Space missions demand the highest levels of reliability due to the hostile environment of space and the inability to perform repairs once a spacecraft is launched. Wiring harnesses are critical components that interconnect various systems, and their design and manufacturing must ensure fault-free performance throughout the mission lifespan. To achieve this, the European Cooperation for Space Standardization (ECSS) and NASA have set stringent standards that guide the design, assembly, and quality control of wiring harnesses. Two important standards in this domain are ECSS-Q-ST-70-61C and NASA-STD-8739.4A. These standards provide detailed guidelines to ensure high-reliability harnesses for space applications.
This article provides an overview of the key principles and requirements outlined in these standards, with a focus on design, material selection, and quality assurance for harnesses used in space applications. As an example some basic harness design using coaxial cables will be used.
Main goal in this example is to connect two signals from two different PCBs to M1.5 screws terminals. For this purpose two coaxial cables will be used with solder lugs. Shield of both cables connects with one more additional lug.
Figure 1: Basic harness design
Right side will be soldered directly to the PCBs as figure 2 shows:
Figure 2: Connection of coaxial cables to PCBs. Source: ECSS-Q-ST-70-61C
Both standards emphasize the importance of using materials that can withstand the harsh conditions of space, including radiation, extreme temperatures, vacuum, and mechanical stresses like vibration. The selection of conductors, insulators, shielding materials, and connectors must meet stringent criteria to prevent degradation over time:
Figure 3: Example of individual shield termination. Source: NASA-STD-8739.4A
ECSS-Q-ST-70-61C and NASA-STD-8739.4A both stress the use of qualified materials that have undergone space-specific testing to ensure their performance in the operational environment.
With this requirements in mind it will be used Habia RG-178BU coaxial cable with PTFE insulation and AXON ZLA 2419 single wire (grounding) with ETFE insulation material.
The design and layout of the harness are critical to reducing electrical noise, mechanical stress, and the potential for wire failure. Key principles include:
Figure 4: Bend Radius for completed Interconnecting Cable or Harness. Source: NASA-STD-8739.4A
The assembly process is a critical step in ensuring the reliability of harnesses. Both ECSS-Q-ST-70-61C and NASA-STD-8739.4A provide comprehensive guidelines on the assembly methods, which include:
For the assembly process you can prepare as much detail diagrams as technician needed.
Figure 5: Assembly drawing
Contamination is a critical concern for space systems, as particles or residues on harnesses can degrade electrical performance or interfere with sensitive equipment. Both standards emphasize strict contamination control practices:
To ensure that harnesses meet reliability requirements, comprehensive testing is required at every stage of production, from material selection to final assembly. Key testing methodologies include:
Both ECSS-Q-ST-70-61C and NASA-STD-8739.4A emphasize the importance of quality assurance and strict adherence to workmanship standards to ensure the reliability of harnesses. Every step of the design, assembly, and testing process must be meticulously documented, and personnel must be trained and certified to perform their tasks:
High-reliability harness design is a cornerstone of ensuring mission success in space exploration. By adhering to standards like ECSS-Q-ST-70-61C and NASA-STD-8739.4A, engineers can design and assemble wiring harnesses that withstand the extreme conditions of space while providing reliable electrical performance throughout the mission lifecycle. These standards guide every aspect of harness design, from material selection and assembly techniques to rigorous testing and contamination control, ensuring that space systems remain operational in the most demanding environments.
As space missions become more complex and ambitious, the role of well-designed, reliable wiring harnesses becomes ever more critical. Understanding and implementing the best practices outlined in these standards are vital steps in building space systems that perform flawlessly over long-duration missions.