Space Technology Special Report - Version B. July 2023 - 8

Figure 1. A heat transfer simulation of a satellite in orbit,
showing the temperature distribution. (Image: COMSOL,
Inc.; Earth image by Visible Earth and NASA)
O
ver the last few years,
there has been a dramatic
increase in the number
of satellites in orbit. A
significant portion of this increase is
thanks to the smaller size of newer
satellites. Although the largest orbiting
structure, the International Space
Station, is larger than a football field,
most of the satellites in orbit today
are much closer in size to a football.
This is in part due to the popularity
of the CubeSat form factor, with a
so-called 1U satellite fitting within a
10 cm x 10 cm x 10 cm envelope. The
small size makes it possible to launch
multiple satellites from a single rocket.
Although originally envisioned for
mostly academic purposes, there is
now a robust commercial ecosystem
providing design solutions ranging from
1U to 24U - and the use of CubeSats
is growing at a remarkable rate.
One of the characteristics of the
CubeSat designs (and other small satellite
designs) is that they are very compact.
Many miniaturized cameras, sensors,
instruments, antennas, batteries, attitude
control systems, and other electronics
are closely packed and can generate
waste heat. Designing the satellite to
properly radiate this heat to surrounding
space is one of the primary engineering
concerns. Engineers must ensure that
the various electronic components
stay within certain temperature ranges,
but this can be challenging, as thermal
gradients can lead to undesirable
structural deformations. Since it is quite
8 JULY 2023
difficult to do any kind of truly realistic
preflight testing, the design process has
to rely heavily on numerical modeling.
Once the satellite is in orbit, it might
be tempting to think that the numerical
model is no longer needed, but this is
not true. Components will fail, often for
unknown reasons, and the remaining
electronics may need to be driven
in unanticipated combinations. The
satellite operator still needs the thermal
model to predict behavior in such
circumstances, with the objective of
increasing operational lifetime (Figure 1).
Working with Numerical Models
All numerical models involve solving
an approximation of the governing
equations describing heat transfer.
They can range from being very simple
models to nearly full-fidelity models that
include many of the geometrical and
physical aspects. The most simplistic
numerical model would reduce the
geometric complexity of the satellite
structure and only compute, in a lumped
sense, a single temperature over time
for the satellite. From there, one could
work toward introducing temperature
variations across various subsystems or
components of the satellite. This would
require the numerical analyst to introduce
many approximations, assumptions, and
separate calculations into their model.
On the other hand, a full-fidelity
model is based directly on the CAD
design and takes the opposite approach.
By starting directly with the CAD
design, much of the tedious manual
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Space Technology Special Report - Version B. July 2023

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