Low Earth orbit

Low Earth Orbit (LEO) refers to the region of space around Earth that encompasses altitudes from approximately 160 kilometers (about 100 miles) to 2,000 kilometers (approximately 1,200 miles) above the planet's surface. It is characterized by its proximity to Earth compared to other orbital regimes, such as Medium Earth Orbit (MEO) or Geosynchronous Orbit (GEO). Objects in LEO travel at high speeds of around 28,000 kilometers per hour (about 17,500 miles per hour), completing an orbit around the Earth in about 90 to 120 minutes. This orbital regime is heavily utilized for a variety of purposes, including communication, Earth observation, and scientific research. Due to the lower altitude, LEO allows for shorter signal transmission times, making it advantageous for real-time data applications, such as telecommunication and internet services. However, it is also the region most affected by space congestion and debris, making monitoring and management crucial to ensure the safety and sustainability of operations in this region. LEO is the orbit of choice for most satellites, the International Space Station (ISS), and is a starting point for missions to higher orbits and beyond.

Medium Earth orbit

Medium Earth Orbit (MEO) is a region of space around the Earth located at altitudes between Low Earth Orbit (LEO) and Geostationary Orbit (GEO), typically ranging from 2,000 kilometers (approximately 1,243 miles) to about 35,786 kilometers (approximately 22,236 miles) above the Earth's surface. MEO is commonly used for various types of satellite operations, including navigation, communication, and scientific research. Satellites in MEO have an orbital period that varies depending on their specific altitude, allowing for coverage that balances between the low latency and higher frequency of passes of LEO satellites and the broader coverage but higher latency of GEO satellites. This orbit is particularly important for Global Navigation Satellite Systems (GNSS) such as the Global Positioning System (GPS), GLONASS, Galileo, and BeiDou, which require medium altitude to optimize coverage, accuracy, and stability for positioning and timing functions across the globe. MEO satellites often have more extended operational lifespans and larger coverage areas per satellite when compared to LEO satellites, but with less total constellation size than those required for constant global LEO coverage.

Geostationary Earth orbit

Geostationary Earth Orbit (GEO) refers to a specific orbital regime directly above the Earth's equator, approximately 35,786 kilometers (22,236 miles) above mean sea level. In this orbit, a satellite's orbital period matches the Earth's rotation period, which is approximately 24 hours. Consequently, a satellite in GEO appears to be stationary relative to a fixed point on the Earth's surface. This unique characteristic makes GEO an ideal choice for telecommunications, weather monitoring, and broadcasting satellites, as they can provide continuous coverage over a specific geographic area. The GEO belt is highly sought after, leading to regulations and coordination efforts to manage satellite positions and frequencies to prevent interference. The ability to remain in a fixed position relative to the Earth also allows for efficient use of ground-based antennas that do not need to track moving satellites.

Sensor

A sensor is a device or instrument that detects, measures, and responds to a physical property, such as temperature, light, sound, pressure, motion, or any other environmental variable. In the context of space situational awareness, sensors play a crucial role in tracking and monitoring orbital objects, including satellites, space debris, and other potential threats in space. They convert physical signals into electrical signals for processing and analysis, allowing for the collection of data necessary for precise observation and decision-making in various applications, such as satellite maneuvering, collision avoidance, and risk management. Sensors can be of various types, including radar, optical, infrared, and others, each suited to specific conditions and requirements for data acquisition and processing.

Ground-based sensor

A Ground-based sensor is a type of sensor system that is positioned on the Earth's surface to detect and collect information about various objects or phenomena. These sensors play a critical role in gathering data from Earth, which can be utilized for a wide range of purposes including environmental monitoring, weather forecasting, space surveillance, and defense applications. In the context of space situational awareness, ground-based sensors are pivotal in tracking satellites and orbital debris, providing vital data that informs collision risk analysis, orbital behavior monitoring, and strategic decision-making for space traffic management. These sensors can include a variety of technologies such as radar, optical telescopes, and radio frequency receivers, each designed to capture specific types of data depending on their application. Ground-based sensors offer several advantages such as ease of maintenance and operation, cost-effectiveness, and the ability to provide continuous monitoring from fixed locations on Earth's surface.

Defence operator

A Defence Operator is an organization responsible for the management, operation, and oversight of defense systems and activities related to national security. These organizations typically work with defense and national security agencies to manage military operations, oversee the deployment and functioning of defense technologies, and ensure compliance with security protocols. Defence Operators play a critical role in strategic planning, threat assessment, and the implementation of defense strategies to protect a nation’s interests. They may be involved in various domains including land, air, sea, and increasingly, space, providing crucial support in tracking and managing threats, coordinating with state and commercial entities, and enhancing overall defense capabilities.