Up Port Alpha is built more or less to Traveller TL 9. The major difference between CT's tech level progression and my ATU's technology is that reaction drives are still used, at least by Terrans. Several sublight expeditions have been launched to Saturn and the outer worlds as well as the Oort cloud (they're very good reaction drives.) The port was built as a joint effort by the UN and the Lunar Republic. The Republic feels very strongly about weaponizing space and further antagonizing the Asteroid Coalition. Earth is determined to defend itself and its lukewarm ally.
Alpha is 2000 displacement tons. 1500 tons is in a ring 20 meters in radius rotating at four revs per minute. This spin gravity takes some getting used to. The ring is 6 meters thick and 35 meters wide. It contains most of the space port systems. The ring is mounted on a central shaft that doesn't rotate and contains two shuttle (95 ton) hangars and two 50 ton berths for the two cutters. A smaller 15 ton berth is for miscellaneous couriers that come calling.
The shaft also contains two lab/workshops that are capable of building a courier in a few days. The tip of the central shaft has a 20 ton docking arm that currently holds a 100 ton asteroid (more on that later) in a cargo bay.
Alpha's reaction drives allow it to thrust at 1 gee for 8 hours. It orbits earth in a very eccentric orbit taking it into the upper atmosphere to rendezvous with spaceplanes. Its thrusters make up the slight loss in velocity from air resistance. Alpha can obviously change its orbit to go where its needed. It requires a lot of reaction mass (an orbital transfer alone uses 100 tons of fuel but it's way more mobile than the ground port.) When the first orbital bolos go into operation in a few months the port will service them as well.
The ring has two levels. Going from the inner level to the outer level the gravity increases from .35 g to .41 g. That and the rapid spinning causes vertigo in many people when they first board. Drugs and special earphones can alleviate this condition almost immediately. Hostiles boarding will not have this luxury.
A ten ton berth in the inner ring can hold a small courier or lander. In practice this craft usually rolls around the ring on a track powered by monopropellant or maglev to assist EVA. However it can be launched and operated like any space craft. A water tank serves as a counter weight to keep the ring's balance. If the ship does launch the water is pumped out of the tank to secondary tanks to restore balance.
In view of recent hostilities the port was equipped with ten hardpoints. Against Lunar protests Earth has installed ten triple turrets. The turrets each mount a missile rack, sandcaster and pulse laser. The Earth insists this is defensive weaponry.