■ FIGURE 3. The recovery parachute
for this near spacecraft is visible
between the balloon and its capsules.
Below the parachute is its spreader ring.
In the multiple balloon recovery
system, two or more balloons lift the
meteorological payload to altitude.
Together, all the balloons can lift the
payload, but not when one or more
have burst. The remaining balloon(s)
“offsets” some of the weight of the
payload as it drops earthward at a
constant, but slow speed. Upon
touchdown, the balloon(s) remains
floating, signaling the location of the
payload to the chase crew. With the
advent of the radiosonde — which
telemeters data to ground stations —
instrument, recovery became less
important and the parachute became
a device to protect private property
from the descending payload.
COMMERCIAL
PARACHUTES
You can always purchase a
parachute for your near spacecraft.
Amateur rocket parachutes sold by
companies like Rocketman ( www.th
e-rocketman.com) are perfect for
recovering a near spacecraft. In fact,
I’ve used a slightly modified six foot
Rocketman parachute to recover
several of my near space payloads.
cannot be adequately tested for the
recovery of living beings that are significantly aware of pain and suffering.
The parachute described here is
a hemispherical. It’s a popular
parachute design but now obsolete
for the recovery of personnel. With
a coefficient of drag between 0.62
and 0.77, it’s in the mid range of
parachute effectiveness. I use this
type of parachute because it’s easy
to design and make.
■ FIGURE 4. A 1944 radiosonde
launch. Notice the recovery
parachute blowing in the wind.
Image from the National Oceanic
and Atmospheric Administration.
MAKING YOUR OWN
THE GORE PATTERN
Where is the challenge and
satisfaction of using a commercially
manufactured parachute? Over the
years, I’ve made half a dozen
parachutes (like those in Figures 3
and 5) for my near space program, so
let me explain how I did it and saved
money. Afterwards, there’ll be a little
parachute science and
engineering. First, never
use a parachute that
you’ve designed to recover
living objects, except for
insects and microbes.
While your parachute may
work perfectly well to
recover payloads from
near space, it’s unethical
to use a parachute that
The hemispherical parachute in
this article has a radius called R and
consists of eight gores. Knowing R,
we can use a spreadsheet to calculate the width of the gores as we run
down its length. To do this, we’ll
need a dose of geometry. We’ll start
at the top of our hemisphere drawing
and draw a line at an arbitrary angle
(labeled as A in Figure 6). That angle
intersects the parachute at a point
that is at a length called L. The end
of L intersects the hemisphere of the
parachute to form a ring (with the
radius called r in Figure 6) drawn
around the parachute. Now we’ll
divide the circumference of the ring
around the parachute by eight to
calculate the width of the gore at
length L and call that width W.
To help us see the relationship
between angle A and the width of a
gore, let’s look at a two-dimensional
thin slice of the parachute. We can
see this becomes a problem of
calculating the length r as angle A
goes from 0 to 90
degrees. R (radius of the
parachute) is the only
constant length in this
■ FIGURE 5. While
overkill for the typical near
spacecraft, this 19 foot
diameter parachute is
identical in overall design
to the six foot diameter
parachute I’ve used.
September 2008 83
