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This meeting conflicted with a monthly Sector67 meeting, so was less formal. It was also a planned Cold Test. These notes will describe the cold test that took place.
Isaac got caught up and couldn’t make it.
The purpose of the cold test was to determine if the foam would be sufficient to protect the phone at temperatures at altitude and if the phone would continue to operate for the duration of the flight. We expect the flight to take up to 2 hours total, and thus need to make sure that the foam can insulate the phone sufficiently for that long so that the phone doesn’t freeze. Research done by others indicates that temperature drops down to -60C but then warms slightly, so we wanted to make sure that whatever we did would simulate those conditions.
Brett brought two pounds of dry ice, which at -70 is colder than conditions we could expect to find at altitude. We put one of the blocks directly in the cooler and crushed up the other block to provide more surface area and cool the cooler faster. We also hooked up a small fan to hang inside the cooler and circulate air, keeping the cold air constantly on the cage and simulating to a small extent the constant wind that would be present at altitude. If the fan was NOT blowing, there wouldn’t be enough cold air against the cage and we wouldn’t have a valid test.
We acquired a few thermocouples and attached one inside the cooler in the air to capture the ambient temperature. We also attached one directly to the phone inside the cage to measure how cold the phone got.
To make the test as accurate as possible, the cage was made as it would be for a real launch, with an acrylic window. The layers of foam were sealed together with hot glue, and the small opening for the thermocouple was also glued shut. The phone was left running the GPS and an application that recorded the temperature and level of the battery every minute.
The test was then run for a couple hours. Data of the test is not yet available, though initial findings are promising. The phone after the test was still on and had <30% but >15% battery left. The screen was covered in frost, but apparently no permanent damage was done.
One consideration we might have to keep in mind is frosting of the window. If we don’t have a window then there will be too much cold applied directly to the phone and we risk freezing components. With a window, though, there is the danger of condensation on the window that obstructs the view. We may have to find some solutions for this problem.
One observation during the test was the fan struggled to stay running. We intentionally chose a low power fan to avoid generating heat, but the fan eventually built up ice that slowed and eventually stopped it. We were able to thaw it quickly and put it back inside, after which we didn’t have any more problems.