VITA 90: Small Form Factors for UAVs and Other Space Constrained Platforms
The VITA 90 family of standards, also known as VNX+, is being crafted to support the government and commercial requirements for ruggedized, small form factor (SFF), Modular Open Systems Architecture (MOSA) compliant, electronic systems suitable for deployment on small aerial platforms, C5ISR pods, spacecraft, ground vehicles, as well as man-wearable applications. The VITA 90 VNX+ standards borrow heavily from VITA 65, also known as OpenVPX, the family of standards which are arguably the dominant MOSA standards used in today’s avionic, vetronic, and space systems. VNX+ has been selected by the Sensor Open Systems Architecture (SOSA) consortium as a SFF standard to be used for C5ISR sensor payloads in space constrained applications, typical in manned and unmanned air vehicles and spacecraft.
VNX+ traces its roots back to 2010 when OpenVPX was first ratified and the VITA 74 (VNX) SFF Technical Committee was founded. VITA 74 was developed as a down-scaled derivative of VPX to be used for deployments in small commercial and military platforms with limited space, weight, and power (SWaP) availability. In 2017, after a three-year trial-use period, the VNX standard was ratified by ANSI and VITA as ANSI/VITA74.0-2017. In 2021, SOSA adopted the VNX form factor, but the results of a trade study directed some changes and additions that created better alignment with OpenVPX, as well as SOSA’s overarching objectives, quality attributes, and architectural principles.
The changes and enhancements proved so beneficial that VITA made the decision to stand-up a new technical committee which would create a new SFF standard which is based on legacy VNX, heavily influenced by OpenVPX, optimized for maximum performance and signal integrity, and incorporates all necessary changes driven by the SOSA consortium requirements. The result is the VITA 90 family of standards, supporting all necessary high-speed serial fabrics and protocols as used in today’s C5ISR applications, allowing VNX+ modules to communicate amongst themselves at speeds twice as fast as legacy VNX, allowing for twice the power dissipation per module, and enabling subsystems with up to eight times as many addressable modules.
The VITA 90 family of standards is on-track to be complete and ratified by the end of 2023. Due to the interwoven nature of the standards, all standards will be held in draft status until all of the related standards have been completed. Using the draft standards available to participating VITA and SOSA members, several manufacturers and programs have already begun prototype system design, fabrication, delivery, and test.
The VITA 90 Family of Standards
The VITA 90 family of standards include the following:
VITA 90.0 VNX+ Base Standard
VITA 90.1 VNX+ Slot Profiles and Naming Conventions
VITA 90.2 VNX+ Coaxial/Optical Connectivity and Aperture Blocks
VITA 90.3 VNX+ Power Conversion, Energy Storage, and Power Filter Modules
VITA 90.4 VNX+ Alternate Mounting, Cooling, Keying, and Retention Mechanisms
VITA 90.5 VNX+ Space Use Considerations
VITA 90.x System Application Guide
It should be noted that the VITA 90.x VNX+ standards are module standards, not system standards. The VITA and SOSA committees have striven to fully define the module’s electrical and physical interfaces. However, the committees have specifically not dictated specific chassis design attributes, when and how specific cooling designs are to be employed, or the size and scope of VNX+ deployments, which can range from a single module mounted as a standalone processor, to a disaggregated array of single modules using available platform space, to a large ATR-style chassis in an avionics bay. The “Flagship” VNX+ 19mm module measures 78mm × 89mm × 19mm, about the same size as a deck of ordinary playing cards.
The 19mm module is typically used for compute modules, Ethernet switches, software defined radio (SDR) modules, and typical payloads such as a tactical grade MEMS Inertial Measurement Sensor with GPS. For optimal cooling and minimal development risk, VNX+ 19mm compute modules are generally designed utilizing a multifunction basecard and a MOSA processor board, often a computer on module (COM) mezzanine, built to a published mechanical size and electronic interface, such as PICMG’s COM Express Type 10 COM standard.
The VNX+ basecard hosts the Samtec SEARAY™ high-speed data connector, an optional aperture block with positions for coaxial RF/Video contacts and MT Ferrules for fiberoptic connectivity, a connector for a MOSA COM mezzanine processor, as well as circuitry for miscellaneous power, I/O and overhead functionality. For example, the MOSA COM mezzanine is typically an Intel® Architecture (IA) SBC with multi-core Atom or Core processors, or an NVIDIA Xavier Supercomputer Edge Processor System on Module (SoM), or a Xilinx Zynq Ultrascale+ MPSoC/RFSoC SoM.
The VITA 90 standard also defines a smaller module measuring 78mm × 89mm × 12.5mm. The 12.5mm module is targeted for less complex tasks such as discrete and analog I/O, MIL-STD-1553/ARINC-429 data bus interfaces, mass storage, and chassis management. A typical 12.5mm I/O or storage module hosts some combination of up to two mPCIe I/O modules or two mSATA SSDs. The VNX+ standard will additionally define a 26mm (double 12.5mm) module, and a 39mm module that will be selectively used when it is necessary to accommodate larger components, such as those used for rad-hard space applications, or when tight timing cannot be achieved if typical module-to-module connectivity is used.
VNX+ Deployments In Typical UAV Platforms
The VNX+ standard has been designed to accommodate a variety of deployment options. The non-traditional deployment options are being defined in VITA 90.4, whereby the top face of the module, is modified with features to allow the installation of a set of wedge-locks which may be used to facilitate easy insertion and extraction, as well as to allow the mounting of the module on an available bulkhead using the provided mounting holes.
These “wings” on the top face of the module are generally coplanar with the hottest surface in the module, the surface which usually is touching the CPU or GPU, providing an ideal sink to carry heat from the module. Either one of these mounting schemes many be used when a single module is all that is needed to accomplish the desired mission, or when multiple disaggregated modules are needed with inter-module connectivity accomplished using a cabled backbone. A prime example of this is when simple compute functionality is all that is needed, and the module is going to be operated from clean power available in a small UAV. These mounting features are being defined in VITA 90.4, the dot-standard which describes alternative mounting and cooling schemes.
In addition to using standard backplane connectivity for a multiple module deployment, the standard allows the creation of a cabled “backbone,” with appropriate connectivity utilizing Samtec’s SEAC series connectors, cabled databus and signal connections, as well as optical and coaxial signals using aperture receptacles which can mate with the module’s aperture block with its included array of contacts.
For a UAV deployment, in addition to a cabled backbone, a typical chassis and backplane arrangement is appropriate for both sensor pod and traditional avionics bay deployments. Most such deployments will include a power supply module (PSM) and optional MIL-STD-461 filter module, compute module (SBC), sensor I/O processor (GPGPU, FPGA, MPSoC), storage module, and/or radio frequency (RF) module for real-time telemetry and control. Such a system would require up to six slots in one.
In conclusion, building scalable systems for UAV or other space-constrained deployments is made easier when the VNX+ family of standards is used. From a single-module deployment to a disaggregated set of modules on a cabled backbone, to a fully integrated system on a monolithic backplane, the use of MOSA solutions and VNX+ drives lower technical risks and lifecycle costs, and ensures better out-year sustainability.
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