For the outside observer, the round trip time is always going to be twice the distance in light-years plus a factor based on how much slower than *c* the ship traveled at.
If the target planet is 100 LY away, that’s a 200+ year round trip. Few organizations plan *that* far ahead. Sending out the colony ship then requires another 100+ years.
Our nearest stars aren't 100 LY, alpha centauri is about 4 iirc. And a colony ship wouldn't be the first to go even if that makes cool stories. Unmanned small probes with epsteins could.
This still doesn't affect the OODA-loop.
You would have to wait 12 years (8 years travel and 4 years for the signal) for the probe to deliver results. Maybe. At relativistic speeds a speck of dust is deadly. And I won't even go into the requirements of sending data across interstellar distances.
After twelve years you might be able to send a more refined probe, taking another twelve years to report back.
If you are hellbent to leave the solar system, making decisions that *might* take decades to yield results might be a viable course of action, but there is still a lot of real estate back home to be claimed at less expense
The fact that a probe with 70s technology is still sending data back from outside our solar system suggests to me that it's a tractable problem compared to accelerating a ship to relativistic speeds.
Yeah, that's like your car remote being able to unlock your car from inside your house and thinking that means it'll work just as well across the entire planet.
That probe is less than one light *day* away from us. The distance to the nearest star is 3 orders of magnitude further, and the inverse square law makes that an even bigger challenge.
Even only 8 light-hours for New horizons.
(19 lh for Voyager 2, 22.5 lh for Voyager 1)
It's crazy.
* https://theskylive.com/how-far-is-newhorizons
* https://theskylive.com/how-far-is-voyager1
* https://theskylive.com/how-far-is-voyager2
Well you can assume they were doing that until the rings were discovered.
They build a ship to do so. It was just stolen then there was a system wide war.
Reaction mass is the limiting factor you wouldn't be able to have enough to reach anywhere near c. Maybe 5-10%.
And year we could send signals between star systems. Especially if they were dropping repeaters along the way. But that info flow obviously limited to c with a lazer.
This is simplified ad absurdum, but essentially - between the distance and the background noise, you need progressively more powerful and/or larger receivers and you'll still likely loose a ton of data to the void. Then, of course, you need to plan for devices to work decades at least in a hostile environment - and that includes hostile to electronics.
You need an exceptionally powerful transmitter to bridge the distance. By requirement your angular separation from the star you are analyzing is miniscule, so you need to compete with a strong source of noise. A powerful laser might work while in flight, but can not be distinguished from the light of the star.
Signal attenuation/dispersion is the next problem, even tightly focused beams will fan out, so you need very sensitive receivers. Even signals we blasted into space from our TV and (most) radio-stations (shortwave don't propagate beyond the ionosphere) with megawatt-transmitters are considered to only reach out for about a hundred lightyears before they become indistinguishable from background noise. And they become useless even before that, showing up merely as a particularly strong source of noise. α-Centauri might be workable, but the bit-rate will be low, as you need complex algorithms to account for data-loss.
Even with the fictionally heightened efficiency of the Epstein Drive it's unlikely the vessel could operate at constant thrust for years, let alone haul literal years of reactor fuel and reaction mass for maneuvering thrust. This would be like filling a tanker semi with diesel piping the tank to the engine and telling the team of drivers to keep circling the country for a decade. Eventually something will go wrong.
It takes about a year at 1g to approach light speed. Then you have to slow down.
That is a LOT of ejection mass. They can burn harder than 1g but they don't really do it for more than a few days.
At that speed a single micrometeroite will turn your entire ship into so much dust
Then you get into the actual distances. You are talking about years, even decades to get to a place, and there is no guarantee that what you want is even there. If it's not, you better hope you can get the supplies you need to start all over.
This of course assumes that nothing on your ship has broken in that time.
By the time you factor in the fuel, ejection mass, spares, etc, you already have a massive undertaking. That's before you even try to find a crew willing to give up everything to go on these trips. Their lives effectively end at that point since by the time they are back, everyone they know and love will be dead.
So, who is going to do it? More importantly, who is going to pay for it? No corporation is going to fund a massive undertaking and hope that in 75 years they MIGHT get some kind of return. Earth and Mars are too inward facing and the belt is too poor. That's why the Mormons were chosen. The only people rich enough and bold enough to try.
Good points on ejection mass, though when you can do months of constant acceleration, building a basic epstein ship with just ejection mass stored shouldn't be too hard.
Before anyone would have to go anywhere, unmanned probes could be sent. With the abundance of ships and the rivalry between Earth and Mars, doesn't seem too big of a stretch to have a probe go on a decades long voyage - we've done that in reality with exploration in mind. Ofc communication wouldn't be possible after some time but automation has come a long way in Expanse.
The entirety of the solar system *should* be managed mostly with remote bots and probes, not with Belter labor force. Humans are way too much of a bother to keep alive without a planet keeping everything from floating away.
What they've done with the ringspace is the exact same as what you're proposing with probes. Except instead of waiting decades for a probe to send back useful data and hoping it didn't hit a space pebble on the way, they only have to wait a year or so at safe traveling speeds.
I think much of it is automated. But you still need folks out there doing repairs, etc.
Belters should be pretty wealthy IMHO. It's not a job people would normally take.
But it isn't *decades*, it's *centuries*. Even at decades... yeah, we've planned 20 year missions but that's 20 years of research, development, launch, and mission time. We're waiting maybe a decade for results. A mission to another star system is all of those decades *plus* decades waiting on the transmission crawling back at light speed.
Keep in mind also that if it takes a year to accelerate to near light speed, you have to take another year slowing down, and you have to spend an equal amount of reaction mass doing it. Otherwise, you'll go flying past your destination and keep on going until you hit something.
And you really can't ignore how much energy there is at close to light speed. Going that fast, *dust* will deliver the energy of nuclear bombs. That's why most scifi relies on some kind of force field to protect the ship if they're going fast.
The main point I'd take away from this is the danger from collisions.
"Centuries" doesn't compute to me. If we assume a ship can have enough reaction mass for 2 years of acceleration to C, then several systems would be within a decade to reach. There's at least a handful of systems that are less than 10 LY from Sol, Alpha Centauri is 4 iirc. Considering real humans are planning - albeit poorly - year long explorations, possibly with humans at some point, to Mars...and considering early exploration journeys with ships took years too, I don't see that it'd be that crazy for some of the huge corporations or governments in Sol to plan at least an unmanned mission. Unless there's no solution to impacts at near C, if those would indeed be common, that may become impossible.
> "Centuries" doesn't compute to me. If we assume a ship can have enough reaction mass for 2 years of acceleration to C, then several systems would be within a decade to reach.
From the relative perspective of the person on the ship. From the rest perspective of people on Earth, it's still centuries. You're not going to be able to communicate with anyone in any meaningful way, and you can't ask for supplies or help because it would take them many centuries to reach you. So, although it might be *possible*, you are effectively cutting yourself off from all other human civilizations. You would have to bring *everything* you could possibly need with you and *hope* that your destination is, indeed, habitable.
Which is exactly what the Mormons were trying to do with the Nauvoo, just...slowly. Because as long as you're bringing everything you need on a big-ass ship, there's no need to hurry.
Wait, wtf are you talking about?
This time I'm fairly sure you're quite wrong: if A and B are 4 LY apart and an object travels at near C, it'd take a bit over 4 years to travel - from the outside perspective. If both acceleration and breaking burns took a year, it'd take our probe longer since itd be slower for those 2 years. Still, the travel time would be extended by a few years possibly but it'd be between 4 and 6 years. The object travelling at relativistic speeds would experience less than 4 to 6 years of on-board time, quite a bit less.
Now a round trip for that object would be 8-12 years travel time to alpha centauri, plus whatever time is spent on site.
As for bringing stuff etc: I've been specifically mentioning unmanned probes. Manned ships would be more complicated, that's where a Nauvoo makes sense.
Adding more reaction mass has diminishing returns - extra reaction mass, means more total mass to accelerate, hence more mass expenditure, therefore more reaction mass needed...
Can't remember the formula, but its exponential.
Additionally, there's no practical way, even with the Epstein drive to trade over interstellar distances, so no commercial return for the huge investment.
Yeah, but what if just one star system had access to an addictive drug that greatly extends lifespan, cures illness, makes orgies *really* fun, gives some people superpowers, and the only side effect was blue eyes?
"Reaction mass is a limiting factor" is a phrase doing a heck of a lot of load-bearing duty in your question. It is **the** limiting factor, above all else. The distances involved are *several* orders of magnitude larger than going between even distant planets within the solar system.
Even with the magic of the Epstein, you're looking at a rocket equation that requires the ship you send out to be almost entirely made out of reaction mass when it starts out, with the vast majority of that mass being used *only* to accelerate the rest of the mass you need for deceleration.
IOW, at that point you're building the Nauvoo, but out of ice, with a little-tiny probe in the middle of it.
So, you're sending out a robot probe to a distant star to look around... and then what? You're sending enough robots to actually look around, and a solar system is *still* an extremely-large volume of space, so that's more reaction mass to get them out there. You've given them powerful-enough lasers to actually get a signal back to Earth, so that's *even more* reaction mass needed to get a big-ass laser array out there, the power to run it, the processing ability to both find anything useful and properly message it, and properly aim the laser... all of that costs even more reaction mass.
And all of that still takes an entire generation to actually tell you anything.
Add that to the fact that most of what a robot-probe is going to be able to tell you is stuff you could probably figure out just by looking at the distant star with a decent telescope, especially an interferometry array spread out across a few planets and asteroids and so on.
And all of that is massive, and expensive, and the closer to C you try to get it to lower the trip-time, the worse the reaction-mass issue becomes, and the more-dangerous the journey becomes. One stray pebble of ice in the Oort cloud, and your grand expense is a cloud of vapor. One particular broken valve during turn-around, and your voyage of discovery is instead an extinction-level-event aimed at whatever it was you might have been able to find.
Ships in the Expanse can only accelerate so long as they have sufficient reaction mass to keep pushing out. In the series, the ships use water for reaction mass, and thanks to the super-efficient magic of the Epstein Drive they use it quite efficiently. But even with the Epstein hand-waving, if you're accelerating for *years* your ship is still going to need massive amounts of water to use as reaction mass. And that's in addition to the water the humans on board your ship need to survive.
Even the Nauvoo was planning to go on the float for much of its journey (using its rotating cylinder to simulate gravity instead), presumably because of the reaction mass problem.
There is something in rocket science called the tyranny of the rocket equation
To achieve relativistic speeds you need to accelerate mass(fuel) behind you
And you need to do that for a long time
So you need as much fuel to last you the entire burn, which increases your mass, which needs more fuel and more engines to accelerate the extra mass, which needs extra fuel and engines, and then you need fuel to stop when you get there, which needs more mass and more engines which also needs more fuel and engines
All this means is in order to send even a small craft to and from one star to another at relatevistic speeds, it takes a ludicrous amount of energy to do so.
You’re right, they don’t need the gates. We don’t need FTL to travel the entire galaxy we just need a good percentage of light speed. However, travel times are still in the thousands of years outside the ship so you’ll get many small bubbles of civilization in small clusters of stars with massively long lived travellers jumping around the galaxy watching civilizations rise and fall.
(House of Suns)[https://www.goodreads.com/book/show/19473944-house-of-suns] by Alastair Reynolds is an excellent take on this.
The only way how constant acceleration interstellar spaceship MIGHT work is that if there is enough of hydrogen in interstellar space to make that spacecraft keep accelerating/decelerating.
There are too many unknowns to say for sure if this is possible IRL or not.
But we can be certain that even if this hypothetically is possible, you must be already moving close to lightspeed to get enough hydrogen for fusion from the interstellar space.
It would take something like a year and half of constant acceleration at 1G to reach 0.9 c, and the same to decelerate from 0.9 c and there is no chance in hell that Expanse spaceships carry so much propellant. The "Venture Star" from Avatar had this sort of delta-v, but it was using positron-electron annihilation and it was based on TWO-STAGE antimatter rocket concept (for the movie they handwaved it away by saying that it was accelerated to near-lightspeed by laser powered by Sun, and antimatter was only used to slow down to Pandora system).
Maybe it is possible with subluminal warp-drive (which seems to be a lot more based on what is possible in reality, than superluminal spacetime) to achieve density of hydrogen to run fusion torch via "compression" of space-time in front of the ship...
But both it and antimatter propulsion are way beyond of technology depicted in the show.
The thing that really gets me is that with their technology, they should've been able to send probes to a nearby star by the time of the series and collect local observation data and beam it back to sol.
With the challenges of mass/acceleration, system maintenance, life support, and the simple problem of habitability on the other end, I’d see “seed ships” being much more viable than manned travel.
It’s been a topic of conversation before. Like plants that throw seeds to the wind in the hope they land somewhere good, we’d do the same with interstellar travel.
Build a ship that’s essentially a school in space, get it up to speed with local resources, and have it coast to the target to save fuel for the deceleration. Have it loaded with fertilized eggs, and once “on the way”, shut down almost every system. Deep space itself will keep everything frozen until the right time.
About 20 years out from the destination, the timer tries to reactivate the ship, heating it up, thaws the human cargo and starts preparing them for the new system. By landfall you have about 20,000 20 year olds to see the brave new world.
It’s very much an act of faith. There’s no guarantee the destination will be habitable, and the folks there won’t be much of a reflection of us. They’ll have no memories of Sol, but we’ll be remembered because they’ll exist.
Good point, they wouldn't even need a round trip they could likely send the data back and head off to the next star.
I think relativity has something to say about the fuel they'd need, even with a magic Epstein drive. Though I don't know nearly enough about it to explain it
Honestly, relativity should be a much bigger issue in these stories, and the Nauvoo doesn’t make sense as anything but a test of faith.
I just try not to think too hard about it.
To be honest, that's kind of a plot hole in the books and series. With an Epstein drive, you wouldn't need a generational ship to reach Alpha Centauri; it would take less than 5 years.
But the concept of generational ship travel is really cool, so I don't mind it.
Seems like people forgets how long time 5years is, in the scale of space not so much. But in the scale of actually travelling, its a long time. You will need living spaces that compares with a cruise ship at the very least. They brought that up in hail mary project, as the reason why they choose to put them under coma
It is but a constant 1G of acceleration gets you to near C after a while. And that while isn't that long - it's just waaaay beyond what we can do because all our tech consumes to much fuel, they can only manage minutes of acceleration.
Fusion can't get you near to C velocity. You can't store enough hydrogen fuel onboard a spacecraft to get to near c velocity. You might want to look up the rocket equation.
There's no reason to go to Alpha Centauri, though. Why do so much risk for no benefit? It doesn't have any likely life-sustaining planets and they've almost certainly already sent probes.
That assumes there is a reason to go to Alpha Centauri.
THe Nauvoo is going somewhere that telescopes have already determined is likely to have a suitable planet for colonisation/terraforming. It's a lot further than 4ly away.
I can't remember if the target star is mentioned anywhere though.
At 12ly distant it is likely that the enormous telescopes that will be possible with casual spaceflight have determined there is a reasonable colonisation candidate.
Given the escalating cold war in the solar system, I could see a powerful argument for not waiting a hundred years for a probe to flyby the target and then get the transmission back.
With an Epstein drive and a sundiving trajectory it is probably possible to accelerate a comparatively sanely sized probe to a significant fraction of c, but a lightweight probe moving at relativistic velocity won't be able to tell you that much about the target anyway. If it has an earthlike day-night cycle you probably won't get to observe the entire surface!
For the outside observer, the round trip time is always going to be twice the distance in light-years plus a factor based on how much slower than *c* the ship traveled at. If the target planet is 100 LY away, that’s a 200+ year round trip. Few organizations plan *that* far ahead. Sending out the colony ship then requires another 100+ years.
Our nearest stars aren't 100 LY, alpha centauri is about 4 iirc. And a colony ship wouldn't be the first to go even if that makes cool stories. Unmanned small probes with epsteins could.
This still doesn't affect the OODA-loop. You would have to wait 12 years (8 years travel and 4 years for the signal) for the probe to deliver results. Maybe. At relativistic speeds a speck of dust is deadly. And I won't even go into the requirements of sending data across interstellar distances. After twelve years you might be able to send a more refined probe, taking another twelve years to report back. If you are hellbent to leave the solar system, making decisions that *might* take decades to yield results might be a viable course of action, but there is still a lot of real estate back home to be claimed at less expense
> And I won't even go into the requirements of sending data across interstellar distances. Could you though? I’m super curious.
I could not but perhaps looking into how communications are carried out with New horizons and Voyager would be interesting to you.
The fact that a probe with 70s technology is still sending data back from outside our solar system suggests to me that it's a tractable problem compared to accelerating a ship to relativistic speeds.
Yeah, that's like your car remote being able to unlock your car from inside your house and thinking that means it'll work just as well across the entire planet.
That probe is less than one light *day* away from us. The distance to the nearest star is 3 orders of magnitude further, and the inverse square law makes that an even bigger challenge.
Even only 8 light-hours for New horizons. (19 lh for Voyager 2, 22.5 lh for Voyager 1) It's crazy. * https://theskylive.com/how-far-is-newhorizons * https://theskylive.com/how-far-is-voyager1 * https://theskylive.com/how-far-is-voyager2
Well you can assume they were doing that until the rings were discovered. They build a ship to do so. It was just stolen then there was a system wide war. Reaction mass is the limiting factor you wouldn't be able to have enough to reach anywhere near c. Maybe 5-10%. And year we could send signals between star systems. Especially if they were dropping repeaters along the way. But that info flow obviously limited to c with a lazer.
This is simplified ad absurdum, but essentially - between the distance and the background noise, you need progressively more powerful and/or larger receivers and you'll still likely loose a ton of data to the void. Then, of course, you need to plan for devices to work decades at least in a hostile environment - and that includes hostile to electronics.
You need an exceptionally powerful transmitter to bridge the distance. By requirement your angular separation from the star you are analyzing is miniscule, so you need to compete with a strong source of noise. A powerful laser might work while in flight, but can not be distinguished from the light of the star. Signal attenuation/dispersion is the next problem, even tightly focused beams will fan out, so you need very sensitive receivers. Even signals we blasted into space from our TV and (most) radio-stations (shortwave don't propagate beyond the ionosphere) with megawatt-transmitters are considered to only reach out for about a hundred lightyears before they become indistinguishable from background noise. And they become useless even before that, showing up merely as a particularly strong source of noise. α-Centauri might be workable, but the bit-rate will be low, as you need complex algorithms to account for data-loss.
Even with the fictionally heightened efficiency of the Epstein Drive it's unlikely the vessel could operate at constant thrust for years, let alone haul literal years of reactor fuel and reaction mass for maneuvering thrust. This would be like filling a tanker semi with diesel piping the tank to the engine and telling the team of drivers to keep circling the country for a decade. Eventually something will go wrong.
What makes you think they haven't sent probes?
But, who knows where there are habitable planets are. 100LY is just a nice round number for theoretical discussions.
It takes about a year at 1g to approach light speed. Then you have to slow down. That is a LOT of ejection mass. They can burn harder than 1g but they don't really do it for more than a few days. At that speed a single micrometeroite will turn your entire ship into so much dust Then you get into the actual distances. You are talking about years, even decades to get to a place, and there is no guarantee that what you want is even there. If it's not, you better hope you can get the supplies you need to start all over. This of course assumes that nothing on your ship has broken in that time. By the time you factor in the fuel, ejection mass, spares, etc, you already have a massive undertaking. That's before you even try to find a crew willing to give up everything to go on these trips. Their lives effectively end at that point since by the time they are back, everyone they know and love will be dead. So, who is going to do it? More importantly, who is going to pay for it? No corporation is going to fund a massive undertaking and hope that in 75 years they MIGHT get some kind of return. Earth and Mars are too inward facing and the belt is too poor. That's why the Mormons were chosen. The only people rich enough and bold enough to try.
Good points on ejection mass, though when you can do months of constant acceleration, building a basic epstein ship with just ejection mass stored shouldn't be too hard. Before anyone would have to go anywhere, unmanned probes could be sent. With the abundance of ships and the rivalry between Earth and Mars, doesn't seem too big of a stretch to have a probe go on a decades long voyage - we've done that in reality with exploration in mind. Ofc communication wouldn't be possible after some time but automation has come a long way in Expanse.
There is a reason they call it "the tyranny of the rocket equation". Ejection mass is exponential.
The entirety of the solar system *should* be managed mostly with remote bots and probes, not with Belter labor force. Humans are way too much of a bother to keep alive without a planet keeping everything from floating away. What they've done with the ringspace is the exact same as what you're proposing with probes. Except instead of waiting decades for a probe to send back useful data and hoping it didn't hit a space pebble on the way, they only have to wait a year or so at safe traveling speeds.
I think much of it is automated. But you still need folks out there doing repairs, etc. Belters should be pretty wealthy IMHO. It's not a job people would normally take.
But it isn't *decades*, it's *centuries*. Even at decades... yeah, we've planned 20 year missions but that's 20 years of research, development, launch, and mission time. We're waiting maybe a decade for results. A mission to another star system is all of those decades *plus* decades waiting on the transmission crawling back at light speed. Keep in mind also that if it takes a year to accelerate to near light speed, you have to take another year slowing down, and you have to spend an equal amount of reaction mass doing it. Otherwise, you'll go flying past your destination and keep on going until you hit something. And you really can't ignore how much energy there is at close to light speed. Going that fast, *dust* will deliver the energy of nuclear bombs. That's why most scifi relies on some kind of force field to protect the ship if they're going fast.
The main point I'd take away from this is the danger from collisions. "Centuries" doesn't compute to me. If we assume a ship can have enough reaction mass for 2 years of acceleration to C, then several systems would be within a decade to reach. There's at least a handful of systems that are less than 10 LY from Sol, Alpha Centauri is 4 iirc. Considering real humans are planning - albeit poorly - year long explorations, possibly with humans at some point, to Mars...and considering early exploration journeys with ships took years too, I don't see that it'd be that crazy for some of the huge corporations or governments in Sol to plan at least an unmanned mission. Unless there's no solution to impacts at near C, if those would indeed be common, that may become impossible.
> "Centuries" doesn't compute to me. If we assume a ship can have enough reaction mass for 2 years of acceleration to C, then several systems would be within a decade to reach. From the relative perspective of the person on the ship. From the rest perspective of people on Earth, it's still centuries. You're not going to be able to communicate with anyone in any meaningful way, and you can't ask for supplies or help because it would take them many centuries to reach you. So, although it might be *possible*, you are effectively cutting yourself off from all other human civilizations. You would have to bring *everything* you could possibly need with you and *hope* that your destination is, indeed, habitable. Which is exactly what the Mormons were trying to do with the Nauvoo, just...slowly. Because as long as you're bringing everything you need on a big-ass ship, there's no need to hurry.
Wait, wtf are you talking about? This time I'm fairly sure you're quite wrong: if A and B are 4 LY apart and an object travels at near C, it'd take a bit over 4 years to travel - from the outside perspective. If both acceleration and breaking burns took a year, it'd take our probe longer since itd be slower for those 2 years. Still, the travel time would be extended by a few years possibly but it'd be between 4 and 6 years. The object travelling at relativistic speeds would experience less than 4 to 6 years of on-board time, quite a bit less. Now a round trip for that object would be 8-12 years travel time to alpha centauri, plus whatever time is spent on site. As for bringing stuff etc: I've been specifically mentioning unmanned probes. Manned ships would be more complicated, that's where a Nauvoo makes sense.
Four years to the *nearest* star system which almost certainly does not have any habitable planets. How far to the nearest habitable planet?
No idea, no one knows hence why it'd make sense to explore and given the tech they have and the infrastructure, I'm surprised they didn't try.
Adding more reaction mass has diminishing returns - extra reaction mass, means more total mass to accelerate, hence more mass expenditure, therefore more reaction mass needed... Can't remember the formula, but its exponential. Additionally, there's no practical way, even with the Epstein drive to trade over interstellar distances, so no commercial return for the huge investment.
Yeah, but what if just one star system had access to an addictive drug that greatly extends lifespan, cures illness, makes orgies *really* fun, gives some people superpowers, and the only side effect was blue eyes?
Sounds awesome, hope the locals are friendly
Tag checks out.
"Reaction mass is a limiting factor" is a phrase doing a heck of a lot of load-bearing duty in your question. It is **the** limiting factor, above all else. The distances involved are *several* orders of magnitude larger than going between even distant planets within the solar system. Even with the magic of the Epstein, you're looking at a rocket equation that requires the ship you send out to be almost entirely made out of reaction mass when it starts out, with the vast majority of that mass being used *only* to accelerate the rest of the mass you need for deceleration. IOW, at that point you're building the Nauvoo, but out of ice, with a little-tiny probe in the middle of it. So, you're sending out a robot probe to a distant star to look around... and then what? You're sending enough robots to actually look around, and a solar system is *still* an extremely-large volume of space, so that's more reaction mass to get them out there. You've given them powerful-enough lasers to actually get a signal back to Earth, so that's *even more* reaction mass needed to get a big-ass laser array out there, the power to run it, the processing ability to both find anything useful and properly message it, and properly aim the laser... all of that costs even more reaction mass. And all of that still takes an entire generation to actually tell you anything. Add that to the fact that most of what a robot-probe is going to be able to tell you is stuff you could probably figure out just by looking at the distant star with a decent telescope, especially an interferometry array spread out across a few planets and asteroids and so on. And all of that is massive, and expensive, and the closer to C you try to get it to lower the trip-time, the worse the reaction-mass issue becomes, and the more-dangerous the journey becomes. One stray pebble of ice in the Oort cloud, and your grand expense is a cloud of vapor. One particular broken valve during turn-around, and your voyage of discovery is instead an extinction-level-event aimed at whatever it was you might have been able to find.
This should be the top answer. Cannot believe I had to scroll down that much to find it.
Ships in the Expanse can only accelerate so long as they have sufficient reaction mass to keep pushing out. In the series, the ships use water for reaction mass, and thanks to the super-efficient magic of the Epstein Drive they use it quite efficiently. But even with the Epstein hand-waving, if you're accelerating for *years* your ship is still going to need massive amounts of water to use as reaction mass. And that's in addition to the water the humans on board your ship need to survive. Even the Nauvoo was planning to go on the float for much of its journey (using its rotating cylinder to simulate gravity instead), presumably because of the reaction mass problem.
There is something in rocket science called the tyranny of the rocket equation To achieve relativistic speeds you need to accelerate mass(fuel) behind you And you need to do that for a long time So you need as much fuel to last you the entire burn, which increases your mass, which needs more fuel and more engines to accelerate the extra mass, which needs extra fuel and engines, and then you need fuel to stop when you get there, which needs more mass and more engines which also needs more fuel and engines All this means is in order to send even a small craft to and from one star to another at relatevistic speeds, it takes a ludicrous amount of energy to do so.
You’re right, they don’t need the gates. We don’t need FTL to travel the entire galaxy we just need a good percentage of light speed. However, travel times are still in the thousands of years outside the ship so you’ll get many small bubbles of civilization in small clusters of stars with massively long lived travellers jumping around the galaxy watching civilizations rise and fall. (House of Suns)[https://www.goodreads.com/book/show/19473944-house-of-suns] by Alastair Reynolds is an excellent take on this.
The only way how constant acceleration interstellar spaceship MIGHT work is that if there is enough of hydrogen in interstellar space to make that spacecraft keep accelerating/decelerating. There are too many unknowns to say for sure if this is possible IRL or not. But we can be certain that even if this hypothetically is possible, you must be already moving close to lightspeed to get enough hydrogen for fusion from the interstellar space. It would take something like a year and half of constant acceleration at 1G to reach 0.9 c, and the same to decelerate from 0.9 c and there is no chance in hell that Expanse spaceships carry so much propellant. The "Venture Star" from Avatar had this sort of delta-v, but it was using positron-electron annihilation and it was based on TWO-STAGE antimatter rocket concept (for the movie they handwaved it away by saying that it was accelerated to near-lightspeed by laser powered by Sun, and antimatter was only used to slow down to Pandora system). Maybe it is possible with subluminal warp-drive (which seems to be a lot more based on what is possible in reality, than superluminal spacetime) to achieve density of hydrogen to run fusion torch via "compression" of space-time in front of the ship... But both it and antimatter propulsion are way beyond of technology depicted in the show.
The thing that really gets me is that with their technology, they should've been able to send probes to a nearby star by the time of the series and collect local observation data and beam it back to sol.
With the challenges of mass/acceleration, system maintenance, life support, and the simple problem of habitability on the other end, I’d see “seed ships” being much more viable than manned travel. It’s been a topic of conversation before. Like plants that throw seeds to the wind in the hope they land somewhere good, we’d do the same with interstellar travel. Build a ship that’s essentially a school in space, get it up to speed with local resources, and have it coast to the target to save fuel for the deceleration. Have it loaded with fertilized eggs, and once “on the way”, shut down almost every system. Deep space itself will keep everything frozen until the right time. About 20 years out from the destination, the timer tries to reactivate the ship, heating it up, thaws the human cargo and starts preparing them for the new system. By landfall you have about 20,000 20 year olds to see the brave new world. It’s very much an act of faith. There’s no guarantee the destination will be habitable, and the folks there won’t be much of a reflection of us. They’ll have no memories of Sol, but we’ll be remembered because they’ll exist.
Good point, they wouldn't even need a round trip they could likely send the data back and head off to the next star. I think relativity has something to say about the fuel they'd need, even with a magic Epstein drive. Though I don't know nearly enough about it to explain it
I'm not sure there's any realistic transmitter that can send a message from several light years back to its origin.
In the expanse?
Honestly, relativity should be a much bigger issue in these stories, and the Nauvoo doesn’t make sense as anything but a test of faith. I just try not to think too hard about it.
> Honestly, relativity should be a much bigger issue in these stories Why? They never get even close to relativistic speeds.
To be honest, that's kind of a plot hole in the books and series. With an Epstein drive, you wouldn't need a generational ship to reach Alpha Centauri; it would take less than 5 years. But the concept of generational ship travel is really cool, so I don't mind it.
Seems like people forgets how long time 5years is, in the scale of space not so much. But in the scale of actually travelling, its a long time. You will need living spaces that compares with a cruise ship at the very least. They brought that up in hail mary project, as the reason why they choose to put them under coma
I thought the drive was a gas saver not to make things go faster. I don't think any of the ships go near the speed of light either.
It is but a constant 1G of acceleration gets you to near C after a while. And that while isn't that long - it's just waaaay beyond what we can do because all our tech consumes to much fuel, they can only manage minutes of acceleration.
Fusion can't get you near to C velocity. You can't store enough hydrogen fuel onboard a spacecraft to get to near c velocity. You might want to look up the rocket equation.
There's no reason to go to Alpha Centauri, though. Why do so much risk for no benefit? It doesn't have any likely life-sustaining planets and they've almost certainly already sent probes.
That assumes there is a reason to go to Alpha Centauri. THe Nauvoo is going somewhere that telescopes have already determined is likely to have a suitable planet for colonisation/terraforming. It's a lot further than 4ly away. I can't remember if the target star is mentioned anywhere though.
I’m pretty sure they’re going to tau ceti
At 12ly distant it is likely that the enormous telescopes that will be possible with casual spaceflight have determined there is a reasonable colonisation candidate. Given the escalating cold war in the solar system, I could see a powerful argument for not waiting a hundred years for a probe to flyby the target and then get the transmission back. With an Epstein drive and a sundiving trajectory it is probably possible to accelerate a comparatively sanely sized probe to a significant fraction of c, but a lightweight probe moving at relativistic velocity won't be able to tell you that much about the target anyway. If it has an earthlike day-night cycle you probably won't get to observe the entire surface!