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High Altitude Weather Balloons
TUESDAY, 4TH MAY 2010 - 9 Comments
Recently I have considered launching a hobbyist high altitude weather balloon. The idea has been running around in my head for some time, but up until this evening I had not seriously researched the viability of such a project. Recent innovations in embedded microelectronics have led to the project becoming significantly easier (and cheaper) than in previous years. This article will serve as a catalogue of my initial foray into this intriguing hobby.
A typical high altitude vehicle of this type has two major components: The payload and the flight system. The payload consists of an insulated sensor package with associated controller and communications device. The flight system contains the balloon itself, a recovery system, a radar reflector and the means to attach it all together.
Upon launch of the vehicle, the balloon will lift the payload continuously, but will also expand as the external air pressure decreases with altitude. Eventually the pressure differential will be significant enough to burst the balloon, at which point the parachute recovery system will increase drag sufficiently to slow the vehicle so as to mitigate payload damage upon impact.
Many teams have created balloons of this type, primarily to take photographs and video of the "near space" environment. Notable examples include:
Payload Systems
The sensors and communications components of the payload will require an embedded microcontroller. After some poking around it seemed that the open-source Arduino platform was suitable for this project. The Arduino (Duemilanove) is essentially an Amtel ATmega328 microcontroller connected to a USB-port, which can be programmed via a C/C++ type language. The Arduino can be enhanced with multiple stacked PCB "shields" providing additional functionality such as wireless communications, GPS and servo motor control. The Arduino would serve as the "brain" of the vehicle.
In order to locate the payload once it lands it is necessary to transmit it's location in a discrete, but frequent manner. An embedded GPS system provides this capability. One example is the SIRF Star III GPS Engine from US Global Sat which provides a 1Hz update rate (more than sufficient for a vehicle of this type). These GPS units can be easily connected to the Arduino, which would process the NMEA strings output by these devices. Communicating this information from the payload to the ground station requires a long-range wireless communications device. Such devices exist but are not cheap!
The microcontroller will also handle communications and logging of the sensor data as well as the camera. The firmware of the camera can be temporarily modified to provide more granular control of the timing facilities. An example for Canon cameras exists here.
Flight System
The balloon itself is a "standard" weather sounding balloon. The market leader for these balloons is Kaymont. They are relatively inexpensive and have extremely high bursting altitudes. The majority of these altitudes lie between 20-30km, which is 2x-3x the height flown by commercial airliners! It is necessary to fill the balloon with the correct volume of helium such that it does not rise too fast (and hence burst too early) or too slow (and hence drift too far due to winds).
Other aspects of the flight system include the parachute for payload recovery and a radar reflector to allow radar-equipped aircraft to detect the balloon. Parachutes are readily available from hobby stores as they are used to recover model rockets. A radar reflector can be a simple cardboard shape wrapped in tin-foil. That pretty much sums up the flight system.
Summary
That about wraps up my initial foray into hobbyist weather balloons. The next logical step is to form a team of like-minded individuals who would be keen to help build it out. I'm also going to be purchasing an Arduino Experimentation Kit to get the hang of programming microcontrollers. I'll let you know how I get on!
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