Tech Level D

Tech Level D is the technology level at which the Barnes-Gutierrez Hyperspace Engine was developed, so it was the tech level of early twenty third century Earth.
The B/G engine is in reality a spin off of gravity control technology. So it should be no surprise that contragravity use of the B/G engine allow for both the suspension of large structures, even cities, and artificial gravity independently of a massive body.
Scaling of B/G technology to both small extremes and large extremes turns out to be no more challenging than was scaling the steam engine, resulting in bullet sized B/G missiles and floating cities within decades of their development.