The Smaller VITA 73 Small Form Factor and MicroATR chassis

Inspired by a 2.5-inch disk drive, VITA 73’s “MicroATR” box is really tiny…and rugged.

Small form factor military needs are increasing as the battlefield evolves from big, manned crafts to small, unmanned crafts.  Why is this trend happening? The different theaters throughout the world require more and more “safe” reconnaissance and intelligence as activities are shifting from face-to face combat to highly computerized and integrated electronics platforms where humans are further away from direct enemy contact.

Where only years ago an intelligence unit would be sent out on foot to scope out the enemy, today’s field units utilize drones, IP radio networks, small unmanned crafts and electronic equipment. Whether they have cameras, software defined radio units, weapon systems or any other electronics in their cargo bays and pods, the emphasis is always on small. With its stated goal of defining standards and specifications for mission-critical systems like defense, avionics and UAVs, VITA’s smallest standard is the successful 3U size (100 mm). But add several modules, a backplane and a chassis and the system might be too big for unmanned UAV crafts. That’s where VITA 73 comes in as a smaller alternative to 3U systems.

The Smallest Was 3U VPX
VITA’s 3U VPX (officially called VITA 46) is the organization’s latest ratified standard and was used in Afghanistan and Iraq on the bigger, unmanned UAV drones such as Northrup-Grumman’s Global Hawk.  As the benefits of this technology where accepted, smaller and smaller crafts have been developed for air, sea and land use. Although general funding has been slacking in the defense industry, new technologies ranging from electronic armor for tanks and fighting vehicles to unmanned crafts and intelligence electronics has increased.

Yet despite the newness and rich features of VPX and its flavors like OpenVPX (VITA 65), over time this standard will again hit the “form factor wall” as did the industry’s previous “darling” 6U CompactPCI when 3U VPX took over the marketplace. SWaP designs need a high ratio of the available board area for components compared with the total outside dimensions of the given chassis. By radically eliminating everything that is not really needed—like wedgelocks or bulky VPX MultiGig RT connectors—smaller, rugged modules are possible.

Small Requirements
If a small form factor standard is to be comparable to 3U while using less system real estate in some sort of rugged enclosure, VPX provides an excellent baseline. The requirements are:

  • Capable of sustained operation in any combat or extreme industrial environment
  • Minimization of size, weight, and power consumption
  • Maintains high-levels of availability-including high MTBF and low MTTR
  • Competes with bigger standards like 3U VPX by using the same powerful multicore CPU chips and FPGAs like the Xilinx Virtex-7
  • Has a fault-tolerant design (diagnostic and prognostic capabilities)
  • Has a long-term maintenance and non-obsolescence plan
  • Designed with future technologies in mind
  • Supports optical data transfer as well as FPGA usability.

VITA working groups have formed to address this need for a very small rugged form factor. Three key efforts have surfaced and are actively being worked on, already delivering prototypes and development kits to interested parties as work progresses on the standardization efforts.

The Small Future of 3U VPX
VITA 73 (Rugged Small Form Factor), for example, is a small form factor based electrically on VPX and backwards compatible to 3U VPX when using carrier cards. It can accommodate the same board surface for components (in double-wide) as 3U VPX, but in a form factor that’s about 1/4th the size.  Not much taller than a soft drink can and with GEN3 PCIe backplane speeds, the small 3 x 4-inch VITA  73 modules can be inserted into conduction cooled chassis (Figure 1) or into sealed, forced air-cooled microATR rugged military-style computers. They present the integrator with an entirely new approach to SWaP with blazing fast speeds.  There are two flavors available: Single modules with a 11.5mm pitch; and double-slot modules with a 23mm pitch where the two PCBs are interconnected with 400 pins from board to board.

Figure 1: VITA 73 conduction cooled 8-slot chassis. The VITA working group calls for dimensions of 4.5 x 4 x 6 inches (W x H x D).

Inspired by the 2.5-in SSD form factor, the most important goal during development was to eliminate any bulky parts like connectors, wedgelocks and big guide pins. Instead, the chassis itself is used as a “clam shell”. The biggest benefit of VITA 73 is increasing the usable board real estate for components while reducing the cubic footprint ratio. By creating a double slot pack, the available component area is as big as a 3UVPX board but requires only a fraction of chassis real estate.

VITA 73 modules have a full set of I/O pin outs and do away with multiple backplane profiles. Since there currently are only three backplane profiles and a customizable active backplane mezzanine, designers are able to connect and configure everything as they wish by only changing out the design of the active backplane mezzanine. A designer can place anything from an FPGA to fabric switches to optical module interconnects here to meet any customer demands without confusing them with backplane profiles or slot profiles for each and every different application.  [Editor’s note: VITA 65, the interoperable version of VPX called OpenVPX, requires these kinds of profiles to assure interoperability.]

Figure 2: A VITA 73 chassis compared to a 3U VPX chassis. The savings comes primarily from the smaller LRUs and efficient backplane.

The system connects to the outside world with a full predefined set of electrical and optical I/O pins to keep NRE out of the purchase order. As well, there are several bonus features included in VITA 73. A 10 MHz single-ended frequency is defined to aid in system wide data acquisition and synchronize power supplies. Also, a star trigger and other trigger functions are implemented. For next generations of PCI Express, the usage of the PCIe 100 MHz clock is defined for all boards used in the chassis and a separate instrumentation frequency of 100 MHz is part of the specification.

All Boxed Up
To get a feel for how much smaller these systems are, see the below picture of the VITA 73 8 slot chassis sitting on a 3U VPX 6 slot chassis:

The functional density is higher with VITA 73 than any other small form factor currently on the market in this class of product. The chart in Figure 3 shows available board space compared to cubic volume in the three VITA small form factor working groups.

Figure 3: Various size metrics compare VITA 73 with other SFF working groups VITA 74 and 75.

The VITA 73 workgroup does not define a chassis, only modules and backplanes. Describing only footprints, stack-ups and pin locations lets the integrator build chassis variants that fit into any space, all the way to making the chassis an integral structural component on any application. This entirely new approach can save space and weight. Naturally, a standard setup of a chassis on an air duct or cold plate can be used, but also possible are free standing conduction cooled chassis variants.

The main features of a typical 8 slot microATR application as shown in Figures 1 and 2:

Figure 4: VITA 73 microATR™ sealed and forced air cooled chassis, available from PCI-Systems.
  • Smallest footprint 8 Slot: W:4.5” H:6” D:4”
  • Lowest possible weight
  • Based on the VPX (VITA 46/48) electrical standard
  • No edge connectors used; connectors are capable for 10Gb
  • High speed Gen3 PCIe backplane
  • 10 GB high speed module to backplane transfer
  • High density design
  • Unlimited active backplane mezzanine capability
  • Zero wires in the entire system.

For this latter item, PCI-Systems, the originator of the VITA 73 standard has a “No.Wires™” engineering solution for rear I/O. As well, PCI-Systems Inc. also has VITA 73 compatible sealed, forced air cooled chassis as shown in Figure 4.

In summary we can say that VITA is once again at the forefront of standards development, with the three small form factor working groups being on-time and on-track to position themselves as “the industry standard” for unmanned systems. Each form factor working group has its place in the critical embedded small form factor systems marketplace. But the VITA 73 design is based on good engineering instead of politics, ensuring the safety and readiness of our fighting forces who increasingly rely on jam-packed electronic UAVs, drones, and small crafts.


Marc Benjamin Gross, CEO Sales and Marketing. Marc previously worked at the advertising agency BBDO as Junior Art Director before joining the family company four years ago. His first product design at PCI-Systems Inc. was the “Desert Gecko” 3U VPX chassis.

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