Electronic design for the stratosphere
At HDDG23, Nikolai Chernyy discusses obscure info about designing high-altitude electronics
Supplyframe’s mission is to create more access to information about electronics design and manufacturing. As such, we do a meetup in San Francisco called, Hardware Developers Didactic Galactic. These events include talks by industry experts in hardware and software. The speakers are often building hardware for recreation or as part of their employment. The common thread is that they want to give a view “under the hood”.
HDDG23 was held August 3rd, 2017 at the Supplyframe San Francisco office. We welcomed Nikolai Chernyy (@breadboard), creator of high altitude electronics. His past work also included studying neuromodulation and then working on surgical electronics.
Environment and Effects
Creating electronics that will go high in the atmosphere provides unique challenges. Lower pressure, lower temperature, higher amount of radiation, inclement weather and turbulence all impacts devices you’re trying to fly up in the stratosphere. Aside from keeping the device in the air (normally a balloon), there are effects on the electronics themselves.
Most parts are not rated to lower temperatures experienced in the upper atmosphere. Off the shelf components are only rated to -40C and temperatures in the stratosphere can reach as low as -100 or -120C. This also impacts the parts via thermal stress, as different sections of the component expand or contract at different rates. If there are bond wires internally, the different rates of “movement” even means the bond wires might shear off. Due to the lower temperatures and pressure, batteries freeze up and ions aren’t as mobile. The lower pressures also means the electrolyte can boil off, lowering the amount of charge capacity in the battery.
It’s possible to lower the risk by simplifying the overall system. The electronics should not be particularly complicated and instead should focus on the main functions; if the main purpose is to take pictures, do not add a multitude of other sensors. Simplicity also takes the form of larger components. Super small consumer based components not only are a risk for thermal stresses, but also any vibration that happens due to turbulence. The cooling and heating will not only come from the atmosphere but also from the components themselves. Plan for removing heat in the PCB, because the thinner atmosphere means you don’t get convection cooling.
From a mechanical perspective, it’s possible to lower risk by using wire crimps instead of soldering any wiring harness. This will ensure better connections, especially if the metals between the connectors, wires and crimps are all similar. Other practical connector considerations are things like using latching and keyed connectors, to prevent plugging things in backwards or insecurely.
A balloon with electronics needs to be treated like any other flying object. The flight plan should be cleared with Air Traffic Control (ATC) and all restricted airspaces (like airports) should be avoided. As Nick mentioned:
…if you land on the runway of SFO by accident…you will be arrested.
Though there is less control over a balloon, understanding air currents will help determine which way you’re headed. Monitoring the current altitude and bearing of the balloon also helps to alert other airborne vehicles of their presence.
Should you try it?
Regardless of whether your balloon will be taking pictures, monitoring sensors or even delivering WiFi, the electronics involved in high altitude flight can create a unique set of challenges. This talk was an interesting offset to one of our past talks about deep sea electronics, but the ideas presented were the same:
Take special care when designing for extreme environments and learn from other projects in the space.