In our high altitude balloon experiments our group has attempted to test the payload that were sending in conditions that they will likely be experiencing, or that we want them to survive through. Things like: drop / shock tests, RFI tests, battery longevity. We didn’t really know how to test for the extreme temperatures though.
Temperatures at altitude are likely to reach -60C (that’s -76F)! Non of us have convenient access to freezers that will go that low in temperature.
About a month ago I thought of a simple test that would reach these temperatures. Dry ice, frozen carbon dioxide has a surface temperature of -78.5C (-109.3F) at standard pressure. Putting the payloads in a cooler surrounded by dry ice, they will be sure to eventually reach and pass the desired test temperature of -60C.
For the test setup a temperature probe could be setup in and out side of the payload under test. We thermally insulate our packages, so it will be interesting to note how fast the inside of the payload cools. If the test plateaus at a temperature above -60C (because of warming from the electronics), the test should also be run after cooling the electronics while off. This will simulate a cold start at altitude, which is not something planned but it would be interesting to know the results of this test.
Interesting quantities to look at: frequency drift of the transmitter, rate of cooling of insulated payload, power supply anomalies (if any), correct operation of the payload.
Dry ice can be picked up at local stores and is relatively cheap. I can’t wait to see how it works on some of our payloads. Once I try it I’ll update the blog with the results.
KG4SGP - Jim