Flight TV01A

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Insect Habitat

TVNSP has modified two 20 ounce pop bottles as cabins for housing insects on flights into near space. The temperature and pressure of the two cabins are monitored and telemetered to ground stations by the capsule's CC/PS. Future modifications will give us the ability to adjust the temperature inside the cabins and scrub carbon dioxide from the air. All this for fruitflies and cockroaches.

Pressure is monitored by PC140 pressure transducers. Temperature is monitored with LM335s. The voltage conditioning and sensor board is on the left

On flight TV01A one of the bottles was sealed using teflon tape while the other bottle was wrapped in aluminized mylar. This allowed TVNSP to determine which design is best for the cabins. The aluminized mylar wrapped cabin maintained a warmer temperature throughout the flight. Unfortunately both bottles leaked air during the flight. We still have a bug to work out. Below is a graph of the temperatures of each bottle through the ascent of the capsule.

The covered cabin remained warmer than the unwrapped cabin after 38 minutes into the mission (just past 36,000 feet). By the time the capsule entered the stratosphere, the wrapped cabin was some 20 degrees warmer.

Thermo Experiment

What is the smartest color to use when covering a near space capsule? The Thermo experiment on flight TV01A was designed to find out. Four identical 2" cubes of polystyrene foam where given different colored coverings. LM335 temperature sensors were then inserted into the center of each one. Throughout the flight, the temperatures of each cube was telemetered to ground stations.

Flight TV01A Thermo Experiment and Temperature Sensor Array

The colors selected where black, white, silver, and natural blue. The cubes where mounted above the capsule where they would receive constant exposure to the Sun. From the graph below, you can see that the temperature of each cube did not differ until 35 minutes into the flight (at an altitude of 33,000 feet). By the time the cubes reached the stratosphere, the temperature spread between the cubes had grown to ten degrees farenheit. Late into the mission the temperature spread had grown to 20 degrees.

If the goal is to keep the capsule warmer by incident solar radiation, then cover the capsule with the color black (not an unexpected finding). White keeps the capsule the coolest. What I found surprising is how badly silver failed to keep the capsule warm. I expected the silver to reflect solar radiation, but to keep what radiation that did managed to enter, inside the cube, and therefore keep the cube's temperature higher than it did.

The results also show that the altitude of the tropopause on this flight was 42,700 feet.

Dallas' iButton Thermochron

Three iButton Thermochrons were flown on this mission. The Thermochron is a self-contained iButton, about the size of five stacked dimes, that records the temperature and time. It's also able to record alarms, where the temperature exceeds a predefined limit.

The night before the launch, TVNSP launch crews programmed the Thermochrons for their mission. We found the programming software easy to use. One button each was loaded into the two capsules. The third button was mounted outside the capsule, exposed to the frigid air of near space. A delay of eleven hours was programmed into each button, so they would not begin recording data until shortly before the launch.

From the graph above, you can see that the Thermochrons bottom out at -40 degrees. They cannot record temperatures any lower. The temperature outside the capsule was lower than inside the capsule, as expected. However past flights have indicated that the temperature inside the capsules never dropped below freezing until after balloon burst. Future tests, using multiple temperature sensors will be needed to clear up this issue. Notice also that the command module stayed a little warmer than the experimental module. Had the camcorder inside the experimental module functioned, I believe the experimental module's temperature would have been the greatest. Also note that 93 minutes into the flight, the outside temperature plummetted. This is at the time of balloon burst. The two inside temperatures don't show a drop until several minutes after balloon burst.

One of the nice things about near space flights is that they seldom clear up a question. There's always a need to fly again.

More information on Thermochrons, and iButtons in general, can be found at the iButton website.