Cable Assemblies for High‑Altitude UAV Operations

High-altitude UAVs often fly at altitudes above 60,000 feet (≈ 18,300 meters), encountering pressures below 5 kPa and temperatures ranging from -60 °C to +85 °C. In this harsh stratospheric environment, every cable assembly must maintain power, control, and data integrity.

1. Environmental Challenges

Stratospheric operations impose:

• Low Pressure: The equipment must pass the RTCA DO-160G Section 4 altitude test (Class D2: up to 50,000 ft; Class E1: up to 70,000 ft) without insulation outgassing or dielectric breakdown.
• Temperature Extremes: The cable material must be able to withstand rapid temperature fluctuations from -60°C to +85°C, as specified in DO-160G, Section 5, Thermal Cycling.
• Weight Sensitivity: Every gram of weight lost extends flight time, which is critical for drones with long endurance.
• Mechanical & EMI Stress: Vibration, shock, and solar/atmospheric radiation require robust shielding and strain relief.

2. Advanced Material Selection

2.1 PTFE Insulation

Polytetrafluoroethylene (PTFE) has one of the widest temperature windows of all commonly used plastics, as it can be used continuously over a temperature range of -200 °C to +260 °C, with short-term temperatures up to +300 °C, in addition to excellent dielectric properties and low outgassing under vacuum.

2.2 Silicone Jackets

Silicone rubber jacketing is ideal for aircraft cable jacketing because of its flexibility at temperatures as low as -55 °C, its ability to withstand continuous temperatures up to +205 °C and short-term peak temperatures up to +250 °C, and its excellent resistance to UV rays, ozone, and moisture.

3. Conductor & Mechanical Considerations

3.1 Lightweight Conductors

Silver Plated Copper Clad Aluminum (SPCCA) conductors are 69% lighter than solid copper conductors of the same size, yet they maintain the high-frequency conductivity of the cable surface.

3.2 Minimum Bend Radius

To avoid kinking and conductor fatigue, the long-term bend radius should be at least 10 times the overall cable diameter. Smaller bending radii may lead to insulation cracks and impedance shifts.

3.3 Shielding & EMI Control

Combine metal foil shielding (for high frequency attenuation) with braided metal shielding (for mechanical strength) and ground both ends to maximize EMI/RFI suppression in solar and RFI-rich flight environments.

4. Strain Relief & Overmolding

Molded strain relief bushings utilize thermoset elastomers, such as polyurethane or silicone, to absorb vibration at the connector terminals. Overmolding combines the cable jacket and connector backshell into a single, sealed assembly, ensuring both environmental sealing and mechanical robustness.

5. Environmental Testing & Certification

5.1 RTCA DO‑160G

• Section 4 (Temperature & Altitude): Verify performance in unpressurized locations up to 70,000 feet, per D2/E1 category.
• Section 5 (Thermal Cycling): Rapid cycling of the assembly from -65 °C to +85 °C to demonstrate material fatigue.

5.2 Vacuum‑Chamber Trials

The assembly is subjected to a pressure of less than 5 kPa to verify the low outgassing insulation and sealing of the connector under near-vacuum conditions.

5.3 EMI/EMC Screening

Conducted/radiated emissions and susceptibility certification according to MIL-STD-461G to ensure that UAV avionics equipment is not interfered with or damaged by external electromagnetic fields.

Conclusion

By utilizing PTFE and silicone materials, SPCCA conductors, rigorous mechanical design (bend radius, shielding), robust overmolding/strain relief, and rigorous DO-160G/MIL-STD-461 testing, you’re delivering cable assemblies that enable reliable, lightweight performance in the stratosphere to enable successful high-altitude UAV operations missions.

Apple Liu

Apple Liu, Romtronic’s Marketing Manager, specializes in driving Asian market growth. With a degree in International English and eight years of sales experience in the electronic cable and harness industry, she brings deep industry expertise and a global perspective. She is passionate about Romtronic’s leadership in digital engineering and is dedicated to advancing the brand’s presence and innovation.