that’s easy to machine and that
doesn’t outgas in the vacuum of
space. Mounted to the outside of the
airframe are the CubeSat’s solar cells
CubeSats use metal tapes for
their antenna elements. The antenna
elements are lengths of metal
measuring tape. The metal tape is
flexible, so it can be bent back tightly
against the sides of the airframe.
However, because of the curl
along their length, the metal tape
snaps back straight if it’s not
restrained. As a result, after releasing
their restraint, the metal tapes snap
straight out and wobble back and
forth until their motion dampens out.
The antennas are tied to the
bottom of the CubeSat with plastic
fishing line prior to being loaded into
their launcher. After the CubeSat’s
deployment, a timer triggers a circuit
to melt the restraining fish line with a
hot nichrome wire. This frees the
ends of the measuring tape so they
spring straight out, creating the
CubeSat’s antenna. I guess you could
say that good things come in small
The avionics inside a CubeSat
consist of a stack of PC/104 cards.
According to the PC/104 Embedded
Consortium, these cards are a smaller
version of the ISA PC and PC/AT bus.
They are too small for PC use; their
small size makes them more
appropriate for embedded systems.
Each PC/104 printed circuit card
measures 3. 55 inches by 3.775
inches on a side. There is no vertical
insertion of cards like those that we
find in a PC back plane. Instead, the
cards are stacked together like
Arduino shields using stackthrough
connectors. These connectors have a
female receptacle on top, and long
male header pins on the bottom.
The stackthroughs are located on
one side of each PCB (printed circuit
board). There are also four mounting
holes: one for each corner of the
PCB. The corners of the PC/104 cards
are attached together using spacers.
This makes the stack of PCBs more
rigid and less likely to break apart.
By the way, the number 104 in
PC/104 comes from the fact that
there are 104 pins in the
stackthrough. The 104 pins are
arranged into four rows. The first two
rows contain 32 pins each and are
for the eight-bit bus. The remaining
two rows contain 20 pins each and
are for the 16-bit bus.
Like PC cards, there are four bus
voltages in the PC/104 standard:
12V, -5V, +5V, and +12V. Needless to
say, ground (0V) is also included in
the rows of pins via multiple
redundant ground pins.
The first CubeSat launch took
place in June 2003, but not as the
primary payload of an American
rocket like the Atlas or Delta.
That’s because CubeSats are far too
small to make enough money for
rockets like these.
The first CubeSats were the
payload of a repurposed Soviet era
ballistic missile called the SS- 19. Ten
years later, we find CubeSats are
launched by the larger rockets, but
are used as rocket ballast. For proper
performance, rockets need dead
weight (or ballast) to even out the
distribution of their weight.
Secondary payloads like CubeSats
make more sense as ballast than a
passive chunk of metal.
Remember Opal, the late 1990’s
microsatellite? Its picosatellite
launcher became the basis for
P-POD, or Poly-Picosatellite Orbital
Deployer. The P-POD mechanism is a
hollow square-shaped tube
containing a spring operated ejection
plate in its base. Each P-POD
contains a stack of three CubeSats.
All three CubeSats rest on top of the
compressed ejection plate. At the
time of release, a latch on the lid of
the P-POD springs back, opening the
top of the P-POD and letting the
ejection plate push all three CubeSats
out into space.
There’s a switch at the base of
each CubeSat. As long as this switch
APPROACHING THE FINAL FRONTIER
December 2014 73
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Two stackthrough connectors of
the type I use in my projects.
The long length of their pins
ensures there's plenty of
clearance between the
PCBs for the components
soldered to the boards.
A diagram showing how PCBs like those found in PC/104 cards are
stacked together. The stackthrough connectors maintain the electrical
connection between the PCBs, while the spacers maintain
the structural integrity of the stack.