MIL-DTL-38999 Connectors: Functions, Interfaces and Integration in Rugged Systems

MIL-DTL-38999 connectors are a family of high-density circular electrical connectors designed for harsh environments. They are widely used in defense, aerospace, naval and land-based systems when mechanical, environmental or integration constraints make conventional computer connectors less suitable.

Depending on the selected configuration, this connector family can be used to integrate very different functions: power, Ethernet, serial interfaces, CAN Bus, USB, video, discrete signals, synchronization signals or interfaces coming from expansion cards.

ECRIN Systems integrates MIL-DTL-38999 connectors into several rugged computers, servers and networking systems, including ONYX, ONYX-Ultra, the nanoONYX family, ONYX-AGX, µTOPAZE, QUARTZ and OPALE-Rugged.

The objective is not simply to replace an RJ45, USB or video connector with a military connector. The interconnection must be designed together with the complete system: electronics, cabling, mechanics, electromagnetic compatibility, environmental constraints, maintenance and integration into the final platform.

• MIL-DTL-38999 defines a family of connectors, not a communication protocol.
• The signal carried depends on the contact arrangement, cabling, pinout and electrical integration.
• The presence of a MIL-DTL-38999 connector does not automatically mean that the complete equipment is qualified to MIL-STD-810, MIL-STD-461 or DO-160.
• In a rugged system, the connector must be considered together with the cable, backshell, shielding, chassis, filtering and platform constraints.

MIL-DTL-38999 defines a family of high-density circular electrical connectors designed for demanding environments.

It does not refer to one single connector model. The configuration can vary depending on the series, shell size, contact arrangement, contact type, coupling method, transmitted signals and application constraints.

This flexibility allows the same connector family to be adapted to very different system requirements.

One point is essential: MIL-DTL-38999 does not define Ethernet, USB, CAN Bus, RS-232 or a video interface.

Ethernet, USB, CAN, RS-232 and RS-422 are communication or electrical interfaces. MIL-DTL-38999 concerns the connector used to implement the physical interconnection, provided that the selected configuration is compatible with the electrical characteristics of the signal.

On conventional computers, interfaces are generally accessible directly through standard connectors such as RJ45, USB, HDMI, DisplayPort or DB9.

In an embedded system exposed to vibration, shock, dust, humidity, salt fog or electromagnetic constraints, the I/O interfaces must be designed as part of the complete system.

The connector layout must remain consistent with the chassis mechanics, platform cabling, available space, environmental requirements, EMC constraints, maintenance operations and the type of signals being transmitted.

The connector therefore becomes a functional part of the system integration, just like the power supply, storage, cooling or I/O cards.

Depending on the connector, contact arrangement, cabling and system configuration, different functions can be integrated: electrical power, Ethernet, serial interfaces, CAN Bus, USB, video, GPIO, synchronization signals and interfaces originating from expansion cards.

Within ECRIN Systems platforms, this approach is implemented in several ways.

On QUARTZ, copper Ethernet interfaces and the fiber interfaces of the relevant versions are integrated into a platform using MIL-DTL-38999 connectors.

ONYX and nanoONYX rugged computers also use this connector family for different I/O functions. ONYX can notably integrate power, Ethernet, USB, serial interfaces, video, audio, GPIO and interfaces associated with internal PMC or MXM expansion.

Some platforms, however, combine several types of rugged connectors. This is notably the case with ONYX-AGX, which uses MIL-DTL-38999 connectors together with dedicated rugged interfaces such as HDMI FTV, USB-C FTV or µCOM for specific high-speed links.

Similarly, nanoONYX-USB3 retains the rugged connector approach of the nanoONYX family while adding two USB 3.0 interfaces using rugged USB-C connectors.

This distinction is important: the presence of MIL-DTL-38999 connectors on a platform does not necessarily mean that every interface exclusively uses this connector family.

Connector selection should be addressed early in the system development process.

The correct approach is therefore to define a complete interconnection solution rather than selecting a connector independently.

• Connector integration varies depending on the function of the system and the interfaces required.

These examples illustrate a fundamental point: connector configuration depends on the purpose of the system and its integration environment. There is no single MIL-DTL-38999 configuration that can be applied to every rugged computer.

MIL-DTL-38999 and MIL-STD-810 do not define the same thing.

MIL-DTL-38999 concerns a family of circular electrical connectors.

MIL-STD-810 provides environmental test methods used to evaluate equipment against various environmental constraints.

The presence of a MIL-DTL-38999 connector therefore does not mean that a computer, server or Ethernet switch is automatically qualified according to MIL-STD-810.

Qualification must be considered at complete equipment level and for the selected configuration.

Depending on the ECRIN Systems platform, products may also be concerned by MIL-STD-461 for electromagnetic requirements, DO-160 for aerospace environmental constraints, MIL-STD-1275 for power requirements on certain military platforms, or an IP protection rating.

Applicable standards, test methods and qualification levels must always be checked product by product.

In an embedded platform, connectors directly influence internal cabling, mechanical layout, signal routing, EMC, maintenance accessibility and I/O distribution.

Connectivity must therefore be taken into account from the first stages of system integration.

Depending on the platform and project constraints, ECRIN Systems’ Modified COTS approach can support adaptation of selected I/O interfaces, connector areas, front or rear panels, expansion cards and hardware configurations.

This flexibility is particularly relevant when a rugged computer must interface with existing cabling or with a connector definition imposed by the final platform.

No.

This connector family is mainly used on ECRIN Systems platforms designed for harsh environments.

Other platforms may use conventional computer connectors or provide specific rugged connector adaptations depending on the project.

For example, µOPALE V2 can be equipped with rugged MIL-SPEC rear I/O connectors on request, while the OPALE V2 family offers different customization possibilities for front and rear interfaces.

The exact configuration of each product should therefore be checked individually rather than applying a single connector characteristic to the complete ECRIN Systems portfolio.

In embedded equipment designed for demanding environments, connectivity cannot be considered as a simple accessory. It is part of the mechanical, electrical and environmental integration of the complete system.

Connector selection must take into account the interfaces to be transmitted, cabling, shielding, EMC, environmental requirements, maintenance constraints and integration into the final platform.

ECRIN Systems designs and adapts rugged computers, servers and networking equipment with these constraints in mind. For projects requiring MIL-DTL-38999 connectivity, specific I/O interfaces or adaptation of a COTS platform, our engineering teams can define a configuration suited to the integration requirements.