Project Loon details from the Christchurch event today | Hacker News Reader

Project Loon details from the Christchurch event today

78 pointsmkl12 comments

Pictures: http://imgur.com/a/IrZFq

I went to the Project Loon event today (Sunday June 16) at the Air Force Museum in Wigram, Christchurch, New Zealand. Here's what I learned. (Some of this may be misunderstood or misremembered, so don't take it as absolute truth, and this is all early prototype stuff anyway.)

It was quite a big museum-style exhibit with lots of people (it had been on the news), and several members of the team were there answering questions.

Currently there are four balloons up. Several have recently been successfully been brought down and recovered from the ocean (land landings are easier to recover but there is no nearby land east of here). The main reasons for testing here are that the stratospheric winds are "boring" (basically all west-east) and this latitude has few countries to coordinate with (they're working with Chile and Argentina).

The project involves a "couple of dozen" people and has taken two years to go from "ideas on a chalkboard" to this.

One of the balloons was there, inflated to its maximum size (launch size is smaller because of pressure differences, but it's a superpressure balloon with a maximum size). It was roughly 5m high and 12m in diameter. It has an upper portion with helium and a lower portion with air, with an impeller that can change the pressure in the air part, and thus control the height. The height control is used to navigate, by moving to layers with different wind directions and speeds, and can take it right down to the ground (though that sounds a bit untested). They are aiming for flights of "hundreds of days".

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Clickable: http://imgur.com/a/IrZFq

Edit: that should have said 8m high

There are multiple control and networking systems connected together with a CAN bus (for controller area network, used in cars). It sounds like 4-5 ARM cores total: two Linux systems ("unfortunately" two) and one realtime controller in the main payload, and a failsafe controller up on top of the balloon (which controls helium release and parachute deployment). The controllers are designed to recover from being reset very quickly, since resetting is used as a kind of universal problem solver (sensor issues, cosmic rays flipping bits, etc.).

The stratospheric daily temperature swing (30°C down to -80°C) causes difficulties, so the electronics are in styrofoam boxes about 3cm thick, and a heating system keeps the electronics warm and the batteries warmer. The rough altitude is 20km, but it sounds like they cover about a 5km height range, I think connected to the daily cycle somehow too.

The solar panel provides 100W in full sunlight. It is mounted directly under the transparent balloon (which reduces the amount of energy by 20-25%). The batteries hold about "ten laptop" batteries' worth.

There are three vertically mounted omnidirectional antennas for balloon-to-balloon communication, and one downward facing antenna. The downward one has a 90° cone angle, and is designed so that the signal strength is even across the 40km diameter ground area. 2.4GHz and 5.8GHz, one for balloon-to-balloon and one for ground (I think 2.4GHz is ground).

The communication protocol is custom, to account for the large distances and to coordinate the ground systems so they don't transmit at the same time (since they can't see each other). The system basically acts as a VPN between end users and the ground station (upstream ISP), and traffic inside the VPN is encrypted separately as well. Currently upload and download speeds are symmetric (they don't really know what the speed will end up being, but roughly the same as 3G).

The eventual goal is commercial internet access to parts of the world that can't get it other ways, but there are no concrete plans for how that will work yet, since they expect to go through many more iterations of prototypes first. Commercial use will necessarily involve large fleets of balloons to provide continuous coverage (even if they end up covering more are each), since they move quite a lot. The balloons measure atmospheric conditions themselves and are coordinated from the ground.

Edit: I forgot to mention that there is a standard aircraft transponder (yellow and black cables in first picture), and the corners of the ~1.7m square solar panel have strobe lights to meet air codes.

The protocol uses time division multiplexing to solve the hidden node problem (https://en.wikipedia.org/wiki/Hidden_node_problem) where two nodes can be transmitting at the same time causing a collision.

They also mentioned that they didn't tilt the solar panel to follow the sun for reduced complexity, cost, weight and the risk of failure of a servo system.

They don't know what the speeds will be but 'as fast as 3G' was the marketing line.

To me it seemed like this project still had some large hurdles to viability but it was cool none the less.

Thanks for posting this. I linked to it in a few places from the comments on the link that made it to the top of HN.

I was chatting with some of the Google people at the event, and they said that the balloons have been responsible for a few UFO sightings. In fact, when one of the balloons' transponders failed in flight, they were able to track the balloon by the UFO reports online! This happened while they were testing the balloons in California's Central Valley.

They said the balloons are expected to take two weeks to circle the globe. Given that they said they'll eventually stay afloat for 100 days, that gives them plenty of opportunities to bring the balloons down in a specific location in order to make reuse easy.

I went as well - i don't have much to add and my questions were certainly not as insightful as yours - but i will add that i was told that six balloons had launched, and the real balloons are larger than the demonstration as it's pushed down to fit into the demonstration hall. They didn't have a demonstration of the building antennas.

Multiple balloons in the air form a mesh network, allowing you to put your uplink only where it's convenient for you - which i guess is the key to making this a viable solution somewhere inbetween 3G towers and satellite internet.

It was a fun event, i hadn't been to the airforce museum before - lots of kids with helium balloons, poster giveaways and folded balloon animals. Someone was wearing the first Google Glass i've seen and lending it to people to try (that must get old pretty quickly).

Most of those facts weren't from my questions :-D I asked a few, but there were lots of others asking questions too, so I did a lot of listening.

Do you think that project loon has anything to do with the recently acquired Makani Power? http://cleantechnica.com/2013/05/24/google-buys-makani-wind-....

It would be interesting if they were to merge these two projects.

It seems pretty unlikely, if only because of the very different altitudes the projects operate at (the kites can't be high because of tether weight, and the balloons can't be low because of weather and aircraft).

Apart from the commercial model that these will use (what they'll cost to make use of, etc.), the thing I'm wondering about is how visible they'll be at sunrise/sunset.

Google is saying that they'll be barely visible to the naked eye, but just after sunset/before sunrise, they will be illuminated by the sun when the rest of the earth is still dark, which should make them more visible than they would be during daylight hours. In my mind, I'm imaging a dark sky that's full of little orange dots. I have no idea whether or not it would happen like this though.

Thank you for sharing! This technology is definitely interesting. I will be following news about it closely and would appreciate it if you could post more updates in the future.

I think certain countries will suspect that these balloons are used as spying devices, and probably shoot them when they enter their airspace.

Are they going to add downward facing camera(s) to capture close to real time Aerial imagery?

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