Understanding PPTC Resettable Fuses Qualified for Outgassing Test ECSS-Q-ST-70-02C and Thermal Cycling Test

Introduction

PPTC (Polymeric Positive Temperature Coefficient) resettable fuses play a vital role in circuit protection, especially in high-reliability applications such as aerospace and space missions. These fuses must meet stringent outgassing and thermal cycling requirements to ensure performance in harsh space environments. This article delves into the significance of PPTC resettable fuses that meet the outgassing requirements of the ECSS-Q-ST-70-02C standard and their applications in low Earth orbit satellites, while also addressing the thermal cycling requirements crucial for space environments.

The Importance of Outgassing Tests

What is Outgassing?

Outgassing refers to the release of gases trapped within materials, which can occur when they are exposed to a vacuum or high temperatures. In high-reliability applications such as aerospace and space missions, outgassing can cause contamination of sensitive instruments, leading to malfunctions or failures.

ECSS-Q-ST-70-02C Standard

The ECSS-Q-ST-70-02C standard, developed by the European Cooperation for Space Standardization (ECSS), specifies the requirements for the outgassing properties of materials used in spacecraft. Materials that pass this standard are deemed suitable for use in space environments, where low outgassing is critical to prevent contamination.

Outgassing Test Procedure

According to the ECSS-Q-ST-70-02C standard, the outgassing test involves several steps:

• Pre-conditioning of samples at 22°C and 55% relative humidity for 24 hours.
• Weighing of samples, empty sample cups, and collectors.
• Conducting a thermal vacuum test at 125°C in a vacuum of less than 10^-5 mbar for 24 hours.
• Weighing of samples and collectors after the thermal vacuum test.
• Post-conditioning of samples again at 22°C and 55% relative humidity for 24 hours.
• Final weighing of samples.

The test results include:

• Total Mass Loss (TML):Total mass loss relative to the initial sample mass.
• Recovered Mass Loss (RML):Mass loss after water absorption during post-conditioning relative to the initial sample mass.
• Collected Volatile Condensable Material (CVCM):Mass gain of collectors relative to the initial sample mass.

Thermal Cycling Requirements in Space Environments

What is Thermal Cycling?

Thermal cycling involves subjecting materials to repeated temperature changes, which can cause stress due to differential expansion or contraction. In space, components frequently experience extreme temperature fluctuations as they move in and out of direct sunlight or between different operational states.

Importance of Thermal Cycling Resistance

Components used in space must withstand these repeated temperature changes without degradation in performance. Thermal cycling resistance is crucial to prevent cracking, warping, or other failures that could compromise the mission.

Testing for Thermal Cycling Resistance

Thermal cycling tests involve exposing the component to a series of temperature cycles, typically ranging from low to high temperatures, to simulate the thermal conditions in space. The component's performance is monitored to ensure it can withstand these conditions without failure. For more detailed information on thermal cycling tests, you can visit the NASA S3VI Knowledge Base.

Importance in Space Applications

Spacecraft Reliability

Minimizing outgassing helps maintain the cleanliness and reliability of spacecraft components over the duration of their missions.

Optical Performance

Controlling outgassing is critical for optical systems where even small amounts of contaminants can degrade performance.

Contamination Control

Outgassing tests are part of broader contamination control efforts to ensure that materials used in space do not compromise mission objectives or the longevity of spacecraft operations.

PPTC Resettable Fuses and ECSS-Q-ST-70-02C Qualification

Importance of Low Outgassing in Space Applications

In space applications, the integrity and reliability of materials are paramount. Low outgassing materials prevent the release of volatile compounds that can condense on and damage sensitive equipment. PPTC resettable fuses qualified to the ECSS-Q-ST-70-02C standard ensure they are safe for use in these demanding environments.

Benefits of Using Qualified PPTC Resettable Fuses

Reliability

PPTC resettable fuses that meet the ECSS-Q-ST-70-02C standard offer high reliability, ensuring consistent performance in critical applications.

Safety

These fuses provide robust protection against overcurrent conditions, reducing the risk of circuit damage and potential mission failures.

Cost-Effectiveness

The self-resetting feature of PPTC fuses eliminates the need for manual replacement, saving time and maintenance costs.

Applications of PPTC Resettable Fuses in Space

Low Earth Orbit (LEO) Satellites

Low Earth Orbit (LEO) satellites operate at altitudes between 180 km and 2,000 km above the Earth's surface. These satellites are increasingly used for communication, Earth observation, and scientific research. The proximity to Earth offers reduced latency for communication signals and higher resolution for imaging applications.

Circuit Protection in LEO Satellites

LEO satellites are equipped with numerous electronic circuits that require protection from overcurrent conditions. PPTC resettable fuses ensure the longevity and reliability of these circuits, preventing disruptions in satellite operations. The harsh environment of space, including exposure to radiation, extreme temperature variations, and thermal cycling, necessitates the use of components that can withstand these conditions while maintaining low outgassing properties.

Satellite Communication Systems

Reliable communication is critical in space missions. LEO satellites, in particular, rely on robust communication systems to transmit data back to Earth. PPTC resettable fuses safeguard communication equipment from overcurrent events, ensuring continuous and stable communication links. This reliability is crucial for maintaining data integrity and mission success.

Earth Observation Instruments

Space missions often carry sensitive scientific instruments for Earth observation, weather monitoring, and environmental studies. These instruments must operate flawlessly to provide accurate data. PPTC resettable fuses qualified for low outgassing protect these instruments from electrical faults, maintaining the integrity of scientific data and ensuring that observations are accurate and reliable.

Selecting the Right PPTC Resettable Fuse

Key Considerations

When selecting a PPTC resettable fuse for space applications, consider the following factors:

Current Rating

Ensure the fuse can handle the normal operating current of the circuit without tripping unnecessarily.

Voltage Rating

The fuse must be rated for the voltage levels present in the application to prevent breakdown or failure.

Trip Current

The trip current should be set appropriately to protect the circuit without causing nuisance tripping.

Reset Time

Consider the time it takes for the fuse to reset after tripping, ensuring it aligns with the application’s requirements.

Compliance with ECSS-Q-ST-70-02C

Always verify that the selected PPTC resettable fuse complies with the ECSS-Q-ST-70-02C standard for outgassing. This compliance ensures the fuse is suitable for use in space environments, minimizing the risk of contamination and ensuring mission success.

Thermal Cycling Resistance

Ensure the PPTC resettable fuse is tested and qualified for thermal cycling resistance. This qualification guarantees that the fuse can withstand the repeated temperature changes typical in space environments without compromising its performance or reliability.

Conclusion

PPTC resettable fuses play an indispensable role in protecting electronic circuits, particularly in high-reliability applications such as low Earth orbit satellites. Fuses that meet the stringent outgassing requirements of the ECSS-Q-ST-70-02C standard and are resistant to thermal cycling provide reliable, cost-effective, and safe protection for critical circuits. By understanding the importance of these components and selecting the right fuses, engineers can ensure the success and longevity of their projects in the demanding conditions of space.

Find out more aboout Fuzetec FSMDH High Temperature Products and ECSS-Q-ST-70-02-C Standards.