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A New Embedded System Specification Takes on Extreme Environments

There are a few open specifications in the embedded industry that have been used in the extreme environments of space over the years. These include VME, CompactPCI, OpenVPX, and MicroTCA. But, prime contractors such as Airbus and others desired a high performance and versatile architecture that was relatively simple and cost-effective. The CompactPCI Serial Space specification was ratified in 2017 to address these requirements, resulting in a compelling architecture for defense and space-based projects.

A Brief History

VITA and PICMG have developed excellent specifications to address the needs of extreme environments. But, CompactPCI and VME are bus-based standards that do not provide the performance and inherent reliability of switched fabrics. OpenVPX and MicroTCA are both excellent, high bandwidth, and low SWaP (Size, Weight Power) standards. But, CompactPCI Serial – the basis for CompactPCI Serial Space (also referred as cPCI Serial Space) – is less complex and has a low-cost design approach. CompactPCI Serial, which was ratified in 2015, is similar to legacy CompactPCI in that it leverages the 3U and 6U Eurocard form factor with 160mm deep cards. But it uses new, rugged high speed Airmax VS connectors. The power is based on 12V (with an option of 5V standby), providing simplicity and cost-effectiveness. Having one main power rail is much simpler to specify the right power supplies and can significantly reduce the costs. The CompactPCI Serial power rails can be either a single plane, or every board could be supplied and controlled individually. Utilizing PCIe (current solutions are up to Gen3) or Gigabit Ethernet (current solutions are up to 10GbE with 40GbE-capable implementations), the aggregate data rates parallel other high-performance standards.

It is a significant benefit to potential users that CompactPCI Serial already has several design provisions for rugged environments. The specification started out in railway applications, having to survive shock vibration, moisture & dust ingress, etc. The transition to CompactPCI Serial Space did not require signification adjustments. See Figure 1 for an example of a conduction-cooled CompactPCI Serial switch card that meets -40° to +85° temperature environments as well as MIL levels of shock/vibration.

Figure 1. CompactPCI Serial has long been ruggedized for extreme environments. This SBC example (courtesy of MEN Micro) shows an example of a 3U version in a conduction-cooled clamshell.

Ready for Space

There were important implementations for CompactPCI Serial to meet space-level ruggedization. These include:

1) Redundancy: A key element for space applications is redundancy. Downtime is extremely costly and hardware maintenance is impossible. Having a Dual Star architecture for both the data traffic and Spacewire was important. Spacewire is a rugged variant of Firewire for space applications. It can be used to connect multiple enclosures in the system, providing a serial point-to-point connection.

2) Control & Monitoring: This is a critical requirement for satellites, positioning, and other space systems. So, each slot of CompactPCI Serial Space allows the use of several dedicated monitoring and control signals.

3) RAD-Hard & Rugged: Naturally, the specification required the rugged implementation of CompactPCI Serial and defines the levels for meeting compliance. Radiation is a problem for all standard CMOS devices, so ensuring the system is RAD-hard is paramount. Significant testing was required.

4) Outgassing: Outgassing is a potential issue for plastic components as they can condense onto optical elements, thermal radiators, or solar cells and obscure them. NASA has a list of low-outgassing materials for use in spacecraft. The issue requires careful selection and testing.

5) Testing & Screening: As mentioned above, testing and screening of components was critical in the specification development process. The PICMG members working on the specification needed to be certain that it could meet shock, vibration, radiation, outgassing, extreme temperatures of -40°C to +85°C, dust and moisture ingress, EMI, etc.

The cPCI Serial Space specification defines a utility connector, which can be controlled and configured via an open management bus. It takes over the hot-plug functionality from CompactPCI Serial. Of course, hot-swap functionality is not required in a satellite in space. But, it can actually be an attractive feature on ground-based systems and for test/simulation systems. System monitoring/management is supported via the CAN (I2C bus is also optional for less critical applications).

Applications

With wide use in railway and other rugged applications, ruggedized CompactPCI Serial is common. The wedge lock clamshells for conduction-cooling provide further stability, and the modules meet MIL specs such as MIL-STD 810 and 901D for shock and vibration levels. CompactPCI Serial has already been used in defense applications, including a fully DO-168G qualified rugged natural convection ARINC600 ATR for an airborne network server.

With cPCI Serial Space’s additional controlling and monitoring capabilities, there is an even stronger solution for failure detection, isolation, and recovery (FDIR). Another application for CompactPCI Serial in defense applications is a conduction-cooled ATR with a 3U backplane and a supplementary internal fan for additional cooling for a data recorder in a military vehicle. The architecture was also recently chosen on a major naval program as an upgrade from a previous CompactPCI design. There are certainly benefits from leveraging CompactPCI boards for the newer serial solutions. The types of Mil/Aero applications for CompactPCI Serial and cPCI Serial Space include (but are not limited to):

  • Simulators (for satellite environment, military systems)

  • Test equipment (for satellites, military systems)

  • Satellite platform control (altitude and orbit control)

  • Satellite payload/instrument control

  • Mass memory (satellite, military data recorders)

  • Networking/communications (satellite & ground station, military)

  • RADAR & SONAR systems

  • Electronic warfare & signal intelligence systems

  • C4ISR & situational awareness systems

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