For years, the military has been trying to use Small Form Factor (SFF) cards in applications with severe Size, Weight, and Power (SWaP) restrictions. A veritable plethora of technical, reliability, and performance problems surfaces when any of the 100-plus existing SFF specifications are considered during critical embedded systems development. However, Themis Computer and PCI-SYSTEMS Inc. are actively working to resolve these problems in two new tentatively named proposals: micro.VPX (referring to a smaller version of the popular 3U VPX cards) and NanoATR (Air Transport Rack), a reference to a very small version of the ATR used in avionics platforms. Both proposals are now active projects within the VITA Standards Organization (VSO).
Problems, problems everywhere
So, what are all the problems with present SFF specifications? For starters, most of them use flimsy, unreliable cable connections between boards. That will never fly (pun intended) in high-shock and -vibration environments such as mil/aero platforms. The same goes for vetronics (military ground vehicle platforms). The connectors used on most of the SFF specifications I have researched use connectors with electrical contacts incorporating the best aspects of Bronze Age metallurgy. And what about cooling? The commodity folks who wrote the present SFF specifications think that snapping on an unreliable chip fan or cramming a low Mean Time Between Failure (MTBF) fan into the “cube” chassis somewhere is adequate. They never considered contaminates, corrosives, salt spray, and little critters getting in the box. Finally, the present SFF specifications were basically designed for use in vending machines, low-level industrial controls, and telecom Femto-cells – commodity applications about as far from critical embedded systems requirements as one can get.
The PCI-SYSTEMS Inc. card is about 3" high by 4.33" deep (the size of a 2.5" disk drive). The PCB is actually held in a metal X-frame to provide rigidity and a thermal transfer surface. The Themis Computer card is smaller, about 2.1" high and 3" deep (the size of a pack of cigarettes) and does not use a metal frame. The thermal interfaces on the Themis Computer cards are on the PCB. The cards from both proposals mount in hermetically sealed “cubes” of different slot counts and use advanced and efficient conduction-cooling techniques that eliminate all the cooling problems with present SFF specifications.
The cards from both implementations plug into a high-speed backplane with rugged high-performance serial connectors from ERNI and Samtec, respectively. And the I/O coming into the “cube” uses gas-tight sealed connectors on the chassis back wall, connected to a transition module that plugs into the backplane that eliminates all the horrific cable problems with present SFF specifications.
Target markets for the “cubes”
It is obvious that these boards and “cube-like” containers are much more ruggedized than anything in the existing menagerie of SFF specifications available. They were designed from the ground up for Unmanned Aerial Vehicles (UAVs), Unmanned Undersea Vehicles (UUVs), vetronics, and other critical applications and segments that were ignored when the existing SFF specifications were written.
Earlier this year, two new programs were initiated that can use these new Themis Computer and PCI-SYSTEMS Inc. and concepts: the NASA/USAF plug-and-play satellite bus and the U.S. Navy/Honeywell plug-and-play cockpit instrument bus for military aircraft. While both projects call it a “bus,” it is actually a standard for a glorified wiring harness, connecting a number of the small computing “cubes” together (probably with optical fiber connections). Just think of each little cube as a dedicated subsystem in a larger system architecture. NASA/USAF wants to be able to build and launch a new satellite in a week using off-the-shelf electronics “cubes.” The Navy/Honeywell program aims to replace any broken cockpit instruments in a matter of minutes – and to send that aircraft on its mission without moving it off the carrier’s flight deck for repairs.
These small “cubes” fit right in with the new two-level maintenance concept that the military is embracing: Line Replaceable Units (LRUs). Here is what two-level maintenance is all about:
- Remove and replace the broken unit on the line.
- Send the inoperable unit to a maintenance depot where highly trained technicians open up the unit and repair the boards.
- Seal it back up, and put the repaired operable unit back in stock.
This need for two-level maintenance ties into the military’s new mandates for future critical electronic systems:
- All combat military platforms must be repaired and battle ready within 30 minutes.
- No tools can be used to remove the inoperable unit and install an operational one.
- The military personnel on the line replacing the units can have no more than 10 minutes of training.
- An LRU can weigh no more than 37 pounds for a two-man lift. (Yes, there are women in the services today.)
None of the previous SFF specifications come anywhere close to meeting these mandates. But the PCI-SYSTEMS Inc. and Themis Computer engineers had these in mind when they developed these new SFF concepts. There will be thousands of these micro.VPX and Nano-ATR “cubes” deployed in the next few years. And the standards are now under development in VITA.