Food and its mass

[Cal'Mihe]

For transportation, my Mun base will use Cal'Mihe's awesome Starspeeder, safely rated for about 5 tons of payload. (But it's a fully reusable SSTO that can get to the Mun, which I imagine makes it cheaper to do multiple trips than to use a heavier/wasteful transport for fewer trips.)

I am Cal'Mihe and I approve of this message

On a related note Kimberly, though it is not really the topic of this tread, I did a small test and it *can* actually haul 9 tonnes to LKO and have around 800 oxidizer to spare. Simulated here with two 4,5 tanks in the outboard spaces between the wings. However with the extra weight that only translates into ~2000 dV left after circularization (screenshot is off, I had messed up the fuel connections), so it would need refueling in LKO in order to proceede to the Mun. This could be done by a second Starspeeder flying in tandem with the first one, up to LKO, and then transfeering fuel to the payload carrier for the Mun trip.

Sorry for the temporary de-railment, back on topic

Edited July 14, 2013 by Cal'Mihe
Messed up the fuel left calculation

[Halsfury]

Considering their star is modeled after our star, and our star emits primarily in the green light (which is why plants are green), and Kerbals are green, that actually makes a lot of sense.

Before anybody asks, the sun appears yellow due to some phenomena with light that is beyond me that causes the yellow light to visually overpower the green.

That makes sense thinking about it. Since most stars emit light across the same spectrum would that mean that supposing the existence of plants in another star system, they would most likely be green?

[Halsfury]

Photosynthesis really isn't that efficient

In fact Photosynthesis is pathetically inefficient, it is really 3% efficiency or so

It's a complex story to do with the Kreb's cycle but if photosynthesis were an efficient means of getting energy plants would walk around, talk and have complex brains, the only thing which stops them from so doing (in this universe) is that they can't waste the energy on something as complex as a brain or legs because they cannot get enough energy to evolve in that direction

[Albert VDS]

Though it is efficient in a way that they use it all to grow, either in plant size, fruit or other energy storage by just collecting light.

Edited July 14, 2013 by Albert VDS

[andrewas]

But a lot of that light is absorbed as heat rather than used to fuel chemical reactions.

[Tarrow]

Considering their star is modeled after our star, and our star emits primarily in the green light (which is why plants are green), and Kerbals are green, that actually makes a lot of sense.

[apologies if slightly off-topic maybe] Plants appear green precisely because they do not absorb green light, they reflect it. Peak absorption for chlorophyll is at the blue and red end of the spectrum (about 420 & 680nm for chlorophyll A and 470 & 620nm for chlorophyll .

[back on topic] if you're looking for a food that can be grown with great efficiency, growth rate and simple feedstock materials, mycoprotein meat substitute is about the easiest. It can double its mass every 24 hours with appropriate levels of nutrients so a 1kg starter colony could weigh about 60kg by the end of the first week and be pushing well up 8-9 tonnes by the end of the second week. Downside would be (and this applies to anything you're trying to grow inside a closed-loop system without 100% perfect recycling) that the mass of nutrients, water etc required to reach that growth would weigh more than you'd get out of it. Meaning you'd have been better off in terms of fuel efficiency from launch in just packing a really big packed lunch

[Kimberly]

Though it is efficient in a way that they use it all to grow, either in plant size, fruit or other energy storage by just collecting light.

Why stand around collecting sunlight if you can let a bunch of plants stand around for you, and then eat them all?

Downside would be (and this applies to anything you're trying to grow inside a closed-loop system without 100% perfect recycling) that the mass of nutrients, water etc required to reach that growth would weigh more than you'd get out of it. Meaning you'd have been better off in terms of fuel efficiency from launch in just packing a really big packed lunch

I'm not sure that's true. I mean, if you don't recycle the waste back into food, then you're missing out on a lot of fuel savings. Recycling is always better in the long run, the question is whether the savings justify the up-front investment, which depends on the cost of implementation and the scheduled life cycle of the system.

[Themohawkninja]

[apologies if slightly off-topic maybe] Plants appear green precisely because they do not absorb green light, they reflect it. Peak absorption for chlorophyll is at the blue and red end of the spectrum (about 420 & 680nm for chlorophyll A and 470 & 620nm for chlorophyll .

This is why I am going to major in astronomy, and not biology in college. That seem really weird though, but it seems science has yet to answer why. Cool.

Anywho... Have we taken into account the dietary requirements? (protein, fiber, vitamins)

[Tarrow]

I'm not sure that's true. I mean, if you don't recycle the waste back into food, then you're missing out on a lot of fuel savings.

Oh indeed, that's how it should work. However unless the recycling and regrowth cycle is 100% materials efficient (i.e. every single atom of waste is sorted and converted to a storable reuseable form, and is reused with perfect efficiency) there will be losses through the system and those losses require material replacement either from stock (which means you had to lift more mass to begin with) or from a resupply mission.

The old rule of thumb for hikinng and other high-calorie activities used to be about 2lb of food per person per day (about 900g) - totaling about 331kg per person per year*. So your average 4-person ISS crew uses just over 1.3 tonnes of food per year (18 people would use just short of 6 tonnes). Unless you can pack a reliable recycling system, growth system for multiple plant types, working space plus the required materials to actually grow the food into that same mass allowance then it's not worth considering. That's before you get to "hey look another piece of tech to maintain and carry spares for" Simplicity counts for a lot.

* short of eating nothing but peanut butter there's not much vegetarian that'd pack that many calories into the same mass.

[Kimberly]

Anywho... Have we taken into account the dietary requirements? (protein, fiber, vitamins)

The figure I used earlier was based off of ISS astronauts' actual consumption, which I assume is a diet that consists of all necessary nutrients (but also includes food waste and whatnot, I think).

. Unless you can pack a reliable recycling system, growth system for multiple plant types, working space plus the required materials to actually grow the food into that same mass allowance then it's not worth considering.

My calculation, derived from actual ISS consumption, ends up at 43 tons of food per year for an 18-man crew. That's only a bit under the weight of the recycling/hydroponics modules in my Mun base put together, so if they had a decent efficiency, you'd break even in two to three years, even if you take into account spare parts.

[Tarrow]

That link makes interesting reading, hadn't spotted it earlier nice one. It'd be interesting to see a breakdown of that data though. I'd be willing to bet a large proportion of that weight is effectively "luxury items" that are in no real way needed. Lemonade for example. Astronauts do not need lemonade to survive. Nutritionally it's the same as recycled water that's had a splash of sugar and some flavourings added.

43 tons of MRE's for example (three a day, max of 0.74kg per MRE, about 1200 calories per) would feed a crew of 18 for three years. Or a 4 person crew for just over 13 years. They'd just hate the taste after a while. You can pack significantly more nutrients into much less mass but the resulting taste is somewhat.. uninspiring

[but enough off topic lol]

[metaphor]

This link says one person needs about 400 kg bare minimum of food for 2 years. So 200 kg per person per year. If you include more variety and taste in your food, and include packaging, it might go up to 500 kg per person per year. That's about 9 tons per year for 18 people. This is assuming all the water is recycled. It would be less for kerbals.

[RuBisCO]

I'm going to drop my foot down and plants and photosynthetic efficiency as that is a matter of my graduate degree.

First off Plants are green because of the LIMITATIONS of Chlorophyll, see here:

They don't absorb yellow/green light as well as blue and red, despite the fact those are present in abundance. Chlorophyll simply is poor at absorbing those frequencies of light, simply because all dyes, all molecules, have different frequencies of light they absorb, reflect or are transparent too. Its like how a muffler of a car will only cancel sound of a specific frequency range, a flute/trumpet will only generate specific tones depending on its size and tubing shape, only difference is its at a quantum mechanical level. If photon absorption efficiency were really that important plants would be BLACK and absorb as much light as possible, simply by combination of different light absorbing molecules to cover each spectrum. As is Chlorophyll is very efficient at converting what light it does absorb into electron motion, the real problem for plants comes in utilizing said energy into reducing carbon dioxide into sugars, and nitrogen into proteins, those processes are so dam inefficient that more efficient light absorption is not going to help much at all, in fact that might be detrimental as their wasted energy translates into heat which makes the plants hotter and all the energy wasted in optimizing light absorption that goes to no good. Plants have thus evolved to absorb energy as well as they can convert that energy into biomass.

[Moon Goddess]

The first things to evolve photosynthesis were bacteria, some of these are still alive today and are purple - because they absorb green light. It's possible that these bacteria were once so dominant that most of the water only let through purple light. Then green bacteria evolved to make use of the spare purple light. Later the green bacteria became the chloroplasts in plants and at some point the plants began to dominate.

I hate that everyone in this thread simply ignored you after this, since this is the prevailing theory on why plants are green.

Yes green photosynthesis is horribly inefficient. It's just a mistake of chance that the green ones took over and the purple ones which get much much more energy got relegated to history's dustbin. A world of purple plants would be cool.

[deepsheep]

Going back to topic. It's about 2kg of food/water per day for a human. This assumes some sort of water recycling system on board.

Although growing food sounds like a good solution, you would need to account for all the systems needed to grow plants. Agriculture is only viable in large scale where you have small colony to support. A few Kerbals in space would almost be fully reliant on supplies.

[Kimberly]

It seems ISS astronauts are quite wasteful in terms of food mass usage, so maybe shipping food over to the Mun is more efficient, after all. How large would a colony need to before agriculture becomes profitable, though?

[RuBisCO]

I think for KSP a "green" panel of algae would look pretty cool, and be more space and weight efficient then green houses, and perhaps kerbals like the taste of pond scum.

Better yet would be electrobiosythesis, organisms that can utilize electricity directly to reduce CO2 to oxygen and produce "food".

[Halsfury]

Hmm what this boils down to is that we can't replicate a self sustaining environment by ourselves, even resorting to plants and algae there is no way to pack sufficient biomass into a spacecraft. In fact about 30 years ago somebody tried to make a self sustaining living environment and put people into it to test it's feasibility and it was a disaster, even though it was a very big hermetically sealed complex in the desert, filled to the brim with plants, 6-12 people could not make it work for them and the project was forced to close down (somebody help me remember what this project was called)

EDIT: I'm thinking of the Biosphere Project, which was a closed loop system imitating the earth, unfortunately even at it's massive size, oxygen levels declined steadily down to 14% causing medical difficulties which forced the scientists working on the project to pump oxygen into the Biosphere, making the project scientifically useless.

It reminds me of a Top Gear episode where Jeremy Clarkson tried to clean a car's exhaust by hooking up a greenhouse trailer to it and extending the exhaust pipe into the greenhouse trailer. Not only was this effort disastrous since wind buffeting destroyed the greenhouse, Richard Hammond pointed out that in order to properly clean up the car's emissions he would need several greenhouse trailers stretching up to 2 miles in length!

Fitting oxygen scrubbers was no help either since is was discovered that you would need to replace the filter once every few minutes if it was going to properly scrub out the CO2

This is an extreme example since cars create far more waste gasses than a human does by breathing, It is a testament to the sheer size of the earth that we would need trillions of cars to overpower photosynthesis however.

Edited July 16, 2013 by Halsfury

[Tarrow]

It seems ISS astronauts are quite wasteful in terms of food mass usage, so maybe shipping food over to the Mun is more efficient, after all. How large would a colony need to before agriculture becomes profitable, though?

Depends very much on how large the colony is. And whether you're dropping habitats or building underground. A bit of lateral thinking can drop the launch masses a lot.

Dropping habs is in itself very inefficient. As a example you'd need a 100m x 100m area to grow 9 tonnes of wheat per 6 months (based on current worldbank stats of wheat yields per hectare). If you did that as a hab 3m high with the same wall construction as the iss (about 5mm aluminum on average) you'd have to haul 171 tonnes of metal per hectare just to build the shell structures. More mass required for fitting out etc. So say around 200 tonnes per hectare.

So for 10 hectares you'd need about 2000 tonnes of materials and fittings. At 90 tonnes total yield per 6 months you'd break even in 11 years or so (and have a crew thoroughly fed up of eating toast by the pound for every meal)

Of course you could reenginneer the entire system so that rather than dropping habs you're digging underground to make space to grow food. One person with a single 30 tonne JCB excavator can dig a 100m x 100m x 3m hole in just over a month. Five of them and you'd be down to a week. Dig out ten spaces, seal the inner walls, roof and ceiling with high strength airtight resin and fit the same 30 tonnes of supporting equipment per space. Total launch mass would be ((5*30)+30)+(9x30) 450 tonnes with breakeven @ 2.5 years. Plus you still have 150 tonnes of excavating gear you can use however you want, even if only to take your mind off the darn toast.

I'm rather fond of the second option

[DerekL1963]

Hmm what this boils down to is that we can't replicate a self sustaining environment by ourselves, even resorting to plants and algae there is no way to pack sufficient biomass into a spacecraft. In fact about 30 years ago somebody tried to make a self sustaining living environment and put people into it to test it's feasibility and it was a disaster, even though it was a very big hermetically sealed complex in the desert, filled to the brim with plants, 6-12 people could not make it work for them and the project was forced to close down (somebody help me remember what this project was called)

EDIT: I'm thinking of the Biosphere Project, which was a closed loop system imitating the earth, unfortunately even at it's massive size, oxygen levels declined steadily down to 14% causing medical difficulties which forced the scientists working on the project to pump oxygen into the Biosphere, making the project scientifically useless.

Nit: Most of Biospheres II's problems stem from the fact that much of it's design was dictated by ecological 'wizards' and stems from their philosophies and politics. It really was not all that well engineered (the expansion chambers were added at the last minute because it hadn't occurred to anyone that air changes volume with temperature), and great deal of the budget was spent on frippery like importing tons of "authentic" soil and sand for the various biomes. So yeah, it was scientifically useless, just not for the reasons most people think.

That being said, building a recycling system that's 80% efficient will be a herculean task - especially as it involves not just processing human waste, but composting vegetable matter as well. Not just food scraps but the inedible biomass food plants produce along side the edible portion. Another problem is preventing the buildup of any kind of toxins. (I.E. the residues of cleaning chemicals, lubricants, etc...) Keeping them out of the atmosphere is a huge problem for submarines on long patrols (so we just exchanged air with the atmosphere every week or so), but you'll be accumulating them in the biomass as well.

[Halsfury]

Nit: Most of Biospheres II's problems stem from the fact that much of it's design was dictated by ecological 'wizards' and stems from their philosophies and politics. It really was not all that well engineered (the expansion chambers were added at the last minute because it hadn't occurred to anyone that air changes volume with temperature), and great deal of the budget was spent on frippery like importing tons of "authentic" soil and sand for the various biomes. So yeah, it was scientifically useless, just not for the reasons most people think.

Oh God that is way worse than I thought, how ignorant,

So they essentially pulled a Kerbal manoeuvre and forgot the equivalent to landing legs. Without a way to relieve any temperature driven pressure changes the leakage would be high at best and at worst it could cause windows to blow out etc.

And importing dirt is just wasteful, especially since it would be preferable to simply choose the most fertile soil possible and just one type of ecosystem instead of having a desert (a drag on O2 production) in one corner and a rainforest in another.

in short Quackery! People always reference the biosphere project as a what not to do, but nobody ever really goes into depth about the ridiculous stuff which they did

Edited July 16, 2013 by Halsfury