For anyone really interested in the science of this who doesn't necessarily want to digest the raw math, I highly suggest Isaac Arthur's Youtube channel eg .
People tend to fall into a number of traps when dipping their toes into this topic.
The first one is the trap of wishful thinking, which is the primary reason for pretty much any attempt to come up with a theory for FTL. Most of these people just don't understand what the domain of a function is. Just because you can plug a negative number into an equation that is otherwise over real numbers doesn't mean that makes sense or is valid.
Second, people oversimplify. I see on this thread and others claims like "if we just accelerate at 1G we can get pretty much anywhere relatively quickly". So that's true superficially but the energy requirements for that are so vast even if you have perfect mass to energy conversion that a significant percentage of your ship's mass is fuel.
To me, laser highways seem like the most likely form of far future interstellar travel. That's largely predicated on commercially viable fusion power however and that's not a given.
Failing that, you're talking about variations of what are essentially generational ships.
For example, a ship could travel 1,000 light years to the Orion Nebula in only 15 years (as perceived by those on the ship). And since they are living in 1G, a lot of the detrimental effects of long-term space travel are eliminated.
Of course, to an observer on earth the trip would take over 1000 years, so don't expect to hear how the trip went.
Consider the ISM: at 0.086 c, ionised helium is the same thing as 14 MeV alpha radiation. Low density regions within the galaxy are 0.2–0.5 particles/cm^3; 0.2/cm^3 * 0.086 c is ~5e12 particles/m^2/second, or about 9.9 watts/m^2 if it was all He4 and therefore 14MeV/particle or about 2.5 W/m^2 for Hydrogen at the same speeds, which is bad enough given what keeping that up for years will do to any solid hull, but molecular clouds can be 10^2-10^6 particles/cm^3 and the upper bounds of that is ~10 MW/m^2.
Even without Relativity (which makes it worse), if you double the speed the kinetic energy per particle quadruples and you also double the number of particles per unit time.
You also recover it's momentum, which means you slow down.
Really you are recovering your own kinetic energy, you are breaking against the interstellar medium, probably very violently and destructively.
That's like saying "a building was moving in the frame of reference of the plane, so it didn't crash - it recovered energy."
A more advanced version of this concept is known as Buzzard ramjet, and it was calculated to be energy negative
If you have a more precise idea and that was an analogy, I recommend giving that idea in a more precise way — I’ve seen my own “what if” ideas wildly misunderstood by my own poor analogies.
not necessarily. For some parts aerodynamic design means loss minimization, while some parts (like [ram]jet engine inlets or pretty much whole body of a scramjet plane/missile) are designed for ram effect, ie. to recover some of the kinetic energy of the incoming air as the air has velocity in the hull's frame of reference.
The same thing for interstellar medium - the "aerodynamic" design would mean either coming up with some means of smoothly redirecting the incoming medium around the ship (probably by ionization and EM field) and/or recovering the energy and collecting the mass, whereis GGP limits the consideration only to the "breaking against the interstellar medium, probably very violently and destructively."
The only engine I’ve heard of that attempts to use the ISM as a source of fusion fuel is the Bussard ramjet referenced by @ClumsyPilot (which uses an EM field), and as they point out, it’s been demonstrated to be a net-loss not a net-gain. An easy way to intuit this result is that the energy per particle of a fusion reaction is similar to the 14 MeV per particle (0.82-22.4 MeV for the most promising reactions) which I used as a starting point in my calculation.
You’d actually have to decelerate the ISM from the frame of reference of the ship in order to increase the rate of fusion to its maximum, but even then most nucleon impacts do not cause fusion and instead bounce, slowing you instead of helping you even if you can solve the problem of efficiently using the energy of any particles you decelerated at the front of your ship to accelerate them again at the back.
ramjet inlet is designed to convert kinetic energy of incoming air into a pressure by slowing down that air, and the higher pressure results in higher efficiency of the engine. In case of scramjet a lot of the energy impacted upon the air pushed away by the hull at those speeds is concentrated in the form of high pressure of the shock wave - so the scramjet inlet is designed to scoop that high pressure air, again for high efficiency of the engine.
>the energy per particle of a fusion reaction is similar to the 14 MeV per particle
option 1. completely absorb the momentum of that particle by the hull and slow down accordingly and waste the collision energy as heat/radiation. Option 2. slow down the particle (thus still of course absorbing the whole momentum) in the EM field thus generating some useful energy and using that particle, if a suitable one, later for fusion - thus recovering significant share or even crossing into net-positive a bit (depends on efficiency of the recovery and the fusion processes)
Consider: take all the energy from bringing the ISM into the same frame as the ship, use it with 90% efficiency to reaccelerate the same matter out the back of the ship in an ion drive, and you merely roughly double the velocity where drag becomes clearly dominant (I am handwaving the relativity correction as the difference between x8 and x10). 99% efficiency, you’re looking at 0.086 c * 2^2 = 0.34 c, still far short of what you need for time dilation to get you 1000 ly in 15 subjective years.
Also, any engineering solution along the lines of what you suggest would turn existing $1000 high-school-project Farnsworth fusors into useful power output fusion reactors rather than mere switchable neutron sources.
(As an aside, learning about the reality of Bussard ramscoops gave me the headcannon that the ones in Trek only refuel the ships while they park themselves in ionospheres; but Trek is big on the “space is an ocean” trope, so not that important).
This, like many non-IT discussions on hackernews, is devolving into "How many angels can dance on the head of a pin?"
What better way to save the earth and solve the population problem than to have the energy production capabilities to simply build e.g. ringworlds? Even that's not out of the realm of possibility with that kind of energy available.
With all the investment in solar and wind we could easily have built a fission based economy. The French proved that in the 70/80s and had a green grid ever since.
Had we done that collectively global warming would be a far lesser issue.
It would also help us understand neutronics and material science so we can eventually switch to fusion.
The same basic technology could also be used for space travel in the solar system and would have advanced space travel by a lot.
But of course for idiotic reasons society went away from that.
Much of that high cost is often wholly-legal corruption that attaches to almost any large, centralized, hard-to-account public-money expenditure. Knowing this does not help. Thus far, solar and wind projects have mostly avoided the corruption tax by their simple accounting framework: N generating units x $C per unit = $CxN; and by their clear value proposition: $CxN is lately, and still increasingly, much less than alternatives whether those are figured with corruption tax included or not.
At this time it is cheaper to build out a new solar-and-wind farm and operate it than to continue just to operate a comparable nuke, wholly neglecting construction and decommissioning cost. We finally got the ramshackle Diablo Canyon and Indian Point contraptions shut down, but it will still cost a $billion to take them apart; or, likely, more, according to the degree of corruption tolerated.
That's why France has cheapest electricity in Europe?
Furthemore, once you take into account damage from climate change for fossil fuels or cost of backup for renewables, their cost triples.
For example Scotland generated 100% of it's energy needs cumulatively in a year from renewables, but in reality the renewables only covered ~30% of demand because it was generating loads when none was needed, and generation little when loads was needed.
But this graph indicates that, unlike in 2009, nuclear is in general much more expensive than PV or wind: https://commons.wikimedia.org/wiki/File:20201019_Levelized_C...
From the cost estimates I’ve seen, PV with battery backups are cost competitive with oil and better than coal, even with pessimistic battery cycle-lifetimes. And we are building battery factories essentially as fast as we can, and batteries are still getting cheaper.
US and many other countries have a random of assortment of one-off reactors with different safety issues and operational requirements, fuel requirements, making this very expensive to operate. This "free market" approach doesn't work for nuclear.
Regarding batteries, we will have a massive shortage for cars, let allone grid from all the forecasts I've seen.
Australia and India will be fine with solar, but Siberia has no sunlight half the year and wind is not great there either
I’ve not seen this. Do you have a link?
> Australia and India will be fine with solar, but Siberia has no sunlight half the year and wind is not great there either
Naturally. I don’t wish to suggest one-size fits all, merely what seems to be the best on average at the moment and with foreseeable trends.
The most mature of these is "stored hydro", in which water is pumped up to a dam reservoir. Obviously this depends on having a dam not too far away, a ready source of water below it, and enough spare generating capacity there to take up the load when needed. Ramp-up is near instantaneous.
In places with deep mine shafts, a similar gravitational storage method is practical: suspend a heavy weight (hundreds or even thousands of tons) at the top of the shaft, attached to cables that turn a motor-generator as they unwind. This has the advantage that it may ramp up to full power in seconds, and the available energy is limited only by the depth of the shaft. Obviously this depends on availability of long vertical mineshafts, but there are very many of these worldwide. The tech involved is all 19th-century, so these only need construction. When excess / cheap power is available, the weight is hoisted back up.
Another is underground compressed air. (This may be combined with the above, pumping air into the same mineshaft, as is being done in one pilot installation.) This, also, relies only on 19th-century technology. Roughly half of the energy stored in compressed air becomes heat, so efficient use requires good heat insulation. Earth serves as excellent insulation. Power is extracted by exhaust through a turbine; existing turbines from older generation schemes may be repurposed. Ramp-up is fast. The reservoir must be charged up for some time in advance to be able to get maximum power out at sudden need. Several examples of this are being demonstrated.
Air liquification is a perhaps surprising alternative. It relies on mature 20th-century technology; there have long been numerous industrial uses for liquified air. For maximum full-cycle efficiency, heat extracted from the air is also banked. A GW-scale plant is under construction in Scotland, and a 50 MW demonstrator is breaking ground in Chile. An advantage of air liquification is that the storage capacity is limited only by the number of cheap insulated tanks built, which may be added to at leisure.
The above are the immediately available alternatives. Efficient hydrolysis of water to produce hydrogen has obvious industrial importance, and it may eventually displace other methods, as there is no upper limit to the useful amount of hydrogen that may be usefully produced from surplus generating capacity, even after local tankage is full.
Nonsense. In the 60 they literally developed 100 of different types of nuclear reactor often for a tiny amounts of money. Any coherent strategy over the last 50 years clearly shows that if would been cheaper to reach basically zero carbon and it could have been done far earlier and earlier with nuclear.
Navy ships in lifetime analysis show that over the ship lifetime its very cost effective. Not to mention that you can do many things you simply couldn't do otherwise.
Real private innovation and capital were never unleashed for nuclear innovation after the early explosion in the 60s. The extreme restrictions on the materials, government picking winners early and shutting out everything else. At least at that point some research was still going on, but no real effort to go beyond. After the government lost interest in the technology almost every single project was shut down and a nuclear became basically no-go when asking for funding inside the government.
And of course if you have incredibly low volume systems, with a tiny base of educated people, based on technology that is essentially from the 60s you are not gone have an effective system.
Like everything else, nuclear plants, even incredibly sub-optimal PWR designs when built in large numbers will get significantly cheaper. This is clearly evident in any analysis on nuclear economics. If you can build essentially the same reactor with many of the same project leader and teams over and again the costs go down massively. Even outside the actual parts production getting cheaper.
The cost per reactor that France achieved during their expansion is actually very low and they did it with pretty old technology that was really not at all optimized to be effectively built.
There is a gigantic design space that has not been explored that could massively reduce both the build cost and the operation cost and even decommissioning cost. Alternative reactor designs can be far smaller, far safer and require less human operation in fact a properly built reactor should have almost no human interaction ever.
This was all known in the 60s and the foundations were clear put down. In the 70s some amazing stuff was shown but at that point budget had already gone down government had already picked the commercial winners.
Check out this picture:
A design of that size would have been possible with 70 technology. Had they actually tried to innovate on technology and attempted different designs or had given real advantages to CO2 free technology at the time and let private investors take care of it, designed like this would have happened.
These main reactor vessels are literally not much bigger then a tiny ship, and could easily be manufactured in a single factory on a assembly line, transported to location and dropped into a hole filled with concrete.
Current cost actually are a result of the massively complex large civil engineering, more then the actual nuclear part themselves. That is high cost construction over a long period that has major disadvantage in financing. Having 10x smaller vessels with 100x simpler cooling system absolutely would make building reactors far cheaper and if you build many of them and have teams that are not doing for the very first time there is no reason why a nuclear plant can be build at cheaper rates then coal plant, more comparable to modern gas plants.
If you have an energy source that has that much advantage in energy density. Not taking advantage of such a dense and easy to obtain energy source is insane. Thorium mining for the whole US could have been done in one small mine for all US needs for the next 100 years or thorium extract Throium from the waste product of other mining operations. The reactor above could run on thorium that was dissolved very simply, you don't even need complex fuel production (not that that fuel production currently matters that much for overall cost of plant operation).
So you have basically zero cost of fuel, basically zero CO2, almost no mining, could have been done in the 70s, for sure in the 80s and 90s.
This is what I am talking about when I say its a missed opportunity. Even the incredibly sub-optimal route France took, lead to results that were far, far better then the route anybody else took and France did the world a huge service.
If fuel were serious concern for cost, real searching for it would find much more.
And even with current technologies and reactors there are many ways to extend this, if you are willing to mix in some more highly enriched materials.
Eating up the absurd amount of nukes the US still has for example would be helpful.
And of course no society that actually bet on nuclear would still be using that fuel cycle in any serious way.
This is just the typical fear mongering that people use for all technologies they don't like, "Not enough lithium for EV".
Fuel reprocessing employed by France uses all of U235 + generates and burns plutonium.
Fast reactors, which exist in small numbers in Russia, etc, take it up by another two orders of magnitude
We also dont know how to model quantum gravity still. That seems pretty fundamental.
Im optimistic there will be physicists who find something new and whacky that no one could predict.
In particular one can imagine outsourcing every high-entropy activity to space and leaving Earth for low-entropy high-value activities.
That means we'd be able to treat the Earth as a great big park, with little-to-no human inhabitants.
Fanciful, but still possible, given such an energy breakthrough. Even if it takes a couple centuries, genetic records and some terraforming (feasible with that kind of energy available) would probably allow us to recover from the damage incurred by the Earth in the time it takes to develop the tech.
>That means we'd be able to treat the Earth as a great big park, with little-to-no human inhabitants.
That's a nice idea, however the resources required to move enough people off the Earth just to keep the population from rising, let alone moving the bulk of the population off the planet, would be astronomical and definitely impractical.
Consider the data:
1. Population: ~7.75 billion.
2. Deaths per year: ~60 million
3. Births per year: ~140 million
4. Annual population growth: ~80 million
Let's start with the idea of keeping the population the same, rather than moving 7 billion humans off the planet.
In order to move 80 million people just into orbit, let alone have some place for them to go would require that we launch (rockets? catapults? space elevators?) about 220,000 people, along with whatever cargo is required (we'll ignore the cargo here) every. single. day.
How many rockets/space elevator cars/catapult ships or whatever would we need just to move that 80 million off the planet?
Let's use space elevators (SE) here since we can (theoretically at least) make space elevator platforms arbitrarily large.
Let's say we use an SE car that can carry 1,000 people and can travel up the elevator at 1000 km/hour.
In order to just keep the population from growing, we'd need to launch 220 SE cars a day.
Unfortunately, a round trip to/from geostationary orbit (yes, rockets/catapults could deliver payloads in much less time to low Earth orbit. But such payloads would likely be an order of magnitude less than a space elevator) at 1000 km/hour would take ~70 hours.
Which means we'd need ~650 SE cars in service at any given moment.
Loading and launching 220 SE cars a day would require enormous logistical effort:
We'd need to launch ~10 cars per hour (220 per day).
How can we load and launch 1000 people times 10 in an hour, every hour?
I suppose we could build ten space elevators, then each site could just load and launch one an hour. Which seems doable.
But where will people stay while waiting to board a car?
Just expending the resources to build (and maintain) the infrastructure for such an enterprise would be enormous. And without some serious energy (commercial fusion on a massive scale), just running these elevators would quite possibly dwarf the total power output of the planet.
And that's just to keep the population flat. Attempting to remove the bulk of Earth's population would require raw materials, manufacturing, construction and maintenance several orders of magnitude larger than the example above.
So no. We're not going to solve any population issues, let alone removing the bulk of the population, by sending folks off-world.
- cheaply access space
- cheaply access cubic miles of asteroid iron
- build whole automated production industries in space, to build however many spaceships we want
- automate the construction of spaceships and that ringwood
- use those ships and tools to automate the construction of more production facilities
You're imagining a single transport into space, but that's a mode of thinking still constrained by expensive and inefficient energy. Imagine hundreds, thousands, or tens of thousands of autonomously constructed ships all available for that population transfer.
That energy is the catalyst for an exponential growth in our ability as a species to move ourselves and control our environment. It just takes some imagination to see outside our current constraints.
It's not the ai singularity, but I think our ability to build stuff cheaply, in space, with materials obtained in the quantity they're available in space, will represent a singularity-esque leap forward.
How will settling Mars or any planet save the biosphere?
We have a few decades to not kill the planet. Settling another planet would take centuries.
Kind of like Olympic gymnasts lift weights and work on flexibility and they want to exceed what their performances require such that the performance is easy and not pushing them to the limits of their ability.
Ie "You have to crawl before you can walk. If you learn to run, walking becomes trivial in comparison."
If that makes sense.
There exists technology that can transport people over short to medium distances really efficiently and without much greenhouse gas emissions. All it would take would be for policy makers to allocate some funding to build out the infrastructure required, yet they don’t.
There exists technology to transport and distribute food wherever there is hunger. Even technology to grow food more efficiently and without additional greenhouse gas emissions. Yet we don’t apply that.
Most countries continue to pour money into their most devastating government institutions (the military and the police) that not only cause a world of societal problems on their own, but also pollute a bunch in the meantime for everybody else. At the same time they could be using that money to build infrastructure that would allow us to live a more sustainable lives. But they don’t.
If the technology existed that would take people to Proxima Centauri in 10 years, and we invented a bunch of good technology that would help us make our current world better. I bet this new technology would be used equally sparingly as our current technology.
I'm personally heavily invested in the pieces of the puzzle that tech, per se, cannot solve. My work in that regard gets little in the way of attention and people have long attacked me as a nutter, etc.
I run a citizen planners forum on Reddit. I try to write about local community development at eclogiselle.com. Sometimes something I wrote gets a few thousand page views, but most of what I write gets very little traffic and that seems to be generally trending down, not up.
And I have mixed feelings about that because I have actively sought to ditch traffic rooted in lurid interest in me, so that's sort of "huzzah. I win? I guess."
I would like to see more focus on passive solar design. I would like to see more development of missing middle housing. I would like to see more walkable, bikable communities where Americans can actually live without a car.
I would like to see social change of the sort that's needed to actually solve these problems with the currently available tech. The problem I see is that tends to require a charismatic leader of the sort that historically founded various religions and I see problems with that approach.
I think it's inherently problematic to just take someone's word for it and do as you are told because they said so and you basically worship them. People need to think for themselves, not dutifully do as they were told.
And I don't know how you put out good info to foster the right kind of change in the amount needed etc and do so in a way that sidesteps the tendency for leaders of any sort to dictate what others should do.
So I have kept my footprint intentionally small in some sense while I figure out best practices. "If you don't have time to do it right the first time, when are you going to find time to do it over?"
(And we don't need to and probably shouldn't spend a lot on this. What we currently spend on space exploration/settlement through agencies like NASA is sufficient for this. And we also get the spin-off technology advantages.)
I’m moderately optimistic.
We have some social problems and some HVAC problems. But the vehicle is already underway.
I think we should consider the whole solar system our galactic ship while making sure to keep the current habitation quarters in top notch shape.
A good rule of thumb to remember is that if you're going fast enough to experience large time dilation, then your kinetic energy is to be large compared to your rest mass. It's the same factor of γ=1/√(1-v²/c²) either way. So if you're traveling 1000 years in 15 years ship time, you've got γ=67 and your kinetic energy is 66 times your rest mass. Ouch! (And here I'm making the incredibly optimistic assumption that you aren't carrying your fuel with you, because if you are then you also have to expend energy to accelerate your fuel, and to accelerate the fuel you use to accelerate your fuel, etc.)
If the rest mass of your ship is about the same as that of an aircraft carrier (the USS Enterprise, CVN-65, seems appropriate), then 66 × 86000000kg × (3×10×⁸ m/s)² = 5×10²⁶J. That's a lot.
Nuclear energy in the ordinary sense is nowhere close to enough. This is thousands of times more energy than we could get with all the U-235 on Earth. Or we could imagine getting this energy from fusion, using the big fusion reactor located a cozy 8.5 light-minutes away from us. Earth gets about 123000TW from the Sun, so another way of looking at this number is that if we captured 100% of that energy, it would take us 130 years to get enough for the ship's kinetic energy.
Accelerating big things to ultrarelativistic speeds isn't easy.
One possibility is:
Are we talking miniature fusion drive or antimatter type energy density required?
An aircraft carrier is powered through the water (horizontally, of course) for 25 years on nuclear power.
Now imagine the power it would take to make it hover for 25 years, and that's your 1G ship.
Though maybe the time to the destination is not a problem if you don't mind a generational ship where generations of humans live (and die) on the journey. It doesn't matter to those on earth, since the trip will still take over 1000 years in their timeframe, so whether it's 1015 years, 1100 years or 2000 years probably doesn't really matter to them.
It like unicorns - beatifull and entirely fancifull. Fusion or fission cant do it, even a ship with pure antimatter drive cannot accelerate like that for decades
We will have hibernation before we have practical antimatter, and lets you travel intersteller without wasting enegy
Sure it can. You just need a decently-sized asteroid and an equally-sized antimatter asteroid for fuel, and you can do it for decades, even with the price you pay early to accelerate the fuel you will use later.
You calculate mass fraction, i.e. for a ship to get to orbit using kerosene, the ship must be 97% made of fuel my mass.
If you have an antimatter ship, if you can produce, store, and 100% efficiently use antimatter and carry nothing else as your reaction mass and don't have issues with waste heat or radiation, your ship will need to be over 90% fuel by mass to maintain 1G acceleration for years.
I'm using the asteroid for mass, to react with the antimatter. So, yeah, it's relevant.
> If you have an antimatter ship, if you can produce, store, and 100% efficiently use antimatter and carry nothing else as your reaction mass and don't have issues with waste heat or radiation, your ship will need to be over 90% fuel by mass to maintain 1G acceleration for years.
Yup. And it's exponential - if the non-fuel mass is 10% to be able to do 10 years, then to do 20 years, the non-fuel mass can only be 1%, and for 30 years it can only be 0.1%. That's why you need the asteroid.
Its still the same formula, nothing has changed. Its combined weight of your ship and it's asteroids. All you are saying is "you need a big fuel tank"
Like I know what's a decently sized car, or a house, or a mountain
Of course to accelerate a 1000 ton spaceship you'd need about 4 quadrillion tons of fuel.
The fact that this also produces liveable conditions is just a nice side effect of a 1G ship.
That's what "1G" means in this concept, you're always accelerating at 1G (9.8 m/sec^2)
On the first half of the trip you're accelerating toward the destination, on the second half, you're decelerating at 1G.
My point was that, due to the highly non-linear time cost, it takes much less time to travel from Earth to X if you accelerate the whole way, rather than accelerate half the way and decelerate the other half. I wanted to know which way gorgoiler used to compute the subjective time.
And, thanks to your link, now I know.
changing courses would be plain impossible
You can steer by vectoring your acceleration. It would take about 3 days for a 1G ship to travel from the Earth to the Sun, so it wouldn't add much time to the journey to steer around an object the size of the sun. Ideally you'd identify those objects so far in advance that it would take little course correction to go around them.
Smaller objects like asteroids that are too small to see in time to avoid would need to be absorbed by the shielding or destroyed or pushed away by some other method. At near relativistic speeds, this would obviously be a non-trivial problem to solve, but hey, you have unlimited energy to solve it.
Not sure this is true, since the stars also get "smaller" and therefore harder to hit. Also, while you have less time to dodge you also don't have to dodge "as much" since your vast speed means you move through any zone quite quickly and therefore don't have much time to heat up/get irradiated. You can probably pass by a star relatively closely as long as you are moving fast enough. (From a heat/radiation perspective, solar wind particles might still mess you up good)
Your genes and spirits will be carried on by the quadrillions that made it, but for now, may you rest in peace.
To a static observer, 1000 generations of labrador will have been bred back on Earth.
It's also far less than 1G acceleration. You don't get big acceleration figures like 1G from laser pumped solar sails.
Energy is a fundamental currency of the universe, up to heat death. It's not something to be casually 'solved'.
We are more likely to 'solve' hibernation, aging and death, and then we can travel to the stars with ease - current tech can get us there in a thousands years, and that isn't much in the grand scheme of things.
Also you wouldn't send one guy in a box without spare parts, would you?
That cannot be true. Nothing escapes the laws of physics. It obviously depends on the engine, but for example current electronics have a lifespan of only a few decades. Even the half-life of DNA might be a problem, depending on the hibernation method.
Unless you're talking about escaping Earth specific gravitation.
The problem is that as you increase burn times (like years at 1G), you need to increase the amount of mass you are pushing out the back. But to do this you increase the mass of your rocket which means you need to push even more mass out and it becomes a vicious circle of exponentially increasing rocket mass.
The idea of accelerating at 1G for the entire trip only works if you have a source of propulsion that doesn't obey Newton's second law. Otherwise there literally isn't enough mass in the galaxy to make it work. The caveat being that if you can somehow exploit relativistic mass to effectively multiply your fuel it might be possible, but my math isn't good enough to work it out. My gut feeling is that it would require an unreasonable amount of power however, even for an extremely powerful nuclear power plant.
If nuclear energy is used, it can be increased in less than linear change in mass.
Apart from the fact that everyone you know is now dead and if you returned home you'd basically be a living caveman museum piece.
But one-way trips have been proposed for planetary colonization as well, and there are a lot of people that would be willing to make that trip.
We don’t even have broad agreement on what a mind is beyond the the everyday folk notion. What are we to copy?
Importantly, how many memories do you think can fit into a human brain? If a 1,000 year old man cannot remember all of his life, has aging been solved?
Maybe the details just get spottier with bigger gaps, but you still remember the big events and when you need more details your Google neural implant tells you more. I'm far from 1,000 but I can't remember every detail of my life, but I don't think it interferes with my quality of life.
But I’m not convinced that somehow expanding brain sizes to accommodate immortality means we have solved aging for humans.
4.2 Braking to Enter Orbit on Arrival - A very difficult challenge is to slow the spacecraft to typical planetary orbital speeds to enable orbital capture once arriving. This task is difficult as the initial entry speeds are so high (~ c) and the orbital speeds are so low (~ 10-4 c). Dissipating this much energy is challenging. We have considered using the stars photon pressure, the stellar wind (assuming it is like our own solar system), using the magnetic coupling to the exo solar system plasma. None of these techniques appears to be obviously able to accomplish this task and much more work and simulation is needed. A simple fly-by mission is clearly the first type of mission to explore in any case to assess the environment in a given system to design (if possible) an optimized braking strategy.
I do not know if somebody devised a solution to this fundamental problem; if not, I am extremely skeptical about highly-accelerated spacecrafts.
I always think that if f=ma, then as velocity approaches light speed, the deceleration of the grain of sand as it hits the hull approaches infinity. So even with a small mass, the force is huge.
> Thus a 1 kg spacecraft going at 0.3 c will have an effective "yield" of 1 MT or roughly that of a large strategic thermonuclear weapon.
Lets not accidentally wipe out a neighbors city and start an interstellar war.
We're far more likely to have destroyed ourselves long before we get a chance to destroy any other civilisation. If we can travel intersteller, we can destroy a planet.
Your quote does remind me of a line from Independence Day I like
"Los Angelinos are asked not to fire their guns at the visiting spacecraft, you may inadvertently start an intersteller war"
(Disclaimer, I work at APL, but not on this)
Only nuclear is really interesting. Chemical rockets are useless at this scale.
There is apparently a BH with 3x solar mass about 1,500LY away - escape velocity at 830 radius (about 820km from event horizon) is about 0.1c.
But how do you get the kit to decelerate? (Remember, you fired it ahead of the ship.) And this problem gets worse as the velocity of the ship goes up. If, say, your construction kit enters a solar system at 0.1 c, it's going to cross it in maybe twenty days. I don't think that's enough time for a solar sail to effectively decelerate it. It's probably going too fast for using planets' gravity to slow it down. And using atmospheric drag is an explosively bad idea.
I don't have an answer...
A funny twist on that idea just came to my mind: if you're flying past a black hole, having just one mirror on the spaceship is enough. Shine a laser from the ship toward the edge of the black hole just right, it will curve around and come back to your mirror, then reflect and come back again, and so on. Needs some tricky positioning of the mirror, but in principle it lets you "push" off the black hole without using rocketry.
Half to the ship, and half to the Earth in the other direction, right?
"The Starshot concept capable of making the journey to the Alpha Centauri star system 4.37 light-years away. It envisions launching a "mothership" carrying about a thousand tiny spacecraft (on the scale of centimeters) to a high-altitude Earth orbit for deployment. A phased array of ground-based lasers would then focus a light beam on the crafts' sails to accelerate them one by one to the target speed. At a speed between 15% and 20% of the speed of light, it would take between twenty and thirty years to complete the journey, and approximately four years for a return message from the starship to Earth."
> The travel times are for the spacecraft to travel to the star and then enter orbit around the star (using photon pressure in maneuvers similar to aerobraking).
Not sure how trustworthy that information is but this kind of "aerobraking" at least seems possible in principle.
I admire the optimism in the paper though, even if its misplaced. Maybe pooling together resources in the scientific and engineering communities to develop an interstellar probe system could give a working result, but there are some significant hurdles to overcome first. It would be a big project, taking many years to see fruition, but at the same time it could also be a game-changing development and a hugely inspiring feat.
Could we see probes in other star systems by 2075? I think its not an unreasonable suggestion.
I think it’s good to attempt such challenges, even if just conceptually, as it makes lots of other things seem a lot more achievable in contrast, sometimes almost laughably so.
Interstellar space exploration will likely be manned-only. As other threads point out, with sufficient acceleration, due to time dilation, humans can reach distant stars within their own lifetimes (at the expense of thousands of years passing on Earth).
And I know you excluded the “closest stars,” but I don’t understand why, except that it undermines your point. There are at least 3 nearby stars that could be reached by probes in a researcher’s (or at least their funding institution’s) lifetime vs just our one star system.
(Besides the 3 stars in the Proxima/Alpha Centauri system there are also at least 11 additional stars—including fusion-capable brown dwarfs—within 10 light years of the Sun.)
This article (Starships & Cathedrals) explains the ideas better than I can in a short comment: https://www.centauri-dreams.org/2020/07/17/the-cathedral-and...
This is the same idea, you send a new an improved probe every 10-20 years and eventually you get data back and over time you have constant data stream from all kinds of different places.
Why would our grandchildren be less interested in interstellar exploration than we are? We need ways to organize (parts of) society for the long term, that seems way easier than inventing magical "accelerate at 1g for a decade" tech.
Hopefully our solar system isn't the only place where human DNA is found; that said, I'm curious what'll be left of humans as we know today.
With tools like CRISPR accelerating adoption to new environments and increased resilience towards hostile situations (zero-g, radiation etc)
Looks like NASA is developing thermal nuclear rocket https://www.nasa.gov/directorates/spacetech/nuclear-propulsi...
Field-reversed configuration, D-H3, aneutronic.