Nob Akimoto wrote:
I hope you meant 5km in circumference.
Because 5km in diameter...well that would be an absurdly large ship.
It WAS an absurdly large ship. That's the whole point: it may have broken (and held) all Federation speed records for over a century, but its transwarp drive was so huge that it could never be a practical exploration vessel. The few practical transwarp vessels weren't quite as large, but the use of exotic materials in their engines and drive cores made them absurdly expensive, maintenance intensive, hard to repair and impossible to replace. They were on the raggedy edge of being useful, and Starfleet barely tolerated their continued existence.
Of course, even that would not be without precedent, considering Terra Prime managed to install a warp drive on the Orpheus Mining Colony without anyone knowing about it.