Traveller: Feeding Rethe

This is the fourth part in a short series mulling over various quirks of Traveller’s Third Imperium background. Part one considered how hazardous low berths are, part two wondered about jump drive fuel tanks, and part three considered Rethe, a Mars-sized desert world where 26 billion people live.

This time, how to feed everyone on Rethe.

Rethe

A quick recap from last time. Rethe (E430AA8 8 Poor. Non-agricultural. Desert World.) is the most populous world in the Regina subsector. (I noted last time that Rethe had grown - apparently that was following the T5 Second Survey, which increased “the size of worlds with thin or better atmospheres to match the physics that small worlds can't hold atmospheres”. So I’ll stick to canon from here on.) There’s barely any air (very thin – respirators needed) and no water.

Yet somehow, 26 billion people (mostly humans) live there.

How do we feed Rethe?

How many calories do we need? (I’m just going to concentrate on calories (kcals), in this post. I’m not going to complicate it by thinking about individual nutrients or factors such as processing.)

On average, humans need about 2,200 kcals a day. Men need slightly more, women slightly less, but we’ll use 2,200.

26 billion people, therefore, need 57 trillion kcals each day. Which is 400 trillion kcals a week, or 21 quadrillion kcals a year.

Where is all that energy coming from?

Homegrown

So let’s assume that everything is grown on Rethe (or in-system somewhere), all 21 quadrillion kcals. How much land is needed?

According to Our World in Data, the most efficient use of land is to grow maize. 0.65m2 of maize will create 1000 kcals. (I’m pretty sure that’s an annual yield and is based on an average of numerous real-life studies, so it includes an allowance for variation in yields due to the soil, weather, nutrients and so on. There may be other foods that are more efficient - I haven't made an exhaustive search, but maize provides a sense of the scale of the challenge.)

So a single km2 of maize generates about 1.5 billion kcals, which is a lot. But not enough, not by a long shot. To feed Rethe, we need 13.5 million km2.

That’s roughly the surface area of China and India combined.

Or imagine the sheer grandeur and majesty of the orbital hydroponic farms. They’re huuuge!

Endless fields of maize

And that’s just the area of maize. It doesn’t allow for space for planting, watering, weeding, packaging and harvesting. It assumes the soil is rich Earth-like.

It also assumes that the 26 billion people of Rethe are happy with a maize-only diet. If they wanted a more varied diet (maybe some spuds to go with their corn on the cob), then that would take up more room. (Although given Traveller is an SF game, I assume other delicious plants are available in the Third Imperium that take up no more room than maize.)

Given that Rethe is a desert world with a very thin atmosphere (maybe like the Tibetan plateau, but drier) at TL 8, perhaps we’d better import the food.

Imported food

So let’s import some food: red kibble.

Delicious red kibble

For the sake of this exercise, let’s assume red kibble is a dehydrated nutritious (if not delicious) foodstuff with an energy density of 1200 kcals per 100g. To compare, 100g of salted peanuts contain about 600 kcals, so I’m probably being generous. But it’s the far future, so let’s go with it.

So 1 kg of red kibble contains 12,000 kcals.

We now need to turn that into a volume. We’ll assume that 1 kg of red kibble occupies 2 litres – or 1 cubic metre weighs 500kg. (To compare, according to this website, 1 litre of peanuts weighs 0.62kg, so I don’t think I’m far out, given this is fictional anyway.)

The volume of each displacement ton is 14 m3, which is 7,000 kg of red kibble. That means each ton contains 84 million kcals. (I’m ignoring packaging.)

How many Far Traders?

A Far Trader has a 63-ton cargo bay, which, if filled with red kibble, can provide 5.3 billion kcals.

However, feeding Rethe for just a week requires 400 trillion kcals, and you would need a fleet of over 75,000 Far Traders. Arriving every week.

Another way of looking at it is that Rethe needs 4.8 million displacement tons of red kibble every week, without fail, not to starve.

But let’s put aside the logistics of delivering nearly five million displacement tons of red kibble every week and think about where it’s coming from.

Sourcing red kibble: local systems

Luckily, within two parsecs of Rethe we have three potential food suppliers: Paya, Focaline, and Inthe. (And all the systems have gas giants, which is fortunate as we need a lot of fuel.)

Paya A655241-9

Paya is the closest and has an A-class starport. It looks the most promising – it’s a reasonable-sized world with 50% hydrographics. The wiki describes it as “a garden world.”

However, Paya has fewer than 1000 people living on it (600, according to the wiki).

I’d like to think that Paya has vast robotic farms churning out red kibble, but as it's not classified as an agricultural world (too few inhabitants), I guess that’s not the case. Perhaps the soil isn’t great.

Focaline EA88544-7

According to the wiki, “Focaline is an agricultural world with an ideal environment for producing food from plants, animals, or other forms.”

There’s just one problem – it only has an E-class starport. Even if it could make five million displacement tons of red kibble every week, it can’t get them easily into orbit.

Inthe B575776-9

Inthe is “an agricultural world with a tainted atmosphere but still a near-ideal environment for producing foodstuffs.” So that’s just what we need. Phew!

It has a decent starport and is big and fertile enough (and not too populated – tens of millions) to provide all the red kibble Rethe needs.

The influence of nearby worlds

This shows one downside of Traveller’s planetary creation system: it’s completely random, with no recognition of nearby worlds. Of course, a world’s physical characteristics should be independent of its neighbours – but in the Third Imperium, I would expect the social characteristics (population, government, law level, tech level, starport type) of nearby worlds to influence others.

In Focaline’s case, if it was a wonderful source of red kibble, then I would expect Rethe to invest in a good starport and have shipped millions of workers over (making barely a dent in Rethe’s population but boosting Focaline’s massively) to make sure the red kibble flows uninterrupted.

But as Focaline only has an E-class starport, then perhaps it’s not fertile after all.

(And the same could be said for Paya. If it’s that great at growing things, why doesn’t someone invest in automated farms and a workforce? There's a ready market one parsec away!)

But at least we have a source for our red kibble: Inthe.

In "reality", I would expect Rethe to import food from all three worlds (and elsewhere). But let's go with Inthe for now.

Next time

Next time, I think about cargo and how to ship all that red kibble, and I might even build a megafreighter.

Update: other sources of food 

I posted this link to Reddit and Facebook and it has provoked some lively and interesting discussion. So I thought I’d capture my responses here.

Soylent Green

A few people have talked about eating the dead. Assuming the cultural implications are easily overcome, there is a bigger problem - corpses don't provide enough kcals.

According to Wikipedia roughly 150,000 people currently die each day here on Earth. Rethe has a population 3x Earth's, so that's 450,000 people every day (or about 170 million people a year). Searching around, the most generous reports are that there are about 150,000 kcals in a human body (my search history is... odd). That means cannibalisation only provides 66 billion kcals a day - and Rethe needs 57 trillion! So way less than 1% of the total calories needed.

Underground hydroponic farms

What about underground farms? This place grows salad crops, which famously aren't energy dense. But it's the far future, so let's make some assumptions that a good, calorie-dense crop can be farmed using underground hydroponics.

Let's assume it's twice as effective as maize, grown on Earth, and 1000 kcals needs only 0.325m2 per year.

This shrinks the area needed to "only" 7 million km2.

But wait, we can stack the units! Let's say we stack them in 10 units high. That gives us 700,000 km2. How big is that? Well, that's a little more than the surface area of France.

Except that we probably need to add 50% onto the area to allow for access for maintenance, cropping and so on. That gives us a little over 1 million km2 - so we have to add Germany as well.

So that's indoor farms with hydroponic beds stacked 10 rows high, the size of Germany and France combined. (Obviously, it's not one farm, but hundreds of thousands of them.)

But what about water?

So far I’ve assumed that water is available on Rethe – either in ice or available via comets. How much water do these underground hydroponic farms need?

This article here suggests that a hydroponics system requires 5-7 litres per day per m2. Let's be generous and assume our miracle food only requires 4 litres per day per m2.

I imagine Rethe is good at recycling its water and recovers 90%. How much more does it need?

With 7 million km2 needing water, this means a daily requirement of 4 x 7,000,000 (km2) x 1,000,000 (m2 in a km2) x 50% (recycled) or 2.8 trillion m3 of water per day. Which is a cube of water 1.4 km on each side - every day. (And this is on top of the water needed for drinking/washing/cleaning/sewage/industry and everything else.) On a desert world.

It's that last bit that I struggle with. A desert world. While I imagine Rethe does grow some food, I would imagine much of it is imported.

Update August 2024

Over on Unchartered Territories (here and here), Thomas Pueyo considers vertical farming in detail – and it looks like vertical farming is what Rethe needs. (The limitations that hold back vertical farming here on Earth don’t apply to Rethe – Rethe doesn’t have the luxury of a surfeit of good arable land for crops. And power isn’t an issue, assuming cheap fusion power.)

According to the article, vertical farming promises up to 200x improvements in land area compared to regular farming. 200x sounds rather like marketing hyperbole, but it’s the far future, so let’s go with it. That means we ‘only’ need about 67,500 km2 of vertical farms, which is a little smaller than Scotland. This is still huge, but much more manageable.

Also, over on my post where I talk about Biospheres, Father Fletch pointed me to this discussion about food on Freelance Traveller.