Ratio of passengers to cargo on colony flights

Question

Sci-fi scenario with flights to a colony planet. Tech level is otherwise close to today (e.g. no androids or desktop nanofactories). Planet is quite similar to Earth, so e.g. agriculture works, you can grow wheat and raise cattle.

What would be the likely/optimal ratio of passengers to cargo transported to said planet?

Let's say it costs as much to transport one passenger as five tons of cargo, and available transport resources could per year bring 10,000 colonists and 50,000 tons of cargo - that would be splitting the available resources equally.

At one extreme, clearly there would be no point hauling 100,000 tons of cargo and nobody to make use of it.

At the other extreme, you don't want to put 20,000 colonists on another planet with nothing more than carry-on luggage; even though it's a nice habitable planet, they will still need tools and supplies.

Does the above even split of one colonist per five tons of cargo make sense, or can we reasonably say each person would need more cargo, or less?

The closest analogy I can think of is the colonization of the Americas. (The main difference being that in the sci-fi scenario, there are no natives.) What was the overall ratio of people to cargo transported from Europe to America during that time period?

Answer 1

Just how earthlike is the planet? Assume it is a shirtsleeves environment for humans, at least in the nice spots ...

• Assuming dehydrated/dry food, with a few supplements, it should be possible to live on less than 1 kg of food per day. Double that for sundries like toilet paper, aspirins, or new socks. 730 kg for one year. (If the world is reasonably Earthlike, the growing seasons should have about the same length.)
• 250 kg per person should be plenty for a sturdy all-weather tent, camping cot, sleeping bag, stuff like that.

So with one ton, your colonist can live for a year.

Say the colonists want to clear fields, put seeds into the ground, and get a bountiful harvest.

• The interior of a standard athletic track is one hektar (ha). Modern grains might required 100 kg of seed for 1 ha, and yield several tons of grain on Earth. Your alien world will have unknown pests and other calamities.
• The figure assumes modern mechanized agriculture.

Still, an off-the-cuff estimate suggests that your colonists should be able to feed themselves with starchy staple foods after the first growing season, if Earth grains will grow. For the second year, the colonist will need much less than a ton -- perhaps some vitamin or mineral supplements, and the occasional imported chocolate bar from home.

Note that I haven't suggested cars, or tractors, or aircraft. Decide on the ratio of jeeps or tractors per colonist. A well-supplied colony could have close to one vehicle per colonist. A bare-bones colony could have less than one vehicle for every 10 or even 100 colonists. Say an average farm has 200 workers and perhaps a dozen vehicles: a few tractors, a few trucks, perhaps a combine harvester.

An off-the-cuff estimate says less than 1 ton of vehicle per colonist. How much fuel and spare parts per vehicle? Unless they will find a way to make fuel locally, bringing vehicles makes no sense at all, so it will be just a little initial stock, until the oil wells and refineries, or solar farms and electrolysis systems, or soyfields and biodiesel refineries are set up.

Other workers will require their own "tools of the trade." Machine shops, hospitals, whatever. Assume that those, too are 1 ton per worker.

That suggests a ratio of 2 tons of cargo for each colonist.

But I made some very back of the envelope estimates here. What is the goal of the colony? Become a self-sufficient technological society as fast as possible? Become a genetically healthy human society as fast as possible? Living room for the crowded masses of the homeworld?

I think anything from 1 ton per colonist to 10 tons per colonists can be justified.

Answer 2

Overpack.

At one extreme, clearly there would be no point hauling 100,000 tons of cargo and nobody to make use of it.

But that would make a fine scifi scenario, and give some good asymmetric energy to the narrative.

http://www.foxnews.com/politics/2014/04/04/billions-in-equipment-supplies-being-left-behind-in-afghanistan.html

Ultimately, some 170 million pounds of vehicles, equipment and "white gear" -- that's all the non-military stuff that contractors have been using, like furniture, generators, chemical toilets, air conditioners, non-classified computers and more -- are being left behind. What they cannot, or will not, donate or sell to the Afghans or to allies is being destroyed so that it doesn't rot in place or fall into Taliban hands. Some reports indicate that most of the $6 billion worth of materiel will indeed be sold for scrap or thrown in the junkyard.

Modern US military endeavors come with an excess of materiel - given the enormous cost of the endeavor overall and difficulty replacing individual colonists, having any impediment due to lack of equipment is pennywise poundfoolish. So too your colony. Those behind it overpack. Unmanned cargo ships have been coming for years and parking themselves in orbit or on the surface. They do not want their colonists to starve, or struggle for lack of something that is easily provided.

The huge excess of stuff available to the colonists could have shades of military contractors providing loads of whatever they had at top dollar. It might be unusual stuff, or stuff with no practical use on the planet in question.

Answer 3

With the colonization of the Americas, there were cargo ships and passenger ships. The cargo ships delivered nothing but cargo, once the settlers became a viable market.

I suspect that, in any colonization venture into space, even with generation ships, there would be separate cargo ships from the passenger ships. Cargo ships are much more economical, requiring no life support, for instance. They would be launched at the same time, on the same trajectories. at the same destination.

They would be scheduled to arrive roughly at the same time as the passenger ships.

Thus, the passenger ships would be required to take only what was necessary for the trip, and a bit extra to bridge the gap until the cargo ship came.

EDIT

However, there is a different model to that of the colonization of America. There is also Australia. It was established as a not-for-profit penal colony, with no expectation of return (literally and economically). Such a venture would have a different ratio of cargo vs passengers. Creature comforts of the 'settlers' would not necessarily be a consideration, nor would 'development of the profitability of the colony'. Bare necessities only.

Answer 4

I suspect the ratio would change as time passed. Early flights might have more cargo and less passengers, and those passengers being highly specialized and trained to setting up the colony - agriculture, manufacture, building. As things get established, passengers would increase as less materials are needed from the home planet.

That's assuming said planet is close enough that more than one ship is planned. If you're thinking of a more of a "drop the ship and cross your fingers" strategy, I think you'd still have a very carefully chosen team of base staff, with a larger number of laborers and settlers. I'd lay odds there's be no children at all, and depending on the length of the journey, rules against having any on the way. The final breakdown of staff would likely be based on the climate of the planet - what's available as opposed to what would be needed quickly, and what would need building and maintaining.

In either case, I'd bet an initial team would be no more than about 500 people - more than enough to get a colony going, but not so much to put a strain on initial resources. And I'm assuming that a great deal of that initial shipment is building material - prefab housing and the like.

Giter makes the good point about air and water - using your analogy, I suspect a great deal of those early colonists' supplies were used (up) on the journey. I'm guessing that's why you approximate such an expense in carrying a passenger?

Answer 5

I don't think you could ever bring enough cargo to support the colonists. At sub-light speeds, the only viable way to feed your passengers is a self-contained ecosystem.

What cargo you do carry would be a small amount of emergency food, hard to make engine parts and backup seeds & embryos in case you have an ecological disaster mid-flight.

Answer 6

Cargo shipping is always going to be a cost/reward balance - at some point, for almost any possible cargo, it's going to become more viable to produce the cargo at the destination than it is to ship it across. When it comes to interstellar travel, it's likely that the costs for shipping will be very high indeed. In all likelihood, you'll mostly be shipping machinery and similar hi-tech products to enable end-user production and possibly a few ultra-high-end goods, if you have any uber-rich colonists (how much might a billionaire pay for a truffle?).

The exact numbers though are going to depend on how the travel works in your universe, why the colonies have been established and how far away are they. A good start might be how isolated the colonists are - if it's a one-way trip then that suggests difficult travel. Will they be holidaying back on Earth? Then it's probably pretty simple to get between places and trade will be much more likely.