4.1 Ground-based and space-based observation techniques

Space surveillance combines ground and space-based techniques to track objects in orbit. Ground telescopes and radar systems detect debris using visible light and radio waves. These methods have limitations but are constantly improving with new tech.

Space-based sensors offer advantages like continuous coverage and detection of smaller objects. They use electro-optical and infrared systems to observe space debris. Networks of these sensors provide crucial situational awareness for space safety and sustainability.

Optical and Radar Observations

Ground-based Telescopes and Optical Observations

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• Ground-based telescopes are the primary means of detecting and tracking space objects from Earth
• Optical observations involve using visible light to detect and track space objects
  • Relies on the object reflecting sunlight
  • Limited to observing during clear nights when the object is illuminated by the Sun
• Telescopes used for space object tracking often have wide fields of view to cover large areas of the sky (Schmidt telescopes)
• Advances in telescope technology, such as adaptive optics and large aperture sizes, have improved the ability to detect and track smaller objects

Radar Observations and Tracking Methods

• Radar observations use radio waves to detect and track space objects
  • Can operate day and night, and through clouds, making them a valuable complement to optical observations
• Passive tracking involves receiving radio waves reflected off the object, without actively transmitting a signal
  • Relies on the object being illuminated by another source, such as the Sun or the Earth's atmosphere
• Active tracking involves transmitting a radio signal and receiving the reflected signal from the object
  • Provides more detailed information about the object's position, velocity, and characteristics
  • Requires more powerful transmitters and receivers compared to passive tracking
• Examples of radar systems used for space object tracking include the U.S. Air Force's Space Fence and the German Tracking and Imaging Radar (TIRA)

Space-Based Sensors

Advantages and Types of Space-Based Sensors

• Space-based sensors offer several advantages over ground-based observations
  • Not limited by weather conditions or atmospheric distortions
  • Can provide continuous coverage of large areas of space
  • Closer proximity to the objects being tracked allows for detection of smaller objects
• Electro-optical systems are the most common type of space-based sensor
  • Use visible light or near-infrared wavelengths to detect and track objects
  • Examples include the U.S. Space-Based Space Surveillance (SBSS) satellite and the Canadian Sapphire satellite
• Infrared detection systems are also used for space-based observations
  • Detect the heat signature of objects, allowing for detection of objects that may not reflect enough visible light
  • Particularly useful for detecting and tracking objects in higher orbits, such as geostationary satellites

Observation Networks and Situational Awareness

Importance of Space Situational Awareness

• Space situational awareness (SSA) refers to the knowledge and understanding of the space environment and the objects within it
  • Crucial for ensuring the safety and sustainability of space activities
  • Helps prevent collisions between satellites and other objects
  • Allows for the detection and tracking of potential threats, such as debris or hostile spacecraft
• SSA requires the integration of data from multiple sources, including ground-based and space-based sensors
  • Data is processed and analyzed to create a comprehensive picture of the space environment
  • This information is used to support decision-making and operations planning

Collaborative Observation Networks

• Observation networks involve the cooperation and sharing of data between multiple organizations and countries
  • Allows for more comprehensive coverage and improved accuracy in tracking space objects
• Examples of observation networks include the International Scientific Optical Network (ISON) and the European Space Surveillance and Tracking (EU SST) consortium
  • ISON is a global network of telescopes operated by scientific institutions and universities
  • EU SST is a collaborative effort between several European countries to provide SSA services for European space assets
• Observation networks also facilitate the sharing of best practices and the development of common standards for data collection and processing