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Thursday, February 10, 2005

Experiment on Heat Reflection

After seeing all the different payload boxes on the ASTRO-2 flight, I though to myself, "what is the best way to do this" and how I determine that in a way that
1) would involve simple tools found in the kitchen, hobby room and Radio Shack
2) would be easily verifiable and repeatable
3) would stimulate some thought, discussion, and maybe some lightweight math and physics.
4) eventually a computer model could be established to simulate the cabin and outside environments on a future balloon payload.

S0, I picked two "automotive" indoor / outdoor thermometers from Radio Shack for not a lot of change. These make nifty low DC voltmeters too. So I had 4 channels of thermometer.
1) CH1 (a remote probe) for in the test chamber (a.k.a. balloon payload)
2) CH2 (another remote probe) for the area between the test chamber and the desk lamp (a.k.a. "the atmosphere")
3) CH3 (built in) was in the back of the bench and was to measure ambient temp away from the lamp.
4) CH4 (built in) was the same thing, but on the other thermometer. There might be a way to remove some experimental error taking these readings into account.

The next thing was to find a sample balloon payload enclosure. I didn't care what it was made of at first, because I wanted to just test out the theories and equipment. I did know I wanted something of a uniform contruction. I had on-hand:
1) some plastic cups without lids
2) a ceramic coffee mug
3) a plastic tumbler
4) a styrofoam cup
5) a stainless steel insulated mug (a freebie from work)
but either these didn't have a lid, or the lid was made of a different material. I thought that would undermine the integrity of the experiment. So I settled on a glass jar with glass lid. (I'll photograph and weight it out later)

I needed someting inside the "capsule" to heat up. So I filled it up with styrofoam packing peanuts leftover, by this point, from Christmas. This project got delayed a number of times.

So first, I thought I would investigate coatings, then move on to the actual structural material later. I thought if my readings of the instruments were good and the instruments and procedure was good, that I could determine which materials would be desirable for reflecting and absorbing heat. It's good to absorb some heat to keep transmitters on frequency (namely, its the crystal that needs to be kept at temp) but it's also good to reflect away heat that would otherwise kill a biological sample, or trouble other electronics.

I decided to start simple and work with black construction paper, some Hewlett-Packard photo paper intended for an inkjet printer, and some aluminum foil from the kitchen.

I expected to see the black construction paper absorb heat, raising the internal temp quickly while slowly releasing it when the lamp was shut off. This would be handy for parts of the payload in indirect sunlight. I expected to see the aluminum foil reflect heat and keep the inside very cool. I assumed this would be a good coating for parts of the payload in direct sunlight and it would serve as a ground plane for monopole "whip" antennas. The photo paper should have been a happy medium on the reflectivity scale. If I was really crafty, I think this could be folded (orgami ?) into ribs and spars. Then a coating of aluminum foil could be applied.

Someone could fashion a greenhouse by lining a box-shape with aluminum foil, then covering the top with Saran wrap to let in the light... The heat absorbed during the initial ascent could be saved for later (colder ) parts of the flight.

Anyway, over time I found a few spare hours to sit with clip board and stop watch. I keyed the figures into Excel. How I need to learn to publish graphs on the blog.

73
Scott

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