Not all military and avionic electronics need
to be ruggedized, but unprotected systems
would last only minutes in many of these
environments. Thus, solutions such as rugged
cases, conduction cooling, and highreliability
connectors become mandatory
design elements.
Elma’s air transport rack (ATR) 6U VPX is
a good example of the starting point for military
rugged designs (Fig. 1). The conductioncooled
case has machined walls that act as
integrated card guides. Its wedge locks transfer
heat from the cards to the walls of the case.
Designed for environments with temperature
ranges of –40°C to 70°C, it meets a host of
MIL-STD and ARINC specifications as well.
Another sealed ATR system, Mercury Computer Systems’
PowerBlock 50, is available with Intel and PowerPC processors
and Xilinx FPGAs (Fig. 2). It supports x4 PCI Express switch fabric
and can incorporate an internal hard or solid-state disk. Liquid
cooling is an option.
The VPX and PowerBlock 50 highlight two key issues surrounding
rugged designs—military, avionics, or otherwise. The
first is environmental isolation, keeping sand and surf away from
the electrical components. This is usually the easier of the two
issues. The second is heat dissipation, which tends to involve heat
redistribution away from the source (typically the electronics or
its power source).
For example, the airframe houses the electronics in unmanned
aerial vehicles (UAVs) like the Predator from General Atomics
Aeronautical Systems, but containing heat only makes the temperature
rise. Conduction systems provide one way to move heat
to an area where it can be dissipated. However, this approach often
requires heat movement to different places around an aircraft.
Liquid cooling is one alternative to conduction cooling that
promises high heat dissipation, providing a mechanism to move
heat via a fluid to almost any point within a system. The challenge
with liquid cooling is the infrastructure required. Normally,
the cooling liquid is enclosed, and specially designed heatsinks
transfer heat from hotspots such as the processor or GPUs to the
cooling liquid. Also, pumps are required to move the liquid.
SPRAY COOLING
One alternative to liquid cooling is spray cooling from Spray-
Cool, which uses liquid to cool a system without an enclosed fluid
system like conventional water cooling. Instead, it uses a non-conductive
dielectric liquid that’s distributed using a misting system.
The mist condenses into a liquid and is drawn out using a series
of drains. The system then acts like a conventional liquid cooling
system with a pump that moves the liquid to a heat exchanger.
SprayCool offers a number of standard rack systems (Fig. 3).
The company also can apply the technology to custom systems.
The approach can be applied to an entire system with multiple
boards. It also can be targeted like a conventional liquid cooling
system, in which case it typically cools hot chips such as the main
processor or a GPU.
Part of a design includes the spray system and the intakes for
the condensed liquid. The number of intakes and their position
depend on the operating environment. For example, an aircraft
system where inverted operation is a possibility would normally
have intakes all around the case interior, whereas a system that
would be fixed could get by with a couple of intakes on the bottom
where liquid would collect.
The SprayCool system can operate from –65°C to 71°C and
altitudes up to 70,000 feet. As with other liquid-cooled systems,
it can reduce overall weight by providing a more efficient cooling
system. It’s a sealed system that can provide protection in hazardous
environments where sand and water are the enemy. Finally,
liquid cooling systems can handle significantly more heat dissipation
than convection or conduction systems.
One advantage of the SprayCool approach versus conventional
liquid cooling is that SprayCool can handle most hardware without
modification. There’s no need for conformal coating or other
special protection for the boards. SprayCool systems are finding
homes in UAVs such as the Predator and the Northrop Grumman
Global Hawk.
MORE RUGGED TECHNOLOGIES
Sealing and ruggedizing other system components is equally
important. It doesn’t do much good if the electronics continue
to run if the I/O systems no longer work. One example of a ruggedized
display system is Eurotech’s 6.5-in. thin-film-transistor
(TFT) LCD DuraVIS 4300 multifunction display (MFD) subsystem
(Fig. 4).
The VGA-resolution, LED backlit display is readable in sunlight
and can be dimmed down to 4%. It has 18 backlit keys.
The MIL-STD-810F-qualified 4300 also has room for a pair of
PC/104+ boards and comes with a 1-GHz Celeron M-based motherboard
that’s preloaded with Linux or Windows XP Embedded.
It’s essentially a complete ruggedized PC, including the display.
Another trend is the move toward solid-state storage, such as
Elma’s ACT/Technico flash-memory storage. Its SecurStor and
RAIDStor come with magnetic rotating disks or flash drives (see
“ACT/Technico Sports CompactPCI And PMC Disk Storage”). Flash is more
expensive, but it has no moving parts.
BACKPLANES FOR RUGGED SYSTEMS
Though many rugged systems are highly customized, they’re
often based on standards such as VME. These backplane systems,
which usually come in 3U and 6U form factors, are used with a
range of approaches from convection cooling to spray cooling.
Typically, more than half of the backplanes used in these commercial
off-the-shelf (COTS) environments are customized versions of standard products. This is primarily due to the custom I/O
on the backplane. These systems also usually have custom I/O out
front as well.
VME is out in front with products like Kontron’s VM6250
multiprocessor board, which incorporates dual- or single-core
Freescale MPC8640/8641 processors with Altivec vector processing
support (Fig. 5). This 6U VME VITA 57-compliant board,
which only uses 27 W, is available in convection- and conductioncooled
versions. It supports the faster 320-Mbyte/s VME 2eSST
bus speeds and has a pair of mezzanine sockets for PMC or highspeed
serial XMC cards. It also features an FMC slot.
Continue to page 2