Now this is a real issue, although I think your numbers are a touch off. A million seconds is 11.5 days, frex.FrankTrollman wrote:No. the only alternative to jousting matches in the void between worlds is "no deep space combat period." Uranus is 3 trillion meters away. That's Trillion, with a T. Now that's not a huge problem with a constant acceleration drive - at 1G of acceleration you get there in 24 days. It's fine. And I don't have a huge problem if you have some sort of science fiction bullshit where you warp to top speed and maintain it for a few weeks. But think about that for a moment - you're looking to spend a million seconds traveling three trillion meters! That's an average speed of about 3 million meters per second - one percent of the speed of fucking light. That's over Mach eight thousand. The idea that you could do anything in terms of meaningful naval maneuvers and broadside exchanges to someone when you're both traveling at that speed is completely ridiculous. A 1 degree difference in vector would put an extra 52 kilometers between the two vessels every second.
Let's assume a ship that travels at 3 Mkmph, which is ~0.28% of lightspeed. That'll travel the average distance from Earth to Mars (~225 Mkm) in ~75 hours/3 days. It will also travel the average distance from Earth to Uranus (2.5 billion km) in ~833 hours/34 days. That seems perfectly adequate in terms of relative travel times between very near and very far destinations, but the issue of combat at such speeds is still problematic.
Now, I could get into a thing where ships that mutually wish to engage slow on approach to fight, ships that mutually don't wish to engage... don't engage, and when one ship wants to engage and the other doesn't they get into a chase where their relative velocities are probably much more reasonable. But I'm not going to, because 3Mkph is actually still stupidly fast and I don't want to deal with the attendant issues.
My new thought is to give up on solar empire stuff, set the DMD speed limits super low, and have an FTL method be the preferable means of getting around even in-system.