Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[alway]

Yeah, you can do some funny-business with massive amounts of energy being converted into a reaction mass, but the energy requirements for that would be so large as to be even less practical than something which is physically impossible, simply because even anhialating antimatter would give you less stuff than you started with.

However, there are reactionless drives in the form of solar sails, and those are certainly nothing to sneeze at. https://en.wikipedia.org/wiki/Solar_sail
And for small payloads, they're one of only a few potentially viable interstellar craft using only known physics without requiring anything more advanced than slightly improvements on figuring out how to industrially create economical nanotubes.

[GiglameshDespair]

Solar sails aren't reactionless drives.

Solar sails provide thrust by placing "sails" against the flow of particles of the solar wind and transfer its momentum to the spacecraft. Therefore, the solar sail does not carry reaction mass but is not reactionless.

[alway]

Well yes, but you don't need to pack a sun onboard a rocket leaving the atmosphere, and so that point is moot aside from pedantic reasons.

[Radio Controlled]

Well yes, but you don't need to pack a sun onboard a rocket leaving the atmosphere, and so that point is moot aside from pedantic reasons.

When talking science or engineering, correct terminology is important though.

[Rez]

You're gonna need to pack a sun if you're going someplace a long way from one.

ed: or build lots of lasers.

[origamiscienceguy]

Could a space "ark" be built that has foliage and an entire ecosystem inside of it? Could it gain energy from the cosmic radiation throughout the galaxy?

[alway]

Could a space "ark" be built that has foliage and an entire ecosystem inside of it? Could it gain energy from the cosmic radiation throughout the galaxy?

What that looks like depends on the intended payload and destination and such, but on basically every variation, the answers are most certainly and sorta.

For certain scales, that would describe Earth; which is obviously capable of supporting entire ecosystems.
Smaller than that, and you get O'Neill cylinders and Stanford Torus.
Larger, and you get ringworlds.
For the most part, those are intended for habitation near stellar bodies (though if you're constructing a ringworld, you probably have the ability to move or construct stars).

In a stellar environment, you would have all the energy you need, even at relatively large distances, so long as you could collect it efficiently; though that obviously gets more cost prohibitive the farther out you're staying.

From there, it comes down to an energy balance: how much energy is necessary to sustain the amount of life being transported. Certain extremophiles would probably be just fine in interstellar space if they could survive dormancy for very long periods of time; certain bacteria can apparently survive on electricity alone. In deep space, cosmic radiation will give you approximately as much energy as you would get from solar panels collecting the starlight in interstellar space; 10^-13 Joules / cubic meter, or approximately 10^-5 Joules per second per cubic meter, since it is travelling at roughly the speed of light, and assuming 100% collection efficiency and that the collectors don't obstruct one another. So without some other source of energy, you wouldn't be able to sustain any sort of large, growing, or mobile creatures without pretty extensive methods of harnessing the energy from cosmic radiation (extensive in this case meaning basically planet-sized collecters). Humans, for example, require around 5-10MJ of energy in food per day, or around 3600MJ/year. All in all, it means humans are essentially 100 watt lightbulbs.

However, luckily, we have other sources as well. Uranium and thorium both have around 80,000,000MJ/kg according to wiki, which is quite a good number of lightbulbs. While there's certainly going to be a lot of inefficiency in converting that into a form usable by life (unless you're using the aforementioned electricity-consuming bacteria), so you can sustain quite a decent amount of life for quite a decent amount of time using a relatively small stockpile of nuclear fuel.


Note: Do not take these figures as gospel. Except the bit about humans being 100 watt lightbulbs. Humans should be compared to lightbulbs as often as possible in your daily life.

[Rez]

I thought you were thinking about Templar Treeships.

[alway]

In which case, the term to search for is Dyson Tree. https://en.wikipedia.org/wiki/Dyson_tree

[Rose]

I remember an MMO I played before seemed to be going with that premise.

[LordBaal]

Humans should be compared to lightbulbs as often as possible in your daily life.

Don't see why not? They are inefficient, produce heat, pollute, and every once in a while they simply blow out or up.

[WillowLuman]

Damnit, recent re-evaluations have crushed my hope of seeing Betelgeuse explode within my lifetime.

[GiglameshDespair]

In which case, the term to search for is Dyson Tree. https://en.wikipedia.org/wiki/Dyson_tree

That is a cool idea. Brings to mind Yggdrasil.

[i2amroy]

Could a space "ark" be built that has foliage and an entire ecosystem inside of it? Could it gain energy from the cosmic radiation throughout the galaxy?

Hypothetically, yes, but the problem is that radiation is such a small value unless you are very close to a star that you would probably be losing more energy through heat loss and other leakages then you were taking in in radiation. That said if you could lower shields or something to stop energy escaping except when you were close enough to a star to gain more then you lost, it would certainly be a viable option (as others have pointed out).

[alway]

Another Falcon 9 launch and landing attempt tomorrow at 6:10 PM EST. Current weather forecast seems good, so as long as there aren't any problems with the rocket, it has a pretty good chance of launching on time.