[Editor’s Note: The ANSI/VITA 78 standard was recently revised to add additional profiles, additional communication protocols (such as Ethernet), higher-speed copper connectors, and an updated naming methodology for Slot and Module Profiles. ANSI/VITA 78.0-2022 is available at the VITA online store (www.VITA.com/Standards). The VITA 78 working group has begun documenting further enhancements to the standard.]

For decades, open systems architectures and open standards have helped accelerate innovation to end users in aerospace and defense applications through the development of interfaces that are open, key, and well-defined. Today, space system designers and developers are truly embracing the SpaceVPX (ANSI/VITA 78) standard, which leverages the OpenVPX (ANSI/VITA 65.0) architecture through its slot profile and module profile level building blocks, which create interconnect solutions based on the user’s need.

What is the SpaceVPX standard?

SpaceVPX is a standard for creating plug-in cards (PICs) from the slot and module (protocol) profiles. In turn, these building blocks create interconnected subsystems and systems. Developed under the auspices of The Next Generation Space Interconnect Standard (NGSIS), it is the result of a government-Industry collaboration. The primary goal of SpaceVPX is to cost-effectively remove bandwidth as a constraint for future space systems.

SpaceVPX is based on the VITA OpenVPX (VITA 65) standard with enhancements that extend the standard for space applications. The NGSIS team selected the OpenVPX standard family as the physical baseline for the SpaceVPX standard because VPX supports both 3U and 6U form factors with ruggedized and conduction-cooled features suitable for use in extreme environments. The infrastructure of OpenVPX also allows for prototyping and testing SpaceVPX on the ground.

SpaceVPX is built upon several standards from VITA (www.vita.com/Standards) and the European Cooperation for Space Standardization (ECSS) (https://ecss.nl/):

• ANSI/VITA 46.0: VPX baseline standard
• ANSI/VITA 46.11: System management on VPX
• ANSI/VITA 48.2: Mechanical standard for VPX REDI conduction cooling
• ANSI/VITA 60: Alternative connector for VPX
• ANSI/VITA 62: Modular power-supply standard
• ANSI/VITA 63: Hyperboloid alternative connector for VPX
• ANSI/VITA 65.0: OpenVPX system standard
• ANSI/VITA 66: Optical interconnect on VPX
• ANSI/VITA 67: Coaxial interconnect on VPX
• ECSS – Remote Memory Access Protocol (RMAP)
• ECSS – SpaceWire standard
• ECSS – SpaceFibre standard
• Gigabit Ethernet

The limitations of OpenVPX for space applications

An evaluation of OpenVPX for space usage revealed several shortcomings: The key limitation was the lack of features available to support a full, single-fault-tolerant, highly reliable configuration. Utility signals were bused and, in most cases, supported only one set of signals via signal pins to a module. As a result, a pure OpenVPX system has opportunities for multiple failures. VITA 46.11, System management on VPX, is the basis for fault-tolerant management of a SpaceVPX system, but a suitably complete management-control mechanism was not fully defined and so was expanded in SpaceVPX.

From a protocol perspective, SpaceWire is the dominant medium-speed data and control plane interface for most spacecraft, yet the typical OpenVPX control planes are peripheral component interconnect express (PCIe) or Ethernet which are not generally used in space applications. (Note: Gigabit Ethernet was added to the 2022 revision of the SpaceVPX standard.)

SpaceVPX mission: fault tolerance

The goal of SpaceVPX is to achieve an acceptable level of fault tolerance while maintaining a reasonable level of compatibility with existing OpenVPX components, including connector-pin assignments for the board and the backplane.

For the purposes of fault tolerance, a module (defined as a printed-wire assembly which conforms to defined mechanical and electrical specifications) is considered the mini-mum redundancy element, or the minimum fault containment region. The utility plane and control plane within SpaceVPX are all distributed redundantly and are arranged in star topologies, dual-star topologies, partial-mesh topologies, or full-mesh topologies to provide fault tolerance to the entire system. To meet the desired level of fault tolerance, the utility plane signals are dual-redundant and switched to each SpaceVPX card function.

A trade study, conducted in 2010 through a government and industry collaboration with the support of the SpaceVPX Working Group, compared various implementations including adding the switching to each card in various ways and creating a unique switching card. The latter approach was selected so SpaceVPX cards can each receive the same utility plane signals that an OpenVPX card receives, with minor adjustments for any changes in topology. This became known as the Space Utility Management module (SpaceUM), a major foundation of the SpaceVPX standard.

A 6U SpaceUM module contains up to eight sets of power and signal switches to support eight SpaceVPX payload modules – the 3U version of the SpaceUM can support up to five. It receives one power bus from each of two power supplies and one set of utility plane signals from each of two system controller functions required in the SpaceVPX backplane. The various parts of the SpaceUM module do not require their own redundancy. They are considered extensions of the power supply, system controller and other SpaceVPX modules for reliability calculation.

Figure 1 shows the reliability model diagram for the SpaceVPX use case system. The diagram includes the contents of two SpaceUM modules, dual power-supply modules, dual system-controller modules, dual-control switch modules, dual data-switch modules, four sets of dual payload modules, one set with an optionally attached peripheral module. The diagram also includes a peripheral module that is independent. The utility, data, and control planes are all dual-redundant. The utility plane is indicated by P (Power) and S (System) connections. Data plane redundancy is shown as dual redundant but is application-dependent. Additional payloads, peripherals, and switches can be added according to the application and the redundancy. Note that the SpaceUM module is distributed across the various modules and not as a standalone module that must be spared.

[Figure 1 | Typical SpaceVPX reliability model diagram. Illustration source: VITA.]

Profiles for space defined

Each slot, module, and backplane profile in OpenVPX is fully defined and interlinked. Adapting these profiles for use in space requires specification of a SpaceVPX version of each profile.

A slot profile provides a physical mapping of data ports onto a slot’s backplane connector, which is agnostic to the type of protocol used to convey data from the slot to the backplane.

Module profiles are extensions of their accompanying slot profiles which enable mapping of protocols to each module port. A module profile includes information on thermal, power, and mechanical requirements for each module. Some module profiles for SpaceVPX are similar to OpenVPX, which enables use of OpenVPX modules and backplanes for prototyping or testing on the ground. However, most module profiles for space applications are significantly different from profiles for ground applications, so full specifications consistent with SpaceVPX are required. The section of the SpaceVPX standard that defines these profiles forms a majority of the standard.

Standardized SpaceVPX interconnects

Interconnects are another critical part of SpaceVPX. As with other elements of the standard, they are based on interconnects developed for OpenVPX, but designed for the extreme space environment. Problematic temperatures, vibration, outgassing, and other factors can catastrophically compromise interconnect systems as well as signal and power integrity. For decades, designers for space applications have relied on customized interconnect designs to ensure the reliability of embedded electronics exposed to the extremes of space. The high cost and long lead times of a custom interconnect solution were once considered a worthwhile investment against failures that are extremely costly or impossible to fix in space.

Today, the use of standard interconnects drives down cost, improves availability, and maintains a path for future expansion. By leveraging the OpenVPX architecture, SpaceVPX brings in the interconnect solutions which are defined in VITA standards and have gone through extensive testing to support their use in space.

The SpaceVPX slot profiles define the use of VPX connectors (VITA 46 or alternate VPX connectors) and enable implementation of RF (VITA 67) and optical (VITA 66) modules at the plug-in module to backplane interface. Power supplies follow the VITA 62 standard, which also defines the power supply connector interface. For XMC mezzanine cards in plug-in modules, XMC 2.0 connectors per VITA 61 are recommended. Rather than defining new connectors with special characteristics, SpaceVPX slot profiles reference the appropriate VITA connector standards that support the OpenVPX architecture.

RF and optical modules

RF and optical connector modules can be integrated within an OpenVPX slot to carry signals through the backplane to/from the plug-in module. These connector modules are mounted to the boards (including standard aperture cutouts on the backplane) to house multiple coaxial contacts or optical fibers. They can replace select VITA 46 connectors within a slot. These RF and optical connector modules and contacts have been used in satellite systems and are suitable for other applications in space.

VITA 67 is the base standard for RF modules. VITA 67.3 is used for SpaceVPX architecture with apertures defined within specific slot profiles for RF and optical connector modules.  VITA 67.3 offers coaxial contact solutions with the initial sub-miniature push-on micro (SMPM) contacts as well as higher-density coaxial interfaces NanoRF and switched-mode power supply (SMPS), which can increase the contact density two to three times over SMPM. A new revision to VITA 67.3 has begun to add 75 Ohm coaxial interfaces to support higher speed video.

VITA 66 is the base standard for optical modules, with MT ferrules as the primary optical interface between the plug-in module and backplane. The apertures in SpaceVPX slot profiles accommodate optical and hybrid RF/optical connector modules meeting the requirements of VITA 66.5. MT interfaces can be specified for 12 or 24 fibers for highest density.

The future of SpaceVPX interconnects

By leveraging the OpenVPX architecture, SpaceVPX can also leverage the OpenVPX interconnect roadmap which addresses solutions having faster speeds, higher density, smaller size, and lighter weight. There is significant activity with new and revised VITA standards to define technologies supporting next-generation embedded computing.

Higher data rate MULTIGIG RT 3 connectors are available and standardized in VITA 46.30 (compliant pin) and 46.31 (solder tail) to support channels to 25-32 Gigabits/sec, supporting 100G Ethernet and PCI Gen 4 and 5. These can be incorporated in a SpaceVPX slot by replacing VITA 46.0 connectors.

The latest revision of the VITA 67.3 standard includes higher-density RF interfaces NanoRF and SMPS, reducing size and weight – both critical for space systems – and accommodating higher frequencies to 70 GHz. A new revision to VITA 67.3 has begun to add 75 Ohm coaxial interfaces within a connector module to support higher speed video protocols.

The VITA 66.5 standard will be released in 2022, documenting higher-density optical interfaces, bringing up to three MT interfaces into a half-module and enabling integration of a fixed edge-mount transceiver. In addition, VITA 66.5 provides solutions with NanoRF contacts and optical MTs integrated into a common connector module, providing unprecedented density within an OpenVPX slot.

New VITA 62 power supply standards have addressed three-phase power (VITA 62.1) and higher 270VDC input voltages (VITA 62.2). New MULTIBEAM XLE connectors from TE with isolating fins provide this upgrade for higher voltage levels while maintaining the same VITA 62.0 interface.

Key takeaways

• SpaceVPX is a set of standards for interconnects between space system components developed to cost-effectively remove bandwidth as a constraint for future space systems.
• The goal of SpaceVPX is to achieve an acceptable level of fault tolerance while maintaining a reasonable level of compatibility with existing OpenVPX components.
• SpaceVPX interconnect are based on interconnects developed for OpenVPX, adapted for the extreme space environment.
• New and revised VITA standards continue to define technologies that support the next generation of embedded computing while reducing costs, improving availability of components, and maintaining a path for future expansion.
• Numerous space agencies have become VITA members and are key contributors to the development and evolution of the SpaceVPX standard.

Patrick Collier is Open Systems Architect and lead systems engineer at Aspen Consulting Group. He focuses on the development and use of open architectures for both space and nonspace applications. Michael Walmsley, global product manager for TE Connectivity, has more than 40 years of experience with interconnects, primarily in engineering and product management roles.

Aspen Consulting Group · https://www.aspenconsultinggroup.com/

TE Connectivity · https://www.te.com/usa-en/home.html