There's lot's of ways that an Imperium could get the income required to support the sorts of ships required to defend it from all the sorts of ships that other polities would build.
(that's what, IMO, actually determines the size of the IN's ships)
APlummer's scheme could work but I always had the feeling that he first decided that there *must* be gargantuan merchant ships cuz' that's what he wanted & then came up with a way to explain why.
An alternative scheme would be that membership in the 3I, or any polity for that that matter, is not free.
Fees/taxes must be paid or you'll be on your own, as some worlds choose to do.
(There are systems in the 'Marches that have changed from 'Imperial' to 'Independent" & back)
There are mentions in CT that the sector govs have taxing power (The 'Children of the Marches' 'Lightening-class ship was essentially financed that way, even though it supposedly was by contributions) or maybe "the power to raise funds" would be more accurate, so I don't see why both lower & higher levels couldn't also have that ability.
It really just comes down to deciding what you want in your TU & then coming up with a rationale. (My personal preference is to use the original set CT LBB's for the merchant fleet)
Which kinda' describes what MM did back in the beginning when he first pitched the idea of 'Traveller' to the others at GDW & they said, "Go for it!".

Don't forget that in 'MM's Traveller" (T4) 'Pocket Empires' book, it mentions that after Cleon est the 3I many other wealthy families looked at it as a sort of 'vanity project' where his vast holdings where actually what became, in fact, the 3I's government infrastructure. There's mention of "now all contracts will go to his family's companies so maybe we should go find someplace where we can do the same thing he did" <sic>. And, PRESTO!, they're off to get their own (pocket) empire.
While I'm not sure how big the 3I's precursor polity was, I suppose it could be still classified as a 'pocket empire' altho on the high end of the scale, when it was first 'declared'.

p.s. I've always thought of a 'pocket empire' as generally subsector-sized but I suppose one that controls a whole sector could still be called that altho, IMO, it would be a rather large one.

From: Bruce Johnson <xxxxxx@Pharmacy.Arizona.EDU>
To: "xxxxxx@simplelists.com" <xxxxxx@simplelists.com>
Sent: Sunday, January 6, 2019 11:53 AM
Subject: Re: [TML] J3

Yes, in terms of economics the OTU simply does not make sense, in many ways.

If you're restricted to small ships, and interstellar trade is essentially a rounding error as a fraction of total trade, they why is there a need for an Imperium? Where does the money come from to support the gargantuan naval fleet, (plus scout service, marines, and other ancillary branches) the OTU requires? And why?

My opinion has always been that PC-level ship operations are running in the backwaters, 'small package' trade and such. fulfilling the 'tramp steamer' kind of traffic.  Building the kind of interstellar infrastructure that exists costs several orders of magnitude more that the trade is worth. It's akin to building the modern ports of Rotterdam, or  Long Beach...in order to service the equivalent of the cross-indian ocean dhow fleet between the Arabian Gulf and India. ( This episode of 'Michael Palin Around the World in 80 Days' give a great glimpse of that world. https://www.dailymotion.com/video/x1z37k7 )

Way back in the MT days, Alvin Plummer wrote up a great post about the kinds of ships that the Imperial Navy WAS built to protect. http://www.u.arizona.edu/~bjohnson/Majesta.html I think it neatly supports the Large IN /Large Volume of trade model with plenty of space for PC-scaled ships to operate in, because it essentially functions as a backdrop, nothing more; the world of the megamerchants and the world of the Free Trader Beowulf never really intersect; but it supplies a justification for the vast infrastructure that exists.

small ships + little trade + Imperial Navy makes about as much sense as the British Navy being built up to the height of it's strength in the 18th and 19th centuries, if faced no threats from any great powers and there were few if any merchant ships flagged in Britain, and almost nothing was traded between it's far-flung colonies and home.

What is the point of such a huge expense? The imperium faces no serious threat to it's existence (the Zhoodani have never penetrated farther than a subsector or so, and the Solomani likewise, never a threat to more than a subsector.

If commerce is so low level that it's managed by a relative handful of 200dt ships, where does the money come from?

--
Bruce Johnson
University of Arizona
College of Pharmacy
Information Technology Group

Institutions do not have opinions, merely customs

________________________________________

From: xxxxxx@simplelists.com <xxxxxx@simplelists.com> on behalf of Tim <xxxxxx@little-possums.net>
Sent: Friday, January 4, 2019 11:36 PM
To: xxxxxx@simplelists.com
Subject: Re: [TML] J3

As I stated in a previous post, I believe this should be a consequence
of Traveller technology.  But according to canonical price lists and
wages, it isn't.  Despite the advanced technology allowing automation
and nearly free energy, basic material goods are still just as
expensive as on today's Earth, or in some cases even more so.
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