Space Technology Special Report - Version B. July 2023 - 20

APPLICATION BRIEFS
EP21TDC-2LO: Adhesive for Optical Components in Laser and Space
Applications
T
he ability of bonding agents to
withstand thermal and mechanical
stress is vital in any application where
even the slightest loss of structural
integrity can result in performance
degradation or even failure. For military
and aerospace applications in particular,
the stability of bonding agents plays a
fundamental role in ensuring mission
success when bonded structures face
extremes in temperature, vibration, or
acceleration. In the following application,
Master Bond EP21TDC-2LO demonstrated
its ability to maintain structural integrity
under the harshest conditions.
Launched aboard Space Shuttle
Endeavour on Mission STS-134 in May
2011, the Alpha Magnetic Spectrometer
2 (AMS-2) is a second-generation
particle physics detector. Mounted on
the S3 Starboard Truss Segment of the
International Space Station (ISS), AMS-2
integrates a sophisticated tracker able
to precisely measure energy, velocity,
and direction of origin of charged
particles such as protons, electrons, and
antimatter particles such as positrons.
Comprising silicon microstrips,
front-end electronics, and mechanical
structures, the AMS-2 Tracker makes
25,000 detections per second, generating
7 gigabytes of data per second - and
144 W of heat. To move this excess
heat, engineers created a CO2 cooling
system able to survive the stress of
launch and maintain operation in space.
Within this cooling system, Master
Bond EP21TDC-2LO plays a critical role
in maintaining a stable bond between
the critical components required to
ensure reliable heat exchange.
The AMS-2 Tracker Thermal Control
System (TTCS) is a sophisticated thermal
management system built to manage
the thermal load imposed by AMS-2
Tracker electronics, direct solar energy,
and even indirect solar energy reflected
by the Earth. Within the TTCS, CO2 passes
through cooling-loop condensers to dump
the thermal load into a pair of radiators
designed to radiate the heat into space.
20 JULY 2023
Although CO2 offers advantages over
other coolants, a power shutdown of
the AMS-2 can cause the condensers to
freeze when temperatures drop below
the CO2 freezing point (-55 °C). As the
condenser begins to heat up due to
solar energy or power restoration, CO2
thawing can induce pressures as high
as 3000 bar (about 43,500 psi) within
the condenser tubes. Although the TTCS
cooling loops includes heaters to mitigate
this problem, freezing simply cannot be
avoided in the case of power outage.
Without the use of suitable materials, a
rupture in the TTCS cooling loop could
occur. In turn, the increasing thermal load
in the AMS-2 Tracker itself could impact
detector performance, damage sensitive
electronics, and create an unstable
thermal event in a two-billion-dollar
experiment attached to the ISS itself.
AMS-2 scientists determined through
experiment that Inconel 718 tubes with
inner diameter of 1mm and outer diameter
of 3mm could withstand the pressures
encountered during CO2 thermal cycling.
By embedding Inconel tubes between two
aluminum plates, scientists determined
they could create a suitable condenser.
The problem remained one of securing
the Inconel tubes to the aluminum base
plates. For this task, the team required
an adhesive able to reliably bond the
dissimilar materials, provide high thermal
conductivity, and exhibit exceptional
thermal and mechanical stability needed
to withstand the harsh conditions of
launch and ongoing operations in space.
To meet these requirements, AMS-2
scientists selected Master Bond EP21TDC2LO,
citing not only its stability and
performance characteristics but also
its ability to match the differences in
coefficient of thermal expansion (CTE)
between Inconel and aluminum. To
test the design, developers mounted
the manufactured condenser on a cold
plate that simulated a TTCS radiator
and applied repeated cycles of CO2
freezing and thawing. The structure
bonded with Master Bond EP21TDC2LO
fully passed the tests and was
accordingly built into the AMS-2 platform
launched on Endeavour in 2011.
Master Bond Polymer System
EP21TDC-2LO is a two-component
epoxy resin compound that exhibits
high thermal conductivity and
excellent electrical insulation.
Mixed in a one-to-three ratio, the
compound fully cures overnight at
ambient temperatures or in 2-3 hours
at 200 °F. The cured compound
exhibits outstanding toughness and
exceptional tensile elongation for a
thermally conductive epoxy. Unlike
SPACE TECHNOLOGY SPECIAL REPORT
SHUTTERSTOCK/MECHANIK
Space Technology Special Report - Version B. July 2023

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