■ In Aircraft, Outside Temperatures Change Greatly
Aircraft move from the ground to high altitude.
As altitude changes, outside temperature and air pressure also change.
On the ground, it is hot.
At high altitude, it becomes very cold.
However, inside the airframe,
● Electronic equipment
● Motors
● Power supplies
● Batteries
● Communication equipment
generate heat.
In other words, the situation exists at the same time that
outside is very cold.
Heat is generated inside.
■ Having Cold Outside Air Does Not Mean It Can Easily Be Cooled
If the outside temperature is low, it seems easy to cool.
However, at high altitude, air density becomes low.
If there is little air, the ability to carry heat by convection also changes.
In other words,
the air temperature being low
and
air cooling being easy
are not the same.
In aircraft, it is necessary to consider that cooling conditions change with altitude and speed.
■ In Space, Air Cooling Is Not Possible
In space, there is almost no air as there is on the ground.
That is why
releasing heat to outside air with fans
is not possible.
Even if air can be circulated inside the equipment, heat must ultimately be sent into space by another method.
What becomes important there is
radiation.
In spacecraft, heat is carried to the surface of the craft and released into space as infrared radiation.
■ In Space, There Is Also the Problem of "Getting Too Cold"
In space, releasing heat is not the only problem.
The side receiving sunlight becomes hot.
The shaded side becomes cold.
In other words,
large temperature differences within a single craft
may arise.
Electronic equipment.
Batteries.
Optical components.
Sensors.
These must be used within a certain temperature range.
That is why, in spacecraft, both
heat dissipation
and
thermal insulation
are important.
■ There Are Places Where You Want to Release Heat and Places You Want to Protect
For example, inside a satellite,
computing units generate heat.
You want to release that heat outside.
On the other hand,
batteries should not get too cold either.
For optical components, you want to suppress dimensional changes due to temperature changes.
In other words,
cooling everything in the same way
is not possible.
Where to let heat flow.
Where to stop heat.
These must be separated.
■ Temperature Differences Also Affect Dimensional Accuracy
Materials expand and contract with temperature.
In aerospace, different materials are combined, such as
● Aluminum
● CFRP
● Titanium
● Resins
● Ceramics
Each has a different coefficient of thermal expansion.
When temperature changes, dimensions change slightly.
In optical equipment and high-precision sensors, this slight deformation may affect performance.
In other words, heat problems are also a problem of positional accuracy.
■ Temperature Stability Is Especially Important in Optical Equipment
Satellites and aircraft carry
● Cameras
● LiDAR
● Infrared sensors
● Optical communication equipment
In these,
lenses,
mirrors,
and sensor positions
moving even slightly may change optical performance.
That is why it is important not only
to lower temperature,
but to keep temperature from moving as much as possible.
■ Weight Reduction Is Extremely Important in Aerospace
In aircraft and spacecraft, weight is a major cost.
Adding
thick copper plates
or large heat sinks
for thermal management can raise cooling capacity.
But weight also increases.
So using
● Aluminum
● Graphite
● Thin-film materials
● High-performance thermal insulation
it is important to obtain the required thermal performance with little weight.
■ Graphite Can Potentially Be Used as a Lightweight Heat-Spreading Material
Graphite has the characteristics of being
● Light
● Thin
● Easy to spread heat in the in-plane direction
That is why, in fields with severe weight constraints, it can be a strong option as a heat-spreading material.
On the other hand, attention is needed to
● Electrical conductivity
● Brittleness
● Powder shedding
● Edge protection
■ Metal Foils Can Also Be Used for Thinner Designs
Instead of thick metal plates,
placing
● Copper foil
● Aluminum foil
in the necessary parts can also guide heat in the required direction.
Placing material only where needed suppresses weight increase.
In other words, in aerospace, rather than making the entire surface thicker,
the idea of adding high functionality only where needed is important.
■ In Vacuum, Outgassing Becomes a Problem
In space equipment and vacuum environments, volatile components emitted from materials become a problem.
If components released from
adhesives,
resins,
rubber,
and bonding agents
adhere to
● Optical components
● Sensors
● Surfaces
they may reduce performance.
That is why it is necessary to check whether the material can be used in vacuum.
This is a challenge shared with semiconductor manufacturing equipment.
■ Adhesives Cannot Be Used Easily
Adhesives are convenient for fixing thin-film components.
In aerospace, however, they may be subjected to severe environments such as
● High temperatures
● Low temperatures
● Vacuum
● Radiation
● Long-term use
That is why being able to adhere at room temperature is not enough.
Reliability across the entire usage environment is needed.
■ Thermal Cycles Are Repeated
Spacecraft repeatedly move between
sunlight
and shade.
Aircraft also go back and forth between
the ground
and high altitude.
As a result, components repeatedly
expand
and contract.
When dissimilar materials are laminated,
● Warping
● Peeling
● Cracks
may occur.
In other words, not only initial performance, but performance after thermal cycling is important.
■ In Aerospace, Repair After Failure Is Difficult
For equipment on the ground,
it failed,
so replace the part,
is a possible response.
In spacecraft, however, parts cannot be replaced easily.
Aircraft also require high reliability.
That is why, rather than a component with slightly higher performance,
a component that maintains performance stably over long periods is important.
■ Higher-Performance Electronics Increase Heat Generation
In aerospace too,
● AI computing
● Image processing
● High-speed communication
● Sensor processing
are increasing.
In other words, the performance of onboard electronics is rising, and heat generation is also increasing.
On the other hand,
you do not want to increase weight.
You also want to limit power consumption.
Here too,
a trade-off between higher performance and thermal management arises.
■ In Electric Aircraft, Battery Thermal Management Also Becomes Important
In electric aircraft and eVTOL,
● Batteries
● Motors
● Inverters
become large heat sources.
This is similar to EVs.
In aircraft, however,
weight constraints are even more severe.
That is why
thermally conductive materials,
insulating materials,
and cooling systems
must be made to work while being made lighter.
■ eVTOL Demands High Output and Light Weight at the Same Time
Vertical takeoff and landing require large output.
A heavy load is placed on
motors,
inverters,
and batteries.
At the same time, you want to keep the airframe as light as possible.
In other words, in eVTOL,
“thermal performance ÷ weight” may become even more important than in EVs.
■ Thermal Insulation Materials Are Also Important Thermal Management Materials
In space, it is important not only to release heat, but also
to prevent heat from entering from outside
and to protect internal heat.
That is why
● Multilayer insulation
● Thin-film thermal insulation
● Aerogel-based materials
are sometimes used.
In other words, in aerospace, both heat dissipation materials and thermal insulation materials are important.
■ The Researcher's Perspective: In Aerospace, Look at "Temperature Differences" and "Temperature Changes" Rather Than "Temperature"
In aerospace, not only
maximum temperature
and minimum temperature,
but also
● Temperature differences between components
● Temperature change per unit time
● Number of thermal cycles
are important.
If materials differ, the amount of expansion differs even for the same temperature change.
That is why it is necessary to consider heat and structure at the same time.
■ The Shop-Floor Perspective: The Lighter It Is Made, the Less Material There Is to Release Heat
Reducing weight.
Making metal thinner.
Making parts smaller.
Then
the amount of material for carrying heat also decreases.
In other words, pushing weight reduction too far can make heat problems more severe.
In aerospace, it is necessary to optimize weight reduction and thermal performance at the same time.
■ OTIS's Perspective
OTIS is
not an aircraft manufacturer.
Not a satellite manufacturer.
Not a spacecraft thermal design company.
However, aerospace equipment may also use thin-film functional components such as
● TIM
● Graphite
● Metal foils
● Insulating films
● Thermal insulation materials
● Adhesives
● Seal materials
● EMI materials
If OTIS were to be involved, it would be not in
the development of materials themselves,
but in the area of processing them into the required shapes, thicknesses and laminated states.
■ What OTIS Can Do
At OTIS, through
● TIM processing
● Graphite processing
● Copper foil and aluminum foil processing
● Insulating film processing
● Thin-film thermal insulation processing
● Adhesive processing
● Seal material processing
● EMI material processing
● High-precision die-cutting
● Microfabrication
● High-precision lamination
● Lamination of dissimilar materials
we may be able to contribute by processing functional materials for aerospace into the required shapes.
■ Outside OTIS's Expertise
OTIS is not a company that specializes in
● Thermal design of entire aircraft
● Satellite thermal design
● Spacecraft system design
● Rocket design
● Propulsion system design
● Vacuum and radiation environment analysis
Also, for aerospace, the necessary certifications, material evaluations and long-term reliability checks for each individual project are important.
■ Markets Where This Technology Will Be Important
★★★★★ Satellites and spacecraft
★★★★★ Electric aircraft and eVTOL
★★★★☆ Avionics
★★★★☆ Drones
★★★★☆ Optical and observation equipment
★★★★☆ Space communication equipment
■ Summary
Aerospace thermal management is “technology that protects function amid extreme temperature changes” rather than “technology that cools”
In aerospace, there are
high temperatures,
low temperatures,
low pressure,
vacuum,
strong solar radiation,
and large temperature differences.
Furthermore,
it must be made light.
Power is also limited.
Failures cannot easily be repaired.
That is why it does not come down to adding large cooling equipment.
Spreading heat.
Blocking heat.
Guiding it to the necessary places.
Releasing it outward by radiation.
And suppressing dimensional changes due to temperature changes.
These multiple technologies must be combined.
What matters in aerospace is not only the material that cools best.
It is components that are light, thin, and can maintain performance over long periods even in extreme environments.
If OTIS were to be involved, it would be in the area of processing the functional materials used within them, such as
heat, insulation, thermal insulation, adhesion, metal foils and thin films,
into forms that can actually be used.
Column Supervisor: Koji Kakumoto (President, OTIS Co., Ltd.)
After studying abroad and working in planning and development at a trading company, he joined OTIS Co., Ltd. in 2011. While primarily working in the Corporate Planning Department, he has also served concurrently in manufacturing and technical divisions, and since 2018 has served as President, working to drive business growth and strengthen the organization.
This article is a general technical explanation intended for educational purposes and does not refer to any specific company, product, or technology.
