Sub-light travel to nearby stars

[halfeye]

When you say mistaken, do you mean the results were fabricated, or that you don't think the 0-g was the cause of the defects?

I don't think 0-g was the cause of the defects. I'm not aware of the particular experiments, but taking experimental animals up to the ISS would predictably be stressful for them, and I wouldn't be surprised if parental stress is correlated with unwanted outcomes.

At any rate a buoyant environment is not the same thing as 0g, you will still have a pressure gradient across the fluid, and separation effects within the fluid from more or less dense compounds floating and sinking. Reptile eggs in particular develop with a definite up-down orientation, and you can easily kill the developing embryo by rotating the egg. Rescuing reptile eggs requires particular care to avoid this problem. The fact that bird and mammal embryos can survive changes in orientation better than reptiles doesn't mean that gravity is without effect, or at least that is what experimentation has indicated so far.

I was unaware of that problem for reptiles.

I think problems like osteoporosis are due to adaptations to living on land, and that as such they can't be a big deal to sort out, because the whales went back to living in the sea, and they'd have had the problems and survived them, so the answers will be in the genes of whales if we don't want to wait until we adapt in the natural way.

[King of Nowhere]

It's also worth pointing out that we're never going to adapt "the natural way": adaptation and evolution require that a lot of children are produced, most die without generating offspring, a few will leave some offspring, some very few will leave a lot of offspring.
We've generated a society where almost nobody dies young, and most people leave roughly the same amount of children. evolution favors exclusively those who make more fertile offspring. In the current society, it will actually eliminate emancipated women (less likely to have children) and it will favor those who don't care to use a condom.
If we want to push human evolution towards traits we consider desirable, we have to do it artificially by manipulating the dna. It has a lot of ethical problems, but certainly less than the low-tech alternative, which is sterilization of those with unwanted traits and forced reproduction of the others.

[Lvl 2 Expert]

I think the gravity issue is best solved by giving people gills and putting them in water habs, honestly. The pressure and resistance prevents muscle atrophy, and water blocks radiation extremely well.

Water is heavy though. Just a 5*4*3 meter living space weights 60 tons, the weight of a substantial locomotive, before adding walls. It also excerts a lot of force of stuff, doesn't mix well with machines and requires a bunch of secondary modifications for humans to properly live in it. Like changes to our skin, senses, digestive tract and means of moving about. It's almost a bigger gene-job than adapting to zero g.

[halfeye]

It's almost a bigger gene-job than adapting to zero g.

Almost? It's hugely bigger.

We can swim a bit, so we can adapt to zero g. The current problems are mainly so far as I know osteoporosis and some other effects like it, which are mainly down to our bodies using stress as a guage of how much nutrient to use in our bodies.

Radiation is a different matter, we need to avoid that rather than adapt to it.

[Lvl 2 Expert]

Almost? It's hugely bigger.

Well, there is the perspective that we have lots of water dwelling animals to learn from while adapting to zero g is completely new ground. That would probably help.

[Tvtyrant]

Water is heavy though. Just a 5*4*3 meter living space weights 60 tons, the weight of a substantial locomotive, before adding walls. It also excerts a lot of force of stuff, doesn't mix well with machines and requires a bunch of secondary modifications for humans to properly live in it. Like changes to our skin, senses, digestive tract and means of moving about. It's almost a bigger gene-job than adapting to zero g.

In the context of generation ships I don't think the weight is as important, because it already requires an onboard biome and thousands of people (or hundreds of people and thousands of frozen embryos.)

I also think genetic adaptation to water environments is going to happen regardless, it is a 2 birds with one stone thing. We also know how animals in water function, 0G issues have yet to be resolved.

Honestly I don't think we are going anywhere, but water habs seem more practical if we do.

[Lvl 2 Expert]

In the context of generation ships I don't think the weight is as important, because it already requires an onboard biome and thousands of people (or hundreds of people and thousands of frozen embryos.)

So you're saying that because it's already semi-implausibly big and heavy and you would already need an engine and a fuel tank larger than the rest of the ship combined to move it at any reasonable speed we might as well triple the weight by filling the whole thing with water?

If I was hired as an engineer on that project I would probably still prefer spinning for "gravity" over water for ""gravity"".

[Tvtyrant]

So you're saying that because it's already semi-implausibly big and heavy and you would already need an engine and a fuel tank larger than the rest of the ship combined to move it at any reasonable speed we might as well triple the weight by filling the whole thing with water?

If I was hired as an engineer on that project I would probably still prefer spinning for "gravity" over water for ""gravity"".

At that size you are using very slowly accelerating engines like ion drives, the question isn't the size but the acceleration time. You are going to spend decades getting up to speed and centuries at speed, does adding a century to acceleration and deceleration matter so much given the time scale?

[factotum]

At that size you are using very slowly accelerating engines like ion drives, the question isn't the size but the acceleration time. You are going to spend decades getting up to speed and centuries at speed, does adding a century to acceleration and deceleration matter so much given the time scale?

The rocket equation doesn't actually care how fast you accelerate, it cares about one thing and one thing only: the speed of your exhaust, which is defined in rocketry in terms of "specific impulse". The best ion thrusters we've tested have a specific impulse approaching 20,000, which is far better than chemical rockets, but using one of those would still mean your ship would have to be almost entirely fuel to get up to a speed where it would take mere centuries for an interstellar trip.

[Tvtyrant]

The rocket equation doesn't actually care how fast you accelerate, it cares about one thing and one thing only: the speed of your exhaust, which is defined in rocketry in terms of "specific impulse". The best ion thrusters we've tested have a specific impulse approaching 20,000, which is far better than chemical rockets, but using one of those would still mean your ship would have to be almost entirely fuel to get up to a speed where it would take mere centuries for an interstellar trip.

I thought you were supposed to fire particles you found on the way? I thought it was supposed to exploit vacuum force, you funnel the particles through a magnetic field and shove them out the back of you to generate thrust. So basically it is a matter of just running the engine over enough space to get up to speed.

I'm not nearly as scientifically literate as a lot of people here so I could be dead wrong on all accounts.

[gomipile]

I thought you were supposed to fire particles you found on the way? I thought it was supposed to exploit vacuum force, you funnel the particles through a magnetic field and shove them out the back of you to generate thrust. So basically it is a matter of just running the engine over enough space to get up to speed.

I'm not nearly as scientifically literate as a lot of people here so I could be dead wrong on all accounts.

Our current ion engines carry their own reaction mass. The most common is Xenon.

[factotum]

There isn't enough material in space to use as reaction mass for an ion thruster, is the main problem. Purely theoretical things like the Bussard ramjet only "work" by having scoop fields a thousand miles wide, and even then they have to be travelling at several hundred miles per second before they get enough fuel to actually work.

[keybounce]

Bigger than that, the average asteroid is one mile diameter or so? I think for a generation ship you want ten, and the crew should be many thousands.

So, something the size of the death star? :-)

The "best" idea that I've seen in fiction: A light sail type of ship, with a launching laser that is bright enough that it can outshine it's sun if you are in the "line of fire" (if your system is the destination of the probe). A few centuries of launch, a light sail to slow down on arrival, a computer controlling the whole thing, and your passengers as pretty much ... well, shoot, how did the Moties ever expect to survive that trip in the first place?