Tech Briefs Magazine - May 2022 - 49

APPLICATION
BRIEFS
Configuring Spacecraft's
On-Board Computing Systems
Harwin
Portsmouth, United Kingdom
www.harwin.com
4 Links
Milton Keynes, United Kingdom
www.4links.co.uk
F
or decades, space exploration remained exclusive
to large-scale international agencies, such as
NASA and ESA. In more recent years, though, things
have changed considerably. Now numerous commercial
enterprises and academic institutions are
entering this sector, which has led to the 'New Space'
phenomenon.
Among the fundamental dynamics driving this
has been access to more affordable technology and
the emergence of open-source reference designs.
These have helped lower the engineering barriers to entry,
making it possible for smaller players to place the equipment
they have designed and created into orbit.
Based in Buckinghamshire, 4Links plays an essential role in
'New Space' development. The company, founded in 2000,
provides the engineering know-how and consultancy services
SMEs need to complete their space projects.
A recent focus for the 4Links team has been to produce a
platform for both software and hardware that would make
space-bound systems quick, easy, and cost-effective to develop.
Named Loki, after the Norse god, who was known for being
disruptive, the platform encourages design re-use without starting
each new venture from scratch.
The objective of Loki is to provide space customers with a
fully configurable processing platform onto which they can
build their on-board computers. It is designed for satellites using
the increasingly popular SpaceWire network infrastructure
methodology. Based on programmable logic and modular
construction, Loki reduces the engineering effort involved,
leading to faster completion times and lower associated overhead
costs.
Loki consists of an Eurocard format carrier board with a mezzanine
board attached. The mezzanine board is responsible for
all the fixed functionality aspects, including processing, memory,
system management. At the mezzanine's centre is a high-performance
Xilinx Kintex UltraScale FPGA device. It can be reprogrammed
before launch or even updated once in flight. An
I/O carrier board manages all the interfacing. Acting as a gateway,
it covers communication with the different satellite subsystems
and the input for powering the FPGA mezzanine.
The ability to put the mezzanine onto carrier boards with
different I/O configurations makes it much easier to modify
the setup as needed. The other key advantage of Loki is that
the board is only required to be qualified once and can then be
Tech Briefs, May 2022
used for multiple configurations. As a result, everything can be
ready for launch in a dramatically shorter time frame.
" The carrier/mezzanine approach makes this platform very
appealing to our customers. It is much more agile, resulting in
development progressing at an accelerated pace, " said Spencer
Saunders, Engineering Director at 4Links. " Another benefit
for users is that they can initially get one board qualified and
then reconfigure others. This qualification avoids the need for
costly re-certification for each new project that they embark
upon, " he added.
Engineering Considerations
As Loki is intended for use in satellites and other orbiting
hardware, the overall weight of the hardware had to be kept to
an absolute minimum. In addition, the cost-sensitive nature of
most 'New Space' projects had to be recognized, which means
that using MIL-SPEC custom-built components in the design
would not be feasible. Highly resilient commercial-off-the-shelf
alternatives had to be used instead. On top of this, the parts
had to be resistant to damage. All the components selected
needed to function for prolonged periods despite exposure to
extreme temperatures, mechanical shocks, and vibrations.
How the carrier board would interface with each of the subsystems
presented the 4Links development team with several
additional design challenges to overcome. Moreover, conforming
to all the requirements previously outlined, there would be
very little room in which the necessary connectors could be fit.
A high pin density configuration needed to be specified.
Finding an Effective Interconnect Solution
Conventional connector solutions, like Micro-D format,
would have too large dimensions for this type of implementation.
As a result, the PCB would take up valuable room. Also,
such connectors are heavier due to metal housings, so another
option was needed.
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