■ FIGURE 8
■ FIGURE 9
value of 41) and then multiplied by
100% to calculate the relative humidity.
Once you’ve finished editing your
data in Excel or other spreadsheet,
you need to include a column for
altitude. You can look at the TNC log
from the mission to get this information or calculate it by determining the
climb rate of the near spacecraft and
multiplying by mission elapsed time.
When you’ve added the altitude to
the spreadsheet, you can generate
charts like the ones in Figures 6
through 9 (these charts come from a
mission launched in late 2006).
The three I like best are Figures 7,
8, and 9 (the pressure seems boring to
me). So let’s take a closer look at each
of them. Notice that the air temperature decreased with increasing altitude
until the BalloonSat reached an altitude
of 50,000 feet. From there, the air temperature rises with increasing altitude.
The air temperature cools in
the troposphere and rises in the
stratosphere. The transition between
the two is called the tropopause. The
troposphere cools with increasing
altitude primarily because the balloon
is moving away from its major source
of heat — the earth’s surface. The stratosphere, on the other hand, warms
with increasing altitude because the
balloon is moving closer to its primary
source of heat — the sun.
Ozone in the stratosphere blocks
some ultraviolet radiation and
converts it into thermal energy. So it is
the presence of ozone that we’re
detecting above 50,000 feet when we
measure an increasing temperature.
In summer time, I typically see the
tropopause at 50,000 feet and with a
temperature of - 60 degrees Fahrenheit.
In the winter, I typically see it lower to
40,000 feet and drop down to - 90°.
The latitude does affect the altitude
and temperature of the tropopause.
The relative humidity chart in
Figure 7 shows us that the air gets drier
with increasing altitude. But notice
that the relative humidity spiked three
times at 8,000, 12,000, and around
35,000 feet. I don’t recall the weather
conditions on this flight, but I suspect
there were clouds at these altitudes.
The temperature chart in Figure 9
shows that the interior of the
BalloonSat stays significantly warmer
than the outside air. The airframe of
this particular BalloonSat was 1/2 inch
thick Styrofoam. At 80 minutes
mission elapsed time, the balloon
burst. The movement of air over the
BalloonSat as it fell chilled the external
temperature sensor and cooled the
interior of the BalloonSat.
ors (black, white, silver, and light blue).
To reduce variations in the experiment, I
flew all four cubes on the same mission.
That meant I needed four temperature
sensors for the mission. Instead of building a temperature sensor for each cube,
I designed the following circuit board.
There’s no preferred order when
soldering the array together. Do note
ARRAY PARTS LIST
• Four 1K resistors
• Four LM335 precision temperature
• Thin gauge wire
• A 3 x 4 male header (or equivalent)
• Thin heat shrink
• Printed circuit board (see the copper
pattern on the Nuts & Volts website
The last sensor I want to discuss this month is an array of temperature sensors (Figure 10). Many
years ago, I became curious about
how the color of my near spacecraft would affect its internal temperature. To find out, I created four
identical foam blocks and covered
them in materials with different col-
■ FIGURE 10. This is an older version
of the temperature sensor array
than I’m describing in this column.
The new design incorporates strain
relief into the PCB.
September 2007 23