Aerospace & Defense Technology - December 2024 - 10

Acquiring and Telemetering Test
Data from Hypersonic Platforms
H
ypersonic platforms provide a challenge for flight test
campaigns due to the application's flight profiles and
environments. The hypersonic environment is generally
classified as any speed above Mach 5, although
there are finer distinctions, such as " high hypersonic " (between
Mach 10 to 25) and " reentry " (above Mach 25).
Hypersonic speeds are accompanied, in general, by a small
shock standoff distance. As the Mach number increases, the
entropy layer of the air around the platform changes rapidly,
and there are accompanying vortical flows. Also, a significant
amount of aerodynamic heating causes the air around the platform
to disassociate and ionize. From a flight test perspective,
this matters because the plasma and the ionization interfere
with the radio frequency (RF) channels. This interference
reduces the telemetry links' reliability and backup techniques
must be employed to guarantee the reception of acquired data.
Additionally, the flight test instrumentation (FTI) package
needs to perform optimally in and capture the higher acceleration,
temperature, and vibration measurements that the hypersonic
vehicle experiences.
Hypersonic Flight Stages
Hypersonic craft may travel through different flight stages,
including boost, ballistic, reentry, pull-up, glide, and terminal
stages. All hypersonic platforms, irrespective of their launch
angle or trajectory, start with a boost or launch phase. The
duration of the boost phase varies, and the flight test conditions
are marked by high accelerations, temperature rise, and
intense vibrations.
Once the boost phase is completed, and after the stage separation,
hypersonic platforms go through a ballistic phase where
the main forces are gravity and drag. In this stage, flight test
conditions are more benign concerning acceleration, vibration,
and temperature, especially for the exoatmospheric region if the
platforms are launched for a long-range minimum energy tra10
jectory.
Flight test components should be designed to prevent
arcing within the unit and the resulting loss of the telemetry
system in accordance with Paschen's Law (an equation that
describes the conditions for an electric arc to form between two
electrodes as a function of pressure and gap length).
Other launch angles are available, such as the depressed trajectory,
where less time is spent in the exosphere to keep the
platform below a radar horizon. Regardless, the reentry for
both ballistic and depressed trajectory ballistic platforms is
marked by increased temperature and vibration as they enter
the atmosphere. Without delving into the physics and the
impact on the platform surface materials in this paper, flight
test components must be designed for these high-temperature,
high-vibration conditions. The duration for ballistic reentry is
relatively short compared to non-ballistic entry platforms.
Non-ballistic atmospheric entry is a class of atmospheric
entry trajectories that follows a non- ballistic trajectory by
employing aerodynamic lift in the high upper atmosphere. It
includes trajectories such as skip and glide. Skip is a flight trajectory
in which the spacecraft goes in and out of the atmosphere.
Glide is a flight trajectory where the spacecraft stays in
the atmosphere for a sustained flight period.
In most cases, a skip reentry roughly doubles the range of the
suborbital spaceplanes and reentry vehicles compared to a purely
ballistic trajectory. A series of skips can further extend the range.
Since increased range relates to increased flight duration, especially
if the hypersonic platform trades speed for range through
these multiple skips, the flight test equipment must perform
longer in conditions marked by increased temperature and
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Aerospace & Defense Technology, December 2024
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Aerospace & Defense Technology - December 2024

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