the launch vehicle that does the heavy lifting and the near
spacecraft that does the thinking.
The Launch Vehicle
To get into near space, you need a launch vehicle.
Amateurs most frequently use a launch vehicle consisting
of a latex weather balloon, helium, and a length of nylon
cord. Amateurs purchase their weather balloons from
either Kaymont or Kaysam (see Resources). You should
expect to pay about $50.00, plus shipping, for a 1,200-
gram balloon. A balloon this large has enough volume to
get a 12-pound near spacecraft to an altitude of 85,000
feet. If you use a larger balloon or lower the weight of your
near spacecraft, you can reach even higher altitudes.
Purchase your helium from a welding shop and never
from a department store. Department store helium is fine
for filling party balloons, but your 1200-gram weather balloon requires over 300 cubic feet of helium. If you purchase helium from your local welding shop, they'll sell you
a purer grade of helium and a lower cost per volume.
The load line of the launch vehicle is just a length of
nylon cord. This is the same kind of nylon cord or twine
sold in places like hardware stores. The cord is strong
enough to lift the near spacecraft and able to separate from
the balloon nozzle with a minimum of force. The load line is
cut to a length of between 20 to 30 feet and all its knots are
wrapped in small pieces of duct tape for extra security.
The Near Spacecraft
Your near spacecraft consists of a recovery parachute
and one or more modules. If more than one module is
used, you will connect them together with link lines. You
may also use an umbilical to share power and data
between the modules. On some occasions, you might
place a cutdown on the load line between the near spacecraft and its launch vehicle. A cutdown is not required, but
when it is used, it separates the near spacecraft from its
launch vehicle. A cutdown is used to terminate missions
early or to separate the balloon remains from the parachute
during the descent phase of a mission.
The Recovery Parachute
The recovery parachute protects private property and
your near spacecraft. You can either purchase your parachute from a rocketry company or sew it yourself (I prefer
to sew my own). Depending on the porosity of the canopy's
fabric, your 13-pound near spacecraft ( 12 pounds for the
modules and one pound for the recovery parachute) will
require a parachute about six feet in diameter.
Never launch the recovery parachute folded; instead,
the launch vehicle lifts the parachute by its apex in a pre-deployed position. This way, the parachute opens immediately upon balloon burst. Remember how long the load line
was? It's this long to make sure that the burst balloon
(which remains tied to the other end of the load line) can fall
FEBRUARY 2004
Near Space
Preparing for lift-off!
over the side of the parachute canopy, rather on top of the
parachute canopy, possibly collapsing it.
Modules
A module consists of an airframe, avionics, and possibly experiments. Some airframes are purchased ready to
fly while others are specially constructed. The avionics are
either a radio tracker or a flight computer. Some avionics
are mounted to a pallet that fits inside the airframe, while
others are packed in foam rubber. A pallet is a lightweight
means to keep elements of the avionics from bouncing
More spacecraft than the Baikonur Cosmodrome.
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