If Amazon's drone delivery service is to ever get off the ground, it'll need some major infrastructure upgrades to support it. Previous patent documents have shown that these drones might be restocked and recharged in huge hives or launched from airborne blimps, and a new patent awarded to the retail giant could see drones being patched up and launched from mobile maintenance facilities carted around on the back of trains, trucks and ships.

Amazon calls the mobile facilities "intermodal vehicles", and they essentially look like shipping containers with mini fulfillment centers inside them. The patent papers mostly describe these intermodal vehicles as trains, but since they fit inside a standard shipping container, the system could also be carried by trucks, ships or, according to the ever-ambitious Amazon, even spacecraft.

One or more of these vehicles would be loaded with drones and items for delivery, and sent to serve a certain area based on past demand for those items, local demographic data or expected surges like events or the release of the new iPhone. Hot and cold items could be stored in temperature-controlled sections, and a robotic arm would help load and launch the drone, and retrieve it on return. While it's away, an onboard computer system would calculate the best place for the drone and the train to meet up, based on the speed and direction of the train and the battery life of the UAV.

A cross-section of the delivery car, complete with a robot arm that picks items from storage, loads them onto the drone and launches it(Credit: US Patent Office)

A key function of fulfillment centers is UAV maintenance, and so a separate but connected container could be kitted out to repair drones as they come back. Robotic arms could repair the motors, swap out a drained battery for a fresh one from an onboard supply, or quickly replace motors or propellers.

As with any patent, there's no guarantee that any of this will ever come to fruition, but Amazon and other companies like UPS are putting a lot of thought into the practicalities of future drone delivery systems.

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