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THE NEAR SPACE
LUNCH BOX AIRFRAME
Many readers use a soft-sided
reusable lunch box to bring their
meal to work or school. These are
foam-insulated bags with zippered
enclosures. Their insulation and
convenient size makes them a
great airframe for near space.
After beginning a doctoral
program at the University of
Kansas, I modified my first lunch
box into a near space airframe for
the university’s aerospace
engineering department. The result
was an inexpensive backup tracker
for the department’s near space
flights. I’m pleased with the results
and feel it worked well for the near
space APRS tracker.
You can build one with the
■ FIGURE 1.
One of my
• Insulated soft-sided lunch box
• Sheet of Coroplast*
• Thick foam rubber (one or two
inches thick would be ideal)
• One inch wide woven-nylon
• Twelve 10-24 bolts
• Twelve 10-24 nylon lock nuts
• Twenty-four fender washers for
• Four heavy duty 1.5” metal
• Luggage tag
• Loud piezo alarm
• Nine volt battery snap
You’ll modify the insulated lunch
box by first attaching four nylon
straps to the sides of it. The straps let
the airframe connect to a recovery
parachute (above) and other modules
like BalloonSats (below). Then, you’ll
add a Coroplast panel to the back of
the lunch box to support an antenna
and audio beacon.
lunch box and along one of the
edges. Next, determine where you
will place the bolts that will attach
the strap to the lunch box. Note that
each bolt needs two washers, and
that one of the washers must fit
completely inside the lunch box. This
means the top washers can’t be too
close to the top where it interferes
I found that a hot knife or
soldering iron is a useful tool for
modifying a lunch box.
*Coroplast is a brand of
corrugated plastic sheet that’s 1/8”
thick. It’s available from local plastic
distributors and some hobby shops.
**I purchased the nylon straps
from a local fabric store. The store
staff cut six feet of material from the
roll that I brought to the store’s
The first thing to do is attach four
nylon straps to the corners of the
lunch box. Since it’s difficult to sew
straps to the lunch box, they’re
bolted to it instead. Make the straps
by cutting four pieces of heavy nylon
ribbon or strap. The four straps are
cut to the same length; for my lunch
box, they are 15 inches long. If you
are modifying a taller lunch box, you
may need to use longer straps.
After cutting the straps, melt the
cut edges of the strap with a lighter.
This prevents the edges from fraying.
(It takes only a small amount of
melting to prevent fraying.) Next, fold
a strap into thirds with an overlap
that leaves a one inch loop at each
end. Figure 2 illustrates how you
should fold the straps.
Take the folded strap and
position it on the outside of the
■ FIGURE 2.
need four of
at the top
of the nylon
March 2013 69