JEC COMPOSITES MAGAZINE - Issue #83 - August/September 2013 - 74

software

Leaner budgets boost innovation
in small satellite design

Chris Hardee,
Science & technology writer
Parker Group
for Collier Research Corporation

he Common Bus was the brainchild of the Ames Research Center’s director, Pete Worden, who
took over the Silicon Valley facility in
2006. His idea was to design and build
low-cost spacecraft on a quick turnaround, utilizing a commercial off-theshelf (COTS) strategy. The resulting
“small” satellites would be used to
perform modest yet important robotic
tasks like meeting up with asteroids
or investigating the lunar atmosphere.
Within the newly established Small
Spacecraft Division, the COTS concept
promised to cut development time
and, in Worden’s words, enable “faster
science return and more frequent
missions.”
When the original concept team that
was asked to turn Worden’s vision-setting programme into reality started, the
vehicle was going to be a lightweight
lander. Initially they came up with
cartoon-like conceptual models just

Which is it – a lander, an orbiter, or a rover? In the NASA
of old, a vehicle programme wouldn’t have “gotten off the
ground” without an answer to that seemingly simple question. But in today’s financially leaner, commercially oriented
NASA, decisions can sometimes stay up in the air for longer.
That is certainly the case with one project – the aptly named
Common Bus – thanks to a combination of visionary thinking
and creative engineering. The result is an innovative spacecraft system that can be almost all things to all people – a
lander and an orbiter and maybe even a rover.

showing what the lander would look
like and do. Eventually they arrived at
the current, fully-engineered modular
design, which met the objective of
being able to rapidly assemble a variety
of vehicles from off-the-shelf parts.
This modular approach meant that all
three types of spacecraft (landers, orbiters, and rovers) could be customized
from the same starting components for
differing instrumentation and payloads.
It also helped achieve the original
programme time and cost goals, as set
by the director: nimble missions with
design-to-launch in less than two years,
for as little as $50 million, or one-tenth
the price of a conventional unmanned
mission.

The building blocks
for a modular bus
At the heart of the Common Bus
concept is a single monocoque (structural skin) blank that serves as the
backbone of modularity. Each module
is octagonal in shape and approximately
355 mm tall by 168 mm across. Each of

74 jec composites magazine / No83 August - September 2013

its eight sides is comprised of two face
sheets sandwiching a honeycomb core.
Common bolt patterns on the top and
bottom of the structure allow them to
be stacked or interchanged like LEGOs.
This design strategy provides flexibility for mission type as well as easy
replacement if there is damage during
integration and testing (I&T). Before
build-out, every module contains identical requirements and all of them look
exactly alike.
Although metals played their role, early
in design development it was composites – rather than more traditional
aluminium or titanium – that were
selected as the primary materials for the
Common Bus. Composites were chosen
because of their high specific stiffness,
high strength, low weight, and low
thermal distortion.
When each composite module is
fabricated, high load and stress areas
are reinforced during lay-up by adding
more plies locally: the face sheets are
two plies in the centre, four at the

JEC COMPOSITES MAGAZINE - Issue #83 - August/September 2013

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