I'm just plain out saying that the anti gravity field that makes both M drives and J drives possible doesn't work on an object over 7.5K dTon in volume. 75.k dTon is one of the cut points in MgT capital ship designs, so it's a fine upper limit. In theory you could build bigger ships with no A/G fields, but then you have the problem of using reaction drives, with their huge appetite for fuel, and the issues humans have with long term 0 G. Defenders already have a huge advantage due to not needing jump drives or their fuel.

On Saturday, September 13, 2014, Richard Aiken <raikenclw@gmail.com> wrote:

On Sat, Sep 13, 2014 at 1:10 PM, Greg Nokes <greg@nokes.name> wrote:

I've never come up with a good technological reason to limit ship size other than jump fields or gravatics, but both of those have unintended consequence of the defenders have an advantage.

NOTE: I also like small ship Traveller universes.

Suggested Limiting Factor: The structural integrity issues of larger ships.