A Quarter Watt from the Edge of Space

It’s 2:47 AM and I just ordered missile-grade GPS.

That sentence is real. The uBlox MAX-M8Q showed up in my cart because consumer GPS modules lose satellite lock at 18 kilometres — something called COCOM limits, export restrictions originally designed to keep civilians from building intercontinental ballistic missiles. The irony of needing military-spec positioning to track a latex balloon carrying a thermometer and a ham radio transmitter is spectacular.

Let me back up.

Three hours ago I was reading about APRS, the Automatic Packet Reporting System I’ve used for years to track my position on 2-metre simplex. Beacons. Digipeaters. The whole mesh network that lets ham operators see each other on a map. Standard stuff.

Then I found a website showing live balloon tracks.

Weather balloons. High-altitude balloons. Latex spheres filled with helium, rising at 300 metres per minute until they reach 30 kilometres — that’s 98,000 feet, above 99% of the atmosphere — and burst. Then everything falls. A parachute deploys. And if the payload has a working radio, it keeps transmitting its coordinates all the way down to whatever farmer’s field it lands in.

People do this as a hobby.

The physics are absurd. At sea level, a 600-gram balloon is maybe two metres across. At burst altitude, that same balloon has expanded to ten metres. The latex stretches to a hundred times its launch volume before it finally tears. Everything in the payload — the flight computer, the GPS, the transmitter, the batteries — has to survive -40°C temperatures and near-vacuum pressure, then a tumbling descent under nylon.

And I can build this. I have everything except the balloon itself.

The flight computer is just an Arduino with a GPS module and an APRS transmitter. I’ve soldered those. The antenna is a quarter-wave ground plane I could cut from piano wire. The parachute is a ripstop nylon hexagon I could sew in an afternoon. The prediction software — because yes, there’s software that models wind layers at different altitudes and tells you where your payload will land — is open source, using NOAA wind data.

The only thing I don’t know how to do is fill a balloon with exactly the right amount of helium. Too little and it rises too slowly, drifting hundreds of kilometres. Too much and it bursts early, below the stratosphere. There’s a number called “free lift” — the grams of upward pull beyond neutral buoyancy — and getting it wrong is how you lose a payload.

I’m reading forum posts from people who’ve lost payloads. In trees. In lakes. On rooftops in the next province. One guy watched his land in a construction site and got retrieved by a confused forklift operator.

The responsible thing would be to sleep on this.

Instead I’m filling my cart. 600-gram Kaymont latex. Ripstop nylon. Quarter-inch braided Dacron line. The GPS module that doesn’t think I’m building a weapon.

A quarter watt into a rubber duck antenna at 30 kilometres altitude can reach receivers 300 kilometres away. Line of sight is absurd when your horizon is the curve of the Earth itself.

I need to stop. I need to file a NOTAM. I need to check the airspace. I need to call Transport Canada.

But first — first — I need to see if anyone makes insulated payload boxes that fit an Arduino.