and shut down telemetry from your near spacecraft (ever
see the movie, Lost In Near Space?).
There are two things you can do to prevent this. The
first is to use lithium cells. The chemistry of lithium cells
holds up to cold much better than most other battery
chemistries. The second is to cover the exterior of the airframe in dark fabrics. A jacket of dark fabric absorbs solar
radiation and will passively heat the interior of the module. Besides warming the module, a fabric jacket will also
protect the MLI and airframe exterior from abrasion during landing. It's also a great place to attach link lines
between modules. I use ripstop nylon for my fabric jackets, which I call abrasion jackets. You've most likely seen
ripstop nylon used in fabric kite sails.
Avionics for Near Space
The electronics used to operate a near spacecraft are
called avionics (aviation electronics). For your first near
space mission, I recommend using a simple amateur
radio tracker. A simple and
inexpensive amateur radio tracker
consists of a terminal node controller connected to a GPS receiver
and a handheld, two-meter,
amateur radio (see Resources).
The terminal node controller
(TNC) is a modem built for radio
use. When used in avionics, it
accepts sentences from a GPS
receiver and formats them for
transmission over the radio.
Afterwards, it keys the radio
and sends the proper tones. A similar set-up on the ground decodes
the tones and displays the data on
a laptop or PC. This method is
referred to as the Automatic
Packet Reporting System (APRS)
and is very popular with the amateur radio community.
Because of APRS, the position of the near spacecraft in three
dimensions, its speed, and its
heading are known to chase and
The simple tracker costs
around $250.00, but don't let the
cost scare you. Assembling your
tracker is a one-time expense,
because it is used on every mission. Besides, the cost of a tracker
is less than the cost of a good set of
golf clubs. Not only does a tracker
cost less, but the aggravation associated with it is less than the aggravation associated with the same set
of golf clubs.
The next step up from a radio tracker is a flight computer. Most of the flight computers used by amateurs
today are based on programmable microcontrollers like
the PIC, Rabbit, or BASIC Stamp.
Upgrading from a radio tracker to a flight computer
doesn't add much to the cost of avionics, but it does permit complex experiments and mission profiles that aren't
available with a simple tracker. More information on flight
computers is available from groups like ANSR, Project
Traveler, or myself.
Your experiments will change on each mission, but
your modules shouldn't. Give some thought to designing
and building a generic style of airframe and flight computer. This way experiments are designed to meet the
standards for the modules, rather than having modules
designed to match the experiment. Be sure to document
these standards. This is a much faster approach to flying
missions, making failures less likely. Now your near
spacecraft is more like a Space Shuttle than a Mercury
space capsule. NV
Some Helpful Websites — Amateur Near Space Programs
Ralph Wallio (2)
Tiny Trak III (TNC)
KPC 3+ (TNC)
Amateur Radio Clubs