Being inspired by Heath Robinson’s amateur high-altitude balloon project “Icarus” , I’m proposing a similar project based on Beagleboard for the Google Summer of Code this year. I know there’s a separate mailing list for GSoC topics but since this may be interesting for a broader audience, I’d like to post my idea here.
The Icarus project used an AVR microprocessor to control a reprogrammed Cannon A560 camera to take photos every few minutes. There are also a few sensors in the payload to monitory varies environmental parameters. The whole system was wrapped in a thermal insulating box to resist the minus sixty Celsius degree temperature in the high-altitude orbit. Replacing the microprocessor with a powerful ARM processor on the Beagleboard would give the system more horse power to process more images in real time, and to reduce development period by utilizing third-party software for sensors on Linux.
This is a mix of hardware, software and meteorology project. There will be several engineering and non-engineering problems to solve as listed below. I must have missed tons of things and you are welcome to add comments. A project like Beagle Zero G requires good knowledge on multiply areas so if you are experienced in one of any related fields, please don’t hesitate to join the discussion. Thanks!
Issues I can think of right now:
The Icarus project used a reprogrammed consumer camera to take and store all pictures. In the Beagle Zero G project, we will achieve this by utilizing three (pointing to three directions which separates by 180 degrees) or four (plus one pointing downward) webcams through USB connection. The Beagleboard will control the cameras by a fixed interval, or an adjustable intervals according to sensor data (ie shorter interval at higher altitude) and store the pictures in memory card. Both inexpensive high quality cameras and free drivers under Linux (such as this one ) are easy to obtain.
- Sensors, sensors and sensors.
The payload may need to include sensors of temperature, barometric pressure, altitude, humidity and GPS. Some sensors can be sealed in the box and others must be exposed outside. One of barometric pressure and altitude sensors may be alternative since there’s an exponential relation between the altitude and atmospheric pressure . For a compact and robust design, we may need to integrate these sensors on a daughter board.
- Communication between the orbit module and the ground station.
The Icarus used radio teletype (RTTY) to transmit position back to the ground station. I’m not familiar with this area so need to study more on how to implement both the hardware and software. Do you have any suggestions?
The highest altitude the Helium balloon can reach could be calculated by combining the altitude/pressure relation and the largest stress the balloon can take. The maximum stress could be tested on ground.
I saw from a media picture  that in the Icarus project a parachute was placed between the balloon and the payload, as shown below,
so, we need to figure out a way to avoid the parachute being entangled by the imploded balloon.
The area of parachute needs to be carefully calculated to control the impact speed to a certain range. If the landing speed is to high, it may damage the system and harm security of beagles and beagles’ friend (aka human) on the ground. An insufficient falling speed may let the wind blow it too far away from the launch site.
- Working at low temperature and low air pressure.
I don’t have data on how low temperature and pressure the beagle board can work under, but this can be tested on ground before the launch. It’s possible to completely seal the box to prevent losing air pressure.
- Insulating box.
An insulating box is required to resist the cold (due to high altitude) and heat (on the side of direct exposure under sunlight). Cosmic ray may bring error bits to the memory or even destroy part of the circuit so a metal shield may be needed (but it would reduce useful payload and the altitude the balloon can reach).
Depends on the time of flight, the Beagleboard itself may not require much battery power but it could be a problem if we put too much sensors and cameras on board.
- Launch permission.
It’s reported that Heath Robinson had to obtain permission from Civil Aviation Authority to launch the balloon in UK. Not sure if there’s similar regulation in the United States where I’m currently living in. Giving the fact that I’m not an US citizen, it might be even much harder to get such permission in the states. I know in some countries, like China where I’m from, lifting a payload of less than 4kg and 3.2 m^3 don’t have to ask for permission from the government .