Study of Hypervelocity Impact Influence on Spacecraft Computer Operations

Computer boxes are needed for on-board
data processing/handling (OBDH), control-,
monitoring-, telecommunication
(TC), telemetry (TM), avionics and payload
equipment. A share of 20%-40% of
a satellite bus volume consists of computers.
Computer boxes contain Printed
Circuit Boards (PCB) with analogue and
digital components, capacitors, inductors,
resistors, and micro-chips, which
are enclosed in a milled aluminium box
with a thickness of about 2 mm for electromagnetic
compatibility and radiation
shielding reasons. The criticality of electronic
hardware is slightly reduced by
the fact that most electrical components
are redundant. Moreover, the delicate
electronics are shielded passively by
their own housing. However, the complete
failure of an e-box will result at
least in complications until the redundant
system has taken over, if a redundant
system exists. Otherwise failure of
an e-box could mean the loss of a complete
subsystem, ie, the OBDH, TC, TM,
with potentially catastrophic consequences
for a mission. During the hypervelocity
impact tests, the computerboxes
were operating in what is considered
normal mode, performing basic
read- and write-operations. The
observed failure modes were temporary
failure and permanent failure. The temporary
failures caused interruptions in
the operation of the processor, followed
by nominal operation a few milliseconds
later. The reason for temporary failures
is assumed to be related to conductive
penetrating dust-like fragments causing
transient shorts. Any temporary failure
ie, temporary loss of operational performance
of electronic components may
manifest itself to the systems operator as
an in-flight anomaly. Such in-flight
anomalies, including faulty data transmission
and ‘ghost commands’, have
been reported by spacecraft operators
and may possibly be explained by hypervelocity
impacts. The permanent failures
manifested as sudden loss of supply
voltage or loss of nominal operation of
the computer. In Figure 3, a PCB with
severe impact damages (memory chip
and resistors + capacitances removed,
deposits of metallic spray in various
locations) and the corresponding CPU
signals are shown.
This study was a first step towards a
better understanding of vulnerability of
spacecraft equipment to hypervelocity
impacts. Still, considerable efforts need
to be made especially in the experimental
area to generate a comprehensive
picture of all effects related to the vulnerability
of spacecraft equipment to hypervelocity
impacts. However, the investigations
performed have already led to a
drastic enhancement of knowledge that
can now be exploited by spacecraft
designers. Amongst others, the work
performed can be used by spacecraft
operators to possibly provide explanations
for unexplained malfunctions of
equipment operations in satellite missions.