Well its very cold at 100,000 feet so to keep things warm, we will put handwarmers in the capsule. But how many warmers should we use? To answer this, we did a few studies to model the thermal properties of the capsule and the components in it (heat coming off the cameras, heat coming off the handwarmers). Since we can't test the box at -70 degrees F, we can use the models to predict what the temperature in the box will be when exposed throughout the flight with a couple of handwarmers in it and cameras running.
To get the basic equations of the model we did the following experiments:
- We measured the heat coming of the cameras by running the cameras in the box sitting at room temperature. They heat up almost too hot to touch and the box gets to over 100 degrees. By plotting the temperature curve of the inside temperature, we can model the heat from the cameras.
- We then measured the thermal properties of the box by just placing it in the freezer in the basement and measuring the heat loss over time (measured the temperature in the box and in the freezer every minute using remote thermometers from True Value Hardware.
- Lastly we measure the heat from the handwarmers separately by putting one in the box and measuring the inside temperature (since we knew the properties of the box by experiment #2, we could model the heat from the warmers).
Putting all the modeled equations together, we can then predict what the inside of the box will be throughout the flight. To estimate what the temperature of the outside will be throughout the flight we used the output of the Laramie Wyoming balloon simulation. It tells you what the outside temperature will be for each minute of the flight.
So we get the following predictions: With no handwarmers, the box will dip to -20 F. Using 3 handwarmers, the inside of the box will only fall to 30 F (but the camera will still get quite warm when it hits the ground).