Space Technology Special Report - Version B. July 2023 - 12

Satellite Modeling
which is used to charge
the batteries that drive the
electronics. These various
electronics all dissipate heat
while in operation, and these
components may be on
continuously, on at specific
predetermined times, or
switched on in response
to specific conditions. For
example, a heater can be
controlled by a thermostat to
hold a component within a
desired temperature range.
Accounting for all of
these elements while
modeling requires the use
of efficient and reliable
multiphysics simulation
software, such as COMSOL
Multiphysics® (Figure 3).
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.)
Satellite Modeling in COMSOL®
The Heat Transfer Module, an
add-on to COMSOL Multiphysics®,
includes a dedicated user interface
for satellite modeling: the Orbital
Thermal Loads interface. Based on
a hybrid finite-element-radiosity
method, the functionality of this
interface enables engineers to use a
CAD-centric approach to build nearfull-fidelity
models of small satellites.
The interface is seamlessly integrated
into the COMSOL product suite and
offers a simple way to define material
properties, loads, and boundary
conditions; extract results; and define
physics couplings for multiphysics
simulations. The Heat Transfer Module
also has functionality for modeling
fluids, phase change materials, heaters,
and thermoelectric effects, as well
as for lumped system modeling.
The Orbital Thermal Loads interface
provides a convenient way to define
and verify the orbit and orientation, as
well as Sun and planet properties. From
there, it computes the solar, albedo,
and Earth infrared irradiation using
a two-band radiation model, with a
user-selectable division between the
solar (short-wavelength) and ambient
(long- wavelength) bands. This allows
for specifying different emissivity in
12 JULY 2023
different wavelength bands. A singleband
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.
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.
SPACE TECHNOLOGY SPECIAL REPORT
http://www.comsol.com
Space Technology Special Report - Version B. July 2023

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