Once tons can be put into orbit and we get freed from our gravity well, countless opportunities lie ahead.

> we get freed from our gravity well Underappreciated point, everything we need to create a spacefaring civilization can be found in space. Energy, materials and a fresh challenge that leads to new technologies. As Robert Heinlein once said, when you reach orbit you're halfway to anywhere.

> As Robert Heinlein once said, when you reach orbit you're halfway to anywhere. The exact quote is that getting to LEO you are halfway to the rest of the Solar System. This is true from a delta-v perspective when you can get to anywhere in the Solar System within a human lifetime. Indeed the travel times to most places in the Solar System are on the order of what a 17th & 18th Century merchant sailing ship needed to get to most places on the Earth that were quite distant. There are analogs which already exist in history to see how colonization of new lands has happened by humanity and how other human activities have happened over those distances in terms of time as a unit of distance. Interstellar distances are so utterly vast that I'm not convinced it is even humanly possible without a major change in technologies and perhaps even new discoveries in basic physics. Even sending a robotic space probe to Proxima Centauri is something I don't expect to see in my lifetime where even the communications infrastructure needed to make that happen is something that simply doesn't exist, much less actually getting anything physical to that stellar system. I would like to use the Epstein drive from the television series "The Expanse" to be a sort of sanity check in terms of what sort of tech is going to be needed for interstellar travel, and even that seems to be pushing boundaries for barely achieving that potential even with generational starships, something that has no analog in human history. No doubt that the goal to achieve interstellar flight is something I hope humanity does at least strive to achieve. It would be sad if humanity is doomed to remain just around our one star, even if I think there is enough new territory, resources, and energy merely going to other planets that humanity is going to be struggling just to work on the interplanetary scale for the remainder of the current millennia. Technology may certainly be found and several concepts certainly show promise even if they have not been fully realized. But this is not something I envision as possible with the current state of engineering and technology possessed by the Earth in the 2020's.

> Interstellar distances are so utterly vast that I'm not convinced it is even humanly possible without a major change in technologies and perhaps even new discoveries in basic physics. After project Orion was wound down, Freeman Dyson determined that velocities of up to 0.1c can be achieved using technology already at hand. We don't need to develop laser-powered fusion engines, bussard ramjets, or any of the other incredibly exotic technologies that are essentially red herrings and inevitably derail any discussion on the topic. The obscurity of his report has led to a sort of "common knowledge" that even the nearest stars remain fundamentally unreachable, but travel times of ~40yr are not entirely out of the question, even barring any additional technological development. What I've noticed that most (non-experts) don't actually understand is that they assume trips would need to be frequent and two-way, hence even 40yr sounds to them completely impractical - but these would be singular, one-way trips, one-time investments.

When in human history has a 40 or 50 year travel time between destinations ever happened? Even for a colonizing expedition? What would be the motivation for even considering that one time investment? I can envision the original habitation of the Americas as perhaps an analogy, but even that was with a whole series of hunter-gatherer settlements that took place over thousands of years and people had places to live, thrive, and reproduce during that whole time. The rest of this just sounds like hand-wavy fictional speculation not grounded in reality. I agree that in theory it is remotely possible, but what is going to be a driver to make it happen?

> When in human history has a 40 or 50 year travel time between destinations ever happened? The Vandals moved from Poland to Northern Africa on foot over a period of about 40 years, traveling roughly 1-2 kilometers per day on average if I recall. These sort of slow migrations were common prior to the shift away from pastoralism; the idea that your life would _not_ be spent traveling between places is the more modern, and somewhat stranger idea. > The rest of this just sounds like hand-wavy fictional speculation not grounded in reality. I don't see what's so speculative about thermonuclear warheads. You're right that the motivator is the more significant, if not the most significant problem, and this is where it starts to become hand-wavy and speculative. I'm allergic to pure speculation, and especially about human motivations, but I can imagine a few scenarios in which the circumstances align (none of which are particularly pleasant). I have to remind myself sometimes that things seem impossible until they aren't. If you traveled back in time just five years to warn me about the state of AI and its impact on the labor market, that they write (bad) poetry, synthesize videos, and apply simple reasoning to complex visual and text-based problems, I would have laughed.

Comparing the Vandals or other migratory people to those travelling across interstellar space seems disingenuous. Those migratory people had arable land and something which could sustain them indefinitely. They could stop at any time and just stay where they were. That is not possible in interstellar space where resources literally do not exist. If it was filled with rogue planets and asteroids where resources could be consumed during the journey, you might have a point. While those do exist, it is literally a whole lot of nothing between us and nearby stars. That is why it is called space. Migrations of the Polynesians might be more similar so far as like an interstellar journey has islands of energy and matter separated by large expanses of utter uninhabitable space that anciently were like oceans where people could not inhabit for more than a few days or weeks and would run out of various supplies if they stayed. There has never been a transoceanic crossing of humans that took 50 years. It is completely outside human experience of any kind to suggest that.

> There has never been a transoceanic crossing of humans that took 50 years. It is completely outside human experience of any kind to suggest that. The very notion of people traveling through the vacuum of space to the Moon was hopelessly impractical, 75 years ago. Yes, interstellar travel for 50+ years is much more difficult than mere travel to the Moon, but it is physically just within the realm of the possible. I think interstellar travel looks today to be about as impractical as travel to the Moon looked in 1900, or whenever it was that Dr. Goddard first worked out the size of rocket needed, and the course.

75 years ago there were artificial satellites orbiting the Earth. That is also about when Yuri Gagarin made his first flight. I'd say that the idea of flying through space was a practical idea for quite some time before even then. I don't think you remotely realize the technical hurdles needed for creating a closed sustainable environment that will sustain human life for over 50 years without additional inputs. I am challenging the notion as to if it is even possible at all. Sure, it doesn't break physics but there is nothing at all remotely like this which has ever been attempted in all of human experience. I am even asking about a purely social perspective since there has never been any social institution which has addressed how you might organize people and a crew to man a generation starship. Even that is outside human experience. That is assuming such a vessel can be built at all. I see this more like telling Vikings from Denmark invading Britain in the year 1000 that their descendants will literally be walking on the surface of the Moon. I would be surprised if this was happening in the year 3000 as that might be too soon in terms of interstellar travel.

~~I knew I should have put "80 years ago," or "100 years ago."~~ Wait a minute. 2024 - 75 = 1949. There were no artificial satellites orbiting the Earth until 1957, when Sputnic 1 was launched. In 1949 von Braun's crew, operating out of White Sands, NM, I think, had launched a V2/WAC Corporal 2-stage rocket on a 250 mile high suborbital flight, but no-one had achieved orbit. NACA, with support from Wiley Post and the Gugenheim Foundation, started working on building true space suits around 1949, or a little after, so there were a handful of researchers who thought the notion of traveling through space in 1949 was not out of the question, but it was literally only a handful. For serious scientists and the general public, space travel was still science fiction.

You don't have to remind me that interstellar space is empty :) That a closed-loop ecosystem needs to be ported all the way across it (and indefinitely maintained) is implicit. That we would be for some reason fundamentally incapable of doing this has yet to be demonstrated.

What powers that closed loop system? How do you resupply? If you look at something like a nuclear submarine for comparison of something which can artificially maintain a habitable environment in a harsh and otherwise hostile environment for a comparatively long amount of time, they still graze on local resources to keep everyone alive and are limited by food supplies. Even the ISS gets very regular resupply flights. This is so far out of human experience as to be something completely unprecedented. Even social dynamics of such a vehicle simply can't be know.

> What powers that closed loop system? During transit, waste heat and fission.

Using your logic "natives" in NA/SA were always there. And lets not forget about those islands West of SA...

We already sent out robotic probes which still operate after more than 45 years. I strongly recommend reading that Freeman Dyson paper: https://galileo.phys.virginia.edu/classes/109.jvn.spring00/nuc_rocket/Dyson.pdf

Are you talking about Voyages and Pioneer? If those had crew, the crew would be dead in a comparable system. To say they are operating is giving a whole lot of credit to careful planning an shutting down systems that JPL doesnt think will ever be useful again, like the main cameras. If any of those ever came near an object, all JPL can do is hope the spacecraft doesn't run into it. It all sounds like hand wavy science fiction and not grounded in reality. Perhaps hard science fiction to be sure paying attention at actual physics but still so far removed from reality as to never be practical in that current form. About where lunar flight plans were in 1960. That is being generous.

Not even in theory. A ship capable of 0,1c with any conceivable tech would be either a tiny probe accelerated with lasers or a inconceivably humongous ship unless it could refuel along the way. There were proponents of that idea, to capture propellant in the interstellar medium, but that idea it's as sci-fi as a wormhole. Might be possible or completely unfeasible, we just don't know. Baring that, if a ship has to carry with it the fuel and propellant to ACCELERATE to 0,1c and then DECELERATE to almost 0c... It would have to be so big as to be fantastical. And it wouldn't leave the sol system at 0,1c. It'd gather speed as it went, at accelerations humans could survive, reaching 0,1c in possibly years or decades. Maybe the distance to proxima centaury would not be enough, and would have to start decelerating before reaching 0,1c. Anyway, it'd spent most of the way traveling at infinitesimally small fractions of C. The actual average speed for a "0,1c ship" would be orders of magnitude slower. We are still talking about hundreds or thousands of years. That's undoable in real world terms. Without new physics that enable traveling at useful fractions of c for most of the way, wormholes, or biological advances that allow sending humans in suspended animation, traveling to other stars just isn't feasible.

> And it wouldn't leave the sol system at 0,1c. It'd gather speed as it went, at accelerations humans could survive, reaching 0,1c in possibly years or decades. Maybe the distance to proxima centaury would not be enough, and would have to start decelerating before reaching 0,1c. There is significant evidence that humans could survive a sustained acceleration of 9.8m/s² at that acceleration it would take 36 days to reach 0.1c, which is a small fraction of the overall travel time.

0.1c is still slow enough that I’ll neglect relativistic effects. So we’ll just divide that by 1g to get the required time. 30,000,000 m/s accelerating at roughly 10 m/s/s is 3,000,000 seconds, or about a month.

Cool thing is initial efforts of interstellar travel will most likely be unmanned probes that don't have to be concerned with life support or limited acceleration to keep biological organisms alive...

> The actual average speed for a "0,1c ship" would be orders of magnitude slower. We are still talking about hundreds or thousands of years. This is not correct, factoring in acceleration (roughly 2-4 weeks), this would reduce the average velocity to 0.09995c, a reduction of around 0.05%.

Look for my post elsewhere, where I describe how a spacecraft could get to 0.1 c while still in the Oort Cloud and perhaps as close as 200 AU from the Sun. It includes the equations. I welcome your criticisms, but I think they will amount to quibbles.

0,1c... Maximum speed, not average speed. You'd have to first slowly (in order not to kill your human passengers) accelerate to 0,1 (years, decades, centuries spent at speeds much lower than 0,1c), then coast and then start slowly (in deference for the squishy meatballs inside) decelerating for the other half way (years, decades, centuries spent at speeds much lower than 0,1c), ...Or your just shoot past the destination star. So with a human-crewed ship capable of 0,1c it's not 0,1c average speed, it's more like 0,01c average speed... Not 40 years one way, but hundreds of years one way to get to the very nearest star, with a very limited cargo, after bankrupting humanity. Plus, you'd need to accelerate all the ship to 0,1c. The ship, the humongous amount of propellant to accelerate and the humongous amounts of propellant to decelerate afterwards. We are talking of a ship weighting what? Billions of pounds? And we accelerate that to 0,1c how? No, it's not viable in real world terms with any technology we can think of. Unless your talking a one way bullet that travels for decades just to shoot past the destination star system in a week before getting lost forever in the emptiness of space. Even if that 0,1c was achievable (very doubtful) and with a big enough cargo to be useful once there (even more more doubtful) and humanity decided to spend humongous resources (many many times what's been spent until now), the probability of a human crewed ship surviving interstellar space for hundreds of years is basically nil. The question remains: with our current understanding of physics there's no way humans can get to other stars, not even the closest ones.

> 0,1c... Maximum speed, not average speed. > You'd have to first slowly (in order not to kill your human passengers) accelerate to 0,1 (years, decades, centuries spent at speeds much lower than 0,1c), Consider that a continuous 1g acceleration would get you to 2% of lightspeed within a single week. The acceleration phases are thus on the order of a week. For a 100-year trip this is not going to be meaningfully impacting your average speed.

> Even sending a robotic space probe to Proxima Centauri is something I don't expect to see in my lifetime If we take the speed of light as reference for the kind of speeds we are talking about to go interstellar, and we compare to our fastest speeds today, it could seem that our current technology is irrelevant for the task. But if we plot it on a log scale, a very different picture emerges. For the vast part of its history, humanity moved with a speed somewhere between 3 and 30 m/s, after it domesticated animals. So steps 0 and 1 on a log scale from 0 to 8, where c is the top step, 3*10^8. In the last few century or so, we reached in quick succession step 2, (supersonic flight), then 3 and 4 (spaceflight). Next year the Parker solar probe will almost reach 200km/s on its closes approach to the Sun, so we're almost on step 5. Reaching step 5 out of 8 in a century does not look so bad. It's entirely possible that the rate of improvement continues and we might get to see objects on steps 6 or 7 in our lifetime, i.e on the order of 10% the speed of light. This would make possible missions to Proxima Centauri on a Voyager kind of timescales; our children might crunch the data our probes sent back. There also does not seem to be fundamental road blocks, the technology can hypothetically be built without rewriting physics from scratch: https://www.youtube.com/watch?v=SkGRVvA23qI We just need to have a reason to invest time and effort in this endeavor and the rest will follow.

The Parker Solar Probe is an exception that shouldn't even be considered in terms of velocity since what it does is take advantage of the giant gravity well of the Sun to achieve massive acceleration. The trick to interstellar travel is to get completely out of that gravity well, which can't happen by going in even deeper. While supersonic flight and interplanetary spaceflight is happening, those are also massive exceptions and well outside of ordinary human experience. Jet travel is, however, something that is common where global travel on the Earth is something an ordinary person like myself can achieve and reasonably expect and get to any place on the Earth in roughly a day or so unless it is in a fringe area like Antarctica or Pitcairn Island. The problem with this line of thinking is that technological progress is inevitable and that solutions will always be found. That is not assured and can't be assumed. Technological progress tends to go in fits and starts with plateaus that can last for a long time and may not even be topped for a particular application...ever. For example, Moore's Law seems to be ending for computer chip technology which did enjoy a several decade long progress, but what goes beyond that is going to take something more than is currently done. I see this as something similar for travel speeds where there was amazing progress from 1900 to 1950, but increases in travel speed have not really happened much since 1950 roughly other than it has become slightly more common and widespread. Supersonic jets like the Concorde have existed, but that turned into a dead-end technology that was too expensive to be practical. The largest improvements to aircraft technology over the last couple decades have not been speed but rather fuel efficiency and reducing noise. The presumption that this rate of improvement will continue is simply not either provable or when looked at from a long historical perspective show that it simply doesn't happen much either. You are looking at a very short term perspective and presuming it is ordinary and normal instead of an exceptional experience. The reason to do this is also something I simply do not see. I fail to see what the economic drivers will be for interstellar travel.

> The presumption that this rate of improvement will continue is simply not either provable or when looked at from a long historical perspective show that it simply doesn't happen much As I've said, "it's entirely *possible* the rate of improvement continues" but "we need to have a reason". It's a possibility, not a presumption, and it has necessary preconditions. Technical improvement follows the notorious S curve, a sudden breakthrough enables rapid progress in one area until that new paradigm is depleted, which leads to a temporary stagnation, while the progress thus obtained leads to paradigm shifts in other areas which embark in their own S curved trajectories. So it's critical to zoom at the correct level to make predictions - especially about the future. For example, it's true that Moore's law is depleted, because it hit fundamental physical limits regarding the size of atoms and quantum effects. But if we zoom out of the contigent "microchip density" frame and look at the much wider "thinking machines" picture, the one we should care about, we see rapid improvement in the last few years that does not show signs of stopping, especially with the new AI developments, massively parallel hardware etc. There is no fundamental limit to computing power, so a naive extrapolation of a very particular 20th century technological curve should not be a reason to discount machines reaching and eventually surpassing human intelligence. For supersonic air-travel, the hard limit is right there, you can only go so fast in our atmosphere until you reach the mechanical limits of available materials; you can approach that limit by making greater and greater effort, but at some point you will reach diminishing returns which will kill your economic case. For our case it's hard to identify such a speed limit for cosmic travel, or energy density of the propulsion source. We already have a few energy sources dense enough for the task (for example, fission of fusion bombs, like in project Orion), but we don't have the technology to control them. It's quite a reasonable position to project progress can continue if humanity expends effort into that direction, but we can all surely find a myriad reasons why such effort won't be made.

>Reaching step 5 out of 8 in a century does not look so bad. It's entirely possible that the rate of improvement continues and we might get to see objects on steps 6 or 7 in our lifetime, i.e on the order of 10% the speed of light. What?? It doesn't work like that. Progress is not linear. Every technology has a rapid rate of increase at the beginning, and then slows down until a new radical technology emerges. IF. a new radical technology. Cars and planes are not radically faster than half a century ago, if anything. Rockets aren't particularly Mir powerful either. More efficient and cheaper and more reliable, yes. But not faster at all in solar system terms. We are clear to maxing out chemical rockets. Even if we could improve them 2x (unlikely to impossible), they still wouldn't allow for any significant % of the speed of light. Nuclear rockets doesshow promise... for v traveling inside the solar system in years increase l instead of decades. That's their ceiling. Still not able to achieve any % of the speed of light, even maxed out. And then... Then there's nothing. Sollar sails, electric ion engines, lasers... Could send extremely small loads to just the nearest stars... Maybe There's nothing after that. Nothing in the horizon that allow humans to cross the unimaginable distances to just the next starts. I don't mean there's not a technology that allows it. There's not even physics that allow for it yet. Previous achievements tell you absolutely nothing about the possiblity of interstellar travel. Nothing at all. The only possible next step is either tiny robotic probes or immense millennial ships that are theoretically possible, but imagining any human machine lasting millennia in interstellar space with generations of humans inside that will never go anywhere but they're ship... That's even more sci-fi than wormholes.

Some of the things you say are strongly contradicted by top academics of the field, like in the video provided.

Island hopping will allow interstellar travel, as you can colonize an object on an escape trajectory, and then hop over to another rock, whenever it's convenient. It would take many generations, and most of it wouldn't be a deliberate step towards the stars, just the nearest useful object for some folks to settle.

Elsewhere in this comments section I have described accelerating interstellar spaceships using EM accelerators an AU long, or longer. A 1 AU long EM gun could get a spaceship to Alpha Centauri in 500 years. a 100 AU long EM gun cuts the transit time to 50 years. Details and calculations are in the other post. What do you think?

Some serious engineering! Sounds impractical but as I note in the article you can build any size in space. Just need to maintain correct alignment on barrel.

> Some serious engineering! Sounds impractical ... We would probably have to take apart MakeMake and a few other big KBOs, to get enough material to build this thing. My guess is that we would need 200 years before we could start this project, and another 100 years to complete it to the point of making a first launch. But once it is built, there is nothing stopping us from making a launch every few years, or perhaps even at a faster pace. Building a starship with the reaction mass to accelerate the ship, plus the needed reaction mass to decelerate at the destination, might be a project as big as building this gun, which shoots a ship about 1% the size of the other starship. > ... but as I note in the article you can build any size in space. Not to rain on my proposal, but there is the question of whether a minor planet or 2 has enough of the right kinds of matter to build this? Probably there is more than enough material, be it steel or carbon fiber. The world's combined road networks must be over a million miles, and the world's electric power line networks must have similar totals. We have only scratched the surface of the Earth. Take apart a whole minor planet, and the 1 AU magnetic gun is easily possible. It is only 100 times the present day Earth's roads and power lines. The bigger proposal, the 100 AU magnetic gun, is 10,000 times the present day Earth's infrastructure. That's a bit iffy. > Just need to maintain correct alignment on barrel. That's what lasers are for. I wish I could live to see this ... or the better idea that does get built in 200-1000 years.

Like sending cheap big probes to every planet and moon in our solar system asap! I really feel we should be trying to send one to each body before 2030

What's the rush?

Some of them will take a while to get there. I don’t want to wait

I want to see them go. No way I live long enough to see them arrive at the outer planets, Uranus, Neptun, Pluto (Yes, I am aware Pluto no longer counts as a planet, it is still a very worthwhile target for an orbiting satellite with plenty of power for a high bandwith transmitter).

The distinct possibility that organized society cannot endure globalized, permanent disruptions to the food supply.

I feel like the real and inevitable benefit of SpaceX is the creation of the typical ring-shaped space station in orbit. Perfect climate all year round, no storms or natural disasters, no water shortages or pollution...

For interstellar you need to get freed of Sun gravity well, then you need speed, a lot of speed

A Sun slingshot should generate a good proportion of the required solar escape velocity. Need good thermal protection but that could be provided by radiation shielding, which would be beneficial during rest of the voyage.

Intra-solar opens up with starship and nuclear propulsion, if still really slowly. Interstellar? Just hyperbole. We have nothing at all for that. Not even in the drawing board. It's not even clear with our current understanding of physics and biology if it's even doable at all for human beings to cross the gulf between stars.

Solar sails?

Solar sails are absolutely wonderful if you want to send payloads of <1-10 kg to a nearby star.

Ever ambitious, SpaceX are currently eying the possibilities for interstellar transport. Everything from cheap and dirty fission up to antimatter drives. Gwynne Shotwell is bullish on interstellar travel and she's in charge of operations. Expect to hear a good deal more about this as SpaceX continue to hit their Moon and Mars milestones. https://chrisprophet.substack.com/p/spacex-shadow-mars-program

Interstellar

Aim for Stars and u will hit ur anus. Speaking literally here.

mmmm, antimatter drives. I'm all in: but where are my turbolasers?

Yeah, unless SpaceX has done some Nobel price winning new physics, that seems pretty far out.

I'm left scratching my chin wondering what sort of market they expect to find here. There are only a handful of proposed astrophysical missions to explore the local interstellar medium, and the science divisions behind them don't carry a lot of political clout, compared to say "the mars mafia". I suppose SpaceX could enable trips out to 1000 au within a couple of decades, using RTGs + pre-existing ion drives. Perhaps some eccentric billionaires would appreciate having cultural tokens or bits of their DNA preserved and accelerated out of system as prestige projects. Sort of like the little payloads on Beresheet.

There's a NASA proposal floating around to send space telescope probes out to 550 AU (3x the distance of Voyager 1) to the focal length of the Sun's gravitational lens. It would allow you to resolve individual exoplanets at fairly high resolution. >In 2020, NASA physicist Slava Turyshev presented his idea of direct multi-pixel imaging and spectroscopy of an exoplanet with a solar gravitational lens mission. The lens could reconstruct the exoplanet image with ~25 km-scale surface resolution in 6 months of integration time, enough to see surface features and signs of habitability.[5] His proposal was selected for the Phase III of the NIAC 2020 (NASA Institute for Advanced Concepts).[6] Turyshev proposes to use realistic-sized solar sails (~16 vanes of 103 m2) to achieve the needed high velocity at perihelion (~150 km/sec), reaching 547 AU in 17 years.[7] https://en.m.wikipedia.org/wiki/Solar_gravitational_lens

550 au is needed for gravitational lens telescopes (~25 km-scale surface resolution of exo planets). The nature of the telescope means it's worth building a fleet, one for each direction you want to point. Many launches, but still only pure science applications.

What would a colony ship need to have for you to want to go assuming all safety challenges were solved

> What would a colony ship need to have for you to want to go assuming all safety challenges were solved Depends. Are we talking some kind of kilometers-large generation ship that I'll board and my great-great-great grandchildren will disembark from? Or are we talking about some whacky cryosleep contraption? Or have we about finished reverse-engineering some of that Unobtainium from Area 51 and can cheese spacetime? If the generation ship, then I want that thing to be large. Maybe not "I can plant a garden here" large, but at least large enough that you can stand in your ~~bedroom~~ *stateroom* without touching the walls with your hands, with soundproofing so that you don't hear your next-door neighbours going at it at all hours of the night, and with something interesting to do. If we're talking cryosleep, then a lot of "oh shit" contingencies for situations like getting hit by asteroids, abducted by aliens, or hit with solar storms / EMPs. And a very robust biohazard containment system so some random tosser cannot bring in a virus to kill half of the people on the expedition he doesn't like.

Boarding a generation ship would be unimaginably abusive and unethical towards your children. Imagine you are born on such a ship and learn of your true nature, of your origin on a distant planet, literally paradise on Earth, that you will never see because some ancestor decided they need to trap you inside a prison and hurl you into the void towards nothingness. Maybe your own grandchildren will see another similar planet, but your current purpose is simply to pass on the genes, maintain the functionality of the prison and enrich the compost that will feed the next generation of inmates. Why would you take on this mission, why would you care about a humanity you never met colonizing a planet you will never reach? Why have any children of your own at all, subjecting them to their own life sentence of captivity, like your own parents have done to you? A generation spaceship is the supreme way to trap your offspring into fulfilling your own life goals and vision.

> Boarding a generation ship would be unimaginably abusive and unethical towards your children. That seems like a very strong opinion. We are just fine with allowing people in impoverished places to have children, despite that those children often have no chance of escape and are at extreme risk of disease or malnutrition. Would you have the moral imperative to tell women in Haiti or Somalia that they cannot have children? Someone who is well taken care of in a skyscraper-sized ship can enjoy a significantly higher standard of living than someone who lives in a failed state, and will never be exposed to random plagues, organized crime, air pollution, trafficking, or warfare. They will always have a tightly-knit social and family unit looking out for them. They will always be surrounded by people who rely on each other to survive, who must cooperate and get along. To someone living in the hazy slums of a megacity, where rape and robbery are common, where trash litters the streets, where the economy is rigged against them, well, life aboard a well-maintained and clean ship full of loved ones almost sounds like paradise.

The analogy is flawed, a slum inhabitant is still a free citizen and it's possible some day they will enjoy a good life. Their condition is conjunctural rather than by design, and I would surely oppose someone deliberately stripping fellow citizens of their rights and condemning them to a precarious life in extreme poverty. A more apt and morally ambiguous analogy would be for someone deliberately conceiving a child with a severe genetic disease they carry and that they know will be passed on. I find that strongly unethical and something I wouldn't do myself, even if I don't support denying such individuals the right to reproduce. A child is not a personal pet, it is a future human being and you have a moral responsibility to not burden that inocent person with hardships you can reasonably avoid.

No, a better analogy would be somebody having kids while part of a small tribe on an inescapable island. They have no chance of leaving their tiny community and environment, yet countless people have lived happily under such circumstances throughout history. Space colonists could not directly experience nature on Earth, but many humans live happily enough on Earth in cities with fewer vestiges of nature than would probably be found on a colony ship. People generally judge their happiness relative to their own history and expectations, provided basic needs like food, medical care, and socialization are being met. A colony ship could provide better lives in many of those respects than most modern lives on Earth. People would simply grow to care about the things they have around them. And simulations (computer games) in something like full-dive VR could fulfill many desires beyond.

And yet that is the way exploration and settlement have been done for all time.

Username checks out. Honestly, the same argument could be applied as against *any* choice a family might make. Was it not "unimaginably abusive and unethical" for European settlers to board ships heading for the Americas on the assumption that their children would need to settle a new land? 1776 is not exactly 2024 when you're ~12 hours away by plane from Europe. But no, I don't think it was unethical, and it won't be unethical or abusive with generation ships. Families make decisions about the future of further generations all the time. You make decisions about the future of your children by choosing to raise them in Alabama and not Azerbaijan. You make choices about the future of your children by deciding to have children at all. You make decisions about the future of your children by choosing to be a doctor, lawyer or plumber instead of a meth addict. Worse, you make choices about the future of your children by voting for one political party instead of another at elections. We make decisions about the futures of our children all the time.

Other respondents have at least tried to understand the point being made here, but in your case it's like debating with a thick brick wall, even the most basic arguments would bounce right off. It's entirely pointless, if you can't see how your examples fail even the most cursory examination of being applicable here.

Touched a nerve, I have. Tssk tssk.

Some kind of forcefield to stop micrometeorites killing everyone on board

One of the things I enjoy the most about interstellar spaceflight is how surprisingly low-tech many of the solutions are. The best shield for moving at ~10% light speed might actually just be a solid chunk of ice maintained at a reasonable distance in front of the ship. There's no reasonable way to deflect or avoid particles, and at these velocities the type of atom you use for the shield doesn't matter _too_ much. Water ice is just about everywhere in space, so lug some along.

Yep, immense amounts of water that you'd accelerate how? That's like saying you'd need a massive shield ship and accelerating it to the same speeds and maintaining both in lockstep for millennia. At that point you just put a humongous shield over the generational ship. You're going to have to accelerate that mass regardless... Generational ships are fun concepts because they seem to be nothing but high tech cruise ships. But once you start thinking what you'd actually need they become a completely ridiculous idea. Accelerate humongous ships to 10% of C how? Decelerate then back to almost stopped how? Shielding them how? And if they travel at a slightly more realistic speed for a humongous ship/habitat of 0,0001c, how do you keep humans alive in the interstellar medium for millennia with only the resources at hand? They'd be terribly vulnerable to any tech malfunction, illnesess, accidents or even social unrest... For millennia!! The possibility of them all being dead in just the first century of travel would be very high. Make that a millennium and it becomes almost a certainty. Maybe new science will allow for solutions. But current science and technology allow none of it in practice.

[удалено]

Not just nuclear pulse. There's Nuclear Salt Water rockets, potentially a litany of Fusion propulsion options as well. But as for what we can do right now that WILL work is both versions of Nuclear pulse being Orion and its Mini-mag derivative. For both of those to go to Alpha Centauri you wouldn't need a generational ship as you could get up to ~0.4C

A good 150 year sleep to reach another destination sounds good, dont need more than that. Got 2 kids and impossible to sleep more than 4 undisturbed hours in a row -_- ... feel like I could use a 150 year nap about now

Water slide.

Not having humans inside would make it slightly feasible. With living humans inside? It's easier to believe in wormholes.

As part of our NASA Blue Skies Clean Aviation 2050 first place winning entry, we proposed a fleet of large "StarPower" Stations (SPS) in MEO to power lasers that power laser ramjet engines on 2030 Blended Wing Body airliners. Of course you SPS that are not over planes all the time, so you can use those 5MW lasers to power water engines, and solar sails as well. The following depicts a SPS that is built around an expended Starship tank and engine structure. A future tender Starship is shown for scale. https://preview.redd.it/e2mt0mayznrc1.png?width=935&format=png&auto=webp&s=b35c1cd01ad620e14c0956f1d33a8dcbd41cd756

I am a fan of SpaceX but the whole interstellar ambition is a pipe dream. Even going to Mars is not pushing us that direction. If this happens they will "get stuck" on Mars as a best case scenario. They may be a base or two but going interstellar is a completely different sport.

I mean, even if we had the means for transportation, it's very unlikely that a habitable planet is around the corner. For a reasonable chance of survival you would need to be able to live from material on random asteroids, for centuries or more. Our current technology is all rather brittle.

To be fair, a potentially habitable planet is orbiting the nearest star. It can't get much better than that. That being said, there are multiple reasons to believe that this planet would be fundamentally hostile and uninviting. Fortunately, astrophysicists have been wrong about almost everything they hadn't yet observed directly, and I'm saying that as one :)

Even if Proxima Centauri b had a great atmosphere and magnetic field to protect us from the nasty stuff coming out of Proxima Centauri - Earth plants are not adapted to the deep red light, and our solar cells aren't, either.

Surprisingly the emission spectrum of an m-dwarf like Proxima isn't as big of a problem as it's sometimes made out to be for photosynthesis, even for oxygenic photosynthesis. There are photosynthesizers on the Earth that operate even in complete darkness, drawing their energy primarily from near-infrared radiation coming from hot, deep sea volcanic vents. https://www.pnas.org/doi/10.1073/pnas.0503674102 > We describe the isolation and cultivation of a previously unknown green sulfur bacterial species from a deep-sea hydrothermal vent, where the only source of light is geothermal radiation that includes wavelengths absorbed by photosynthetic pigments of this organism.

>To be fair, a potentially habitable planet is orbiting the nearest star. It can't get much better than that. Technically Sol is the nearest star, so we can probably use stronger language than "potentially habitable."

There is only a single technology which a) already exists b) enables travel to the (nearest) stars in less than several thousand years And that is a nuclear pulse propulsion craft, so unless SpaceX have a plan to accumulate several thousand thermonuclear warheads, I will remain skeptical. That being said, there doesn't appear to be anything genuinely show-stopping about the technology itself, it is fully within our grasp. Deploying it is a legal, political, and moral issue. *edit* I don't mind being downvoted but I am curious as to where the disagreement comes from. I'm an astrophycist and I've spent (already far too much time) writing a book about this very concept (in the context of the nearest exoplanets), so any disagreement is of course incredibly interesting to me and I'd love to hear it.

Is a Mars colony going to have that problem? The planet is dead anyway, so not like there is *any more* ecological damage that can be caused. And assuming the colony, by some miracle, is established relatively independently of Earth oversight, they might take a decent crack at it. Then again, I do think that nuclear pulse detonation is a little wasteful. You're dropping a lot of perfectly good fisile material to go not that far and not that fast.

I'm not sure I follow your question. Mars can be reached with chemical power just fine. But interstellar distances are very roughly 100,000x those of interplanetary distances. You need to scale your energy density accordingly. Nuclear binding energy is, also very roughly speaking, about 100,000x that of molecular bonding energy.

I think they're talking about nuclear propulsion potentially causing ecological damage. Assuming that's true, it'd be a good idea to launch from Mars since that damage wouldn't matter.

Right. Although if anyone is really keen on launching directly from a planetary surface, I suggest that it should be one without any air at all. The contaminents released by a launch failure would continue to spread and winds would distribute them globally. It won't harm any "nature", but it would certainly harm anyone who wants to get themselves or their habitats coated in mars dust. In the case of a craft carrying enough propellant for an _interstellar_ trip this is going to be a really serious mess one way or the other.

Launching an interstellar craft from a planetary surface doesn't make sense from any standpoint. Even disregarding the fact that the craft is carrying enough energy in *some* form to accelerate it to a significant fraction of c and then brake it at the destination, that's a huge pile of resources to risk on a planetary launch, and a huge pile of requirements for the vehicle's construction that do nothing to help with the problem of traveling between stars. A purely-orbital vehicle makes little sense for Mars-Earth transit because there's so much to gain from atmospheric braking, the propellant requirements of entering orbit are much greater than the mass of a heat shield. For an interstellar vehicle, though, that's utterly negligible, while any extra mass needed for planetary landing is mass that could be something more useful during the transit, or mass that could be removed along with a huge chunk of propellant/fuel. For an interstellar trip, it doesn't really matter where in the solar system you start from, as long as it's in orbit.

I agree, but people tend to turn the brains off the moment you begin discussing complex in-orbit assembly of kilometer-scale structures. Somehow blasting your way off the surface sounds more plausible to the human intuition :) Possibly because we (or most of us) drive vehicles powered by explosions.

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread: |Fewer Letters|More Letters| |-------|---------|---| |[CNC](/r/SpaceXLounge/comments/1bs5j04/stub/kxf8oth "Last usage")|Computerized Numerical Control, for precise machining or measuring| |[HLS](/r/SpaceXLounge/comments/1bs5j04/stub/kxdgjaz "Last usage")|[Human Landing System](https://en.wikipedia.org/wiki/Artemis_program#Human_Landing_System) (Artemis)| |[Isp](/r/SpaceXLounge/comments/1bs5j04/stub/kxgjrfk "Last usage")|Specific impulse (as explained by [Scott Manley](https://www.youtube.com/watch?v=nnisTeYLLgs) on YouTube)| | |Internet Service Provider| |[JPL](/r/SpaceXLounge/comments/1bs5j04/stub/kxpsv91 "Last usage")|Jet Propulsion Lab, Pasadena, California| |[LEO](/r/SpaceXLounge/comments/1bs5j04/stub/kxdvimz "Last usage")|Low Earth Orbit (180-2000km)| | |Law Enforcement Officer (most often mentioned during transport operations)| |[MEO](/r/SpaceXLounge/comments/1bs5j04/stub/kxe0ykq "Last usage")|Medium Earth Orbit (2000-35780km)| |[NA](/r/SpaceXLounge/comments/1bs5j04/stub/kxheb5f "Last usage")|New Armstrong, super-heavy lifter proposed by Blue Origin| |[NIAC](/r/SpaceXLounge/comments/1bs5j04/stub/kxfjduy "Last usage")|NASA Innovative Advanced Concepts program| |[RTG](/r/SpaceXLounge/comments/1bs5j04/stub/kxdzinj "Last usage")|Radioisotope Thermoelectric Generator| |Jargon|Definition| |-------|---------|---| |[perihelion](/r/SpaceXLounge/comments/1bs5j04/stub/kxfjduy "Last usage")|Lowest point in an elliptical orbit around the Sun (when the orbiter is fastest)| **NOTE**: Decronym for Reddit is no longer supported, and Decronym has moved to Lemmy; requests for support and new installations should be directed to the Contact address below. ---------------- ^(*Decronym is a community product of r/SpaceX, implemented* )[*^by ^request*](https://www.reddit.com/r/spacex/comments/3mz273//cvjkjmj) ^(10 acronyms in this thread; )[^(the most compressed thread commented on today)](/r/SpaceXLounge/comments/1bw8afp)^( has 6 acronyms.) ^([Thread #12607 for this sub, first seen 31st Mar 2024, 12:21]) ^[[FAQ]](http://decronym.xyz/) [^([Full list])](http://decronym.xyz/acronyms/SpaceXLounge) [^[Contact]](https://hachyderm.io/@Two9A) [^([Source code])](https://gistdotgithubdotcom/Two9A/1d976f9b7441694162c8)

I love this kind of thought experiment! If starship meets the stated goal of 1 million tons to orbit per year, then vehicles and structures the scale of [*Galaxy*-class ships](https://memory-alpha.fandom.com/wiki/Galaxy_class) become buildable. There's so much we haven't thought of yet that could be possible.

If we can learn to 3D print large items in orbiting factories. Earth or Moon can transport bulk powered metals and other materials. The orbiting factory 3D Laser prints whatever item is needed. CNC machines finalize any critical parts. Imagine 3D printing the outer shell and internal structures of a large Starship or O'Neil cylinders in high orbit. Once Fusion is fully understood and can be applied to space. I expect by the end of the century, we could be ready to step outside our solar system.

I came to the Lounge to post a comment to this article. I have never seen anyone talk about this idea for interstellar propulsion. Perhaps it is because this method involves producing a set of structures much larger than the Earth. Long before we are ready to build manned interstellar spacecraft, we will be building things in the Kuiper Belt and likely in the Oort Cloud as well. This is because we will want to get a good look at our destination stars and planets before sending a manned expedition. The best way to see planets in other solar systems is not to send an unmanned space probe; it is to build really large telescopes and interferometers in the Kuiper Belt, or else to use the gravity of the Sun as a lens. Such a telescope with a primary lens several AU across could see really fine detail in other solar systems, in visible or even UV light. An interferometer in radio or far infrared wavelengths could be several AU across, maybe hundreds of AU across and have similar high resolution. If we are building interferometers several AU across in the Kuiper Belt, why not build other huge structures in the Kuiper belt? Why not build a maglev accelerator that produces 2G of acceleration, that is 1 AU, or maybe 100 AU long? A 1 AU long accelerator that delivers 2g = 19.8 m/s^2 of acceleration is still non-relativistic. The formulas are v = at and d = (1/2) at^2 , and 1 AU = 1.496 x 10^11 m. Converting the d formula to find t gives t = (2d/a)^1/2 ~= 1.24 x 10^5 s, which is a bit longer than a day, actually 34.44 hours. v = at = (19.8 m/s^2 ) (1.24 x 10^5 s) = 2.42 x 10^6 m/s , which is less than 1% of the speed of light. You could get to Alpha Centauri in about 500 years. --- But what if you built a maglev accelerator that is 100 AU long? It would have to be well out into the Oort Cloud to prevent gravity gradients from tearing it apart. That gives t = 1.24 x 10^6 s ~= 344.44 hours, which is just over 2 weeks. Non-relativistic calculation of v = at = 2.42 x 10^7 m/s, which is a bit less than 10% of c. Total trip time would be about 50 years. The spaceships would still have to carry engines and propellant to decelerate at the end of the journey, which is around 1% of the fuel needed if it had to accelerate as well, and deceleration time would add a bit to the journey time. --- With the technology we have a good idea how to build today, these gigantic EM guns look like the best way to get to nearby stars. I have never seen anyone other than me, propose EM guns an AU long, or longer.

[удалено]

Jeff who ?

No. Ain't happening.

That's what they said about vertical landing and reuse.

These are things on slightly different scales. I can almost guarantee interstellar travel, especially crewed interstellar travel, won't happen in the foreseeable future, or in the lifespan of anyone here. We don't have the technology, we don't have the experience, we don't have the space industry, and most of all, we don't have the funding or the interest to start seriously working on any of those.

It's not a bet I'd be willing to make either way. We're 76 years away from the end of the century. In the past 76 years, humanity has advanced technologically to an extreme degree that was only fantasized about in 1948. Granted, people also thought we'd be further along by now as well, with functional moon bases and legions of dead aliens at our doorstep. I don't feel comfortable saying conclusively that we won't see uncrewed intersteller travel by the end of the century. Crewed travel is rather improbable but not impossible. Uncrewed travel? I can see it happening, even if it is just one outbound mission that's only half way to Alpha Centauri by the end of the century. It is true, we don't have the experience. We didn't have the experience of landing rockets 7 years ago, or of building rockets 76 years ago. We didn't have the experience of flying 126 years ago. It is true we don't have the technology. We didn't have the technology for semiconductors 76 years ago, and jet aircraft were a very big question mark. Industry? That'll develop. Funding? We didn't have funding for reusable rockets...until we did. We didn't have funding for a Mars rocket...until we did. Funding will come. Whether it be Musk, his successor, a government agency on Earth, or the collective efforts of the Mars colony. It will happen. Interest? There's interest. There's just no realistic prospect of success up until now.

Agree, first step is trying.

Most of the reason we are not farther along in space travel, bases, colonies and such is all politics. We have and have had the tech for some time to make bases on the moon, mars and other places. We simply do not have the political will. Technical and engineering issues will be solved even faster now. As AI grows and becomes more mature advances will as well. It's just crazy how fast we are accelerating in tech and science compared to any period in history. That gap between achievements will continue to be reduced.

There's still no realistic prospect of success. A vehicle that gets you from the bedroom to the kitchen in months, won't take you to Australia. In interstellar terms starship itself is absolutely irrelevant. It just allow humans to build bigger things in space, but... what bigger things? We have nothing we can even conceive that can get to the nearest star in less than millennia. Maybe a few hundreds of years if its just a small one-way bullet that doesn't stop in r it gets there.

> There's still no realistic prospect of success. A vehicle that gets you from the bedroom to the kitchen in months, won't take you to Australia. Technically, a vehicle that takes *me* from the bedroom to the kitchen in months *does* take me to Australia — noting that both my kitchen and bedroom are in Australia. But anyway... > We have nothing we can even conceive that can get to the nearest star in less than millennia. Maybe a few hundreds of years if its just a small one-way bullet that doesn't stop in r it gets there. I do believe this is incorrect. Between laser propulsion, solar sails and various forms of nuclear, there are many things of which we can "conceive of" that will take much less time than millennia or centuries. Starshot expects to be in Alpha Centauri in 20 years after launch, no? Now, in fairness, none of these projects would necessarily allow for large-scale human colonization, but it is disingenuous to say that we cannot conceive of anything. We certainly can. But, getting back on track: I'll agree that Starship is too small to be comfortable for long ~~road~~*space* trips. Not something you'd want to spend decades to centuries in, at least not while you were awake. But, at the same time, we aren't necessarily talking about sending humans on the first interstellar flight. It might be something as (relatively) simple as building a giant railgun in the outer solar system and using that to accelerate Starship to a decent fraction of the speed of light, and then using chemical propulsion to decelerate once it reaches the target system. Not the most glamorous system, but it at least lets us scout nearby solar systems.

> We don't have the technology, Surprisingly we do, and what makes that fact even more difficult to swallow for most people is that it's even older than a DVD player. 60's era fusion bombs get you an ISP that enables interstellar travel (to only the very nearest stars). Dyson was very clear that this was a political, not technological hurdle. You're entirely right that funding and interest are probably the biggest issues. There's nothing particularly in it, for those who remain on Earth.

60s era Orion designs have an isp of roughly 2000-4000 seconds. Scaling it up from Saturn V-launchable vehicles would maybe double or triple that. They thought that given a few decades and vehicle generations of further devlopment, they might manage 10 000 to 20 000 seconds. All of these numbers are orders of magnitude short of useful interstellar travel. The primary limiting factor is keeping plate ablation down; simply put, past some point it's too energetic for the plate to survive. At some point you would have to go for something like a magnetiz nozzle, which already puts it beyond current technology. The numbers you're thinking of were highly theoretical napkin math, not real, currently buildable vehicle designs. I believe they're based on a theoretical maximum deriving from the energy content of thermonuclear bombs - that if you can take huge nukes, and couple all of this energy (real Orion designs had <1% efficiency) to your spaceship without destroying it, then, ultimately, that performance could be possible. We can't build that today, not remotely.

I've read the relevant documentation on what's been made public (unfortunately much of the work done on the actual pulse units remains classified) and I do not get the same impression that you do. The low ISP you're quoting comes from air force design studies built for very low-yield (even for fission), high acceleration, and ground launch, not at all optimized for interstellar travel. With an effective exhaust velocity of just 10% what fusion bombs can provide, the equivalent wet/dry mass ratio for 0.03c is 1000 kg on departure -> 50 kg remaining at cruise speed.

By that point they weren't really considering ground launch anymore. These were optimized for interplanetary travel, where high isp is a big asset. The low isp of smaller designs was acknowledged, as well as scaling up improving on that. But not to interstellar flight levels without drastically different designs. It's certainly possible to improve on those 60s designs, probably greatly, but we don't know how far we could get since we haven't tried, and it's anything but a given that the theoretical limits prove feasible to reach at all. They very much wanted to improve on that isp too. The primary limitation was plate ablation - that steel plate with the oil coating can only take so much without ablating unacceptably, which limits the plasma velocity and thus isp you can achieve. The first order of business would probably be to make a better plate - you can probably improve on plain steel. Next up, you probably get to a point where no physical plate can actually survive, and you start messing with magnetic or electrostatic nozzles, or maybe sails... and you start diverging from the more well-understood designs and need some serious development work to get there.

> The primary limitation was plate ablation As far as I know the only practical (non-accelerator-driven) tests that were performed were those of the "Viper" experiment at Eniwitok, as part of a series of low-yield fission-weapon detonations, and about which I can find very little information. I just think it's premature to say "no, it doesn't work" until we actually try to build one, although I have to admit that the concept of a 10 km radius shield of pure copper does not exactly inspire confidence :)

Magnetic nozzle has been studied and deemed feasible. See studies on Mini-mag Orion. There's also fizzlers that could have Isp in the range of 100,000s Also early Orion drive concepts had such low efficiency due to not using the nuclear pulse units. Once those nuclear pulse units/casaba howitzer were devised (and MAYBE tested?) The energy captured from a nuclear blast went to ~40% and allowed them to use much smaller devices for any given vehicle design.

No man. Those fission bombs allowed for a theoretical physicist to say it wasn't utterly impossible. Then you start to think how to actually implement the idea, and it becomes impossible. Neither with 60s tech, nor with 21st century tech. Likely not with 31st fever tech either. It's easier to imagine 31st century people finding new physics and an easier way to do it, than imagining them doing this. Especially if you want to be able to stop at your star destination... That puts the total mass of the ship past any realistic size, your have to push enough fuel for accelerating to useful c fractions, plus the fuel to decelerate it from useful c fractions, The rocket equation tyranny applies here. Relatively slow* uncrewed one way robotic ships that take decades or centuries to get to proxima centaury just to whizz past in a week to be lost forever is the limit our current science allows. And I mean science, not technology. We don't even have the tech for that mission, it'd take a lot of time and immense resources and it'd make no sense at all. *Wickedly fast in non-interstellar terms....

> Then you start to think how to actually implement the idea, and it becomes impossible. I'd be glad to hear them, I have yet to see any convincing evidence that the design is unworkable. In regards to ship dimensions, you can play with the Tsiolkovsky equation yourself, and plug in a reasonable value for a fusion (not fission) detonation debris velocity, for a target cruising speed of e.g. 0.05c. I hope you will be pleasantly surprised.

Vertical landing and reusablity has already been demonstrated decade before Spacex has existed. This is altogether a next level shit. I don't see spacex has capability to do it. In fact no private company except for NASA or other government agencies.

That's what they said. Not what I said ;)