JEC COMPOSITES MAGAZINE - Issue #83 - August/September 2013 - 77

composite design and modularity
details had already been worked out.
If the software had been available from
the start, the team could have taken
advantage of some of its additional
capabilities, including weight reduction
during preliminary design and also
further manufacturability improvements. They would also like to try using
it as a data hub and exchanger for other
software tools.
This additional functionality could
be put to use on the Bus’ as-yet-unspecified second flight programme. In
the past, designs at Ames have been
overweight. HyperSizer has now
enabled the facility to be competitive
in lightweight designs where more
and more failure modes and stress
interactions are possible and must be
checked. Additionally, while physical

testing of all composite flight structures
is still required at NASA, that practice
is costly and will have to be scaled
back to maintain missions with fewer
resources. As managers and administrators become more confident in upfront
analysis tools, they will be able to push
physical testing further out in the development cycle or eliminate some tests
altogether.

The company he is joining plans on
designing an all-composite airframe.
So he would like to start with the basic
outer mould line (OML) shell model
and just let HyperSizer go wild. It can
handle so many different material types
and construction techniques. It is a
great optimizing code, and it can take
you all the way through full build and
into flight certification.

While HyperSizer is likely to stick as
a standard tool for analysis at NASA
Ames – having played an important role
not only on LADEE and the CCM, but
on other Agency projects such as the
ARES I and V launch vehicles and the
Orion Multi-Purpose Crew Vehicle –
the software’s full capabilities will also
be relied on by Fernandez in his new
position with a commercial aerospace
start-up.

In the future, aerospace design will
undoubtedly lean more heavily on
newer advanced materials and novel
weight-reducing structural strategies.
As it does, early design optimization
and analysis can provide an invaluable
– and cost-effective – window into the
performance of spacecraft in harsh
flight environments. n
More information:
http://hypersizer.com

The material menu for the NASA Common Bus
There are two main reasons that composites were selected over metals for the NASA Ames Common Bus, both having to do with the overarching modularity and multiple-mission-scenario strategies. For one, in missions requiring tall module stacks, high specific stiffness is a must.
So M55J, a carbon cyanate composite with a specific stiffness two-and-a-half times higher than aluminium, was chosen after early trade studies predicted significant weight savings for the structure housing the internal propulsion system. High specific strength for minimum-weight
lander vehicles was also deemed important. To satisfy this requirement, T300, a carbon epoxy composite, was also shown to have significant
weight savings over aluminium. Low thermal distortion, which is important for the pointing accuracies of instruments, was another material
property of these composites that made them a logical choice over metals.
In the Bus’ first flight programme iteration – the LADEE spacecraft – the composite panel
structure utilizes T300 and M55J fibres with a Tencate RS-3C resin. Since T300 is a stronger and lower cost fibre, its usage is maximized. M55J, on the other hand, is used only in
those areas where stiffness is needed to maintain first-mode frequency requirements. Both
are heritage materials from legacy NASA programmes like the Super Lightweight Interchangeable Carrier (SLIC) that flew on the Space Shuttle’s Hubble Space Telescope service
mission.
Metals are used more sparingly, but where needed, on the Bus’ modules. All panels
incorporate an aluminium honeycomb core. An aluminium-faced panel is utilized for the
heat-rejecting radiator. There are also various metallic elements throughout the structure.
They serve as hard points for interfaces, bracketry for mounting components, and connection fittings between panels. Most interfaces are bonded aluminium inserts, their shapes
optimized so that the material is sufficient for thermal survivability; this is important since
aluminium is a lower-cost alternative to titanium. In addition, most brackets are aluminium, and of either sheet metal or machined construction. Panel-to-panel interface fittings,
however, are bonded machined titanium, since their larger size prevents the use of the
lighter aluminium.
The result of this material recipe is the lightest vehicle possible with strength and rigidity
characteristics capable of satisfying the broad range of mission goals required by the Common Bus’ modular design strategy.

Fig. 5: LADEE has passed its structural tests and
is scheduled for launch in summer 2013 (Credit:
NASA/Ames).

No83 August - September 2013

/ jec composites magazine 77

http://www.hypersizer.com

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

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #83 - August/September 2013