Google Project Loon: 10 Mbps for users, 50 Gbps ultra-bright LED links between backbone super-nodes 100 miles apart
So far Google has been describing their Project Loon balloon internet initiative in very general terms.
Yes, we know that the idea is to provide internet access via a network of balloons floating in stratosphere 20 kilometers high, and use rather stable atmospheric winds at different altitudes up there to keep balloons on station by moving them up or down. But that’s about all that Google told us about Project Loon.
How exactly those balloons keep their station and move up or down? How big the Loon network can be? How do they communicate with each other, with ground stations and internet access points on the ground? What kind of speeds can we expect from it? We had no idea.
Recently several patent applications related to Project Loon became public in USPTO database, with a lot of details about Google’s balloon Internet. Including an expected 10 Mbps speeds for users on the ground, and 50 Gbps backbone network of Super Balloons 100 miles apart, covering huge areas via ultra-bright LED free-air optical links.
The balloon network with 50 Gbps super-node backbone and 10 Mbps downlinks
In the patent apps Google talks about various kinds of possible network configurations. But the most interesting and ambitious one is this:
The high-altitude balloon network consists of two types of balloons:
- The backbone of super-nodes that use ultra-bright LEDs to talk to each other via free air optical links, over the distances of up to 100 miles. According to Google, such network of super-nodes can achieve data transmission rates of 10 to 50 Gigabits per second
- A number of sub-node balloons that connect to super-nodes and to the access points on the ground, providing ordinary users with 10 Mbps wireless Internet connections
Super-nodes may also talk to each other using lasers, but that may be problematic due to various regulations regarding laser comms.
Super and sub-node balloons form balloon clusters (BC) over certain defined geographic area. Sub-nodes can move between nearby clusters and their density may be adjusted according to the data throughput requirements. E.g. a cluster with a lot of sub-nodes may be needed above the city, while rural areas may make do with one super-node a few sub-nodes. The network is also able to temporarily create and move balloon clusters as needed, for example for an event like rock festival, or disaster relief effort.
There is also one more type of balloon – that stays more or less above the project ground stations and connects the network to them via optical or high throughput radio link.
Balloons move around and keep station above certain area by using relatively constant different direction winds in stratosphere. They are configured for altitude control via variable buoyancy system that moves balloon up and down by inflating or deflating it.
The part that keeps balloon in the air is the envelope, filled with lighter than air gasses like hydrogen or helium. Balloons are inflated or deflated at need with the help of the “Bladder”. It’s an elastic chamber configured to hold gas and/or liquid. The buoyancy of the balloon is adjusted by changing the density and/or volume of the gas in a bladder. It can be done via a heating/cooling process, or by adding/removing gas via specially designed pumps and valves.
In one version of balloons, the envelope is filled with helium, and the bladder is treated as a ballast tank that can be made lighter or heavier by sucking in or pumping out the air from it.
Alternatively, Google considers more passive buoyancy system, were the gas is heated and cooled by the sun. They do that by painting different sides of balloon envelope in different colors, e.g. black and white. The black side absorbs more solar energy than the white one. When Google needs to take balloon higher, they turn it towards the sun, the gas heats up and balloon goes up. To go down, they turn the white side towards the sun and the gas inside cools. By adding the third intermediate color, e.g. grey, to the envelope, they can calibrate buoyancy and movement even more precisely.
Balloons may also have an airfoil, such as a kite, wing, or sail, that can be adjusted to control its direction of motion. Just like a modern sailboat, airfoil equipped balloon would be able to move not only along with the wind, but at some angle to it, greatly increasing maneuverability and overall network flexibility. Alternatively, the airfoil may be of a type that can convert the vertical motion generated by changing buoyancy of the balloon, into horizontal motion. Such airfoil can be used to achieve the desired movement without relying on ambient winds. This approach may be thought of as using the airfoil to convert lift into thrust, which is essentially the opposite of how a conventional airplane works (the wings of a an airplane convert thrust into lift).
Attached to the envelope of the balloon is the payload with all the electronics and power generation system. Those include the processor, memory, various sensors for navigation and buoyancy/movement control, radio and optical data transmission equipment.
By tuning up the hardware and software control algorithms, Goolge says they expect to be able keep the balloon in the air and on station for up to 100 days.
Between the envelope and payload, there’s a “Cut-Down” system, to cut the payload so all electronics can be recovered on the ground, when balloon has to be brought down.
In the patent apps Google also describes in some detail how they can effectively navigate and keep all the balloons on station. But the math and science involved there is way over my head. If you are interested you can check out the USPTO yourself: