The economics of interface travel
We now know what our space and interface propulsion looks like: Fusion torches, probably using water. What remains to be defined is the impact our technology has on the economy - how much does it cost to transport cargo or passengers?
This is quite important since it arguably shapes most of the setting. For a comparison, just look at real life colonization and economic development, which mostly followed coasts and rivers (i.e. cheap transport). It will also tell us what’s economical to ship - raw materials, food, fabricated goods, luxury goods, or information?
Let’s start with the basic case: How much does it cost to move cargo from the ground of an inhabited planet? For simplicity, let’s assume we’re talking about Earth.
Our Shuttle
Which I will nickname the Cargolifter for now, looks as follows:
| Front Hull | System |
|---|---|
| [1] | Light Alloy Armour |
| [2-6] | Cargo Hold (75t) |
| Centre Hull | System |
| [1] | Light Alloy Armour |
| [2-6] | Cargo Hold (75t) |
| [core] | Control Room |
| [core] | Cargo Hold (15t) |
| Rear Hull | System |
| [1] | Light Alloy Armour |
| [2] | Cargo Hold (15t) |
| [3-4] | Fuel Tank (30t, 15km/s) total |
| [5-6] | Water Fusion Torch (3g) |
SM+7, 300 tons, winged, 165 tons cargo
| TL | Spacecraft | dST/HP | Hnd/SR | HT | Move | LWt. | Load | SM | Occ | dDR | Range | Cost |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 10^ | Cargolifter | 50 | -1/5 | 12 | 3g/22.5km/s | 300t | 180t | +7 | 3 | 3/3/3 | - | $8.75M |
Top air speed is 6,500km/h (Mach 5.3), Air Hnd/SR +3/6
Originally, I had it designed with two ram fusion torches, but they are hugely expensive, costing $60M (!) for two systems. That would have been more than 95% of the total cost. This shuttle is far cheaper, although it cannot hover for an extended time.
Now, it’s time to look at costs. There are two categories of them: Fixed costs (occurring no matter how often the shuttle starts) and variable costs (essentially costs per flight).
These are:
- Purchasing cost (written off over a certain period)
- Crew salaries
- Insurance
- Annual maintenance
- Fuel/provisions
- Regular maintenance
- Docking/berthing fees
where the first items are fixed costs, and the last three are variable costs.
Operations
However, we have to start with operations - how does a flight with the Cargolifter look like?
On the Ground The Cargolifter will start on an airplace-style starport, with runways and loading equipment. There, it will be loaded with a total of 180t of cargo, probably with the equivalent of today’s containers. Judging from the maximum load of today’s Twenty-foot equivalent units (TEU), we’ll see them loaded with six. Let’s call it one hour to load including preflight checks.
Into Space As SS1:37 tells us, we’ll have to spend about 8.4km/s to get to LEO, or 10.5km/s to get to any arbitrary orbit around Earth. This is easily within the Cargolifter’s dV capabilities. SS1:37 also tells us how long we’ll take to reach LEO: Slightly more than five minutes at 3G, or about eight minutes at a more comfortable 2G.
Rendezvous Once in orbit, the Cargolifter is going to meet with either a spacecraft in orbit or an orbital cargo storage station. Unfortunately, SS1 doesn’t actually tell us how to rendezvous. Real-life suggests we either directly launch into the correct orbit, or we have to change to a more eccentric orbit to synchronize orbits. The former restricts us in our launches, so we’ll take the second one and arbitrarily assume we spend 2km/s and an hour on that.
Freight Transfer Close to their target, the Cargolifter is now unloaded by either the target’s infrastructure (robot arms, probably) or by an orbital tug nearby. For inspiration, look for the Panama class tug in SS6:14. Let’s call this another hour.
Reentry and landing Spending the last of its dV, the Cargolifter now reenters atmosphere and glides back towards its spaceport. Again, we don’t have rules for how long a gliding reentry takes, but we have a maximum time: The Space Shuttle took an hour from firing its manoeuvring system to touchdown while spending less than 100m/s. By spending more, we can reduce that, so I’m calling it another hour for reentry and landing.
In total, therefore, we’re going to take about four hours per cargo transport flight, meaning we can guess a comfortable two flights per day.
Now, on to costs!
Variable Costs
Fuel/Provision Fuel is at most 30t per flight, which comes out to $600 following SS1:46. The pilots can eat when on the ground.
Regular Maintenance This is arguably a weakness in the Spaceships series: Either spacecraft have a constant need for maintenance (have workspaces), or they don’t require any. Instead, we’ll look at Transhuman Space, p. 190. Here, time between four-hour maintenance periods is computed as 20/sqrt(price in $M). In our case, that’s 6.8 hours. Let’s call it one eight-hour maintenance period after every two flights, which happen overnight. That means we also have to pay a mechanic. Unfortunately, the system does not give us any cost for spare parts.
Fixed Costs
Purchasing Cost This is $8.75M. Let’s say this is written off over 12 years at 8% (matching SS2:27), which makes it roughly 1% per month, i.e. $87.5K per month.
Docking/Berthing Fees This is supposed to be $0.2/day and ton for longer-duration stays; I’ll assume we have to pay that for the spaceport. This will cost about $2,000 per month.
Crew Salaries We have two pilots, one mechanic, and one cargo master for two hours per day (which we’ll share with other people, either with the freight shipping company or via starport). Let’s call it 2.25 people at Merchant Rank 0, and one at Merchant Rank 1, for a total of $23.8k per month.
Insurance Insurance is about 0.1% of the total value (i.e. $8.75k) per month. Cargo insurance will be covered by the cargo owner.
Annual Maintenance Again, we don’t have numbers for that. However, Traveller Far Trader gives us 0.1% of the purchasing price per year in spare parts (this is regular maintenance), plus another 0.1% for annual maintenance. Both together are $17.5k per year or less than $1.5k per month.
In total, this gives us $600 per flight, and $123.55k per month in fixed costs. With sixty flights per month, this gives us a total cost of $141.55k for 10,800t of cargo to orbit. Let’s call it $15 per ton, $25 if we include handling and other charges - that’s less than 1/100,000th of today’s price!
The Cost of Fuel
Is GURPS’ $20 per ton of water plausible? Is that on the ground or in orbit?
For comparison, let’s look at today’s prices. Drinking water costs something like $2 per ton, delivered to your home. At least where water’s cheap, and you don’t have to construct your spaceport anywhere else. Assuming propulsion water has to be of similar quality, this would mean fuel costs $2 per ton on inhabited planets.
This changes the costs we have calculated above, decreasing them to about $12. Including handling charges, that’ll still come out to about $25 for the end user.
It does tell us something else, though: Since most of your cost is fixed, prices might decrease to less than $1 per ton (or less than $4 if you could also fire people).
Passengers
Modifying the Cargolifter to transport people, we can fit 240 people in there. Assuming operation stays somewhat similar, transporting one passenger to LEO costs less than $10. It’s probably more expensive (we need more people, better transport etc; you can’t just stack people in a warehouse [citation needed]), so we’ll call it again $25 per person.
Fuel
Fuel itself can mostly be treated as cargo, except with significantly lower handling charges: You attach a hose to your spacecraft and wait. Including cost to buy the water, we can now actually use GURPS Spaceship’s numbers and charge $20 per ton in orbit.
Summary
So, it will usually cost $25 to ship a ton into orbit, the same for a person (who, ideally should have organized some place to stay in orbit, otherwise it’s going to be a bit cold), while fuel in orbit of an inhabited planet will cost $20 per ton.
