Easter Balloon

Launch was at: Parc Russel, St Sulpice, VD, Switzerland.

Images from payload 1 (polaroid cube), left: EPFL Campus, right: roughly 30km altitude

Images from payload 1 UART camera, shortly after launch:

13:05:15 UTC 13:03:13 UTC

The Octanis Rover will eventually go to some very cold places. This is for example why we need special batteries that can bear temperatures down to -50°C. But also all the electronic parts need to be working at this kind of conditions, as energy is limited and cannot be wasted on heating the rover. Therefore all components we use have are rated to operate at -40°C or lower.

But still, even if in theory everything should work, we have to make real tests with the complete system. For doing this, we pack all our electronic boards on a weather balloon and let it rise to a very high altitude. This is a convenient way to test our electronics in the extreme cold, without having to move. On top of that, we will be able to collect a big amount of sensor data and test the reliability of the LoRa communication link. GPS, which will be transmitted over a backup GSM connection, will enable us to find the payload again to recover the data and hardware.

End of March/Beginning of April. Exact date will depend on the weather and the trajectory predictions. It could happen that the weather will not allow us to launch with very short notice (hours!).

It is planned to launch in the Park Russel, St Sulpice.

  • Functional live tracking of the Balloon
  • Payloads retrievable
  • Parachute deployment successful
  • 30km target altitude achieved
  • Flight software runs without resetting
  • Impact velocity at 4.5m/s
  • Live tracking via LoRa achieved with gateways receiving over 60 km away (TTN Zurich)
  • Parachutes successfully deployed and gradually slowed down the descent to 3.5m/s
  • Flight path prediction gave a very good general direction. Due to slower descent rate, the destination was far off.
  • Update 1.4.16 23:00: GSM modem #2 is offline (combox when called). #1 is still online (ringing when called).
  • Update 2.4.16 12:00: GSM modem #1 is still online.
  • Update 2.4.16 20:00: GSM modem #1 is now offline.

The following was made with the help of the visualizer:

  • Landing site (green), last red points were at 81404Pa (~1.5km altitude):
  • GPS track received via LoRa (started at ~6.5km):
  • Extract of data received from LoRa payload (#2):
  • Preliminary summary using GSM and LoRa logs (it incorrectly uses the words “online” and “signal lost”, which in this context means that the GPS FIX WAS LOST. data with no geolocation is not displayed on the map currently!: gsm_lora_track.png.pdf

Lessons Learned

  • Plan more time for inflation of balloon.
  • Implement a parachute cut off mechanism (nichrome wire), to release the payload from entangled cords.
  • Configure the GPS modules for high altitude operation (default is 12km, details on setting higher here).
  • Implement remote control commands that can shut down the board, to preserve all data stored in flash.
  • Pressure sensors are usually not rated for very low values, so they don't give accurate information about the flight height. (Ours was rated for a range of 300 hPa to 1100 hPa)
  • From now on flight experiments (parachute) must be finished, tested and ready at least a week before launch.
  • While we did not launch in rainy weather, rain would have impaired LoRa range significantly.
  • However, the range of LoRa is was surprisingly high (>100 km) and it turned out to be a more reliable backup connection than GSM, even on ground level.
  • For recovery vehicle:
    • 12/220V car transformer
    • Torches
    • Very, very long telescopic stick
    • Various cords
    • Potato canon

Post-retrieval Results

Retrieval of payload was on Sunday, April 10th, 10 days after the launch. Unfortunately there were some rainy days meanwhile.

Payload box 1 (hi-res cam, uart cam, no LoRa) state after retrieval

  • hanging in the correct orientation (topside up).
  • completely dry inside, despite the visual holes for 2 cameras.
  • all cables still connected.
  • double-sided tape loosened.
  • Battery discharge state (@ room temperature): 2.04 V (2 cells in parallel)
  • Solar cells directed towards evening sun.
  • EPS still functional, also battery charging.
  • one solar cell slightly damaged. might have happened during tree descent.
  • Sensirion logging data: device reset at some point.

Payload box 2 (lo-res cam, LoRa with external antenna) state after retrieval

  • haning in reverse orientation in the tree (bottomside up).
  • humid/wet inside, due to rainwater coming through the LoRa antenna hole.
  • all cables still connected.
  • double-sided tape loosened.
  • Battery discharge state (@ room temperature): 1.92 V.
  • PCB's covered by grey substance, probably due to humidity in forest. Maybe a reactionin combination with solder flux. Has no influence on electrical signals. –> EPS still functional.