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Balloon launch
Test launch of the driftsonde in Wyoming, summer of 2006. Photo by JoeVanAndel, courtesy of and copyright by UCAR.

Linux at 20,000 Meters Above the Sea

At our October, 2006 meeting, Joe VanAndel at NCAR discussed how Linux ran the NCAR/CNES dropsonde project that investigated the hurricane formation zone off the west coast of Africa.

NCAR worked with the French Space Agency to create and carry a payload that would float west from Africa into the hurricane formation zone. The balloon floated at 20,000 meters and higher, which is above the tropopause, the altitude at which the troposphere (where most of our weather takes place) gives way to the stratosphere. The gondola consisted of a single-board Linux system and batteries well-insulated from the cold, with an array of 24 to 40 dropsondes beneath it. Each dropsonde was connected to the Linux system, which was able to heat its batteries (the atmosphere is -70 degrees C up there) and drop the sonde on command. To the casual observer, the payload and dropsonde array looked as if it was constructed from cardboard, but Joe assured the audience that it was really a "cellulose composite." (Amazing what you can get away with when you're above the weather.)
Balloon launch
Joe describing the parachute opening from the dropsonde
Balloon launch
The gondola (left) and its dropsonde array (right) were built from "cellulose composite."

The Linux control system was accessible through a 2400-baud connection to the ground station in France through the Iridium network. Remember this global network of satellites that was supposed to connect satellite phones across the globe? In the dot-com bust its assets were bought for less than the cost of building and launching a single satellite, let alone worldwide ground support. Its infrastructure has been put to uses such as this (and a lots of military customers). Both the balloon and its dropsondes each had GPS receivers, so that the balloon could be tracked, and so that the dropsondes' horizontal movements could be translated into wind speeds at the altitudes through which it dropped by parachute. In addition to wind speed, the dropsondes transmitted temperature, and humidity information to the gondola through a 400 MHz radio connection.

One of the exciting parts of the project came when the project engineers discovered that the heating protocol for the dropsondes needed to be changed. Apparently, the on/off pattern of when heat was applied to the dropsonde's batteries wasn't sufficient to prevent the electronics from flaking out as the probe parachuted to the ground. Because the system was just a Linux box, Joe could modify the control software, use old-fashioned xmodem to upload a new control system, kill the old process and start the new one. Joe anticipated that this wouldn't be the last time the heating protocol would have to be changed, so he made it programmable through his favorite scripting language, Python. Once he uploaded the new control software, he could tweak the heating patterns simply by uploading a new script, much easier over a 2400-baud connection.

Joe's presentation slides are available here (PDF 6.7MB).

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February 15, 2009

February 2008: FRUUG Enters Quiescent Phase
After 27 years running, we're suspending operations.

Future Meetings:
None planned

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