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The Environmental and EMI Testing for Satellites

Updated: Aug 27, 2023


Vibration Test

The environmental and EMI testing for satellites are rigorous processes aimed at ensuring that the satellite will function reliably in space and won't interfere with other systems. These tests simulate the harsh conditions of space and the launch vehicle environment to validate the satellite's design and its tolerance against these conditions.


1. Environmental Testing:

a) Vibration Testing:

  • Purpose: To simulate the mechanical loads a satellite might experience during launch.

  • Process: The satellite is subjected to vibrational forces on a shaking table. It undergoes both sine vibration (at specific frequencies) and random vibration (across a spectrum of frequencies).

  • Outcome: The satellite should not have any structural damage, and its functionality should remain intact after the test.


Vibration test of the CHEOPS satellite by ESA

Vibration testing is fundamental in satellite development because satellites are subjected to significant vibrational loads during their launch. The rocket's engines and aerodynamic forces, as well as stage separations, generate these vibrations. Vibration tests ensure the satellite can withstand these conditions without damage or malfunctions.

Values and Parameters to Look For:

  1. Frequency Range: This is the spectrum over which the test is performed. Satellites are tested over a wide frequency range, which typically spans from low frequencies (e.g., 5 Hz) to high frequencies (e.g., 2000 Hz or higher).

  2. Acceleration Levels: Expressed in 'g' or gravitational units, this denotes the severity of the vibration. The satellite might experience different g-levels based on its position in the launch vehicle and the specific launch vehicle being used.

  3. Test Duration: The length of time the satellite is subjected to the vibration. This can vary but is typically long enough to represent the entirety of the launch process.

  4. Test Axes: Satellites are generally tested in three orthogonal axes (X, Y, Z) to ensure they can withstand vibrations from all directions.

  5. Vibration Profiles:

    • Sine Vibration: Here, the satellite is subjected to specific, individual frequencies one at a time. This is to ensure the satellite can withstand resonant frequencies where vibrations can be amplified.

    • Random Vibration: In this test, the satellite is subjected to a spectrum of frequencies all at once, more closely representing the random nature of vibrations during launch.

  6. Resonance Points: These are specific frequencies at which the satellite or its components amplify the external vibrations, potentially leading to damage. During sine vibration testing, it's crucial to identify and analyze these resonance points.

  7. Sine Bursts: Used to simulate the shock-like loads during events such as stage separations. The satellite undergoes sudden and sharp vibrations for a brief duration.

Optimum Operational Ranges:

  • The satellite should remain fully operational within the vibration levels specified by the launch vehicle provider. These specifications are based on the specific rocket's history, design, and other launches' empirical data.

  • For most commercial launches, satellites must withstand random vibrations in the range of a few grms (root-mean-square gravitational units) up to 14 grms or higher across the specified frequency spectrum.

  • Sine vibration tests usually have acceleration levels that peak at specific resonant frequencies. The actual values depend on the satellite's design and the launch vehicle.

  • During tests, it's crucial to monitor the satellite for any signs of damage, malfunction, or shifts in resonant frequencies, which could indicate a structural change in the satellite.

In conclusion, while there are general guidelines for vibration testing in the aerospace industry, the exact parameters and optimum operational ranges will often be dictated by the specific launch vehicle's characteristics and the satellite's design and intended operational environment.


b) Thermal Testing:

  • Purpose: To simulate the temperature extremes the satellite might face in space, as it transitions from the sunlit side to the shadow side.

  • Process: The satellite is placed in a thermal chamber where it's subjected to extreme temperature variations, from cold to hot cycles.

  • Outcome: The satellite should operate properly under both temperature extremes and demonstrate thermal stability.



Thermal Testing of Konnect Satellite

Satellites operate in the harsh environment of space where there is no atmosphere to regulate temperature, leading to vast temperature differences between the sunlit and shaded sides. Thermal testing is crucial to ensure the satellite's functionality in these extreme conditions, to check the performance of thermal control systems, and to validate thermal models.


Values and Parameters to Look For:

1. Temperature Range: Depending on the satellite's intended orbit and mission profile, the satellite and its subsystems might be exposed to temperatures ranging from near absolute zero in deep space to several hundred degrees Celsius when exposed to direct sunlight.

2. Duration: The amount of time the satellite or its components are exposed to a specific temperature or temperature cycle.

3. Thermal Cycling: This involves changing the temperature from one extreme to another repeatedly to simulate transitions from sunlight to shadow in orbit.

4. Steady-State Thermal Test: Maintains a constant temperature for an extended period to simulate continuous exposure to a particular space environment.

5. Gradient: Spacecraft can experience temperature gradients where one part might be hot while another part might be cold. Testing ensures components can handle such differences.


Optimum Operational Ranges:

· Operational Temperature Range: This is the temperature range in which the satellite and its components are expected to perform their primary functions without any degradation. For example, electronic components might have an operational range of -40°C to +85°C.

· Survival Temperature Range: This is the temperature range the satellite and its components can endure without suffering permanent damage, though they might not be operational. This range is broader than the operational range.

· Thermal Balance Test: This test is a subset of thermal testing where the satellite is exposed to simulated sunlight in a vacuum chamber to observe how it achieves thermal equilibrium. The aim is to validate that the onboard thermal control systems (like radiators, insulators, or heaters) work as intended.


Considerations:

· Thermal Vacuum Testing: Combines the vacuum of space with temperature extremes. This is considered one of the most critical tests as it closely simulates the space environment.

· Thermal Modeling: Before actual tests, engineers often use software to predict how the satellite will behave thermally in space. This modeling helps in planning the tests and interpreting results.

In conclusion, the exact parameters and optimum operational ranges for thermal testing are highly specific to the satellite's mission and design. Testing ensures the satellite's durability in space's challenging thermal environment and the effective functioning of its thermal control systems.


c) Shock Testing:

  • Purpose: To simulate the mechanical shock loads a satellite might experience during events like stage separation during launch.

  • Process: Short, sudden impacts or shocks are imparted to the satellite using specialized equipment.

  • Outcome: The satellite should not sustain any damage and should remain operational post-test.


Shock testing for satellites is crucial to ensure that the satellite and its components can withstand the transient dynamic loads (shocks) they might experience during launch and other mission events. These shocks can be caused by various events such as stage separation, pyrotechnic device activation, or the impact of micrometeoroids in orbit.


Values and Parameters to Look For:

1. Shock Response Spectrum (SRS): The SRS provides a graphical representation of a shock in terms of acceleration vs. frequency. It gives a concise description of how the satellite might respond to a particular shock input.

2. Peak Acceleration: The maximum acceleration value that the satellite or component experiences during a shock event.

3. Duration: The length of time over which the shock event occurs. This is typically very short for shock events, often measured in milliseconds.

4. Impulse: The integral of force with respect to time, representing the total momentum transfer during the shock.

5. Frequency Range: The range of frequencies over which the shock event has significant energy. This is important as different components might be sensitive to shocks at different frequencies.


Optimum Operational Ranges:

· Operational Shock Limits: These are the shock levels (often defined in terms of SRS) that the satellite and its components are expected to experience and still perform without any degradation.

· Survival Shock Limits: These are the maximum shock levels the satellite and its components can endure without suffering permanent damage, even if they temporarily go offline or malfunction.

Considerations:

· Test Severity: It's essential to ensure the shock tests' severity is representative of the actual loads the satellite might experience but with added safety margins.

· Test Direction: Shocks can occur in different directions (axial, lateral). It's crucial to test the satellite in all relevant orientations.

· Isolation and Damping: Some components might be shock-sensitive. In such cases, shock isolators or dampers might be used to protect these components. Their effectiveness needs to be validated during testing.

· Pyroshock Testing: This simulates the shocks produced by pyrotechnic devices, such as those used in stage separations or deployment mechanisms.

· Component vs. System-Level Testing: While individual components might undergo shock testing, it's also vital to perform system-level tests to understand how the entire satellite behaves under shock loads.

In conclusion, shock testing is an essential part of satellite qualification to ensure its survival and functionality during and after launch. The exact parameters and optimum operational ranges depend on the satellite's mission, design, and launch vehicle.


d) Thermal Vacuum (Thermovac) Testing:

  • Purpose: To simulate the space environment where there's both a vacuum and temperature extremes.

  • Process: The satellite is placed in a vacuum chamber, and the air is pumped out. While in this vacuum, it undergoes temperature cycles, similar to thermal testing.

  • Outcome: The satellite should function correctly in the simulated space environment, ensuring that materials don't outgas excessively and that the satellite doesn't suffer from thermal distortion or malfunction.


Thermal vacuum (ThermoVac) testing simulates the space environment by placing the satellite or its components in a chamber that can control both temperature and pressure. The objective is to verify the satellite's functionality and robustness under space-like conditions, ensuring it can withstand the cold vacuum of space and the thermal radiation from the sun or planets.


Values and Parameters to Look For:

1. Temperature Range: The temperature extremes the satellite is expected to encounter in its mission profile, from the deep cold of space shadow to the intense heat when exposed to direct sunlight.

2. Pressure Range: The pressure within the chamber is reduced to simulate the vacuum of space. Values can go as low as 10^-7 torr or even lower, depending on the mission requirements.

3. Thermal Cycling: Subjecting the satellite to repeated temperature transitions, mimicking the satellite's movement from sunlight to shadow.

4. Rate of Temperature Change: How quickly the temperature changes, both in heating and cooling, can be crucial, especially for satellites that transition frequently between thermal extremes.

5. Test Duration: The total time the satellite or its components spend in the ThermoVac chamber, which can range from several hours to several weeks.


Optimum Operational Ranges:

· Operational Temperature Range: This range is where the satellite and its subsystems will function as expected without any degradation.

· Survival Temperature Range: Beyond the operational range, this is a broader range where the satellite and its subsystems can endure without suffering permanent damage, though they might not function optimally.


Considerations:

· Instrumentation: Ensuring that the right sensors (like thermocouples) are in place to accurately monitor the satellite's temperature and other vital parameters during testing.

· Outgassing: In the vacuum, materials can release trapped gases, a process called outgassing. This can contaminate sensitive surfaces or instruments. Materials used in the satellite should have low outgassing properties, and ThermoVac testing can be used to identify any problematic outgassing.

· Solar Simulation: For satellites that will be exposed to sunlight in space, powerful lamps can be used to simulate solar radiation and ensure the satellite's thermal control systems work effectively.

· Functional Tests: During the ThermoVac test, it's crucial to periodically check the functionality of various satellite systems and subsystems to ensure they operate correctly under test conditions.

· Validation: ThermoVac tests help validate thermal models developed during the satellite's design phase, ensuring they accurately predict the satellite's behavior in space.

In summary, ThermoVac testing is a rigorous process that subjects satellites to the harsh conditions of space within a controlled environment on Earth. It's an essential step to guarantee the satellite's resilience and functionality throughout its intended mission duration. The exact parameters and optimum operational ranges depend on the specific mission and design of the satellite.


2. Electromagnetic Interference (EMI) Testing:

  • Purpose: To ensure the satellite does not emit radiation that interferes with its own or other satellites' electronics and instruments. Also, to ensure the satellite can operate without interference from external RF sources.

  • Process:

    • Emission Testing: The satellite is placed in an anechoic chamber (a room designed to prevent reflections of either sound or electromagnetic waves). Monitors and sensors then measure any electromagnetic radiation the satellite emits to ensure it's within acceptable limits.

    • Susceptibility/Immunity Testing: The satellite is exposed to external RF fields of known amplitude and frequency to determine if it can operate without interference.

  • Outcome: The satellite should neither produce excessive EMI nor be overly susceptible to external RF fields.


EMI testing, also known as electromagnetic compatibility (EMC) testing, ensures that the satellite's electronic systems can operate without interference from internal or external electromagnetic sources and won't produce emissions that could interfere with other systems. Given that satellites operate in the radio-frequency-heavy environment of space and rely on intricate electronics, ensuring they are immune to EMI is crucial.


Values and Parameters to Look For:

1. Emission Levels: Measure the electromagnetic energy emitted by the satellite to ensure it doesn't interfere with its own systems or other satellites. This is particularly important for communication satellites.

2. Susceptibility/Immunity Tests: Determine the level of external electromagnetic energy the satellite can be exposed to without malfunctioning.

3. Frequency Range: The range of frequencies over which the testing is conducted. This usually spans from low-frequency magnetic fields (tens of Hertz) to high-frequency radiated fields (up to Gigahertz levels).

4. Modulation Techniques: Various modulation techniques may be used to simulate real-world interference scenarios, such as amplitude modulation or pulse modulation.

5. Antenna Parameters: Including gain, radiation pattern, and polarization, as antennas can be sources of unintentional radiation or points of susceptibility.


Optimum Operational Ranges:

· Operational Emission Range: The frequency range within which the satellite's systems operate without producing harmful interference.

· Operational Susceptibility Range: The range of external frequencies and their corresponding power levels that the satellite can be exposed to without degradation of its performance.


Considerations:

· Near-field vs. Far-field: EMI tests might be concerned with either near-field (close proximity) interactions or far-field (long-distance) interactions, depending on the potential interference sources and distances.

· Conducted vs. Radiated Emissions: EMI can be conducted through power or signal lines, or it can be radiated through the air. Tests can be designed to measure both types.

· Environmental Conditions: EMI testing can be performed under various environmental conditions to replicate the conditions in space (e.g., temperature, pressure).

· Test Setup: Proper calibration of the equipment, setup, and positioning of the satellite and antennas is crucial for accurate results.

· Enclosure Shielding: Ensuring that the satellite's enclosures (for instruments, computers, etc.) provide adequate shielding from external electromagnetic sources.

· Grounding: Proper grounding practices are vital to reduce EMI. The grounding strategy must be carefully considered and tested.


In summary, EMI testing for satellites ensures that onboard electronics and systems function correctly without interference from internal or external electromagnetic sources. It verifies the satellite's ability to operate in its intended electromagnetic environment without introducing intolerable electromagnetic disturbances to any entity in that environment. The exact parameters and optimum operational ranges are determined based on the satellite's mission, its systems, and the environment in which it will operate.


The table below summarizes the various tests with testing parameters and purpose.

Test Type

Parameters

Purpose

Vibration Testing

Frequency Range, Acceleration levels, Duration of test

Simulate launch and in-flight conditions. Ensure structural and functional integrity during rocket launch and various dynamic conditions.

Thermal Testing

Temperature Range, Duration at extreme temps, Cycle count

Simulate space's extreme thermal environment. Validate the satellite's performance under varying temperature extremes, as experienced in orbit.

Shock Testing

Shock Pulse Shape, Peak Acceleration, Duration

Replicate mechanical shocks encountered during launch, separation events, or potential malfunctions. Ensure the satellite can withstand sudden and severe forces.

Thermo-Vac Testing

Temperature Range, Vacuum Level, Duration

Replicate the space environment: vacuum & extreme temperature. Test satellite's performance in space-like conditions.

EMI Testing

Emission Levels, Frequency Range, Modulation Techniques

Ensure satellite's systems operate without interference. Confirm the satellite doesn't emit interference to its own or other systems.

These tests are crucial because once a satellite is in space, repairs are challenging, if not impossible, depending on its orbit. Ensuring that a satellite can withstand the physical and electronic demands of space while on Earth is paramount to its successful operation once launched.


Cite this article as: Kumar, Yajur. “The Environmental and EMI Testing for Satellites” Space Navigators, 26 August 2023, https://www.spacenavigators.com/post/The-Environmental-and-EMI-Testing-for-Satellites


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