Tech Briefs Magazine - January 2023 - 13

as Sun and planet properties. From
there, it computes the solar, albedo, and
Earth infrared irradiation using a twoband
radiation model, with a user-selectable
division between the solar
(short-wavelength) and ambient (longwavelength)
bands. This allows for specifying
different emissivity in different
wavelength bands. A single-band model
additionally provides a simplified approach.
If an even higher level of detail
is needed, it is possible to use a multiband
radiation model.
COMSOL® can either read in vendor-neutral
CAD formats or be bidirectionally
linked with popular CAD packages,
such that any changes to the CAD
model will be instantaneously updated
in the numerical model. This CAD geometry
can be cleaned up using defeaturing
tools or simplified for meshing
using native functionality. Alternatively,
it is also possible to create geometries
within the software.
Computing the Results
Once all this information is assembled
and put into a thermal numerical model,
the computed results will show the temperature
variation over time. For a very
simplified model, this might just be a
bulk temperature. For a higher-fidelity
model, the spatial temperature variation
within all components is computed (Figure
4). This information can be used to
check if the satellite will stay within all
operational thermal limits. From there,
the analyst may want to move on to other
types of analyses, such as computing
structural deformations that happen due
to thermal gradients to see how such deformations
alter the optical performance
of a telescope. This kind of extensive numerical
modeling reduces the need for
physical testing and can make satellite
engineers confident in their designs prior
to launch.
Since the solar, albedo, and Earth infrared
irradiation can be considered
nearly periodic between orbits, the total
irradiation over one orbit can be
computed prior to the thermal transient
calculation, which typically spans
several orbits. This order of operations
makes it simpler to test what-if scenarios,
such as different combinations of
surface emissivities. When iterating
through designs, it is possible to use
the Batch Sweep capabilities on large
single computers or the Cluster Sweep
node capabilities on cluster and cloud
computing resources.
Tech Briefs, January 2023
Once the design iterations are complete
and the satellite is ready for delivery,
the COMSOL numerical model can
be packaged as a standalone application
and given to the satellite operator so that
they can test unexpected operating conditions
as needed (Figure 5).
Conclusion
Thermal management of satellites is a
complex design task, and the operational
environment is hard to replicate in physical
tests. For instance, there are variables
that can only be foreseen with the use of
simulation, such as the temperature variations
that may occur as satellites travel
through orbit or the heat generated by
onboard equipment. With COMSOL
Multiphysics®, engineers can quickly iterate
and improve designs, verify operational
conditions, and share their numerical
models with coworkers and customers
as simulation applications.
COMSOL and COMSOL Multiphysics
are registered trademarks of COMSOL AB.
This article was written by Walter
Frei, Principal Applications Engineer,
COMSOL, Inc. (Burlington, MA). For
more information, visit www.comsol.com.
Figure 4. A simulation application showing the computed temperature variation of a cube satellite.
(Image: COMSOL, Inc.)
Figure 5. A standalone application can be provided to a satellite operator for additional analysis during
operation. This simulation app shows a satellite surface's maximum and minimum temperatures over
time. The satellite's exposure to the Sun is indicated by the red curve. (Image: COMSOL, Inc.)
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Tech Briefs Magazine - January 2023

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