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[TheBiggerFish]

unfortunately, the ship would have to be extremely large to accomidate enough plants for one human so the idea of an indefinite escape pod is out of the question.

Exactly how large, again?

[TheDarkStar]

unfortunately, the ship would have to be extremely large to accomidate enough plants for one human so the idea of an indefinite escape pod is out of the question.

We know that one working one already exists (Hint: Look down.)

[Arx]

unfortunately, the ship would have to be extremely large to accomidate enough plants for one human so the idea of an indefinite escape pod is out of the question.

Exactly how large, again?

Biosphere 2 was 204000 cubic metres and supported eight people, aside from the large number of unforeseen issues (many of which could now be dealt with). A similar structure as a spac evessel would probably have to be larger to compensate for increased difficulty losing heat and more complicated support restrictions.

[origamiscienceguy]

unfortunately, the ship would have to be extremely large to accomidate enough plants for one human so the idea of an indefinite escape pod is out of the question.

Exactly how large, again?

Biosphere 2 was 204000 cubic metres and supported eight people, aside from the large number of unforeseen issues (many of which could now be dealt with). A similar structure as a spac evessel would probably have to be larger to compensate for increased difficulty losing heat and more complicated support restrictions.

Didn't they forget to add a certain fungus or something?

[Arx]

Not one of the significant issues IIRC, although there are far too many to mention here. The main one was soil bacteria going crazy and consuming all available oxygen, in terms of it as an experiment into space self-sufficiency.

[i2amroy]

unfortunately, the ship would have to be extremely large to accomidate enough plants for one human so the idea of an indefinite escape pod is out of the question.

Exactly how large, again?

The exact numbers depend a bit on how far you want to go from a light source. Here's the basic assumptions:
1) I'm going with the solar panel design, because it scales better at long distances form the sun then the direct plant design does, and captures all types of light a bit better. I'll be using a solar panel efficiency of 80% (which is about double our current best ones, but still well under the theoretical maximums of ~90-95%).
2) We're going to go out to pluto and back.
3) You're going to grow sugar cane, since it has the best caloric storage of about pretty much any edible plant. I hope you like sweet things.
With these assumptions each person is going to need to have about 150 m^2 of solar panels stretching out on the outside of your ship, and probably around a 10m x 15m x 20m square cube to actually grow their sugarcane in, based on the normal adult human energy consumption.

To put that in perspective, each human is going to need about a volleyball court's worth of solar panels, and 1.2 olympic sized swimming pools worth of space to grow their food/purify water/make air (though you might need additional space for more air/water purification, I haven't run the numbers on those aspects). That's on top of whatever space you actually need for the ship itself and any area for the person to live in.

Alternatively for interstellar distances you may want to go the hydrogen scoop method where each person would need about 437 m^2 (2.7 volleyball courts) worth of scoop on the front of your ship to harvest the hydrogen needed when traveling at solar escape velocity speeds; the main benefits being that while the amount of solar panels you need keeps increasing as you go farther from a star, the amount of hydrogen scoop area you need remains relatively constant no matter where you go in the milky way galaxy.

[Culise]

Alternatively for interstellar distances you may want to go the hydrogen scoop method where each person would need about 437 m^2 (2.7 volleyball courts) worth of scoop on the front of your ship to harvest the hydrogen needed when traveling at solar escape velocity speeds; the main benefits being that while the amount of solar panels you need keeps increasing as you go farther from a star, the amount of hydrogen scoop area you need remains relatively constant no matter where you go in the milky way galaxy.

Well, give or take.  We're sitting in the middle of the Local Bubble, unfortunately, which is around 300 l.y. of interstellar void at around a tenth of the average hydrogen density of the Milky Way as a whole.  We're really lucky in that we just happen to be in the middle of a slightly denser area (relative to the Local Bubble, at least) that happens to abut another such dense area (again, relatively speaking), but it does mean that anything that ends up going to, say, Sirius or Procyon is going to need to deal with a drop in local hydrogen density of anywhere from 50% to 80%, give or take.  I'm not exactly well-read on the latest material, however, so I'm a little curious how they manage allowing for a constant hydrogen scoop area under such wildly fluctuating densities.

[GiglameshDespair]

The exact numbers depend a bit on how far you want to go from a light source. Here's the basic assumptions:
1) I'm going with the solar panel design, because it scales better at long distances form the sun then the direct plant design does, and captures all types of light a bit better. I'll be using a solar panel efficiency of 80% (which is about double our current best ones, but still well under the theoretical maximums of ~90-95%).
2) We're going to go out to pluto and back.
3) You're going to grow sugar cane, since it has the best caloric storage of about pretty much any edible plant. I hope you like sweet things.
With these assumptions each person is going to need to have about 150 m^2 of solar panels stretching out on the outside of your ship, and probably around a 10m x 15m x 20m square cube to actually grow their sugarcane in, based on the normal adult human energy consumption.

To put that in perspective, each human is going to need about a volleyball court's worth of solar panels, and 1.2 olympic sized swimming pools worth of space to grow their food/purify water/make air (though you might need additional space for more air/water purification, I haven't run the numbers on those aspects). That's on top of whatever space you actually need for the ship itself and any area for the person to live in.

Alternatively for interstellar distances you may want to go the hydrogen scoop method where each person would need about 437 m^2 (2.7 volleyball courts) worth of scoop on the front of your ship to harvest the hydrogen needed when traveling at solar escape velocity speeds; the main benefits being that while the amount of solar panels you need keeps increasing as you go farther from a star, the amount of hydrogen scoop area you need remains relatively constant no matter where you go in the milky way galaxy.

What if you used something like algae? Would that decrease space needed?

[Egan_BW]

Now, why bother with all these complicated biological processes when you could just upload your mind to a computer and live purely  off of solar panels?

[Culise]

Now, why bother with all these complicated biological processes when you could just upload your mind to a computer and live purely  off of solar panels?

Probably because we have yet to figure out the whole "brain uploading" thing, whereas we've made a bit more progress on the whole "closed-cycle ecosystem" thing.  Not much more, but a bit more by comparison. 

[GiglameshDespair]

No, I think we've made a lot more progress on the closed-cycle ecosystem than we have brain uploading.

[Reelya]

There's also the issue that brain-uploading is not likely to use less actual energy than a brain, for quite some time even if you could do that.

http://www.extremetech.com/extreme/163051-simulating-1-second-of-human-brain-activity-takes-82944-processors

The K-supercomputer with 82,944 processors modeled a brain of about 2% of the size of a human brain. It took 40 minutes to simulate 1 second of brain activity. While that's kinda impressive that we can even do that, it's clearly not up to scale for uploading peoples' brains to save energy.

Assuming the brain scales up linearly (which is being generous) that's 50 x 2400 = 120000 times less powerful than a human brain. The K computer is about 10 petaflops. So to model a whole human brain in real-time with this level of tech would need about a 1 million petaflop processor. The most efficient supercomputer gets about 2 teraflops / KW, so you'd be looking at energy consumption of 500 gigawatts. Which 5 billion times more than the energy consumed by an average human's body.

To make brain uploading viable, the energy requirements for running the simulated brain must basically fall below 100 watts for 1 million petaflops of processing. That might not be possible with silicon / von Neumann architecture. In either case, improved computing tech would be competing with other ways of providing for space travellers, which will also be improving technology, pushing further out the point at which brain uploading is the viable alternative.

[Putnam]

Assuming the brain scales up linearly (which is being generous)

that is probably the most generous estimate i've ever seen for such a thing

[origamiscienceguy]

There's also the issue that brain-uploading is not likely to use less actual energy than a brain, for quite some time even if you could do that.

http://www.extremetech.com/extreme/163051-simulating-1-second-of-human-brain-activity-takes-82944-processors

The K-supercomputer with 82,944 processors modeled a brain of about 2% of the size of a human brain. It took 40 minutes to simulate 1 second of brain activity. While that's kinda impressive that we can even do that, it's clearly not up to scale for uploading peoples' brains to save energy.

Assuming the brain scales up linearly (which is being generous) that's 50 x 2400 = 120000 times less powerful than a human brain. The K computer is about 10 petaflops. So to model a whole human brain in real-time with this level of tech would need about a 1 million petaflop processor. The most efficient supercomputer gets about 2 teraflops / KW, so you'd be looking at energy consumption of 500 gigawatts. Which 5 billion times more than the energy consumed by an average human's body.

To make brain uploading viable, the energy requirements for running the simulated brain must basically fall below 100 watts for 1 million petaflops of processing. That might not be possible with silicon / von Neumann architecture. In either case, improved computing tech would be competing with other ways of providing for space travellers, which will also be improving technology, pushing further out the point at which brain uploading is the viable alternative.

Yeah, the brain is one of the most complex and amazing things. Maybe in the future we could build our own and have organic computers that use the same system that our brain uses. That would be pretty cool.

[i2amroy]

What if you used something like algae? Would that decrease space needed?

As best as I can tell sugar cane is still the best option for photosynthetic efficiency (3-4x more than most competitors), so I don't believe so.

There's also the issue that brain-uploading is not likely to use less actual energy than a brain, for quite some time even if you could do that.

Honestly I think one of the big advantages of brain uploading would be the ability to slow yourself down to limit energy consumption, sort of a halfway mark between normal activity and total cryogenic stoppage. It would let you still react to things if they occurred, albeit at a slower processing level than normal. It would be like if suddenly time went into double speed for everything but you, you could still interact, but you might find it a bit difficult to process things when twice as much was happening in any given period of time.