot pole, and when they'd finally figure out thermodynamics, I could imagine a planetary thermal engine created by bridging the hot and cold areas...
So that'd be more advanced than us I think.
So there might be a season change every so often
That said "I can imagine" isn't terribly good science. Articles like https://en.wikipedia.org/wiki/Dynamo_theory don't make mention any role of the Moon, and googling around drowned out the actual question by talking about how the Moon might have once had a magnetosphere, along with articles about how smaller planets might be able to.
It doesn't. The planet was spinning when it coalesced from a planetary nebula and conservation of angular momentum means it sped up as it coalesced. As the moon moves further away it _slows down_ the rotation of the planet.
I tried to find some discussion on this subject. I found this  quite recent paper (2016-03-31) that states that influence of Moon is necessary to maintain Earth's magnetosphere. Just food for thought. There are articles that quote this paper on the Web, but they have this suspicious date of 1st April (but paper was published day before) :)
We can't calculate those odds. We can't even start. It's like trying to calculate the likelihood that future AI will destroy humanity. We just can't know because it's so deeply theoretical.
For that reason, it seems absolutely absurd to me that someone would say with certainty that life exists elsewhere in the universe. We just can't know. The unlikelihood of its existence could be infinitely high and we might just be lottery winners. Who knows?
And frankly, I hope we're alone. I really don't want to share the universe. It would be so much nicer just to have it to ourselves. Let us do what we want, wherever we want, without interference until the heat death of everything.
As for not sharing the universe: what a depressing thought.
I'm not sure you have a conception of how truly BIG the universe is. In fact, according to current cosmological evidence, it is infinitely big.
But even if we confine our discussion to our Hubble Sphere, there is almost certainly life elsewhere in the universe. It's just that that life might be very, very far away.
I think the law of large numbers applies here. The likelihood of life existing being high enough that we are the only ones, but low enough that our existence isn't winning some 1 in a googolplex chance just strikes me as an anthropocentric conceit.
We don't know how difficult it is to create life. The universe is big, but the difficulty of creating life might be much bigger.
Thus. It is not certain that there is life elsewhere.
The closest star. But, we struggle to observe it in any capacity. Indeed, only today we did. And that's nothing to say of the next closest star, or the next, or the next, ad (nearly) infinitum.
If planets in this zone aren't as rare as we think, life in the universe might also not be as rare as we think.
To me, the question is more "where," rather than "if."
Something that's probably a lot more rare is favorable conditions over a long time period. It took a long time for life on planet earth to evolve into more complex forms.
I'm pretty sure we're not the only ones out there. But will mankind and our space neighbours exist long enough to facilitate communication?
Is every species that is competitive enough to subdue all other life on its planet doomed to disintegrate due to internal conflict?
e.g. imagine a universe containing a million intelligent civilisations, but each of those intelligent civilisations is in a separate galaxy at least 100 million light years apart. If that is our universe, we might not encounter any of those other civilisations in the next million years. The odds of human extinction could easily be higher than the odds of having any contact with them.
The alternative is the anthropocentric view that the entire universe was created merely for our viewing pleasure on Earth.
What you are talking about is "anthroexclusive", or something like that.
See my response to whom you agree with: https://news.ycombinator.com/item?id=12359111
We know how stars form, how galaxies form, how solar systems form. We know the general consistency of the galaxies around us, and some systems in our same galaxy. It's not a big leap to assume that some percentage of them will be hospitable (for a time) for life, at least life as we know it.
I'd say the arrogant views are that the whole universe was created for us, or that life must be thoroughly plentiful throughout the universe. The least arrogant view is that it's somewhere in-between, but more importantly, to always adapt to the latest evidence.
So to try to extrapolate that to the "inevitability" of complex life in the universe is like saying that your name will be spelled out in ASCII in the repeating digits of Pi somewhere. Maybe? Can you prove it? No?
I'm not a philosopher of science, or statistician. But the assumption that somewhere there are things "like us" seems to be both arrogant and very teleological -- an implication that the universe proceeds towards an order very similar to us. (Popular science fiction is infested with this kind of telelogical narrative.)
And contrary to arrogantly thinking earth-life is special and unique my argument is that we are just one of a rather infinite variety of "things" in the universe. Life is amazing and complex -- but so are the clouds of Jupiter.
Well, "like us", inasmuch as an entity that is self-regulating, and capable of response to external stimuli. The most basic assumptions for life.
So yes, at some level it is arrogant to assume there's anything else like us. Your view is very nihilistic. But, until we know of other sentient species, it is all about us. We are, as far as we know, very lonely, ex-nihilio orphans in the vast universe. It's only arrogance to nothingness to posit there might be more life in the universe. It is not arrogant to humanity.
So, yes, we are in many ways better than clouds of Jupiter. But of course it is us making that claim. So what? Allow humanity some slack. If we have offended some unknown creator with our supposed insolence, perhaps it should make itself more easily known.
But we make no use at all of 99.999999999999999999999% of the universe, so how does it hurt us if some other species do?
Liu Cixin's The Dark Forest has an interesting take on this. Basically it's conceivable that the game-theoretically optimal policy is to kill any other sentient species you come across, even if it means you lose access to whatever resources they currently have. This argument falls apart at some point, because it's (presumably) not optimal for all humans to try to kill each other all the time, but it's an interesting idea nonetheless.
Basically we can't say a much about what the fraction of planets that develop life to planets that have conditions for developing life is based on just one example, but there's no apriori reason for particular pessimism about that number just yet.
Now how likely the conditions are to begin with is a different matter. They've certainly improved in the last decade, since planets at least seem to readily form and earth-sized things too, and apparently easily end up in orbits that could allow for water to exist etc. There's clearly a bunch of other potential conditions that may be necessary for abiogenesis -- untill we know more about how exactly it happens, we can't tell (and actually finding separate origins of life would greatly help in undestanding what that is)
I for one think it very likely this particular planet isn't habitable, because Proxima is such a lousy star, but it's certainly not ruled out. But also that microbes are likely reasonably common in the universe. Around a small fraction of the total number of stars, only some small percentage of what we'd consider candidates today based on their sizes and orbits -- but still that leaves immense numbers.
If further climate outcomes continue to track Hansen's thus-far correct 35-year-old predictions , then we've already passed some kind of tipping point and "the heat death of everything" could potentially mean Venusian-style anthropogenic cooking of Earth in some worst-case scenarios, and mass population dislocations and mega-scale environmental disruptions in milder scenarios.
If it turns out that life as we know it is exceedingly rare (and I must admit that the more we find out about exoplanets, the more disconcerted I am while realizing that the hazy possible solution space to the Fermi Paradox is becoming rather uncomfortable as the resolution grows with each passing decade), then that would be truly a tragic outcome.
Somehow we always feel that aliens would be always bad to humans, there might be good aliens also somewhere who might help us in solving our current diseases/share advance knowledge or even give us new resources!
For all practical purposes we have it all for ourselves and we are doing nothing with it.
There is no serious investment in seeking a different home outside of earth.
The universe is huge, really huge, so huge that even the distances to other planets in our solar system are so vast, that when you would consider the earth 1mm big, these distances would still cover thousands of kilometers. It's not possible to draw a liniarly scaled map of our solar system, so big is it.
Good news: life has plenty of space and probably also plenty of planets to find its way multiple times in the universe :)
Bad news: we probably won't find this life ):
Ever since I saw it done in the new Universe series, a pet peeve of mine has been treating the giant impact hypothesis as some kind of established fact. Even the name on the wikipedia page includes the term "hypothesis":
The hubris surrounding the presentation of that particular hypothesis to the public is really, really awful. I actually stopped watching that new Universe series mid-episode after hearing it presented as fact (this was sometime in the first few episodes, maybe the first episode) and stopped reading this wikipedia page just now.
It is actually the most active flare star we know. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1063292/
Should I admit on HN to having watched a Vin Diesel film? Pitch Black, anyone?
Astronomy nerdship aside, I loved Pitch Black. Such a good movie. I haven't watched any of the sequels, though.
The first game that they released, surprisingly for a movie to game adaptation, was also quite good.
Fabulously geeky dude, I like his style.
 - https://www.goodreads.com/book/show/99245.Nightfall
Fun to think about, anyway.
The distance between the planet and the star is ˜7,000,000 km. The diameter of the star is roughly 1.5 * the diameter of Jupiter: 207525 km. The angular size of the star from the surface of the planet will be the arcsin of (207525 / 7*10ˆ6) or about 1.7 degrees.
This is a little bigger than three times the apparent size of the full moon or the sun from Earth.
The speaker even mentioned the previous incorrect HARPS announcement, which was later found to be an artefact due to the windowing function they used - a pretty embarrassing mistake. This new finding involves a completely different period: 11.2 days instead of the previous 3.24 day signal.
Also, link to the Nature paper for the lazy: http://www.eso.org/public/archives/releases/sciencepapers/es...
This is around Proxima Centauri, the previous one was around Alpha Centauri B. Proxima is a really really small red dwarf, just 12.3% the mass of sun, while Alpha Centauri B is a K-type star, ie somewhat smaller than sun but not that much; around 90% of Sun's mass (And there's also Alpha Centauri A, 10% more massive than the sun). We're not even 100% sure that Proxima is part of the Alpha Centauri system, though I gather it's considered highly likely - it's pretty distant from the Alpha Centauri system, some 15 000 AU (1 AU = distance between Sun and Earth), almost a quarter of a light year.
I'm just not sure if that's what the speaker in your video was talking about, of if the embarrasing mistake that was actually announced was the Alpha Centauri Bb planet (or maybe there were other candidates I didn't hear about); I'm gonna watch the lecture you linked and see. Thx for an interesting link, btw!
If by "interesting" you mean constant hurricane force convective flows going 24/7 between a scorching hell and frozen wastelands.
Before there was soil, or sky, or any green thing, there was only the gaping abyss of Ginnungagap. This chaos of perfect silence and darkness lay between the homeland of elemental fire, Muspelheim, and the homeland of elemental ice, Niflheim.
Perhaps it could be "the chaos of perfect silence," because the wind noises generated would render any unprotected human ears deaf within minutes?
Seems like this would allow surface habitation some way onto the bright side. Wind at the surface would be blowing from cold to hot, with the return at some altitude.
Hey, at least it's a short walk between cooking your food and icing your drink!
But there were various modelling attempts to see how a tidal lock affects the climate, and it may not be a dealbreaker; not too thick an atmosphere could effectively transport that heat around, at least so that it doesn't risk freezing the atmosphere on the dark side and making it uninhabitable. But its just modelling so..
Maybe even more problematic is that a tidal lock could imply no internal dynamo, and so no protective magnetic field, and Proxima flares quite a lot, so it could have totally eroded its atmosphere and sterilized the surface with UV etc. Plus Proxima was much much hotter early on; would that period have permanently made the planet uninhabitable?
We just know so very little about habitability of M-dwarfs, and particullary the really small ones; we'll just have to find out,
Before we took a close look with probes, we thought Mars had lichens living on it, to explain its color variations or some such; there's no reason to think we have any more clue about M-dwarf planets than we had about mars then, for we have yet so study any.
Good thing one just happens to be in our backyard :D Though realistically, perhaps it turns out easier to study more distant M-dwarf planets, because this one seems not to transit from our perspective. And I think we could study the spectra and hence atmospheric composition of transiting planets sooner than we can hope for direct imaging of them. Not perfectly sure though.
s/M-dwarfs/planets around any star/
But on the other hand, we see all kinds of planet types around all kinds of different stars that pose similar problems (say superearth habitability), so even that only applies to questions about planets more similar so some of the types we can find in our own solar system.
Previously on HN: https://duckduckgo.com/?q=site%3Anews.ycombinator.com+cixin+... https://hn.algolia.com/?query=Cixin%20Liu&sort=byPopularity&...
You can watch it live here: http://livestream.com/viewnow/NIAC2016
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.
Sounds like the interstellar version of Zeno's paradox.
A single probe in orbit could obviously do this but with this idea there's no way to slow down.
>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.
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.
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
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.
Nothing that could be implemented in any foreseeable future though.
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.
It made me realize that the civil defense films we watched in the '50s weren't so misguided after all:
it might be prudent to first consult with the legal experts and diplomats of the Galactic Council, to clear this type of activity with them first, minimize interpretation of this probing as a hostile interstellar act.
Clearing it with the Galactic Council definitely sounds like a good idea. Do you have their phone number handy? I seem to have deleted their contact info by accident.
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.
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).
 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).
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.
> 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.
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...
> 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. 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. Results have been reported as "inconclusive".
Also, the energies involved are absurd.
An updated design from the 80ties calculated a time of 100 years:
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.
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.
It might be just around the corner in space travel time, but those are quite a few light years still.
Edit: Nuclear pulse propulsion is good for about half that (80yr, not 1000).
Many missions to the outer planets are flybys since we can't have enough fuel to actually slow down.
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.
Although I'm not sure these probes are at all steerable, either autonomously or remotely.
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.
What about orbiting the planet and using the lasers when the craft is orbiting towards us in blasts to slow it down gradually?
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?
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).
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!
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.
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.
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).
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.
tbh I think storing enough food for the journey is going to be the least of all problems
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.
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.
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.
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.
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.
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.
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.
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.
- 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
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?
You're looking at closer to 75,000 years - not 1,000 years - to reach Proxima Centauri.
Did actual maths. Closer to 75,000 not 100,000.
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
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.
This is a bloody big country.
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.
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!
>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.
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?