■ BY L. PAUL VERHAGE
NEAR SPACE BOOMS AND SOUNDS
THIS MONTH, WE’LL LOOK AT two near space experiments. The first one is an
engineering test and the second a traditional science experiment.
A TEST OF COMPOSITE
In Chapter 5, Section 3. 3 of my
book Near Space Exploration with the
BASIC Stamp (which is available online
as a free download from Parallax at
www.parallax.com), you’ll find
directions for making strong, stiff, and
lightweight composite booms for near
spacecraft. The booms, which are
mounted to quad panels, let me
quickly switch out antennas and
experiments on a near spacecraft.
After testing the strength of different
types of Styrofoam for my BalloonSat
article, I wanted to test the strength of
my composite booms. Before describing the test and its results, let me
briefly explain how I make booms. I
believe you’ll find these composite
booms are useful not just for near
space, but also for robotics.
MAKING A BOOM
I lucked out. Back in 1997, I stumbled upon how to make these booms.
I had just completed my second near
spacecraft airframe and needed a
boom to mount experiments and
antennas away from the airframe. As a
test, I cut a Styrofoam sheet to the
dimensions of the boom I wanted and
laminated four of its sides with thin
modeling plywood (I got the idea
from a 1980’s Sky and Telescope
article about laminating Styrofoam in
fiberglass). The results were so
outstanding that I’ve been using
composite booms ever since.
The Styrofoam core of my booms
comes in four by eight foot sheets and
is available from a local home
improvement store. I don’t use the
soft white Styrofoam of cheap ice
coolers because it has large grains that
don’t adhere well to each other.
The laminating plywood is sold by
a hobby store in town. The plywood is
1/32 inch thick and I usually purchase
it in two by four foot sheets. While at
the hobby store, I also purchase epoxy
in four ounce bottles. I don’t recommend the tiny tubes of epoxy sold at
hardware stores. You’ll need a lot of
epoxy to make booms and, in those
quantities, the larger bottle of
hobby store epoxy is cheaper.
Besides, I suspect the hobby
store epoxy is better quality.
Now that you have the parts,
let’s make a boom.
Begin by cutting the
Styrofoam to size. Next cut
four pieces of 1/32-inch thick
plywood a little larger then
the four largest faces of the Styrofoam
core. Then laminate the first two
pieces of plywood to opposite sides of
the Styrofoam. To limit the mess, mix
the epoxy right on the face of the
Styrofoam and spread it thinly with a
Popsicle stick. After gluing the first
two faces on the Styrofoam, wrap
several pieces of masking tape around
the boom to hold the plywood in
place while the epoxy sets.
After the epoxy sets, remove the
masking tape and sand the two
unlaminated sides of the boom until
the edges of the plywood are flush
with the Styrofoam. A stationary belt
sander is a great tool for doing this as
it quickly creates flat surfaces on the
boom. After sanding the bare sides of
the boom, apply epoxy to the two
remaining bare sides of the boom and
cover them in plywood. Again wrap
the boom in masking tape to hold the
plywood in place until the epoxy sets.
After the second batch of epoxy
sets, sand the boom one last time to
clean up the two new plywood edges.
I cover one of the small ends of the
boom in plywood, but the exact
dimensions and shape depend on the
boom’s function. The remaining end is
epoxied to a quad panel, so I don’t
laminate it like the other sides. I like to
finish my booms by giving them a coat
of spray paint to seal out the weather
and make them look nice.
TESTING MY BOOMS
■ FIGURE 1. A completed
boom, painted and mounted to
a quad panel. It’s ready to rock
In my previous column on
BalloonSats, I tested the strength and
stiffness of both 1/4” thick foam core
and 1/2” thick Styrofoam by hanging