For a long time, Amazon has been looking into applications for self-driving vehicles — and testing fleets of self-flying drones for making package deliveries. So it only makes sense that the Seattle-based online retailing giant would meld those vehicles for a warehouse-to-doorstep delivery system virtually untouched by human hands.

In a patent published today, Amazon inventors Hilliard Bruce Siegel and Ethan Evans describe a system that has autonomous ground vehicles transport packages to a customer’s neighborhood — perhaps even the street in front of the customer’s door — and coordinate the doorstep delivery with a drone.

Both types of robo-carriers would be in contact wirelessly with a central computer network that would manage the operation. The ground vehicle could be directed to head over to a fulfillment center, pick up shipments and plot a course for deliveries. Drones could flit back and forth to drop off packages and charge up at the vehicle.

Various diagrams show how the drones could pick up packages from a vehicle in the street, then fly over to drop off deliveries on doorsteps, designated drop zones and upper-floor balconies. Some diagrams show big delivery truck as the base of operations, while other show a smaller delivery robot like the ones that are being tested north of Seattle.

The drones could be owned or operated by an entity that’s distinct from the ground-vehicle service — for example, by the managers of the apartment building that’s being serviced. You could have different companies put in charge of deliveries in different neighborhoods. The important thing is that everything’s coordinated through a central network.

Such a combination system would solve several challenges: For example, the battery-powered drones wouldn’t have to use as much juice as they would if they were flying directly from a fulfillment center to make a delivery. There’d be less noise, and less need to fly over other people’s property.

For ground vehicles, the system not only bridges the “last mile” of a delivery route — it addresses the last 100 feet. Siegel and Evans, who are veterans in the patent business, say that’s becoming increasingly important.

“Over time, an increasing frequency and volume of deliveries of items from e-commerce and mail-order companies has resulted in an increased need for faster and more efficient delivery methods,” they write.

There’s one more twist to the application: It cites a GeekWire story about Google’s patent for using drones to pick up shipments and fly them to a mobile dropbox.

The application was filed back in 2016, and there’s no guarantee that Amazon will develop an all-autonomous delivery system like the one described. But the description does provide an indication of what Amazon has been thinking about as it builds out its own end-to-end delivery system.

For what it’s worth, Amazon has been investing what’s thought to be hundreds of millions of dollars with transportation startups such as Rivian and Aurora. Amazon plans to buy 100,000 all-electric Rivian vans for its delivery fleet. And recentlypublished patent applications indicate that both Rivian and Aurora are putting a lot of effort into making their vehicles autonomous, even under challenging conditions.

The big question is, what took so long for someone to get the patent for this idea? We’ve reached out to Amazon for comment, and will update this item with anything substantial we hear.

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GeekWire aerospace and science editor Alan Boyle is an award-winning science writer and veteran space reporter. Formerly of NBCNews.com, he is the author of “The Case for Pluto: How a Little Planet Made a Big Difference.” Follow him via CosmicLog.com, on Twitter @b0yle, and on Facebook and MeWe.