Near Space
measured in units of knots, then create a new column for
mph data called “Speed.” In this column, multiply the
speed (S) measured in knots by 1.15. The equation will
look like this:
= S * 1.15
for Excel:
= +J3 * 1.15
Copy and paste this equation into every cell of the
column.
Create Your Charts
Circle #127 on the Reader Service Card.
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There are two charts I want to discuss in detail. On
the “Altitude Over MET” chart, notice that the climb of
the NS craft is very constant, except for a funny
transition around 20,000 to 30,000 feet. For some
reason, the balloon changes its ascent rate around this
altitude. Before and after this transition, the climb
remains uniform. Also notice the plunge after balloon
burst. The parachute is opened constantly during
descent, but, because of the low air density in NS, the
first part of the descent is far more rapid. The increasing
air density slows the module down as it approaches the
ground.
In the “Wind Speed Over Altitude” chart, look for the
jet stream. Around an altitude of 40,000 feet, the wind
speed will peak. Depending on how close you got to the
center of the jet stream, these winds can exceed 100
mph. Just wait until you chase a NS craft that is traveling
at 120 mph! Fortunately, you’ll notice that the jet stream
is very narrow. It doesn’t take the module very long to
rise above the jet stream and slow down.
More advanced charts can be created using spherical
trig to calculate NS craft range azimuth and elevation
from the launch site as a function of MET or altitude.
We’ll look into this in a future column.
If you used a Tiny Trak 2 for your mission, you can
still get useful data with a little more effort. Just remember
the frequency for data transmission that was programmed
into the Tiny Trak 2. After you create the MET field, increment
each MET cell by the time between transmissions. To
determine the location of missing posits, create a chart
of altitude over MET.
Remember that the ascent into NS is smooth, so
abrupt changes in altitude show where your spreadsheet
is missing posits. Increment the MET cells involved with
abrupt altitude changes until the final chart has a smooth
altitude over time. Once this is done, you can create your
charts as discussed above.
In next month’s column, we’ll compare a variety of
data loggers, learn how to program them to collect the
data required, and convert some of this data into easy-to-understand charts. NV
94
MAY 2004
