Figure 9. BalloonSat closure.
Rubber bands make quick and cheap
closures. My near space experiments
have demonstrated the ability of
rubber bands to function in the ozone,
increased UV, and the cold of near
space. So, I currently use rubber
bands on all closures of my near
Using rubber band closures
requires a simple modification to a
BalloonSat, adding and gluing two
wooden dowels (3/16-inch diameter
dowels work well) into the airframe.
Cut the dowels 1-1/2 inches longer
than the width of the BalloonSat. I
found it best if I carved trenches (for
the dowels) into the side, or top and
bottom walls of the BalloonSat before
gluing the airframe together.
After the airframe is glued together, cover the BalloonSat exterior,
insert the dowels, and then lock the
dowels into place with a little hot glue.
The hot glue also prevents the
BalloonSat exterior covering from
ripping where it meets the dowels.
Styrofoam airframe, the flight line
will eventually cut its way through the
airframe. To prevent this destruction,
BalloonSats have a tube running
through their center. I’ve seen both
metal and plastic tubes in
BalloonSats. The metal ones add
unneeded weight and their edges can
chafe the flight line. An alternative is
to use a ballpoint pen case, as
recommended by the University of
The plastic is lighter than metal
and plenty strong, however, it
has a limitation. Most ballpoint
pens have bodies only 4-1/2
inches long (their diameter is
fine). What if you want your
BalloonSat to be six inches
Many hobby stores sell
polystyrene modeling materials.
So, purchase a package of plastic tubes, 3/16 inches in diameter from your local hobby store.
Each tube in the package is
over 12 inches long and since
they’re made from polystyrene,
they’re easily cut with an
If you place a plastic tube
down the center of a BalloonSat,
the tube will reduce the
BalloonSat’s useable volume. So, I
experimented with placing tubes
inside the wall of the airframe and
found that it works well. Of course,
this means the tubes are off center
and will tip the BalloonSat.
However, this modification leads to
my recommended changes in the
BalloonSat carrier, which I describe
later in this article.
So, instead of using a single tube
Figure 10. Rubberbands on a
BalloonSat. Note that BalloonSats
don’t have to be square.
If the flight line for the
BalloonSat goes though a hole in the