did I fall asleep and missed like 100,000 years? … what are the usual generation ships you mention?
thats kinda like saying the usual aliens are smallish pale-green creatures …
In reality that is what we NOW THINK it might look like … not what it really will be (HUUUUGE difference, here)
e.g. our today’s airplanes (F-16) look way different than people in 1850 thought they would look (which was like a mechanic bird) - and the propulsion mechanism is way different as well.
Ha! Quite right. I meant to say that most generation ship concepts envisage a slower journey.
There have been several fairly detailed descriptions of generation ships written since Tsiolkovsky wrote The Future of Earth and Mankind in 1928.
So would any other food-synthesis system.
The stardrive adds up even more. On any sort of interstellar mission, you’re going to need huge fuel tanks, probably many times more weight of fuel than weight of payload. There’s no way around that, because the engines need it. And life support is a lot less power-hungry than the engines.
Radiotrophic fungi aren’t any better at absorbing gamma rays than any other matter. They just do something useful with a fraction of the energy, instead of converting all of it to heat. And the fungi are, themselves, made of matter. If you want to make 100 kg of fungus, you’ll need at least 100 kg of fungus-food. And if you want 100 kg of radiation shielding, you could just use that fungus-food instead of the fungus.
This thread has prompted me to research the subject a bit and the consensus is that engines will need a lot of fuel, as you point out. The farther the trip, the more fuel needed. But I’m confused as to why. Once you get up to speed you wouldn’t need any more fuel, would you? Unless I’m missing something, it seems you would be coasting without any noticeable friction no matter the distance.
What am I missing?
Most generation ships would coast for most of their trip. But the longer the trip is, distance-wise, the faster you can go, the better, so more fuel needed for a longer acceleration period.
Also, it depends on the nature of your engines. High thrust vs low thrust engines often have very different fuel efficiencies. As well, a low-thrust engine that can run much longer can often achieve much greater velocities overall. If fuel were not an issue, the fastest way to get anywhere would be to accelerate continuously throughout the voyage, turning around at the half-way point to slow down again. Your average velocity would be much higher than a ship that coasts most of the way.
You’re rifght there’s no enroute friction, unlike with car, boats, planes, etc.
Simplistically speaking, however much fuel you spend to get up to speed you’ll need a similar amount to slow back down at the other end.
But actually it’s far worse than that. The reason is the
The very short version is that for fast speeds you end up consuming an insane amount of fuel accelerating all the fuel you’ll use later. And that applies all the way along the acceleration process.
For a one-way trip you’ll spend a huge amount of your speed-up fuel speeding up the fuel needed to slow down later.
One of the reasons Mars missions are conceived as using Mars-produced fuel to return with is entirely that carrying enough fuel to decelerate back at Earth, and accelerate leaving Mars, and decelerate arriving at Mars and accelerate all 3 of those other slugs of fuel leaving Earth the first time is simply insanely big numbers beyond out present abilities.
This is probably off topic, but I imagine that if radiotrophic fungi have a couple eons to evolve in a high radiation environment (for example, on the moon of a gas giant, or on an Earth that gets blasted by nukes until it glows) they might develop structures that block radiation for the same reason that trees developed structures that make shade.
OK, got it, thanks.
But that does raise an interesting point, if a ship can reach 10% c then, on average, the passengers would go through about 7 + generations. If the first several generations can’t make it there alive, what’s the hurry?
If we can build an enclosed ecosystem that really works, then current technology should be OK - even though it would take over 70, 000 years.
Thoughts?
I think the problem comes back into what was said earlier - what works for 7 weeks may not for 7 months, which may not for 7 years, 7 decades, 7 centuries, etc.
70k years is a loooong time for something unexpected to crop up. Or more likely, several something unexpecteds. Too long a trip has it’s own risks in other words.
I think its “risk” … ONE motivated guy could probably have the whole ship go under … which isn’t really a danger on earth.
it’s like crossing the street: the shorter a timefram you are on the street (the dangerous part of the world), the lower the chance of getting hit (think: a cautious hare vs. a cautious snail crossing the street)
No matter what, your ship will only carry a finite amount of usable energy, and that finite supply of energy must last for the entire trip, and provide all of the energy needed both for life support and for propulsion. The more of it you spend on propulsion, the quicker the trip will be, and hence the less you’ll have to spend on life support. At some point, there will be some optimal fraction of your energy to spend on propulsion, though calculating that optimal fraction would require a lot of details that we don’t have.
Pretty much by definition, we’re launching them into the unknown, and as such, we don’t know what problems they’ll encounter. We can guess at some, but we’ll never know for certain if we’ve accounted for all possibilities.
In that case, the shorter the time they spend on the ship, the better. Every year has some small chance of an accident or disaster, so the more years you plan to take, the higher the overall probability of an accident that we didn’t account for.
Again, it all comes down to what we’ll be capable of, but in general, faster is better for everything except fuel usage. Figuring out the right balance will be a challenge in itself.