There were 3,300 starships in GDW 2300AD, of which about 2,000 were commercial trade ships.
By the Nyotekundu SB, 12 ships per day entered the system, which sets the rate at which starships from the French Arm reached Earth, ca. 4 per day. Given the much smaller economic weighting of the other arms, probably on the order of 5-6 ships per day call at Earth from the colonies.
If these were all (GDW) Anjous, then about 165 million metric tons on imports per year is coming into Earth. If the average long-range trade ship is larger (bigger than a Metal, which is an old ship) then a billion tons is imports and exports is quite possible.
In 1975, global trade excluding oil was about 1.4 billion tons shipped annually. The volume of trade is thus fine. It just doesn't resemble globalised trade, because there are gravity wells involved.
If you want more trade, the economical way is to up the size of the transports. Bigger and slower transports work better, and we can easily move a million tons on one*, and 10 million tons on a fusion reactor driven ship. We can easily carry high trade volumes on relatively small numbers of ships.
* French Ville (City) class Nuclear Modular Carrier
Original date of design: 2251
First example laid down: 2252
First example completed: 2254
Fleets in service: France (mainly French government registry)
Number in service: ca. 50, named after French cities (Ville de Maestricht, Ville de Eindhoven, Ville de Bonn, Ville de Gand, Ville de Geneve etc.)
The Metal class modular carrier was a huge success, but the conventional MHD turbine meant the vessel had to make halts at essentially every outpost or colony on her route. This was fine for exports from Tirane, but exports from the French Arm were not as efficient as possible. Thus a nuclear powered vessel was desirable.
The question was whether to make the vessel faster or carry more. Whilst for some goods, faster delivery was an advantage, for ore and grain, there was no advantage. A deep load speed of 0.4 was acceptable, that being the deep load speed of a Metal. Given this speed, 432 standard modules of ore or grain could be carried, with nearly a million tons of deadweight. The modules have been designed to stack in rings of 9, and upto 48 rings were thus carried in the aft stack.
Ville ‘s were designed to go from Earth to BCV-4, a logistical hub, and return. A round trip, carrying less dense manufactured goods on the outbound leg, and deep loaded with grain and ore on the return leg, takes around six or seven months, and so a hamster wheel spin habitat was installed. Loading and unloading is relatively quick, due to the modular system. At the logistics centres at both ends, modules are prepared and loaded onto the stack by both the manipulators at the logistics centres, and the pair of grabbers carried. The grabbers also facilitate cargo manipulation outside ports.
From BCV-4, modules for further up-arm are transferred to smaller vessels, and modules containing good from further up-arm are loaded.
With not quite a million tons of deadweight, the Ville is now regarded as a relatively small modular carrier, and the earliest ships are being retired at the end of their reactor lives, and the lead vessel, the Ville de Maestricht, was officially retired in 2299. The Ville de Eindhoven, Ville de Bonn and Ville de Gand are due to decommission in 2300. The latest ships being built have fusion reactors and can carry 10 million tons of deadweight.
Notes: In combat, when hit the shot may hit the “tug” or the stack. If the shot is from the forward aspect, it automatically hits the tug, and for the aft, it automatically hits the stack. For lateral fire, role d10, on a role of 10 it hits the tug, and for all others it hits the stack. Stack hits destroy one module and its’ cargo.
Crew: 29 (10 bridge, 14 engineers, 4 cargo specialists/ grabber operators and a medic)
Performance Characteristics
Warp Efficiency: 0.40 deep load (432 modules with sg3 ore/grain), 0.82 light load (432 modules with sg0.3 manufactured goods), 1.52 unloaded (432 empty modules) and 3.58 bare (no modules)
Power Plant: 15 MW fission
Fuel: nil (incidental fuel carried for the grabbers)
Range 7.7 ly
Mass: 1,350 tons bare, 17,550 tons empty
Cargo Capacity: 742.5 m3 per module (upto 432 carried)
Comfort: 0
Life Support: 30 for 180 days
Construction Cost: MLv28.19 bare (i.e. exclusive of modules and grabbers)
Hangars: for 2 15m3 grabbers (launch 1 per 3 turns)
Ship Status Sheet
Movement: 1 (loaded)
Screens: nil
Radiated Signature: 5
Reflected Signature: lateral = 14, radial = 6 (with 432 modules)
Profile: lateral = +4, radial = 0
Targeting Computer: 0
Armour: 0
Hull hits: main “tug” 6/3/2
Power plant hits: 20/5
Armament: none