Suppose the world is fairly grounded in real physics (I consider Star Trek relies on way too much space-magic and overly optimistic projections of human accomplishments in the 23-24th century). The Alcubierre drive/warp field is still out of reach as the necessary exotic matter is yet to be discovered.

Humans have colonized habitable planet(s) discovered orbiting Alpha Centauri and Barnard's Star. These were initially explored with probes, then with small teams of manned solar-sail missions by NASA, and eventually an international collaboration recruited sufficient volunteers for genetic diversity willing to devote their lives to colonization. This trip likely would take 20-40 years by solar sails, so it was not entirely impossible to find volunteers who want to pioneer a new chapter of mankind, and not entirely impossible to get the minimal funding required.

It has been a few hundred years. By my estimate an initial population of 100 with non-monagamous couplings under ideal conditions with present-day life-expectancy could populate to just shy of 1 million people after 300 years. Naturally, they would form their own local government structure, and grow detached from Earth's space authority.

Let's assume further that perhaps Pre-FTL spaceflight is further advanced and travel time between Alpha Centauri/Banard's star and Earth takes about 10 years. What forms of regular commerce, travel, or communication at scale would be feasible in this case?

Initially I was trying to analogize with The Silk Road between Rome and China, which I believe takes minimally 2 years to traverse back in ancient times. (Marco Polo spent 4 years, likely exploring/making stops on the way) but I realize the conditions are very different. Space is vast emptiness, and in this hypothetical future the distant civilization isn't some foreign/unknown kingdom, simply distant fellow humans and a planet that was once home to their ancestors.

As you answer, feel free to consider what life, economy, communication might look like, and to explain the motivation for the commerce, travel, or trade you think would arise, such as the commodities to be sent, or how the travellers might use the time as they pass through that vast emptiness of space.

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    $\begingroup$ Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. $\endgroup$
    – Community Bot
    Jan 1, 2022 at 18:31
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    $\begingroup$ What to do while traveling in space? Increase the population by 300% $\endgroup$ Jan 1, 2022 at 19:17
  • $\begingroup$ You need to look carefully at the time dilation you're dealing with on those transits and decide on your measuring reference frame for trip time before we can say anything about anything. Then you need to focus on one particular and answerable question at a time. $\endgroup$
    – Ash
    Jan 2, 2022 at 4:52

7 Answers 7


Energy Economics (highlights)

To move something from point A to B at interstellar distances requires velocities close to the speed of light. For example, to get six light-years away, at $1 \over 3$c takes eighteen years.

The minimal energy required to accelerate and slow the load is

  • ${mc^2}\over{\sqrt{1-{{v^2}\over{c^2}}}}$ or
  • ${mc^2}\over{\sqrt{1-{\%^2}}}$

Some examples:

  • Travelling to Alpha Centauri at 10%c will take 40 years and require a minimum of 2% of the cargo mass to be fuel.
  • Making the same trip at 33%c will take 12 years and require 22% of the cargo mass to be fuel.

Rocket Equation

Absent a kinetic energy pump like emm drive, or boost drive, the cost to move a payload is further limited by the rocket equation $dv = \ln{M \over m}$, and assuming exchaust velocity is close to the speed of light and dv is expressed in a percentage of light speed.

  • A 4 ly trip at 33%c will require about 29% of its mass to be ejected as propellant (which hopefully includes whatever is being burnt for power)

Technology Efficiency

As a tax, there are the theoretical limits to efficiency of certain power technologies : fusion will generate 7 MeV per thousand MeV of hydrogen mass (about 1%), antimatter could potentially be a 100% efficient technology-- but that comes with concerns about safety.

Solar Sails

Per this article, solar sails are limited to an upper velocity of about 0.2% c. A 4 ly trip at this speed will take 200 years.

Reliability of Equipment

You can always trade energy for time, but the upper limit being when enough damage is done by time, radiation, heating and cooling that critical failure is imminent.


The density of space is estimated at 1 atom per cubic centimeter. A single hydrogen atom at rest in space being hit by a vessel traveling through interstellar space at 33% c only delivers a few billionth's of a joule in damage, but it adds up over 9,460,800,000,000,000 kilometers per light-year. A throw-away ice shield will undergo meters of erosion in a single trip.

Economic Models

That all being said, what are some economic models that make this work, anyway?

Highway 66

We keep discovering dwarf planets further from the sun. Depending on how flexible we are with this arrangement, it's possible that in a similar way that the American highways were dotted by tiny towns, you might have trade routes that are, individually, a few hundreds of AU between stops. At one gee, a 100 AU trip would take about one week each way, making it a very good fit from a crew and logistics point of view.

Goods and information eventually make it down this highway, with a host of middle loaders and merchants trading hands along the way. Each colony taking enough off the value of material floating through to keep the lights on and the "trucks" running.

Data Economy

Another alternative is a data economy. If you were to built a communications relay of satellites streched 100 AU apart from one another, you'd be able to create an interstellar data trunk for the cost of about 650 relay stations per light-year.

There's a lot more to a data economy than just what is novel on Planet A or Planet B.

In fact, there exists an enormous backlog (just on Earth) of information that has never been properly examined. Examples : bits of ancient pottery, unidentified or untranslated writing, bones, genetic sequences taken of possible new animals, environmental DNA collection searching for new species, mineral surveys, and so on.

The backbone of the interstellar digital economy may be sending large batches of data light-years away where cheap idle minds will work on it and return the most interesting results.

Adding to this backbone could be flashy stuff like novel materials, biotechnology, art, and other innovations.


Our solar system is situated inside a large natural megastructure : a magnetized tube of ions maybe 1,000 light years long. On Earth, a phenomenon called tropospheric ducting allows radio signals to bounce beyond line-of-site and be clearly received nearly on the other side of the Earth.

It's possible, likely even, that there are multiple locations that are very interesting and that particular locations in the large volume of space between stars are the best viewing spots for the phenomenon. Like Mt. Mauna Kea or Greenbank Observatory, these could be remote "off-the-highway" locations that exist exclusively for the purposes of research.

Exotic Material Extraction

There may be a whole other periodic table (or many) in the universe. Some of these materials, such as dibaryons, are predicted to exist in minute concentrations between stars. Shipping vessels, like a paper towel, will accumulate a good deal of this interstellar material during their trip. Sacrificing the hull for exotic material extraction might be a way to recover some of the cost of a trip.

But exotic material need not be as exotic as new atoms. As this person discovered with magnetic locking at room temperature, macrostructures of minerals can do some amazing things. Using the magnetic locking example, imagine a mineral like opal (consisting of tiny equal-sized spheres) that possessed this magnetic characteristic and stably floated in air at certain frequencies.

It's reasonable to expect new minerals made of the same things we're familiar with, but with useful characteristics of their own. Some of these may be industrially worthwhile enough to merit the cost of freight.

Or, a miner could merely find an asteroid with a high concentration of something incredible rare in the solar system (osmium, for example).


In Search The Sky (Pohl and Kornbluth, 1954) inter-system commerce is handled by oligarchs running multi-generational trading firms. Distances are too great for useful radio communication. An oligarch (or consortium) invests to build and send a Longliner to another inhabited system in the hope of a return trip that brings an enormous windfall to their descendants.

The longliners carry (essentially) intellectual property, usually in the form of goods: Books, plays, music, recordings, games, seeds, machine designs, etc. There's no way to know the demand at a different star, so the best cargo to send is pure guesswork. Upon arrival, consigned goods ("Deliver to Haarland Trading Company, Halsey's Planet") are delivered to the appropriate oligarch for monopoly reproduction and sale. Unconsigned goods (and exclusive rights) are auctioned...the auctions are dominated by the oligarchs.

Unfortunately, the system is unstable. Turns out folks don't particularly like oligarchies or the lack of social mobility that they imply. Local politics or economies sometimes overthrows a trading firm (or the entire oligarchy) before returns on the investment arrive generations later. Then local customs determine how the booty is divided up. But if inhabited systems don't invest in building and sending new Longliners, commercial exchanges of any sort grind to a halt.

  • $\begingroup$ Thanks for sharing this! I think that's a great perspective, I can imagine ancient pioneering merchants did much the same when exploring new worlds; carry loads of assorted cargo and hope for the best. Possibly some entrepreneurs strike it big and some fail. $\endgroup$
    – user93359
    Jan 1, 2022 at 20:06

Communication will look like some form of RFC 7122. There may be other RFCs that fit. Look for Delay Tolerant Network

This will allow the existence of passive communication protocols in your trans-steller network. sg SMTP (email) and streaming

Interactive communications (Zoom meetings. Web pages) will require FTL Communications capabilities to handle effectively.

Copies of databases? Those can use DTN no problem.

However, the data will be 4.4 years old (alpha centauri) and 6 years old (Bernard's Star) from Earth's data.


I think it would be similar to the trade system between the colonies and mainland Europe during the 1600s and 1700s. Messages could not travel faster than light given the technology level, but could travel at the same speed as the ships which carry humans with 100% integrity. The economies would be mostly separate given the vast distances, with commodities like plants and animals being carried by large ships in order to make the long journey economically feasible.

Colonies seeking to terraform planets would need livestock and animals, and plants to feed them, in order to make an ecosystem even possible. Colonies mining asteroids would have extra raw materials or nonperishable goods that could survive the journey to another star. For example, not all asteroid belts contain the necessary amount of fuel for starships or the needed iron and water for construction. Colonies with excess would trade for other goods or labor with colonies that needed those resources. Maybe some specialize in food production or cloning of livestock using energy from a nearby star. Space stations would essentially be specialized to perform one job while waiting to terraform a planet.

Terraformed planets could be self-sufficient for all these except for starships and other technology that needs vast infrastructure to produce.


No. It is an example of putting square peg in a round hole.

It is good you noticed some problem on your own, how Silk road can't be transfered on to this situation.

Exotic materials, if you like to be harder than Star Trek - it does not work as well. All exotic materials(I know elements) are in periodic table of elements, most of them present on this planet and in this solar system, all stable ones are present on this planet.

Your next step is to realise that the whole model is skrewed up, it does not fit space the same way as Silk road does not.

One of the ways to fix things is to be more bold in how to do that other star system move, a billion people depart as an example, and it is possible, and how can it be posible you can see if you dump old cliches and look at how big the solar system actually is, and how it can provie resourcs required for such, billion ppl expedtion, with ease.

What is traded, or may be traded is information, science, technologies. And both sides can be relatively on equal grounds, having some K2 size supercluters for working that science and technology. So relationships of a colony and mainland can be one of cliches to be dumped.

What you realy need, to be harder, is to figure out the scale of resources in solar system, which are available to us. If you see it - you will reconsider the purpose and goals and means of expanding to closest star systems.

  • $\begingroup$ Thanks for the answer. I think between information/technology and assorted commodities "on pure guesswork" referenced by another answer are great ideas, despite the long distance and generational payout, what most likely will happen is financial institutions will use them in speculative trading via options and futures for decades until the cargo ship returns, so these are not simply idle assets but actively traded and fluctuating in value. $\endgroup$
    – user93359
    Jan 2, 2022 at 18:50

I will focus on economy since communications cannot be changed as its presently based on the speed of light.

Initially, the purpose of colonizing these other stars is to ensure the survival of the human race and a bit of adventure thrown in for good measure.

Financially, there is no real reason to set up colonies in these far flung locations. Any resources you need can be found in asteroids, comets or the outer moons. The reality of sending so few people out there and hope for a return on investment in your great grandchildren's life time is unrealistic. In the mean time, Ceres, moons of Jupiter, Saturn Uranus and Neptune will be colonized and mined out to the highest extent, never receiving an ounce of material from Alpha Centauri. The entire time, more and more colonists will flood to the other worlds in search for adventure, accelerating when travel times become shorter.

Fast forward over 300 years. With gradual immigration and rapid birth rate (people would be encouraged to have plenty of children, see the culture on Mars from The Expanse) the population of each system would be in in the millions.

The Population in the Sol system is probably at the breaking point. Earth is becoming uninhabitable due to over population and excessive human activity. humans are migrating to Mars faster than habitats can be built. Most asteroids are depleted. Minerals once extracted from the moons to fuel the Earth economy are now fueling the growing moon economies.

Sol is now being starved of resources. It is now financially feasible to transport raw materials from the colonies to Sol. The last available resources would then be used to build massive transport ships to ferry more colonists over, with large quantities of finished goods and space station components. These ships would be manned by families, if not whole cities of people, developing their own culture on board to justify being away from human society for so long.

On their return, they would return with millions of tons of raw or slightly refined materials to fuel the Sol economy for the year. They would need to launch these kinds of ships at least once a year with the expectation they wont get a return shipment for ~20 years.

However, after another 100 years or so, these colonies would in turn develop robust economies, taxing their local supplies to fuel their desires. This would, in turn, cause Sol to once again wither away, unless they institute some draconian measures to keep the colonies in a perpetual under developed state.


This could go a few ways. The first is by having trading done autonomously. The only real information about tech is that this is Pre-FTL.

  1. If CryoFreezing Exists: They could hibernate the passengers for the trip, except for a few select Technicians, the Captain, and People in charge of Communication.

  2. If Trading does not require Humans Basically, no humans are onboard the ships. These could carry cargo with a programmed path, and that could also carry messages.