Instead of launching costly experience in space, with satellites, for acheiving experiments on the stratosphere, Canadian Space Agency (CSA) has team up with the Centre National d'Études Spatiales (CNES) to create a stratospheric balloon program. This program gives Canadian academia and industry the opportunity to test and validate new technologies and to perform scientific experiments at an altitude where only balloons can be operated. Stratos therefore contributes to the training and development of a highly qualified workforce: the next generation of Canadian engineers and scientists.
The development of a flight recorder prototype was required to acquire data on the Sweden mission of september 2016, in Kiruna. However, the recorder had to be built in a 4 months frame, which imply that it had to be composed of easily prototypable and accessible components, hence it was impossible to use spatial graded electronics.
The biggest challenge ahead was that the electronic components be able to sustain extreme temperature going from -60°C to 80°C, when facing the sun. Moreover, the recorder unit had to be compatible with the telemetry ballon gondola interface and had to be easily portable, with the capability of be quickly dismounted if needed.
What it does and how doest it works?
Powered from a Li-Ion battery, provided from the canadian agency, the unit is able to record and send, via S-band telemetry, GPS coordinates, speed, vertical speed, ambient pressure, ambient temperature, 3 axis acceleration and pictures. The connection to the telemetry unit is done by an ethernet connection and the camera is plugged in the recorder, via an USB cable. Since it is composed of two Raspberry Pi, the unit runs on Linux and provides easy I2C and UART bus communication within the recorder, for the numerous sensors. Telemetry frames are sent to the ground with JSON format and are wrapped by a custom KISS (TNC) protocol.
How I built it
Electrical architecture use component replications within the unit for redundancy purpose. Electronic card are powered by two DC-DC converter connected to the battery. Connection interface with the outdoor is made with IP67 Ethernet and USB connectors as well as a 48 pins utility connector. Since the electronics is embedded in a waterproof Pellican case and use IP67 connectors, the recorder is totally waterproof and dustproof. Moreover, for better GPS fix, two antennas are deported from the unit to the top of it. Electronic cards are supported by custom 3D printed brackets and the camera is also contained in a 3D printed protective case.
Challenges I ran into
Leading a team of 3 students, including myself was not easy. Moreover, I had to work with several engineers from different engineering fields in order to make this project.
Accomplishments that I'm proud of
The recorder really flew in the stratosphere on the 6th of september from Sweden and successfully sent telemetry on the ground.
What I learned
I learned a lot in particular how to manage a multidisciplinary project. Also, it was the first time that I made a project from scratch and learned to use raspberry Pi's and Python along the way.
What's next for FRETS
FRETS is now the base stone for a more advanced stratospheric flight recorder