I know, Battletech & economics, make your Sanity rolls at the door please. I was thinking about Traveller and thought about whether the trading as described in BTU for commodities could work for a trader character.
I thought about the known situation of Kaifeng (mass exporter of rice) to Sarna (known Agricultural Dependence of D), and known to be dependent on Kaifeng for food due to the Capellan novels since that was what gave SLT leverage over Sarna. Thus we have an economic situation where the details are concrete.
Assume:
It is 1 jump to travel. 10 burn-days for Kaifeng and 12.01 for Sarna (22.01 burn-days used, but rest of trip time rounded up to 1 month of 30 days for ease). Assume a Mammoth Dropship, wholly owned. I assume purchased fuel at half standard SO pricing since civilian shipping to large starport and thus likely to buy fuel rather than make their own. Rest of calculations and maintenance costs used Campaign Operations and known data on the Mammoth.
Costs:
Crew salaries 56,200
Payment for 1 jump 50,000
Spare parts consumption 780,000
Fuel 1,381,678
Total costs: 2,267,878 C-bills
Assuming used cargo:
Spare parts of 1% mass 520 tons
30 days consumables for crew and bay personnel 35.25 tons
Available cargo: 36,693.25 tons
Total revenue needed to cover costs: 61.81 C-bills per ton
Converting C-bills to 1999 USD then converting to 2016 USD equates to about $264 per ton of rice. The monthly price index for rice in RL in July 2016 was $456 per ton.
So economically, it seems it could work for a trader character. Granted I had trouble finding the cost for crew consumables, and I did not assume anything like a mortgage on the ship, or a profit margin above and beyond costs. I suppose on a critical shipping route like this, the state would take a hand and might offer subsidies or use state traders to ensure steady supply of food to Sarna.
At 400 grams of rice per day (per World Food Programme), that Mammoth would be able to feed about 1.5 million people for 2 months which is roughly the round trip time to get back to Kaifeng and back to Sarna. Sarn had a population of 3.534 billion in 3067, which assuming its Agricultural Dependence of D means 60% need feeding then 2.120 billion need imported food. That one Mammoth is a drop in the bucket and would need to keep shuttling endlessly back and forth.
This also means that conquest of any such highly populated food dependent world requires the capture of the merchant fleet feeding it, or the redirection of one's own merchant shipping, else the world crashes into mass starvation. I would imagine most of the time, the merchants would flee at the first sign of combat and then others would avoid jumping in, making starvation a much more likely outcome.