How to Select Satellite Sensors: Five Key Considerations

Satellite sensors are used for Earth observation, navigation and positioning, telecommunications, military missions, and scientific research. Custom sensors have specialized capabilities, but commercial off-the-shelf (COTS) products that use advanced technologies can reduce development and launch costs. 

If you’re selecting satellite sensors, consider these four factors.

1. Sensor type
2. Performance specifications
3. Environmental considerations
4. Integration with satellite systems

The following sections explain.

#1 Sensor Types

Satellites are equipped with a variety of sensors, including some that are redundant to ensure continued operations in the event of device failure. The type of sensor to select is a function of your application requirements and the device’s capabilities.

Optical Sensors

Optical sensors detect light within specific spectral ranges, such as visible and infrared (IR), for imaging, monitoring, and navigation. They are highly accurate, compact, lightweight, and can support high-bandwidth transmissions. For satellites with directional antennas, optical sensors are used for positioning, tracking, and alignment. For laser communications with ground stations, these satellite sensors support very fast transmissions.  

Radar Sensors

Synthetic aperture radar (SAR) sensors combine multiple radar signals collected over time as a satellite moves in orbit. They support high-resolution imaging without the use of a large antenna. Unlike optical sensors, SAR operates in the microwave range of the electromagnetic spectrum. Among their advantages, radar sensors can capture images regardless of lighting or cloud cover.

Gyroscopes and Accelerometers

Gyroscopes measure angular velocity and help satellites maintain their orientation in flight. Accelerometers measure linear acceleration and can determine shock and vibration levels during launch, flight, and landing. There are also piezoelectric accelerometers, capacitive accelerometers, mechanical gyroscopes, ring laser gyroscopes (RLGs), and fiber optic gyroscopes (FOGs), each suited to specific applications.

Magnetometers

Magnetometers are sensors that measure changes in magnetic fields. They are essential for navigation and are used in conjunction with gyroscopes and accelerometers for attitude determination and motion tracking. Subtypes include fluxgate, optically pumped, SQUID, hall effect, magneto-resistive (MR), and Lorentz force magnetometers.

Thermal Infrared Sensors

Thermal infrared sensors (TIR) measure land surface temperatures and detect heat signatures. Unlike near-infrared (NIR) and shortwave infrared radiation (SWIR) devices, TIR technology senses emitted energy rather than reflected energy. With their high spatial resolution, TIR sensors can attribute temperature values to specific features, such as urban heat islands.

Radio Frequency Sensors

Radio frequency (RF) sensors detect and measure RF signals for applications that include signals intelligence (SIGINT) and environmental monitoring. By triangulating signals from multiple orbital points, RF sensors for SIGINT can identify distinct emitters and find their precise location. For environmental monitoring, RF sensors can track signals regardless of weather conditions.

GNSS Sensors

Global navigation satellite system (GNSS) sensors provide autonomous geo-spatial positioning. As satellites orbit the Earth, they transmit a unique signal along with orbital parameters. Ground-based receivers use this information to calculate a user’s exact location. GNSS encompasses a variety of satellite-based systems, including the U.S. global positioning system (GPS).

#2 Performance Specifications

Satellite sensors differ in terms of performance specifications. Depending on the specific application, some specs may be more important than others. For example, Earth observation requires sensors with high spatial resolution to distinguish small objects on the ground from their surroundings.

Frequency Range

Frequency range is the range of frequencies over which a satellite sensor is designed to operate. It determines the sensor’s ability to capture specific signals, perform remote sensing tasks, or transmit and receive data. Different sensors are designed to operate within different frequency bands, such as the ultra-high frequency (UHF) band within the RF portion of the electromagnetic spectrum.

Resolution

Resolution refers to a sensor’s ability to distinguish between closely spaced objects or fine details. There are different types of resolution, including spatial, spectral, temporal, radiometric, and angular resolution. Satellite sensors with higher resolution can acquire more data, but they also need more storage and processing power. In addition, higher resolution sensors are more expensive.

Sensitivity

Sensitivity refers to the ability of a sensor to detect small changes or weak signals in the quantity it’s designed to measure. Depending on the type of space sensor, this quantity could be IR or visible light, magnetic fields, temperatures, or RF signals. With SAR sensors, sensitivity determines how well the radar can detect small, reflected signals from objects on Earth’s surface.       

Power Consumption

Sensor power consumption refers to the amount of electrical power that a sensor uses. It includes the power that’s consumed by the sensor itself for signal detection and the power used by supporting electronics for signal amplification, processing, or transmission. Because satellites have limited power availability, sensors with low power consumption are preferred.

Weight and Size

Sensor weight and size are important because satellites have strict payload limitations. These specifications can also affect larger design decisions and overall sensor performance. For example, the size of an optical sensor that’s used with a satellite’s camera determines how much light the camera has available to create an image. In turn, this affects image quality.

#3 Environmental Considerations

When selecting a satellite sensor, consider the environment in which it will be used. Outer space exposes sensors to extreme conditions, and repairing or replacing components can be challenging. 

• Radiation Tolerance: Space environments expose sensors to high levels of ionizing radiation, which can degrade performance over time. Choose sensors and other electronic components that are radiation-hardened.
• Temperature Variations: Satellites face extreme temperature fluctuations, and sensors need to function reliably under these changing conditions. Depending on whether a satellite is in sunlight or shadow, temperatures can range from -270°C to +200°C.
• Outgassing and Vacuum: Choose sensors that are built from materials that do not outgas in the vacuum of space. Outgassing, the process by which materials release trapped gasses when exposed to vacuum pressure, can cloud optical lenses and interfere with signals.

#4 Integration with Satellite Systems

When selecting satellite sensors, consider how the device will integrate with larger systems that are essential for continuous operations. There are several systems that are especially critical.

Data Handling and Communications

Command and data handling (CDH) systems acquire, process, store, format and downlink data to ground-based assets. They include various subsystems, such as telemetry and telecommunications (TTC). For real-time or delayed data transmissions, choose sensors that are compatible with the satellite’s onboard data handling system.

Pointing and Stabilization

Antenna-pointing mechanisms direct a satellite’s antenna toward a specific communication target. A control system receives data that’s acquired from sensors, calculates the required rotation of the antenna, and stabilizes the device. Depending on the sensor type and application, pointing and stabilization may also be used with high-resolution cameras. 

Power Monitoring

Satellites have multiple subsystems, each of which requires different amounts of power. Each subsystem must receive the correct voltage and current, and without power spikes or other anomalies that can jeopardize performance. Power monitoring systems for energy generation and storage must work with satellite sensors and support the use of onboard solar panels and batteries.

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