Abstract
The target of this present MPhil thesis is to define a thermal protection system (TPS) for the protection
of antennas found in hypersonic applications. The term hypersonics is referred to the new generation
hypersonic cruise missiles (HCM) or hypersonic glide vehicles (HGV) whose aim is to glide within the
earth’s atmosphere while travelling at velocities above Mach 5.
The study started with a literature review whose aim was to understand the current advancements in
hypersonic technology, their operational environment, the materials used for their TPS design and the
current testing trends. The literature review concluded that although there is no publicly available
data relating to HCM and HGV, due to their low technology readiness level (TRL) and security
restrictions, some knowledge can be transferred by looking at either space re-entry applications or
University publications.
The first challenge to overcome was relating to the operational requirements of such vehicles and
specifically the aerothermal environment. To understand which materials are appropriate for such
applications, the thermal loads should be quantified. This is addressed in the second chapter of the
report by using aerothermal simulations based on computational fluid dynamics (CFD) and finite
element analysis (FEA). The reference mission for this analysis was provided by DSTL and it is based
on a generic HGV mission profile. The analysis was able to quantify the temperatures, thermal shock,
pressure, and stress levels experienced in such missions. The confidence in those results was also
evaluated using some validation cases. Some analysis uncertainties were also assessed and the
simulations were implemented based on pessimistic assumptions to make sure that aerothermal loads
are not underpredicted.
Using the aerothermal analysis, a large number of TPS architectures were evaluated. It concluded that
an oxide CMC-nanoporousinsulation sandwich panel was the most promising solution. This was based
mainly on thermal, dielectric, damage tolerance, and oxidation resistance considerations. A 15mm
thick TPS consisting of an oxide CMC skin and silica or alumina-based nanoporous insulation was able
to sustain aerothermal loads up to approximately 1600 Kelvin for duration times up to 15 mins. It was
also able to insulate the rear face of the TPS so the antenna does not reach temperatures above its
operational limit. Those theoretical calculations were also backed by simple thermal experiments
using a Quartz IR lamp and a butane torch. The conclusions from the tests and the aerothermal
analysis were in-line and that gave confidence that the proposed architecture can operate in hightemperature environments.
Some fractography analyses using OM, SEM and EDS were undertaken to evaluate the material
damage after the thermal exposure. It was also used to assess the formation of elements that can limit
the TPS RF transmission, such as carbon formation. The suggested TPS did not show any indication of
RF performance degradation in that sense but to validate such a conclusion, dielectric measurements
should be taken. A purely theoretical assessment of how the dielectric strength degrades with
increased radome thickness was also presented. According to that, the 15mm thickness is still within
acceptable limits.
The work concludes that the proposed TPS architecture of oxide CMC-mica-nanoporous insulation is
promising for its use in hypervelocity missiles and its operational limits were defined. This statement
is backed up by low TRL testing and theoretical assessments. For more in-depth conclusions, higher
TRL assessments are required in a representative working environment.