The main function of harnesses onboard
satellites are power distribution and data
transmission. Harnesses onboard spacecraft
are typically arranged in bundles
and can be routed through several paths
throughout the spacecraft. Electrical harness
can claim large areas at the inner
surfaces of the satellite structure wall.
On a typical spacecraft, the total weight
of harness can amount to several percent
of the overall spacecraft weight.
Harnesses primarily are critical due to
the fact that they are often located just
behind the satellite structure wall. An
impacting particle which penetrates the
spacecraft structure may endanger
unprotected harness, since the impact
fragments are dispersed into a ‘spray
cone’ that may hit and severely damage
large parts of unprotected harness. Each
harness submitted to hypervelocity
impact testing consisted of several operating
power- and twisted-pair data
cables, and one radiofrequency (RF)
line, transmitting a 9.35 GHz signal. An
example of data transmission measurements
is shown in Figure 2, where the
differential transmission method is used.
As can be seen, there is temporary data
transmission errors during several tens
of microseconds, followed by nominal
operation of the cables at later stages
after the impact again. Larger impact
energies can lead to more violent impact
damages that can cause longer temporary
perturbations up to permanent
failure of operation e. g. the severing of
cables. It is to be expected that such
damages lead to a functional deficiency
of the entire spacecraft.
The larger the stand-off between structure
wall and harness, the lower the probability
of failure is. Therefore, if it is feasible,
harnesses should be moved away
from structure walls. If additional
spacing cannot be realised, wrapping the
harness in a moderate amount of protective
fabrics, such as Nextel or Kevlar,
should improve dramatically the protection
performance. NASA has followed
such procedures successfully for ISS
harnesses routed outside the manned
modules.
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