With Alpha Centauri being only 4 light years away, interstellar travel seems almost feasible. But then you consider all the inconvenient details, and realize such a journey would have to take hundreds, maybe thousands or even more years on top of some incredible advances in rocket tech.
If you go to something like Trappist (40 ly) at 0.01c (very optimistic), it's not just that everyone you know will be dead when you arrive. Your entire nation will have disappeared to the sands of time. The landfall announcement you send back will be incomprehensible because of language shifts, and you won't live to see the reply. Meanwhile, such a trip would be an enormous investment, requiring multiple nations to bankrupt themselves, with no hope of even surviving to see the outcome.
With that, it's very hard to imagine interstellar travel being feasible with our current understanding. There would have to be something like FTL travel or wormhole. The only "realistic" development, (much) better engines that can do 0.1c, would not actually change much.
I recently read this in an interview with Juergen Schmidhuber:
> Of course, such life-like hardware won't be confined to our little biosphere. No, variants of it will soon exist on other planets, or between planets, e.g. in the asteroid belt. As I have said many times in recent decades, space is hostile to humans but friendly to suitably designed robots, and it offers many more resources than our thin layer of biosphere, which receives less than a billionth of the energy of the Sun. Through life-like, self-replicating, self-maintaining hardware, the economy of our solar system will become billions of times larger than the current tiny economy of our biosphere. And of course, the coming expansion of the AI sphere won’t be limited to our tiny solar system.
Yes, we have a long ways to go before we can be considered a starfaring species, one that can make and keep long–term agreements when they involve round–trip times in the tens of thousands of years. Still, it can be useful to altruistically start colonies before then.
There’s a book called Count to a Trillion which explores these ideas, and others. At the end of it the main character’s wife sets out on a mission to M33 and isn’t expected to return for at least 70,000 years. He gets stuck on Earth, unable to catch up with her, and promises to be here when she returns. The sequel is all about what he has to go through to keep Earth a going concern while she’s away.
Worse, you have no idea what you will find on the other side and weather that includes somewhere that doesn't make the arctic poles on earth look like paradise. And you'll be traveling in a small confined space. For ages. The good news is, you'll probably be unconscious for the journey. The bad news is that a lot can happen in decades/centuries/milennia and there's no guarantee you'll actually wake up. And everything else you said.
That raises the question who would want to travel and why. And what's wrong with them. Because the profile for people that want this would be hard to distinguish from somebody that is depressed and suicidal.
Given those time frames, maybe don't send primates. Send a computer babysitting a diverse zoo of bacteria and algae, with a variety of landing devices and instructions in what order to deploy them under which circumstances.
Same problem: the best-case outcome is that we never hear anything interesting from that rocket ever again. But it should be a lot cheaper.
Those age too. Especially out there without the earth's shields. If you make one that lives longer than a human it's already quite the feat, add only a bit more radiation, it only gets worse. Computers are much worse with failures than brains too.
The nice thing about biological systems is the self-assembly from tiny molecule parts. Worst case, you can create a closed system with birth/death renewal. For tech the machines that build the machines, and the machines that build or repair those in turn, will all have to be brought along too, or you need to have some impossibly tough requirements for the product to last.
We may need some similar automatic self-assembly for tech for such use cases. The whole spaceship and all its components will deteriorate too.
Even when we sent out ships to venture around the world they had to be able to do replacements for broken parts, like masts. We probably need that capability for space ships too, to stop at some asteroid and rebuild. But then you get the equivalent of the rocket equation: On the one hand, you need a lot of stuff to support that manufacturing, on the other hand, every item you add itself needs maintenance and rebuilding at some point. The way out is this molecular-level self-assembly. You throw a few tiny nano-machinery dust spores on an asteroid, and ten years later you grew some useful machinery...
> it's very hard to imagine interstellar travel being feasible with our current understanding.
Even with massive advancements in tech, and getting close to the speed of light, interstellar travel will be a lot of "one way heading into the unknown forever" kind of initiative. Interstellar empires only work with truly sci-fi tech that mostly ignores distances, like in sci-fi (instant subspace comms or warp travel with no relativistic effects)
This will never be the same kind of age of exploration as when we crossed the oceans and explored our planet. The scales are so mind blowing that even the fastest speed known to mankind is too slow. The times and distances involved to move and even just send signals (both ways!) and relativistic effects means at best we can "seed" a distant planet and hope that turns into a new (human?) civilization, forever separated from us for all practical purposes.
> it's not just that everyone you know will be dead when you arrive. Your entire nation will have disappeared to the sands of time.
Humans are just a stepping stone. Earth intelligence will transcend our 77 year lifespans and primate brains.
Our lungs are adapted to gas exchange on this particular gravity well and its unique biogeochemistry. There's no reason redox reactions need to happen like this, or indeed even be the primary propulsion mechanism.
This is our frail biases speaking. We are limited by our biology, but we won't be forever.
Why is everyone so fixed on interstellar travel? What if the galaxy is chock full of rogue planets? There may be hundreds if not thousands of worlds between us and the surrounding stars. Hopefully, Roman Telescope set to launch in 2027 is going to find lots of them.
Developing propulsion technology to reach 0.1c velocity will move the needle on interstellar propulsion from impossible to just barely feasible. Although that is at least 100-200 years away, we can absolutely start expanding into our Solar System, starting with nearby bodies, like Moon and Mars.
> Developing propulsion technology to reach 0.1c velocity will move the needle on interstellar propulsion from impossible to just barely feasible
More than barely. "A 40-year one-way interstellar flyby mission to the nearest stars will require a relativistic spacecraft speed in excess of 6000 AU/yr (i.e., > 0.1c)" [1].
That means, practically speaking, nuclear-fusion, antimatter-annihilation and directed-energy propulsion. All of which are TRL ≤ 2.
My bet would be on fusion propulsion. It's inherently easier than fusion power since you don't need to bother converting the energy to electricity. That said, solar sails [2] and directed-energy anti-drone weapons [3] are seeing quiet progress.
Nobody debates this. The point is that 0.1c propulsion is not necessarily 100+ years away. And its 40-year transit time is not "barely feasible," it's comparable to present deep-space mission timelines [1].
However, travel at 0.1c is not needed for the Fermi Argument to bite. Much slower speeds would allow a colonization wave to sweep a galaxy in time << the age of the universe.
Even at .0006c (our current tech), the galaxy would be filled with (weakly self propagating) robotic probes after just 750 million years. Unless extremely long lived self-propagating probes just ... die out ... that implies no aliens older than 750 million years from our galaxy. It implies no aliens from the nearby galactic neighborhood within 3 billion years. That kind of implies we're all alone.
I have three wild-eyed theories: (1) eukaryotism is an unbelievably exotic step; (2) and/or the moon is required and ultrarare; or, (3) advanced civilizations eschew yellow stars for being inconveniently short-lived: maybe they prefer brown dwarfs, white dwarfs, or black holes for their energy gradient.
The comment by Benjamin Stockton on the article page is spot-on:
>I just wonder if humanity’s adventurous nature is leading us away from a proper focus on the sustainability of our civilization, our specie, and our fragile planetary environment?
But we still need spaceflight at least for planetary defense against asteroids, mining asteroids(so we don't have to mine Earth), etc.
Not only is that comment a false dichotomy (we can both explore space and make humanity more sustainable at the same time), it also presumes that space exploration and sustainability are at odds with one another and not synergistic.
Humans, simply by existing on Earth, have a huge and often negative impact on the environment. If we could somehow shift the human population off Earth, either by terraforming planets (like Mars) or creating artificial space habitats, it would have a huge positive impact on Earth's environment. We don't currently have the technology to do so - we would need space elevators to feasibly move humanity off Earth - but that doesn't mean we should move our attention away from space in the meantime.
> What resources are on asteroids that justify the energy expenditure to get from space and back?
With chemical rockets, not much.
With "a propellant-less propulsion propulsion system such as solar sails or electric sails," bringing water (propellant) to low-earth orbit starts making sense [1], as does mining platinum, but only if "the quantity of platinum from space would substitute an equal quantity of terrestrial platinum," i.e. moving heavy industry off the Earth's surface [1].
Given asteroid-mining profitability is dominated by "the throughput rate, which depends on the mining process," it's possibly to see a path to certain rare-earth minerals becoming profitable to mine in space if environmental controls on Earth are tightened while constant-thrust propulsion technologies advance.
Just skimmed but does this answer the question of getting to and from the surface of earth? Or are we just stockpiling platinum in LEO for some reason?
Or, just fashion the metal into ingots that are coated with an ablator (carbon, say) and allow them to enter as artificial meteorites. Suitably sized they will hit the ground at reasonable speed and can be dug up.
Even better than carbon use an ablative made out of olivine that can sequester CO2 as it ablates.
That way by offloading mining and refining into space to prevent the damage that these activities incur on earth you're also undoing damage to Earth from past human activities.
The energy involved in chemical rocketry is actually not that much. Getting a kilogram to LEO is roughly as expensive (in energy) as flying it to the other side of the world in an airliner. Getting stuff back from an earth-crossing asteroid can also be very cheap energetically, with very small delta-V (if one is willing to wait long enough).
And the delta-V back from a NEO is as little as 1% of that to get to LEO from the Earth's surface.
Also, the materials we're talking about from asteroid mining, like platinum group elements, probably are shipped by air, just for security.
This whole argument is reminding me of the facile and bogus argument that launch to earth orbit from planet's surface is expensive because of the energy needed.
If it's a bogus argument then mount a counterargument. The question is simple: what is worth mining in space?
So far we have... "maybe platinum." Maybe!
Aside from the conspicuous absence of math, "maybe platinum" isn't remotely important enough a factor in earthbound mining to justify asteroid mining on the basis of preserving earth, obviously.
I recently read "Delta-v" and the sequel "Critical Mass: A Novel" by Daniel Suarez. They're very much fiction but there is a certain amount of science underpinning the arguments and I enjoyed that aspect. And the author even states that he's trying to get across, with solid arguments, why humanity should begin planning asteroid mining ASAP. In brief, the arguments are:
Firstly we're now at a point where we have lots of cheap energy available, principally chemical. Depending on many factors it's conceivable that we are in fact at or near peak human energy output (e.g. WW3 or civilization collapse - the next iteration of civilization won't have so much cheap oil to exploit).
Secondly LEO is not yet full of junk, meaning that it's trivial to find launch windows to LEO and beyond. That could easily change very much for the worse in a relatively short time (I infer decades from the books).
Finally it's unrealistic to expect us to colonize the Moon or Mars using only Earth-mined materials. You can launch a spacecraft to Mars easily, but to launch a small city's amount of construction equipment and raw materials is beyond our capabilities.
Conclusion: now is the best time to mine asteroids. We can do all of the processing and much of the construction in LEO (or even better at Earth-Moon or Earth-Sun lagrange points) and then, with relatively low delta-v, we'd actually have a chance of becoming an interplanetary species!
But, the novels warn, the window of opportunity will eventually ("soon") close. Well worth the read.
Maybe someone else more familiar with the arguments, who has also read these novels, can offer a critique?
What's worth mining in space? Everything that we can mine in space. That seems glib but I'll elaborate.
By moving mining off planet to the moon and asteroids we eliminate the carbon emissions and environmental damage that occurs from these processes.
So how do we do it? We don't need to start sending fleets and fleets of crafts into space which is energetically expensive and time consuming, what we need to do is develop self-replicating mining equipment that we can send to turn the things we want to mine into more things that can mine for us. We won't achieve full self-replication immediately but we can definitely send machines that can do partial self-replication at first and work on improving the ratio of material sent to material returned.
What do we send back? titanium, platinum, aluminum, nickel, iron, whatever we find there. If platinum was as cheap and plentiful as aluminum was now we would have all sorts of catalytic uses for it that would significantly clean up our Earth based industrial practices.
How do we send it back? If we're sending it back from the moon that's easy -- a space elevator or rail gun. If we're sending it back from asteroids inefficient but cheap iron ion thrusters. Use iron from the asteroids as fuel.
Bonus points: Send it back covered in ablative material like mined olivine that can react with CO2 in the atmosphere to sequester it, that way the whole process isn't just moving environmentally damaging industrial practices to other solar bodies but we're undoing some of the damage from past human activities.
Not the person you responded to but my 2cents.
You expect to find the vast vast majority of materials for this self replicating mining equipment as well on the same asteroid?
For them to put up the huge amounts of energy generation, materials refining and self fabrication for them to do a large amount of tasks and build reentry packages without us sending a lot of stuff into space lest we very easily surpass the impact of mining on earth.
We'll have to get very very creative with nickle-iron and silicates to build a small automata civilization on big flyby rocks.
I don't need to argue things are practically mineable in space to rebut the point. I just need to argue if they aren't practically mineable, energy consumption isn't a reason.
I have already given you the counterargument.
> we have maybe platinum
Those making the energy argument need to rebut every possibility. The "it takes to much energy to ship back" is ludicrously wrong for platinum. The argument destroyed, why would we need to say more?
It takes as little as 0.1 km/s delta V to get onto an Earth-intersecting orbit from known NEOs. The energy of a mass moving at 100 m/s is 5x10^3 J/kg, or 1.4e-3 kWh. If a kWh costs $1 in space, this would be a fraction of a cent per kilogram. This delta-V is so small that the energy cost of sending back base metals would be affordable. Hell, the energy cost of shipping gravel from space would be affordable! Other costs, probably not, but that's not the claim we're addressing.
"What resources are on asteroids that justify the energy expenditure to get from space and back? Can't be many of them..."
I suggest re-framing the the question as the cost of preserving the objectively limited and to the best of our knowledge singularly unique in the Universe resource, which is the surface of Earth.
Acquiring resources that do not deplete or spoil the future of life on this planet should be in everyone's best interest.
Yeah no. Unless someone can answer basic questions like “what even comes close to net positive in energy expenditure to mine elsewhere,” then this is just a cover story.
The reality is that saving our environment will be a whole set of difficult and profoundly boring solutions to real, known problems.
Would be cool if we could solve it with badass rockets, explosions, big noises, and adventure, but the complete lack of even remotely convincing answers to first order questions on how this actually works belies the fact that it doesn’t. It makes no sense.
We need to develop better plastics, proteins, and pesticides. Not send protein blobs to other planets because it looks cool in sci fi movies.
> We need to develop better plastics, proteins, and pesticides. Not send protein blobs to other planets because it looks cool in sci fi movies
The reality is more people get passsionate about working on things that look cool in sci fi movies than developing plastics, proteins and pesticides for a mediocre paycheque. This lesson--that the path to groundbreaking technologies is through inspirational moonshots, not committees prescribing what is and isn't necessary--is so thoroughly repeated throughout history that it's a wonder we keep missing it.
Groundbreaking technologies are not created via moonshots. They’re created by decades of slog. Moonshots can launch from an unremarkable platform of slog, but the slog had to happen. You just cannot speedrun the vast majority of questions that need to be answered to power a breakthrough.
That’s why I’ll question glory-chasers who want to sit on the rocket but can’t take a few thousands of pay cut to stare for a few years at a true problem that needs solving.
Our species’ actual heroes are those who powered through the slog.
Yeah and usually the moonshot is a lot less circularly defined than “this moonshot is worth achieving because if we achieve it we will have built cool stuff to do it.”
The most compelling economic reason to pursue the technology of asteroid mining (at least as far as Earth's gravity well is concerned) is not to ever actually launch any serious asteroid mining operations, but rather to fool those who own gold into believing that you have the capability to devalue gold at your whim, and thereby accept a small ransom to not go asteroid mining.
Our civilization has been driven by expansion. Without it we'd probably collapse into a neurally-connected well-organized ant colony without need for further technological/social/economic progress (which would naturally select/cull out corresponding features in our brain). And, i'd guess that is possible one of the forms of the Great Filter stopping many civilizations.
At 53 and good health, i'm contemplating that my end in 30-40 years would be me buying a one way to Mars and just exiting the habitat out without suit after enjoying a dinner with a Martian sunset view, breaking, even in such a small way, the chains of "We come from the earth, we return to the earth" :)
Why would we not chase technological progress without increasing our proverbial footprint?
We're not starting to inhabit new bodies of land for a long time now.
We're slowing down our footprint growth among those in the most developed places but chasing new technologies hasn't slowed down accordingly.
That's a truly awful way to die (all your fluids and gases suddenly surging through your tissue).
Seems much easier to reframe the "chains" of earth into acceptance of a remarkable cycle that we're privileged to get a glimpse of from the inside and just die happily here with your loved ones.
> Seems much easier to reframe the "chains" of earth into acceptance of a remarkable cycle that we're privileged to get a glimpse of from the inside and just die happily here with your loved ones
This works for most people. Most humans didn't leave Africa or Mesopotamia or the Old World, either originally or in the Age of Exploration, and most Americans today don't have a passpport.
That is about my point - i want to get as far as possible from such a philosophy as it is taking over the civilization. I lived under similar philosophy in USSR and, as long as it is up to me, i'll be trying to put a distance in all senses.
I don’t know, GPS is quite useful, Landsat is too, along with the various other Earth imaging satellites and systems like modis and sentinel-2. Sure is good having food. Weather forecasts are nice. It’s also quite convenient to be able to use space based data services. It’s also useful for power grids to know when they’re about to be whacked by a CME. I’m sure sailors on sinking ships appreciate being rescued.
But sure, we should solve all the problems on earth with one hand tied behind our backs until we can launch any more rockets.
>To get around thousand-year generation ships, we are examining some beamed energy solutions that could drive a small sail to Proxima in 20 years.
The odds of a spacecraft hitting a single particle of dust while in space are 100%.
A spacecraft hitting a single particle of dust at 0.2c will impart tens of millions of joules into the body of the spacecraft, the equivalent of getting hit with hundreds of pulses from the most powerful laser ever created by humanity-- simultaneously.
Or concentrating several kilogram's worth of TNT into the size of a particle of dust and detonating it.
Most of the designs for a system like this are "chip" designs where a single 1cm x 1cm silicon wafer is towed by the sail.
This design prevents the need for lasers so large that they create enough ozone to kill the entire human race.
The contents of the chip vary, based on who is speculating, but tend to contain exotic, uninvented, circuitry capable of both harvesting energy from the laser and doing "something" of use besides zipping by the target at 0.2c deaf, dumb, and blind. Sometimes it's even an AI-enhanced swarm! (Shoulda figured out how to work blockchain in there, post-doc guy)
Regardless, during the 40 trillion kilometer voyage to Proxima Centauri, that 1x1cm silicon wafer (and the sail) will hit space dust, and numerous other atoms and molecules (including carbon rings) because empty space... isn't.
So it passes through the sail and then hits the spacecraft attached to the sail. Now what? kaboom? small holes in the hull would not be good for the occupants.
When it passes through the sail, enough energy is deposited in the grain to explode it, so if there's sufficient distance to the hull the vapor deposits sufficiently low energy/area to be tolerable.
Ten megajoules sounds like a lot, but a single kilo of TNT produces about 4 megajoules of energy. And the size of particles of dust and how often you’re likely to hit one in the interstellar medium is quite speculative.
> the size of particles of dust ... in the interstellar medium is quite speculative
Technically yes. I think there's a significant variety of sizes of dust or larger-than-dust particles in interstaller medium but I don't really have much to back that up.
> how often you’re likely to hit one in the interstellar medium is quite speculative.
Also technically yes. But unless you can map every single particle of dust, and their trajectories, I think the risk is absolutely real.
Are there any real proposals that deal with this issue for a vehicle that would carry humans and go fast? Something that's not "energy shields".
Edit to add: we basically understand the physics of accelerating something to a high speed, what it would need to be made from, etc., afaik all within the realm of possibility- if we could gather and direct that much energy and then wait long enough to decelerate at the other end.
It seems like the questions that are completely unaswered are: keeping people alive and healthy for that long, and how the ship could survive if it hit something.
"A 0.1 µm interstellar dust grain (≈10⁻¹⁴ kg) striking a spacecraft at 0.2 c carries ≈20 J of kinetic energy—millions of times below “tens of millions of joules.” Reaching 10–50 MJ would require a ≈0.14 mm grain (≈10 µg), vastly rarer than ordinary dust, and even that impact equals only a few shots from the world’s highest-energy laser (~2 MJ per pulse), not “hundreds.”"
I used something something 10^-10 for my dust. To reach ~50MJ.
As far as the laser goes, ~2MJ is the total output. Energy that reaches the fuel pellet due to inefficiencies throughout the path of the laser, the actual "hitting power", is hundreds-ish kJ.
Perhaps, some fraction of the laser energy beamed to move the sail is redirected directly in front of the spacecraft to vaporize any dust particles in its path. Fragments of a circular sail could be angled in the right way so as to take some fraction of the light's momentum in its desired direction with the rest reflected at an angle to clear the opposite side of the sail. For a circular sail you'd then get a circular "clearance beam" of sorts.
You're avoiding the energy that would be imparted by hitting the dust spec by... adding energy to the dust spec? Perhaps splitting it so it damages a larger area? It seems better to let it plow as small a hole as possible in the sail.
alternatively you ionize that particle, may be make in into plasma by laser for ease of "digestion" down in the engine, direct in into the engine where it is used as working mass for your ion thruster, kind of similar to scramjet.
As far as i see with today's tech - like Starlink's ion thruster + classic nuclear reactor - we can get to 300km/s in about 4 stages. Straightforward improvement of ion thrusters - mainly voltage increase and associated engineering (which will immediately happen once we start flying to Mars and beyond as ion thruster currently our best/fastest option inside the Solar system) - can get us to 1000-2000km/s, i.e. under 1000 years to Alpha Centauri (that for a large populated spacecraft, and for just tiny probe to announce our existence (and to send back photos which we'd receive using Sun's gravitational lensing) we can do even better). And using interstellar gas and dust scramjet-style will improve on those numbers (as such ship is mostly limited by the working mass it starts with while the reactors would be able to continue produce the energy much longer).
> alternatively you ionize that particle, may be make in into plasma by laser for ease of "digestion" down in the engine, direct in into the engine where it is used as working mass for your ion thruster, kind of similar to scramjet
This is a Bussard ramjet [1]. The interstellar medium is too thin to make it work. (Maybe we'll find the husk of an ancient ramjet from an earlier era of the universe floating around one day...)
Any autonomous machines in a distant enough future will look neither as the present humans or animals nor like the present robots, because they will have to use a mixture of the technologies developed by living beings and by humans.
Humans have developed various things that are better for certain purposes than anything used by a living being, e.g. metals and semiconductor devices (most of the human-only technologies are a consequence of the control of fire, i.e. of the ability to perform manufacturing processes at high temperatures, unlike the living beings, which are limited to temperatures close to that of the ambient). On the other hand, for other purposes the use of organic substances and of the methods of chemical synthesis used by living beings are unbeatable.
So any future descendants will have to use hybrid technologies, like the "cyborgs" of many SF novels/movies, except that I have never seen any SF "cyborg" that combined the right parts from "machines" and from living organisms.
As an example, for the problem of energy storage for powering a machine, for providing short-time high power bursts capacitors and batteries are better than the chemical reactions used by living beings, e.g. ATP & phospho-creatine hydrolysis and anaerobic glycolysis. On the other hand for storing high-amounts of energy for long-time autonomy at a moderate power level, none of the fuel cell or battery technologies that have ever been attempted appears to have the potential to ever match the performances of the enzymatic oxidation of hydrocarbons that converts their chemical energy into ionic gradients in living beings, e.g. in our mitochondria. So an ideal autonomous machine would combine high-power capacitors/batteries with high-energy biologically-derived fuel cells.
The only way I can see hope for spreading terrestrial life through the galaxy is to send tiny spacecraft. The spacecraft can survey what it finds and send the information back to earth. Earth can send back instructions to the nanobots on the spacecraft to build what is necessary from local materials, and then build life to inhabit it.
So this is another reason why I see Dyson Swarms as being the inevitable evolution of human civilization. Let me explain why.
First, to clarify, a Dyson Swarm is a cloud of orbitals around a star to use most or all of its energy via solar collectors. This was originally called a Dyson Sphere but was renamed because of confusion: people thought a Dyson Swarm was a rigid shell. It never was.
Anyway, the classic orbital is an O'Neil Cylinder, which would be 3-4 miles in diameter and 10-20 miles long. You spin it to get earthlike gravity. With this diameter the rotation isn't likely disconcerting and the centrifugal forces aren't so large as to tear it apart.
This kind of structure could be built with a material no stronger than stainless steel and using solar panels for power. It's relatively low tech. There aren't any exotic physics or exotic static states of matter required. It's basically an engineering problem and can be built incrementally.
Why do I mention this? Because fo rthe distances involved, an interstellar starshhip is basically just an O'Neil Cylinder. You need to support people for centuries. Such a cylinder could get 10s of thousands of people, possibly 100k+ to another system in relative comfort.
So how do you get to another star? The tyranny of the rocket equation means any form of propulsion where you need to carry to propellant just won't work with the possible exception of nuclear fusion.
But what if you didn't have to carry propellant at all? To accelerate or decelerate. That makes it way easier. But how would yo udo that? Easy, at least in theory: solar sails. The solar wind carries pretty significant momentum. A sufficiently large solar sail (and it would have to be large for such a ship) would absolutely be capable of accelerating a ship to at least 0.01c. And you can decelerate with the same solar sail.
You can do even better by collecting energy from the Sun and concentrating it on the sails, which is yet another reason to build a Dyson Swarm.
The energy budget to travel to even our closest star is so vast that we would need to do things like collect most of the Sun's output energy. I personally don't believe FTL is possible. Time dilation only really kicks in meaningfully at >0.99c and I just don't think that's parctical and, if it were, the energy required is even more vast.
In fact, at 0.99c you would suffer drag from the interstellar medium (gas and dust)..
So any intersteallar ship is going to be a generation ship, a habitat.
All life on Earth is going die. Humanity has never been content with staying put, why would we start now? And what do you mean "literally nothing there"? The universe has a loooooot of stuff in it.
By "literally nothing there," I mean there's literally nothing for us. Three stars and a few Earth-sized planets in the habitable zone that are, more than likely, uninhabitable by humans. There's nothing there worth going all that way for.
I like sci-fi as much as the next person but the reality of the situation, it seems to me, is that the universe is mostly empty, vast, and inhospitable to human life.
The difference between a multi-generational interstellar ship and a self-sustaining space colony is the engine. They wouldn’t need inhabitable planets - they would need raw materials to build more ships and habitats.
I’m not sure that after spending a lifetime in an ample space colony its inhabitants would feel nostalgic of the time we spent sitting on round rocks cooking around a star.
>Tragula's wife used to complain to him about the utterly inordinate amount of time he spent staring out into space, or mulling over the mechanics of safety pins, or doing spectrographic analyses of pieces of fairy cake. She would often tell her husband to have some sense of proportion, sometimes as often as thirty-eight times in one day. In response to her pleas for him to find some perspective, he built the Total Perspective Vortex.
>Into one end he plugged the whole of reality as extrapolated from a piece of fairy cake, and into the other end he plugged his wife: so that when he turned it on she would see in one instant the whole infinity of creation and herself in relation to it. To Trin Tragula’s horror, the shock completely annihilated her brain...
~Douglas Adams, The Restaurant at the End of the Universe
>Humanity has never been content with staying put, why would we start now?
For whatever reason, humanity's attitude in this regard has changed drastically in the last century. We can't even bother to make the next generations, and a shrinking population eventually (quite quickly, really) shrinks to zero. Not only do they want to "stay put", they want to lay down and die.
The steelman counterargument is that focusing resources on extraplanetary colonies at the expense of the one habitable planet within reach will hasten humanity's destruction. How are you going to make an Eden on Mars if we can't even make an Eden on Earth? The only large-scale planetary engineering in humanity's history is Veniforming its home world.
>The steelman counterargument is that focusing resources on extraplanetary colonies at the expense of the one habitable planet within reach will hasten humanity's destruction.
That doesn't seem like a strong argument to me. It seems like a distraction from the crowd that would save the planet by extinguishing humanity if that's what it took. Though what value the planet might have with all of us gone I leave as an exercise for the reader.
The first priority of any society that wants to continue to exist into the future must always be to make the next generation. If you do not do this, or if you just leave the task to others hoping that someone else will do it, then you are behaving in a way that will in all probability lead towards there being no next generation sooner or later. The "global warming is the apocalypse" movement constantly talks about how the best way to reduce your carbon footprint is to have no children.
>The only large-scale planetary engineering in humanity's history is Veniforming its home world.
So it is claimed, but from my point of view it looks very much as if it's intent on making itself extinct through fertility decline. But at least carbon dioxide levels will return to normal, eh?
Ask ten different scientists about the environment, population control, genetics, and you'll get ten different answers, but there's one thing every scientist on the planet agrees on. Whether it happens in a hundred years or a thousand years or a million years, eventually our Sun will grow cold and go out. When that happens, it won't just take us. It'll take Marilyn Monroe, and Lao-Tzu, and Einstein, and Morobuto, and Buddy Holly, and Aristophanes, and - all of this - all of this - was for nothing. Unless we go to the stars
There was a time when there was nothing (European) in the entire New World. There was a time when there was nothing known (to the US) about what was in most of the Louisiana Purchase. There was a time when there was nothing (European) in, say, Ohio. And then Nebraska. And so on.
There was literally nothing there? Why go all that way? To see what was there. And then to make something there.
[Edit, because I'm rate limited: No, interstellar space is something to cross, to get to stellar space. You think the New World was rich? How about a whole solar system of untapped resources?
There is many times more water in gas giant moons than on Earth. If we develop the technology needed to make a multi-generation ship we also have the technology to make deep space habitats - enough for trillions or quadrillions of people.
Just imagine the economic output of a civilisation a million times the size of ours.
These people are dreamers that grew up watching Star Wars and Star Trek. The world painted by those shows has lodged in their minds, and no amount of logic will shake it loose.
In the past, I've challenged the "Let's colonize Mars!" people to do something that's far easier: Move to Bouvet island, now.[1]
This is a frozen uninhabited rock that is nonetheless a tropical paradise compared to Mars. It's far easier to reach, has free unlimited oxygen and water, and gets more solar radiation also for power! It's luxurious compared to the colder, dryer deserts of Mars where there's only dry rocks and near-vacuum.
If you really want to spice things up, donate $10,000 to a charity per pound of material you take to the island (what does a shelter weigh?), take 100% of your food and water with you, and never go outside without wearing full scuba gear. For "realism mode" sprinkle a small amount of radioactive powder evenly everywhere around your habitat area.
"Yay! Adventure! Honey, tell the school we're unenrolling the kids and taking them with us to this wonderful opportunity to start a new life!"
No there wasn't. There was a whole continent of untapped resources.
You can argue that the solar system is a lot of untapped resources too. Harder to extract than sailing a piece of wood across an ocean growing some food, and killing the people who are already there. Harder than colonising Antarctica or the surface of the sea too, but there are resources - not just minerals but solar energy too.
But interstellar space? Beyond the Oort Cloud? There's no evidence of anything other than perhaps some very sparse dust. That is nothing, and (jokes aside) completely incomparable to Ohio.
> those of us with an interstellar bent naturally start musing about ‘sundiver’ trajectories, using a solar slingshot to accelerate an outbound spacecraft, perhaps with a propulsive burn at perihelion. . The latter option makes this an ‘Oberth maneuver’ and gives you a maximum outbound kick.
You can't do a solar slingshot like you can with (say) Jupiter because the sun is essentially at rest with respect to the rest of the solar system. You could still do an Oberth manoeuvre.
If you start in our solar system this doesn't help. You could do a gravity assist from a planet to help with an interstellar trip (like the Voyagers) but not a gravity assist from the sun, starting from one of 'our' planets.
> could do a gravity assist from a planet to help with an interstellar trip (like the Voyagers) but not a gravity assist from the sun, starting from one of 'our' planets
Of course you can. Galileo, Cassini-Huygens and Giotto are Earth-launched spacecraft that used Earth for a gravity assist. If you need to accelerate with reference to the galaxy, you can use the Sun’s motion through it to slingshot.
No, you can't. Gravity assists require the assisting body (Jupiter) to be moving, relative to the body that needs the assist (Voyager), in the direction the assisted body wants to go.
They have an unfortunate name because it's not just the assisting body's gravity that provides the assist. It's the combination of gravity and velocity.
As Voyager nears Jupiter, Jupiter's gravity grabs it. Then, Jupiter's velocity relative to Voyager drags Voyager - that is, transfers energy to it. Without that relative motion, all Voyager's gravity does is add energy on the way in and then remove exactly the same energy on the way out.
If you unfurl a solar sail after perihelion, presumably you get more energy while nearer the sun, giving more of a "kick", and lower in the gravity well (would oberth still apply for solar sail)
Your speed once you get to 1AU would I assume be far higher than if you had simply started at Earth
But getting to the sun in the first place (from Earth) is a massive hassle as you have to lose the Earth's significant orbital speed to 'fall' inward [0]. Perhaps better just to use that fuel to head out. Operating a solar sail really close to the sun would also be challenging because of the massive heat.
You first have to build the perpetual motion engine and the reactionless drive.
Current thinking is quite hostile to doing the work. You might not be able to build the things you think you can. You certainly won't build the things you think you can't.
I am not aware of any approaches that even remotely could deliver a perpetual motion engine or a reactionless drive. You need something to start from but there is nothing in sight.
Basically, nothing short of antimatter rockets will get you a self-contained interstellar ship.
Ion propulsion, even with nuclear reactors, can't get you enough speed.
Fission-fragment reactors can get you up to 1% lightspeed, but that's still 400 years to Alpha Centauri--I'm not sure I would trust a generation ship to last that long. Advanced fusion might cut that down to 100 years. Antimatter can reach 20% lightspeed, which means 20 years to Alpha Centauri.
ChatGPT kept asking to design a laser sail (external power source) to avoid the tyranny of the rocket equation, but I just don't think that can scale to crewed travel.
If we assume 100 colonists on the ship, with 10 tons of mass per person, accelerating to 0.2c over 2 ly and then back down, the energy required is quite substantial. Multiple centuries of the total output of the whole planet.
With Alpha Centauri being only 4 light years away, interstellar travel seems almost feasible. But then you consider all the inconvenient details, and realize such a journey would have to take hundreds, maybe thousands or even more years on top of some incredible advances in rocket tech.
If you go to something like Trappist (40 ly) at 0.01c (very optimistic), it's not just that everyone you know will be dead when you arrive. Your entire nation will have disappeared to the sands of time. The landfall announcement you send back will be incomprehensible because of language shifts, and you won't live to see the reply. Meanwhile, such a trip would be an enormous investment, requiring multiple nations to bankrupt themselves, with no hope of even surviving to see the outcome.
With that, it's very hard to imagine interstellar travel being feasible with our current understanding. There would have to be something like FTL travel or wormhole. The only "realistic" development, (much) better engines that can do 0.1c, would not actually change much.
Maybe not humans, what about robots though?
I recently read this in an interview with Juergen Schmidhuber:
> Of course, such life-like hardware won't be confined to our little biosphere. No, variants of it will soon exist on other planets, or between planets, e.g. in the asteroid belt. As I have said many times in recent decades, space is hostile to humans but friendly to suitably designed robots, and it offers many more resources than our thin layer of biosphere, which receives less than a billionth of the energy of the Sun. Through life-like, self-replicating, self-maintaining hardware, the economy of our solar system will become billions of times larger than the current tiny economy of our biosphere. And of course, the coming expansion of the AI sphere won’t be limited to our tiny solar system.
https://news.ycombinator.com/item?id=44330850
But why would we bankrupt ourselves sending those robots at all? Although, if AI takes over in a way or another, who knows what they recommend/decide.
I’m sure if you ask ChatGPT often enough it’ll recommend exactly that!
Yes, we have a long ways to go before we can be considered a starfaring species, one that can make and keep long–term agreements when they involve round–trip times in the tens of thousands of years. Still, it can be useful to altruistically start colonies before then.
There’s a book called Count to a Trillion which explores these ideas, and others. At the end of it the main character’s wife sets out on a mission to M33 and isn’t expected to return for at least 70,000 years. He gets stuck on Earth, unable to catch up with her, and promises to be here when she returns. The sequel is all about what he has to go through to keep Earth a going concern while she’s away.
Worse, you have no idea what you will find on the other side and weather that includes somewhere that doesn't make the arctic poles on earth look like paradise. And you'll be traveling in a small confined space. For ages. The good news is, you'll probably be unconscious for the journey. The bad news is that a lot can happen in decades/centuries/milennia and there's no guarantee you'll actually wake up. And everything else you said.
That raises the question who would want to travel and why. And what's wrong with them. Because the profile for people that want this would be hard to distinguish from somebody that is depressed and suicidal.
Given those time frames, maybe don't send primates. Send a computer babysitting a diverse zoo of bacteria and algae, with a variety of landing devices and instructions in what order to deploy them under which circumstances.
Same problem: the best-case outcome is that we never hear anything interesting from that rocket ever again. But it should be a lot cheaper.
> Send a computer
Those age too. Especially out there without the earth's shields. If you make one that lives longer than a human it's already quite the feat, add only a bit more radiation, it only gets worse. Computers are much worse with failures than brains too.
The nice thing about biological systems is the self-assembly from tiny molecule parts. Worst case, you can create a closed system with birth/death renewal. For tech the machines that build the machines, and the machines that build or repair those in turn, will all have to be brought along too, or you need to have some impossibly tough requirements for the product to last.
We may need some similar automatic self-assembly for tech for such use cases. The whole spaceship and all its components will deteriorate too.
Even when we sent out ships to venture around the world they had to be able to do replacements for broken parts, like masts. We probably need that capability for space ships too, to stop at some asteroid and rebuild. But then you get the equivalent of the rocket equation: On the one hand, you need a lot of stuff to support that manufacturing, on the other hand, every item you add itself needs maintenance and rebuilding at some point. The way out is this molecular-level self-assembly. You throw a few tiny nano-machinery dust spores on an asteroid, and ten years later you grew some useful machinery...
> it's very hard to imagine interstellar travel being feasible with our current understanding.
Even with massive advancements in tech, and getting close to the speed of light, interstellar travel will be a lot of "one way heading into the unknown forever" kind of initiative. Interstellar empires only work with truly sci-fi tech that mostly ignores distances, like in sci-fi (instant subspace comms or warp travel with no relativistic effects)
This will never be the same kind of age of exploration as when we crossed the oceans and explored our planet. The scales are so mind blowing that even the fastest speed known to mankind is too slow. The times and distances involved to move and even just send signals (both ways!) and relativistic effects means at best we can "seed" a distant planet and hope that turns into a new (human?) civilization, forever separated from us for all practical purposes.
> it's not just that everyone you know will be dead when you arrive. Your entire nation will have disappeared to the sands of time.
Humans are just a stepping stone. Earth intelligence will transcend our 77 year lifespans and primate brains.
Our lungs are adapted to gas exchange on this particular gravity well and its unique biogeochemistry. There's no reason redox reactions need to happen like this, or indeed even be the primary propulsion mechanism.
This is our frail biases speaking. We are limited by our biology, but we won't be forever.
Why is everyone so fixed on interstellar travel? What if the galaxy is chock full of rogue planets? There may be hundreds if not thousands of worlds between us and the surrounding stars. Hopefully, Roman Telescope set to launch in 2027 is going to find lots of them.
Because we’re a species of explorers. At least some of us are.
Developing propulsion technology to reach 0.1c velocity will move the needle on interstellar propulsion from impossible to just barely feasible. Although that is at least 100-200 years away, we can absolutely start expanding into our Solar System, starting with nearby bodies, like Moon and Mars.
> Developing propulsion technology to reach 0.1c velocity will move the needle on interstellar propulsion from impossible to just barely feasible
More than barely. "A 40-year one-way interstellar flyby mission to the nearest stars will require a relativistic spacecraft speed in excess of 6000 AU/yr (i.e., > 0.1c)" [1].
That means, practically speaking, nuclear-fusion, antimatter-annihilation and directed-energy propulsion. All of which are TRL ≤ 2.
My bet would be on fusion propulsion. It's inherently easier than fusion power since you don't need to bother converting the energy to electricity. That said, solar sails [2] and directed-energy anti-drone weapons [3] are seeing quiet progress.
[1] https://ntrs.nasa.gov/api/citations/20200000759/downloads/20...
[2] https://www.nasa.gov/mission/acs3/
[3] https://en.wikipedia.org/wiki/Silent_Hunter_(laser_weapon)
1 AU is about 8.3 light minutes. So 6k AU is about 50k light minutes. with ~525k minutes in a year, that means that 6k AU/yr is almost exactly 0.1c.
> that means that 6k AU/yr is almost exactly 0.1c
Nobody debates this. The point is that 0.1c propulsion is not necessarily 100+ years away. And its 40-year transit time is not "barely feasible," it's comparable to present deep-space mission timelines [1].
[1] https://science.nasa.gov/mission/voyager/
However, travel at 0.1c is not needed for the Fermi Argument to bite. Much slower speeds would allow a colonization wave to sweep a galaxy in time << the age of the universe.
Even at .0006c (our current tech), the galaxy would be filled with (weakly self propagating) robotic probes after just 750 million years. Unless extremely long lived self-propagating probes just ... die out ... that implies no aliens older than 750 million years from our galaxy. It implies no aliens from the nearby galactic neighborhood within 3 billion years. That kind of implies we're all alone.
I have three wild-eyed theories: (1) eukaryotism is an unbelievably exotic step; (2) and/or the moon is required and ultrarare; or, (3) advanced civilizations eschew yellow stars for being inconveniently short-lived: maybe they prefer brown dwarfs, white dwarfs, or black holes for their energy gradient.
The comment by Benjamin Stockton on the article page is spot-on:
>I just wonder if humanity’s adventurous nature is leading us away from a proper focus on the sustainability of our civilization, our specie, and our fragile planetary environment?
But we still need spaceflight at least for planetary defense against asteroids, mining asteroids(so we don't have to mine Earth), etc.
Not only is that comment a false dichotomy (we can both explore space and make humanity more sustainable at the same time), it also presumes that space exploration and sustainability are at odds with one another and not synergistic.
Humans, simply by existing on Earth, have a huge and often negative impact on the environment. If we could somehow shift the human population off Earth, either by terraforming planets (like Mars) or creating artificial space habitats, it would have a huge positive impact on Earth's environment. We don't currently have the technology to do so - we would need space elevators to feasibly move humanity off Earth - but that doesn't mean we should move our attention away from space in the meantime.
It is incredibly toxic belief, easily weaponized against space exploration.
There will be never enough resources for "sustainability of our civilization, our specie, and our fragile planetary environment".
Isn't that "There will never be enough resources for..." line of thinking the toxic one?
If we ever end up unable to outrun ourselves we might as well end it?
What resources are on asteroids that justify the energy expenditure to get from space and back? Can't be many of them...
> What resources are on asteroids that justify the energy expenditure to get from space and back?
With chemical rockets, not much.
With "a propellant-less propulsion propulsion system such as solar sails or electric sails," bringing water (propellant) to low-earth orbit starts making sense [1], as does mining platinum, but only if "the quantity of platinum from space would substitute an equal quantity of terrestrial platinum," i.e. moving heavy industry off the Earth's surface [1].
Given asteroid-mining profitability is dominated by "the throughput rate, which depends on the mining process," it's possibly to see a path to certain rare-earth minerals becoming profitable to mine in space if environmental controls on Earth are tightened while constant-thrust propulsion technologies advance.
[1] https://arxiv.org/pdf/1810.03836
Just skimmed but does this answer the question of getting to and from the surface of earth? Or are we just stockpiling platinum in LEO for some reason?
> does this answer the question of getting to and from the surface of earth?
Yes. (Deöbiting from LEO is cheap, like 90 m/s for the Space Shuttle, because you can use the atmosphere.)
… Presumably the problem is mostly getting up…? Is the plan to just drop hunks of platinum or do we need to put reentry vehicles up there?
With a relatively small initial investment, you can build reentry vehicles out of the asteroid, depending on the specific composition.
Or, just fashion the metal into ingots that are coated with an ablator (carbon, say) and allow them to enter as artificial meteorites. Suitably sized they will hit the ground at reasonable speed and can be dug up.
Even better than carbon use an ablative made out of olivine that can sequester CO2 as it ablates.
That way by offloading mining and refining into space to prevent the damage that these activities incur on earth you're also undoing damage to Earth from past human activities.
> With chemical rockets, not much.
The energy involved in chemical rocketry is actually not that much. Getting a kilogram to LEO is roughly as expensive (in energy) as flying it to the other side of the world in an airliner. Getting stuff back from an earth-crossing asteroid can also be very cheap energetically, with very small delta-V (if one is willing to wait long enough).
But we don’t ship mined materials around via aircraft… because it’s obscenely expensive…
And the delta-V back from a NEO is as little as 1% of that to get to LEO from the Earth's surface.
Also, the materials we're talking about from asteroid mining, like platinum group elements, probably are shipped by air, just for security.
This whole argument is reminding me of the facile and bogus argument that launch to earth orbit from planet's surface is expensive because of the energy needed.
If it's a bogus argument then mount a counterargument. The question is simple: what is worth mining in space?
So far we have... "maybe platinum." Maybe!
Aside from the conspicuous absence of math, "maybe platinum" isn't remotely important enough a factor in earthbound mining to justify asteroid mining on the basis of preserving earth, obviously.
I recently read "Delta-v" and the sequel "Critical Mass: A Novel" by Daniel Suarez. They're very much fiction but there is a certain amount of science underpinning the arguments and I enjoyed that aspect. And the author even states that he's trying to get across, with solid arguments, why humanity should begin planning asteroid mining ASAP. In brief, the arguments are:
Firstly we're now at a point where we have lots of cheap energy available, principally chemical. Depending on many factors it's conceivable that we are in fact at or near peak human energy output (e.g. WW3 or civilization collapse - the next iteration of civilization won't have so much cheap oil to exploit).
Secondly LEO is not yet full of junk, meaning that it's trivial to find launch windows to LEO and beyond. That could easily change very much for the worse in a relatively short time (I infer decades from the books).
Finally it's unrealistic to expect us to colonize the Moon or Mars using only Earth-mined materials. You can launch a spacecraft to Mars easily, but to launch a small city's amount of construction equipment and raw materials is beyond our capabilities.
Conclusion: now is the best time to mine asteroids. We can do all of the processing and much of the construction in LEO (or even better at Earth-Moon or Earth-Sun lagrange points) and then, with relatively low delta-v, we'd actually have a chance of becoming an interplanetary species!
But, the novels warn, the window of opportunity will eventually ("soon") close. Well worth the read.
Maybe someone else more familiar with the arguments, who has also read these novels, can offer a critique?
What's worth mining in space? Everything that we can mine in space. That seems glib but I'll elaborate.
By moving mining off planet to the moon and asteroids we eliminate the carbon emissions and environmental damage that occurs from these processes.
So how do we do it? We don't need to start sending fleets and fleets of crafts into space which is energetically expensive and time consuming, what we need to do is develop self-replicating mining equipment that we can send to turn the things we want to mine into more things that can mine for us. We won't achieve full self-replication immediately but we can definitely send machines that can do partial self-replication at first and work on improving the ratio of material sent to material returned.
What do we send back? titanium, platinum, aluminum, nickel, iron, whatever we find there. If platinum was as cheap and plentiful as aluminum was now we would have all sorts of catalytic uses for it that would significantly clean up our Earth based industrial practices.
How do we send it back? If we're sending it back from the moon that's easy -- a space elevator or rail gun. If we're sending it back from asteroids inefficient but cheap iron ion thrusters. Use iron from the asteroids as fuel.
Bonus points: Send it back covered in ablative material like mined olivine that can react with CO2 in the atmosphere to sequester it, that way the whole process isn't just moving environmentally damaging industrial practices to other solar bodies but we're undoing some of the damage from past human activities.
> By moving mining off planet to the moon and asteroids we eliminate the carbon emissions and environmental damage that occurs from these processes.
... but this won't happen unless it's economically advantageous, with all risk, transit, and upfront investment included
We already don't have the political will to force single-digit increases in cost of output to reduce environmental damage. Why would we then?
Not the person you responded to but my 2cents. You expect to find the vast vast majority of materials for this self replicating mining equipment as well on the same asteroid? For them to put up the huge amounts of energy generation, materials refining and self fabrication for them to do a large amount of tasks and build reentry packages without us sending a lot of stuff into space lest we very easily surpass the impact of mining on earth.
We'll have to get very very creative with nickle-iron and silicates to build a small automata civilization on big flyby rocks.
Look at those goalposts shift!
I don't need to argue things are practically mineable in space to rebut the point. I just need to argue if they aren't practically mineable, energy consumption isn't a reason.
I have already given you the counterargument.
> we have maybe platinum
Those making the energy argument need to rebut every possibility. The "it takes to much energy to ship back" is ludicrously wrong for platinum. The argument destroyed, why would we need to say more?
It takes as little as 0.1 km/s delta V to get onto an Earth-intersecting orbit from known NEOs. The energy of a mass moving at 100 m/s is 5x10^3 J/kg, or 1.4e-3 kWh. If a kWh costs $1 in space, this would be a fraction of a cent per kilogram. This delta-V is so small that the energy cost of sending back base metals would be affordable. Hell, the energy cost of shipping gravel from space would be affordable! Other costs, probably not, but that's not the claim we're addressing.
"What resources are on asteroids that justify the energy expenditure to get from space and back? Can't be many of them..."
I suggest re-framing the the question as the cost of preserving the objectively limited and to the best of our knowledge singularly unique in the Universe resource, which is the surface of Earth.
Acquiring resources that do not deplete or spoil the future of life on this planet should be in everyone's best interest.
Yeah no. Unless someone can answer basic questions like “what even comes close to net positive in energy expenditure to mine elsewhere,” then this is just a cover story.
The reality is that saving our environment will be a whole set of difficult and profoundly boring solutions to real, known problems.
Would be cool if we could solve it with badass rockets, explosions, big noises, and adventure, but the complete lack of even remotely convincing answers to first order questions on how this actually works belies the fact that it doesn’t. It makes no sense.
We need to develop better plastics, proteins, and pesticides. Not send protein blobs to other planets because it looks cool in sci fi movies.
> We need to develop better plastics, proteins, and pesticides. Not send protein blobs to other planets because it looks cool in sci fi movies
The reality is more people get passsionate about working on things that look cool in sci fi movies than developing plastics, proteins and pesticides for a mediocre paycheque. This lesson--that the path to groundbreaking technologies is through inspirational moonshots, not committees prescribing what is and isn't necessary--is so thoroughly repeated throughout history that it's a wonder we keep missing it.
Nobody referenced any sort of committee.
Groundbreaking technologies are not created via moonshots. They’re created by decades of slog. Moonshots can launch from an unremarkable platform of slog, but the slog had to happen. You just cannot speedrun the vast majority of questions that need to be answered to power a breakthrough.
That’s why I’ll question glory-chasers who want to sit on the rocket but can’t take a few thousands of pay cut to stare for a few years at a true problem that needs solving.
Our species’ actual heroes are those who powered through the slog.
> They’re created by decades of slog. Moonshots can launch from an unremarkable platform of slog, but the slog had to happen
The slog is almost always in pursuit of a moonshot. The moon justifies the slog. We don’t slog for the sake of it.
Yeah and usually the moonshot is a lot less circularly defined than “this moonshot is worth achieving because if we achieve it we will have built cool stuff to do it.”
The most compelling economic reason to pursue the technology of asteroid mining (at least as far as Earth's gravity well is concerned) is not to ever actually launch any serious asteroid mining operations, but rather to fool those who own gold into believing that you have the capability to devalue gold at your whim, and thereby accept a small ransom to not go asteroid mining.
Wouldn’t work because of the collective action problem among gold owners!
And because someone shorting gold would have a financial incentive to do it himself.
Our civilization has been driven by expansion. Without it we'd probably collapse into a neurally-connected well-organized ant colony without need for further technological/social/economic progress (which would naturally select/cull out corresponding features in our brain). And, i'd guess that is possible one of the forms of the Great Filter stopping many civilizations.
At 53 and good health, i'm contemplating that my end in 30-40 years would be me buying a one way to Mars and just exiting the habitat out without suit after enjoying a dinner with a Martian sunset view, breaking, even in such a small way, the chains of "We come from the earth, we return to the earth" :)
Why would we not chase technological progress without increasing our proverbial footprint? We're not starting to inhabit new bodies of land for a long time now. We're slowing down our footprint growth among those in the most developed places but chasing new technologies hasn't slowed down accordingly.
That's a truly awful way to die (all your fluids and gases suddenly surging through your tissue).
Seems much easier to reframe the "chains" of earth into acceptance of a remarkable cycle that we're privileged to get a glimpse of from the inside and just die happily here with your loved ones.
> Seems much easier to reframe the "chains" of earth into acceptance of a remarkable cycle that we're privileged to get a glimpse of from the inside and just die happily here with your loved ones
This works for most people. Most humans didn't leave Africa or Mesopotamia or the Old World, either originally or in the Age of Exploration, and most Americans today don't have a passpport.
The technicalities would be worked out. The awfulness isn't a goal here.
The acceptance would have me still in Russia :)
Presumably you left Russia to get to something better, not worse on pretty much every dimension except novelty
Yep, and dying on Mars feels to me better than on Earth.
On what dimensions would that be preferable?
> On what dimensions would that be preferable?
Novelty, for one.
Yeah, makes sense. Novelty like what toys provide!
Obviously one is free to want that. When I think of the opportunity costs involved, it seems repugnant to be honest. The opposite of glorious.
> Yeah, makes sense. Novelty like what toys provide!
And art and scientific endeavour and exploration and possibly all the things that make us human, but sure.
But those serve other purposes too, which is why I was asking for ones in addition to sheer novelty.
That is about my point - i want to get as far as possible from such a philosophy as it is taking over the civilization. I lived under similar philosophy in USSR and, as long as it is up to me, i'll be trying to put a distance in all senses.
Eh, pathologies at both ends!
I hope you achieve your dream though (and that you devise a more pleasant way to do it ;))
I don’t know, GPS is quite useful, Landsat is too, along with the various other Earth imaging satellites and systems like modis and sentinel-2. Sure is good having food. Weather forecasts are nice. It’s also quite convenient to be able to use space based data services. It’s also useful for power grids to know when they’re about to be whacked by a CME. I’m sure sailors on sinking ships appreciate being rescued.
But sure, we should solve all the problems on earth with one hand tied behind our backs until we can launch any more rockets.
>To get around thousand-year generation ships, we are examining some beamed energy solutions that could drive a small sail to Proxima in 20 years.
The odds of a spacecraft hitting a single particle of dust while in space are 100%.
A spacecraft hitting a single particle of dust at 0.2c will impart tens of millions of joules into the body of the spacecraft, the equivalent of getting hit with hundreds of pulses from the most powerful laser ever created by humanity-- simultaneously.
Or concentrating several kilogram's worth of TNT into the size of a particle of dust and detonating it.
Only true if the dust grain is stopped by the craft. For a thin lightsail the grain will probably pass right through without depositing much energy
I wasn't even considering the sail.
Most of the designs for a system like this are "chip" designs where a single 1cm x 1cm silicon wafer is towed by the sail.
This design prevents the need for lasers so large that they create enough ozone to kill the entire human race.
The contents of the chip vary, based on who is speculating, but tend to contain exotic, uninvented, circuitry capable of both harvesting energy from the laser and doing "something" of use besides zipping by the target at 0.2c deaf, dumb, and blind. Sometimes it's even an AI-enhanced swarm! (Shoulda figured out how to work blockchain in there, post-doc guy)
Regardless, during the 40 trillion kilometer voyage to Proxima Centauri, that 1x1cm silicon wafer (and the sail) will hit space dust, and numerous other atoms and molecules (including carbon rings) because empty space... isn't.
So it passes through the sail and then hits the spacecraft attached to the sail. Now what? kaboom? small holes in the hull would not be good for the occupants.
The sail is much, much larger than the craft. The odds of that happening are tiny.
In any case, we should launch more than one.
more than one basket for those eggs will be important.
When it passes through the sail, enough energy is deposited in the grain to explode it, so if there's sufficient distance to the hull the vapor deposits sufficiently low energy/area to be tolerable.
https://en.wikipedia.org/wiki/Whipple_shield
Ten megajoules sounds like a lot, but a single kilo of TNT produces about 4 megajoules of energy. And the size of particles of dust and how often you’re likely to hit one in the interstellar medium is quite speculative.
> the size of particles of dust ... in the interstellar medium is quite speculative
Technically yes. I think there's a significant variety of sizes of dust or larger-than-dust particles in interstaller medium but I don't really have much to back that up.
> how often you’re likely to hit one in the interstellar medium is quite speculative.
Also technically yes. But unless you can map every single particle of dust, and their trajectories, I think the risk is absolutely real.
Are there any real proposals that deal with this issue for a vehicle that would carry humans and go fast? Something that's not "energy shields".
Edit to add: we basically understand the physics of accelerating something to a high speed, what it would need to be made from, etc., afaik all within the realm of possibility- if we could gather and direct that much energy and then wait long enough to decelerate at the other end.
It seems like the questions that are completely unaswered are: keeping people alive and healthy for that long, and how the ship could survive if it hit something.
> Are there any real proposals that deal with this issue for a vehicle that would carry humans and go fast?
Whipple shields [1].
> Something that's not "energy shields"
The interstellar medium contains lots of charged particles [2]. Electromagnetic deflection is perfectly realistic.
[1] https://en.wikipedia.org/wiki/Whipple_shield
[2] https://www.space.com/interstellar-space-definition-explanat...
"A 0.1 µm interstellar dust grain (≈10⁻¹⁴ kg) striking a spacecraft at 0.2 c carries ≈20 J of kinetic energy—millions of times below “tens of millions of joules.” Reaching 10–50 MJ would require a ≈0.14 mm grain (≈10 µg), vastly rarer than ordinary dust, and even that impact equals only a few shots from the world’s highest-energy laser (~2 MJ per pulse), not “hundreds.”"
I used something something 10^-10 for my dust. To reach ~50MJ.
As far as the laser goes, ~2MJ is the total output. Energy that reaches the fuel pellet due to inefficiencies throughout the path of the laser, the actual "hitting power", is hundreds-ish kJ.
scifi answer (the particle warps with space around the vehicle)
the other thought is a space ram jet sucking in particles heard of some idea like this
Perhaps, some fraction of the laser energy beamed to move the sail is redirected directly in front of the spacecraft to vaporize any dust particles in its path. Fragments of a circular sail could be angled in the right way so as to take some fraction of the light's momentum in its desired direction with the rest reflected at an angle to clear the opposite side of the sail. For a circular sail you'd then get a circular "clearance beam" of sorts.
You're avoiding the energy that would be imparted by hitting the dust spec by... adding energy to the dust spec? Perhaps splitting it so it damages a larger area? It seems better to let it plow as small a hole as possible in the sail.
alternatively you ionize that particle, may be make in into plasma by laser for ease of "digestion" down in the engine, direct in into the engine where it is used as working mass for your ion thruster, kind of similar to scramjet.
As far as i see with today's tech - like Starlink's ion thruster + classic nuclear reactor - we can get to 300km/s in about 4 stages. Straightforward improvement of ion thrusters - mainly voltage increase and associated engineering (which will immediately happen once we start flying to Mars and beyond as ion thruster currently our best/fastest option inside the Solar system) - can get us to 1000-2000km/s, i.e. under 1000 years to Alpha Centauri (that for a large populated spacecraft, and for just tiny probe to announce our existence (and to send back photos which we'd receive using Sun's gravitational lensing) we can do even better). And using interstellar gas and dust scramjet-style will improve on those numbers (as such ship is mostly limited by the working mass it starts with while the reactors would be able to continue produce the energy much longer).
> alternatively you ionize that particle, may be make in into plasma by laser for ease of "digestion" down in the engine, direct in into the engine where it is used as working mass for your ion thruster, kind of similar to scramjet
This is a Bussard ramjet [1]. The interstellar medium is too thin to make it work. (Maybe we'll find the husk of an ancient ramjet from an earlier era of the universe floating around one day...)
[1] https://en.wikipedia.org/wiki/Bussard_ramjet
Bussard would collect gas to be used as fuel. For ion thruster it is only a working mass.
[dead]
It won’t be us. It will be our descendants — the machines.
Any autonomous machines in a distant enough future will look neither as the present humans or animals nor like the present robots, because they will have to use a mixture of the technologies developed by living beings and by humans.
Humans have developed various things that are better for certain purposes than anything used by a living being, e.g. metals and semiconductor devices (most of the human-only technologies are a consequence of the control of fire, i.e. of the ability to perform manufacturing processes at high temperatures, unlike the living beings, which are limited to temperatures close to that of the ambient). On the other hand, for other purposes the use of organic substances and of the methods of chemical synthesis used by living beings are unbeatable.
So any future descendants will have to use hybrid technologies, like the "cyborgs" of many SF novels/movies, except that I have never seen any SF "cyborg" that combined the right parts from "machines" and from living organisms.
As an example, for the problem of energy storage for powering a machine, for providing short-time high power bursts capacitors and batteries are better than the chemical reactions used by living beings, e.g. ATP & phospho-creatine hydrolysis and anaerobic glycolysis. On the other hand for storing high-amounts of energy for long-time autonomy at a moderate power level, none of the fuel cell or battery technologies that have ever been attempted appears to have the potential to ever match the performances of the enzymatic oxidation of hydrocarbons that converts their chemical energy into ionic gradients in living beings, e.g. in our mitochondria. So an ideal autonomous machine would combine high-power capacitors/batteries with high-energy biologically-derived fuel cells.
Consciousness, once engineered, will make any biology redundant.
The only way I can see hope for spreading terrestrial life through the galaxy is to send tiny spacecraft. The spacecraft can survey what it finds and send the information back to earth. Earth can send back instructions to the nanobots on the spacecraft to build what is necessary from local materials, and then build life to inhabit it.
So this is another reason why I see Dyson Swarms as being the inevitable evolution of human civilization. Let me explain why.
First, to clarify, a Dyson Swarm is a cloud of orbitals around a star to use most or all of its energy via solar collectors. This was originally called a Dyson Sphere but was renamed because of confusion: people thought a Dyson Swarm was a rigid shell. It never was.
Anyway, the classic orbital is an O'Neil Cylinder, which would be 3-4 miles in diameter and 10-20 miles long. You spin it to get earthlike gravity. With this diameter the rotation isn't likely disconcerting and the centrifugal forces aren't so large as to tear it apart.
This kind of structure could be built with a material no stronger than stainless steel and using solar panels for power. It's relatively low tech. There aren't any exotic physics or exotic static states of matter required. It's basically an engineering problem and can be built incrementally.
Why do I mention this? Because fo rthe distances involved, an interstellar starshhip is basically just an O'Neil Cylinder. You need to support people for centuries. Such a cylinder could get 10s of thousands of people, possibly 100k+ to another system in relative comfort.
So how do you get to another star? The tyranny of the rocket equation means any form of propulsion where you need to carry to propellant just won't work with the possible exception of nuclear fusion.
But what if you didn't have to carry propellant at all? To accelerate or decelerate. That makes it way easier. But how would yo udo that? Easy, at least in theory: solar sails. The solar wind carries pretty significant momentum. A sufficiently large solar sail (and it would have to be large for such a ship) would absolutely be capable of accelerating a ship to at least 0.01c. And you can decelerate with the same solar sail.
You can do even better by collecting energy from the Sun and concentrating it on the sails, which is yet another reason to build a Dyson Swarm.
The energy budget to travel to even our closest star is so vast that we would need to do things like collect most of the Sun's output energy. I personally don't believe FTL is possible. Time dilation only really kicks in meaningfully at >0.99c and I just don't think that's parctical and, if it were, the energy required is even more vast.
In fact, at 0.99c you would suffer drag from the interstellar medium (gas and dust)..
So any intersteallar ship is going to be a generation ship, a habitat.
Like "Rendezvous with Rama" by Arthur C Clarke: A mysterious cylindrical spaceship arrives at planet Earth from outer space.
Won't dreams stay dreams?
There's literally nothing there, why go all that way? The distances are so incredibly vast. It seems like we ought to be content with staying put.
> There's literally nothing there
“Literally everything is in space.”
All life on Earth is going die. Humanity has never been content with staying put, why would we start now? And what do you mean "literally nothing there"? The universe has a loooooot of stuff in it.
It's mostly empty, isn't it?
By "literally nothing there," I mean there's literally nothing for us. Three stars and a few Earth-sized planets in the habitable zone that are, more than likely, uninhabitable by humans. There's nothing there worth going all that way for.
I like sci-fi as much as the next person but the reality of the situation, it seems to me, is that the universe is mostly empty, vast, and inhospitable to human life.
The difference between a multi-generational interstellar ship and a self-sustaining space colony is the engine. They wouldn’t need inhabitable planets - they would need raw materials to build more ships and habitats.
I’m not sure that after spending a lifetime in an ample space colony its inhabitants would feel nostalgic of the time we spent sitting on round rocks cooking around a star.
> It's mostly empty, isn't it?
So is the Pacific Ocean for practical definitions of emptiness. You don't got to the empty places.
> The universe has a loooooot of stuff in it.
In fact, technically, there's nothing here. It's all out there.
The Sun: 99.86% of the solar system's total mass.
Jupiter: ~0.095% of the total mass, and ~71% of the non-solar mass.
Saturn: ~0.03% of the total mass, and ~19% of the non-solar mass.
Uranus and Neptune: Contribute a small percentage to the remaining non-solar mass.
All other objects: (inner planets, dwarf planets, moons, asteroids, comets, etc.) account for less than 0.002% of the solar system's total mass.
Your brain mass is about 3 disposable water bottles in weight and we can debate what parts of that are thinking and actually "you".
You are insignificant on the scale of the solar system let alone the universe.
>Tragula's wife used to complain to him about the utterly inordinate amount of time he spent staring out into space, or mulling over the mechanics of safety pins, or doing spectrographic analyses of pieces of fairy cake. She would often tell her husband to have some sense of proportion, sometimes as often as thirty-eight times in one day. In response to her pleas for him to find some perspective, he built the Total Perspective Vortex.
>Into one end he plugged the whole of reality as extrapolated from a piece of fairy cake, and into the other end he plugged his wife: so that when he turned it on she would see in one instant the whole infinity of creation and herself in relation to it. To Trin Tragula’s horror, the shock completely annihilated her brain...
~Douglas Adams, The Restaurant at the End of the Universe
>Humanity has never been content with staying put, why would we start now?
For whatever reason, humanity's attitude in this regard has changed drastically in the last century. We can't even bother to make the next generations, and a shrinking population eventually (quite quickly, really) shrinks to zero. Not only do they want to "stay put", they want to lay down and die.
The steelman counterargument is that focusing resources on extraplanetary colonies at the expense of the one habitable planet within reach will hasten humanity's destruction. How are you going to make an Eden on Mars if we can't even make an Eden on Earth? The only large-scale planetary engineering in humanity's history is Veniforming its home world.
>The steelman counterargument is that focusing resources on extraplanetary colonies at the expense of the one habitable planet within reach will hasten humanity's destruction.
That doesn't seem like a strong argument to me. It seems like a distraction from the crowd that would save the planet by extinguishing humanity if that's what it took. Though what value the planet might have with all of us gone I leave as an exercise for the reader.
The first priority of any society that wants to continue to exist into the future must always be to make the next generation. If you do not do this, or if you just leave the task to others hoping that someone else will do it, then you are behaving in a way that will in all probability lead towards there being no next generation sooner or later. The "global warming is the apocalypse" movement constantly talks about how the best way to reduce your carbon footprint is to have no children.
>The only large-scale planetary engineering in humanity's history is Veniforming its home world.
So it is claimed, but from my point of view it looks very much as if it's intent on making itself extinct through fertility decline. But at least carbon dioxide levels will return to normal, eh?
To quote Babylon 5
Ask ten different scientists about the environment, population control, genetics, and you'll get ten different answers, but there's one thing every scientist on the planet agrees on. Whether it happens in a hundred years or a thousand years or a million years, eventually our Sun will grow cold and go out. When that happens, it won't just take us. It'll take Marilyn Monroe, and Lao-Tzu, and Einstein, and Morobuto, and Buddy Holly, and Aristophanes, and - all of this - all of this - was for nothing. Unless we go to the stars
And those stars will go out as well.
Well true.
That's the fallacy in the given argument.
By then we’d better understand how to implement a “Let there be light” procedure.
Might very well be the last question we need to ask ourselves.
"Implement Fiat Lux" is a hell of a title for a sci-fi story, if nothing else.
Happily when Asimov wrote the same story, he didn't give away the punchline in the title.
Sure, if you put it in the title you need a different punchline. :D
The odds are against us. We will never go to the stars. But it doesn’t matter for us as we will likely die before any of this happpens.
There was a time when there was nothing (European) in the entire New World. There was a time when there was nothing known (to the US) about what was in most of the Louisiana Purchase. There was a time when there was nothing (European) in, say, Ohio. And then Nebraska. And so on.
There was literally nothing there? Why go all that way? To see what was there. And then to make something there.
[Edit, because I'm rate limited: No, interstellar space is something to cross, to get to stellar space. You think the New World was rich? How about a whole solar system of untapped resources?
That's why people will try to go.]
They didn't believe there was literally nothing there. They went all that way to find unclaimed riches.
The hypothetical riches were quite obvious: same stuff we have over here, but not owned by someone yet.
What are they hypothetical riches of outer space?
This is a question we should think about clearly and logically without resorting to stuff like "oh tally-ho the adventure!" type nonsense.
There is many times more water in gas giant moons than on Earth. If we develop the technology needed to make a multi-generation ship we also have the technology to make deep space habitats - enough for trillions or quadrillions of people.
Just imagine the economic output of a civilisation a million times the size of ours.
It’s a lot easier to imagine the economic output of simply raising all of the current Homo sapiens out of poverty and into economic productivity, no?
Then we can use all of that new productivity to start working toward the next rung?
Our economy is not currently throughput limited on water or space so I don’t find this compelling.
These people are dreamers that grew up watching Star Wars and Star Trek. The world painted by those shows has lodged in their minds, and no amount of logic will shake it loose.
In the past, I've challenged the "Let's colonize Mars!" people to do something that's far easier: Move to Bouvet island, now.[1]
This is a frozen uninhabited rock that is nonetheless a tropical paradise compared to Mars. It's far easier to reach, has free unlimited oxygen and water, and gets more solar radiation also for power! It's luxurious compared to the colder, dryer deserts of Mars where there's only dry rocks and near-vacuum.
If you really want to spice things up, donate $10,000 to a charity per pound of material you take to the island (what does a shelter weigh?), take 100% of your food and water with you, and never go outside without wearing full scuba gear. For "realism mode" sprinkle a small amount of radioactive powder evenly everywhere around your habitat area.
"Yay! Adventure! Honey, tell the school we're unenrolling the kids and taking them with us to this wonderful opportunity to start a new life!"
[1] https://en.wikipedia.org/wiki/Bouvet_Island
> There was literally nothing there
No there wasn't. There was a whole continent of untapped resources.
You can argue that the solar system is a lot of untapped resources too. Harder to extract than sailing a piece of wood across an ocean growing some food, and killing the people who are already there. Harder than colonising Antarctica or the surface of the sea too, but there are resources - not just minerals but solar energy too.
But interstellar space? Beyond the Oort Cloud? There's no evidence of anything other than perhaps some very sparse dust. That is nothing, and (jokes aside) completely incomparable to Ohio.
> those of us with an interstellar bent naturally start musing about ‘sundiver’ trajectories, using a solar slingshot to accelerate an outbound spacecraft, perhaps with a propulsive burn at perihelion. . The latter option makes this an ‘Oberth maneuver’ and gives you a maximum outbound kick.
You can't do a solar slingshot like you can with (say) Jupiter because the sun is essentially at rest with respect to the rest of the solar system. You could still do an Oberth manoeuvre.
> the sun is essentially at rest with respect to the rest of the solar system
But not with respect to other star systems.
If you start in our solar system this doesn't help. You could do a gravity assist from a planet to help with an interstellar trip (like the Voyagers) but not a gravity assist from the sun, starting from one of 'our' planets.
> could do a gravity assist from a planet to help with an interstellar trip (like the Voyagers) but not a gravity assist from the sun, starting from one of 'our' planets
Of course you can. Galileo, Cassini-Huygens and Giotto are Earth-launched spacecraft that used Earth for a gravity assist. If you need to accelerate with reference to the galaxy, you can use the Sun’s motion through it to slingshot.
No, you can't. Gravity assists require the assisting body (Jupiter) to be moving, relative to the body that needs the assist (Voyager), in the direction the assisted body wants to go.
They have an unfortunate name because it's not just the assisting body's gravity that provides the assist. It's the combination of gravity and velocity.
As Voyager nears Jupiter, Jupiter's gravity grabs it. Then, Jupiter's velocity relative to Voyager drags Voyager - that is, transfers energy to it. Without that relative motion, all Voyager's gravity does is add energy on the way in and then remove exactly the same energy on the way out.
Earth isn't going in a straight line. If it were, it would be useless as a gravity assist.
If you unfurl a solar sail after perihelion, presumably you get more energy while nearer the sun, giving more of a "kick", and lower in the gravity well (would oberth still apply for solar sail)
Your speed once you get to 1AU would I assume be far higher than if you had simply started at Earth
But getting to the sun in the first place (from Earth) is a massive hassle as you have to lose the Earth's significant orbital speed to 'fall' inward [0]. Perhaps better just to use that fuel to head out. Operating a solar sail really close to the sun would also be challenging because of the massive heat.
[0] https://www.nasa.gov/solar-system/its-surprisingly-hard-to-g...
You first have to build the perpetual motion engine and the reactionless drive.
Current thinking is quite hostile to doing the work. You might not be able to build the things you think you can. You certainly won't build the things you think you can't.
I am not aware of any approaches that even remotely could deliver a perpetual motion engine or a reactionless drive. You need something to start from but there is nothing in sight.
I worked this table out with ChatGPT (with all the caveats that implies):
https://gridwhale.com/program.hexm?id=GCJ5TL7Z&file=GCJ5TL7Z...
Basically, nothing short of antimatter rockets will get you a self-contained interstellar ship.
Ion propulsion, even with nuclear reactors, can't get you enough speed.
Fission-fragment reactors can get you up to 1% lightspeed, but that's still 400 years to Alpha Centauri--I'm not sure I would trust a generation ship to last that long. Advanced fusion might cut that down to 100 years. Antimatter can reach 20% lightspeed, which means 20 years to Alpha Centauri.
ChatGPT kept asking to design a laser sail (external power source) to avoid the tyranny of the rocket equation, but I just don't think that can scale to crewed travel.
If we assume 100 colonists on the ship, with 10 tons of mass per person, accelerating to 0.2c over 2 ly and then back down, the energy required is quite substantial. Multiple centuries of the total output of the whole planet.
[dead]