SpaceVPX extends the embedded computing standard to meet the special demands of space
Space vehicles, whether manned or unmanned, have traditionally relied on custom embedded computing systems. Since standard systems were not designed with space applications in mind, they did not address the critical issues of space flight, such as outgassing, "tin whiskers," redundancy, and ruggedness. Designers and engineers, however, recognize the benefits of using well-established, standardized, open-architecture platforms to create a diverse ecosystem offering more choices, lower costs, and reduced risk. The availability of space-centric standardized platforms brings the advantages of a competitive environment, lower development costs, and higher reliability.
Using open standards means not having to repeatedly climb the learning curve for new designs. Reuse of hardware, firmware, and software shortens design cycles and lowers life cycle costs. It can also allow designers to focus on pressing issues like reduced size, weight, and power consumption (SWaP), which is always a leading priority in space applications.
Designing for reliability
SpaceVPX, also known as VITA 78, uses the VITA 65 OpenVPX backplane standard as the basis for space-capable systems. Developed by the VITA 78 working group as part of the Next Generation Space Interconnection Standard (NGSIS), SpaceVPX enhances the VPX standard with features required for space. Thus, SpaceVPX addresses a number of issues critical to spaceflight not covered by VPX (see Figure 1):
- Single-point failure tolerance through redundant power distribution and fault detection on critical configuration signals
- Spare modules that can be powered on and off as needed
- System management with support for new features
- Robust system diagnostics
SpaceVPX adds a dual-redundant utility-management module and plane to manage the new features. Similar to the profiles created in OpenVPX, SpaceVPX also defines profiles for payload, control, memory, and switching.
The U.S. Air Force Research Laboratory (AFRL), which launched NGSIS in 2011, was searching for a standards committee to host their NGSIS and came to VITA. They determined that VPX would be an acceptable architecture and initiated a Study Group in March 2012 that became VITA 78.
A strawman was developed outside the public realm of the VITA Standards Organization (VSO) until International Traffic in Arms Regulations (ITAR) clearance was achieved. VITA 78 then transitioned to a functioning VITA 78 Working Group in early fall of 2013.
VITA 78 is now in the latter stages of development, having recently gone through a Working Group ballot. From there it will proceed to a VSO ballot, then be submitted for ANSI approval. Time frames on this process are not highly regimented, as the ballots are really tools to solicit comments; the time frame for release can vary depending on the number of comments and the time needed to resolve the comments. The AFRL has led the initiative, assisted by multiple OEMs.
SpaceVPX connectivity: Ultra-rugged
Designing an embedded computing system for space requires a solution that not only withstands the extreme vibrations of liftoff, but also handles the extreme temperatures, background radiation, and other harsh conditions of extraterrestrial travel.
The TE Connectivity backplane connector chosen for SpaceVPX, the MULTIGIG RT 2-R connector, is a backwards-compatible variant of the VITA 46 VPX connector, the MULTIGIG RT 2 connector. The MULTIGIG RT 2 connector, the standard for VITA 46 VPX, represented a huge step forward in the world of rugged embedded computing and is deployed globally in applications ranging from armored vehicle vetronics and helicopter radar avionics to space applications. The modular connector system features a protected backplane connector and uses a pinless wafer design in place of pin contacts, an approach well-established in commercial applications. Wafers – available for differential, single-ended, and power needs – can be easily modified to support specific customer needs for characteristic impedance, propagation delay, and other electrical parameters. Even though the wafers can be “tuned” to specific electrical needs, standard wafers, for instance, 100-ohm wafers for differential signals, suffice in most cases.
The VITA 46 MULTIGIG RT 2 connector is qualified to VITA 47 environments. For optimal design factors of safety, SpaceVPX looks beyond VITA 47 to incorporate both enhanced environmental performance and design redundancy, together with consistent space-design paradigms. Relative to environmental concerns, new testing levels have been explored to characterize the interconnects beyond the severest-anticipated exposure levels. One such public initiative has been the VITA 72 study group. The VITA 72 group devised the vibration “torture test,” exposing a 6U VPX test unit to random vibration levels of 0.2 g2/Hz for 12 hours. To meet the requirements of VITA 72, TE engineers modified the contact system of the VITA 46 connector to provide quad-redundant contact rather than the two points of the existing system. Increasing the points of redundancy increases reliability in a high vibration environment. The new MULTIGIG RT 2-R connector doubles the points of contact between the receptacle contact and the wafer, thereby providing SpaceVPX designers with both access to a massive and time-tested VPX ecosystem and the redundancy desired for space flight applications.
Beyond its ultra-rugged design, the MULTIGIG RT 2-R connector has several other features that make it attractive for space applications.
- The MULTIGIG RT 2-R version is a very light VPX backplane connector. In traditional backplane connector designs, the plug-in module connector is often the heavy half, but the MULTIGIG connector’s minimalistic design takes advantage of significant air gap rather than heavy polymer.
- It meets NASA outgassing requirements total mass loss (TML) of 1.0 percent and collected volatile condensable materials (CVCM) of less than 0.01 percent. Outgassing, which is the release of gases trapped in a solid, is an issue since the gases can degrade performance of charge-coupled device (CCD) sensors in satellites, thermal radiators, or solar cells. Outgassing is a challenge to creating and maintaining clean, high-vacuum environments. Moreover, the closed environment of spacecraft can make outgassing an even greater concern.
- Because the connector avoids use of pure tin, it therefore does not promote growth of so-called tin whiskers that can be a source of shorting between contacts, between printed circuit board pads, and between contacts and pads. Tin whiskers can also lead to metal vapor arcs, which occurs when the solid metal whisker is vaporized into a plasma of highly conductive metal ions that can form an arc capable of carrying hundreds of amperes. Tin whiskers have been demonstrated as a significant potential failure mode for on-orbit satellite failure.
VPX is the prevalent standard for embedded high-performance computing, with a data rate demonstrated above 10 Gbps. Benefiting from several years of evolution, the VPX ecosystem is highly diverse, providing designers with an array of choices for single-ended and differential signals, mezzanine, power, optical, and RF connectivity. As VPX has evolved, new standards have been created to deliver a comprehensive range of interconnection needs. Figure 2 shows a notional configuration of signal, RF, and optical possibilities on a single card edge.
The additional connectors available for the ecosystem have not been fully evaluated for SpaceVPX applications, but initial examination has not identified any insurmountable issues. As designers look for additional connectivity solutions, those already part of the VPX ecosystem are leading candidates.
VPX takes to space
SpaceVPX builds on the well-established philosophy of combining open architectures and commercial off-the-shelf (COTS) products for high-performance embedded computing (HPEC). Not only does it enjoy the advantages of a robust competitive environment, it can also tap into the rich availability of products already introduced. At the same time, SpaceVPX extends the VPX standard to accommodate the unique needs of space flight to create a system that puts a top priority on redundancy and reliability in hostile environments. SpaceVPX can be seen as a prime example of dual-use technology, using the same connector deployed in countless VITA 46 VPX programs in development and putting it to work in space flight hardware.
The interconnect as offered by TE is already in production and has already flown, with VITA 78 SpaceVPX higher-level products currently in development. Release and flight or fielding of those products has not been announced; the public nature of those announcements may vary depending on whether it is a military or civilian mission. It is likely that integrators offering SpaceVPX-compliant product will make press announcements of product availability/fielding without naming specific missions.
TE Connectivity 610-893-9800 www.te.com