[Kosh]

As you said, it would be nice to have gravity during long voyages, but by the time we're talking about "even interplanetary travel" and artificial gravity, we'll have the technology to more easily solve the problem with biology. With use of growth factors, we could "force" the body to maintain muscle and bone mass in zero G

Yeah, we can turn into Shivans!

Heat dissipation is another big one because you are completely dependent on radiant heat exchange.

I thought the other guy was talking about ambient heat

Surely there must be a better way to protect against radiation (ambient radiation, as well as radiation from your own reactor(s), solar flares, etc) than just piling on the lead.

[Herra Tohtori]

There isn't.

At least, where gamma/röntgen radiation are concerned. Mass is the only thing that stops that stuff... no, "stops" is the wrong word, even mass only absorbs a percentage of gamma radiation, some will always statistically get through the thickest wall of lead you could imagine.

Mind you, any kind of mass works just fine, it's the amount of mass that is important... or rather, the density of the matter and the thickness of the "wall". Lead is commonly used radiation shielding material because it's conveniently dense and thus you don't need to stack it as thick as, say, concrete, steel or water. In a case of space ship, the best bet is to have the ship big enough to work as radiation shielding and have a natural "shelter" zone in the middle. Alternatively, it could be possible to only shield one part of the ship to work as a shelte, or shield the whole ship sufficiently so that it's safe to hang out anywhere during the fiercest radiation conditions imaginable.

Obviously, the problem with first method is the general scope. The second method is possibly the most sensible. Both of these solutions require a sufficient warning time to evacuate the crew to the shelter before intense radiation conditions. The third one doesn't have these problems, but instead it means that the mass/payload ratio of the ship will reduce dramatically.

Particle radiation is easier to stop completely than electromagnetic ionizing radiation, but even that requires rather thick walls on the space ship or radiation shelter. Or a magnetic field strong enough - perhaps it would be possible to actually use the coils of tokamak fusion reactor to generate a strong external magnetic field, which would guide the brunt of particle radiation to the poles of the ship.

[Kosh]

At least, where gamma/röntgen radiation are concerned. Mass is the only thing that stops that stuff... no, "stops" is the wrong word, even mass only absorbs a percentage of gamma radiation, some will always statistically get through the thickest wall of lead you could imagine.

So it doesn't respond to any sort of electromagnetic fields or anything?

[Flipside]

I seem to recall some experimentation around gravity and a magnetised super-conductor, apparently, by spinning the superconductor, it's possible to influence gravity in centre of the unit, sort of like the London Moment in electromagnetic fields.

Of course, the downside to this is that the cure is probably less healthy than the problem....

[Nuke]

if youre using water as a propellant, it might be feasible to stick the living quarters in the middle of the propellant tank. 12 feet of water is enough to keep you safe from material which would probably kill you in a couple minute of exposure. and for interstellar flight youd definately need that much propellant. hell drill out the core of pluto or other ice dwarves, strap a few nuclear-water rockets to it and use that as a space craft (just dont fly too close tot he sun or you will turn into a comet). you can probibly use crushed ice as fuel quite effectively.

i dont think you would need full duration gravity for interstellar travel as a generation ship. sence a good many generations would exist never knowing gravity. when you get close enough to a habitable planet (within a couple hundred years travel), you could just induce a spin on the ship, slowly building up to the g level of the planet youre colonizing. in the hollowed out ice dwarf scenario, there would probibly be enough gravity inside to allow you to walk around on the inside walls.

genetic engineering will almost certainly be a plus. not only will you need to adjust youre dna to space flight, you would also have to re-adjust it to your destination at some point in flight. in the process you might actually become a zero g race, as the people who reach another star may simpley be so used to it that the thought of living on a planet would be alien. at that point it might be better off for humans to stay spaceborne and not land on anything with more gs than you could get off of with a vehicle the size of a vw beetle.

[Herra Tohtori]

Yeah, and water has the advantage of being the second most common molecule in the universe... It's also easier to store great masses of it, much easier than hydrogen, which is very light even in liquid form and requires a really low temperature or high pressure to stay liquid.

[Flaser]

if youre using water as a propellant, it might be feasible to stick the living quarters in the middle of the propellant tank. 12 feet of water is enough to keep you safe from material which would probably kill you in a couple minute of exposure. and for interstellar flight youd definately need that much propellant. hell drill out the core of pluto or other ice dwarves, strap a few nuclear-water rockets to it and use that as a space craft (just dont fly too close tot he sun or you will turn into a comet). you can probibly use crushed ice as fuel quite effectively.

i dont think you would need full duration gravity for interstellar travel as a generation ship. sence a good many generations would exist never knowing gravity. when you get close enough to a habitable planet (within a couple hundred years travel), you could just induce a spin on the ship, slowly building up to the g level of the planet youre colonizing. in the hollowed out ice dwarf scenario, there would probibly be enough gravity inside to allow you to walk around on the inside walls.

genetic engineering will almost certainly be a plus. not only will you need to adjust youre dna to space flight, you would also have to re-adjust it to your destination at some point in flight. in the process you might actually become a zero g race, as the people who reach another star may simpley be so used to it that the thought of living on a planet would be alien. at that point it might be better off for humans to stay spaceborne and not land on anything with more gs than you could get off of with a vehicle the size of a vw beetle.

There's just one problem: no embryo will develop into a human without gravity.
Even if for just a specific part of the term, the mother (or the artificial womb) will have to be in gravity or its semblance.

[Admiral_Stones]

Why?

[Herra Tohtori]

Apparently cell structures and even some types of individual cells demand a gravity vector to develop properly. Mind you, any kind of weight can do, be it caused by gravitational acceleration or centripetal acceleration.

Interestingly, roaches apparently grow faster, stronger and tougher in weightless conditions...

[Admiral_Stones]

Kewl 
Go russia.

[Herra Tohtori]

You won't think it's kewl when them space roaches escape the Russian research facilities and spread a deadly zombie virus all over the world!

Grrr. Argghh.

[Nuke]

think a roach could survive re-entry?

[Herra Tohtori]

Well, better than your average Joe Astronaut for sure.

[Nuke]

i meant minus space vehicle, flick the thing retrograde and watch it burn up

[Herra Tohtori]

Hmm...

They would probably survive the lack of pressure and oxygen for long enough, but the re-entry heat is a problem for them. Unless they are flicked hard enough that they gain the pro-grade vector's opposite and fall right out of sky. That, they would probably survive - they can take some serious acceleration, so put a bunch of roaches on a barrel and the barrel on a coil gun that accelerates the bucket onto reverse orbital velocity, or close enough. Then them roachys would just plummet down from the sky. And as freaky as it sounds, some probably would survive the treatment.

But re-entry at orbital velocities... no. Just no.