An Inclined Geosynchronous Orbit (IGSO) is a type of orbit that combines the characteristics of both geosynchronous and inclined orbits. Similar to a geosynchronous orbit, an IGSO satellite orbits the Earth with a period equal to the Earth's rotation period, resulting in the satellite appearing to remain stationary relative to a fixed point on the Earth's surface.

• Inclination: Inclination refers to the angle between the orbital plane of a satellite or object and the equatorial plane of the celestial body it is orbiting. An ISSO has a non-zero inclination, meaning its orbital path is tilted concerning the equatorial plane of the celestial body.
• Synchronization: Synchronization implies that the orbiting object, despite having an inclined orbit, maintains a fixed position relative to the rotating celestial body below. This position synchronization can be achieved through the careful adjustment of the object's orbital parameters.

IGSOs are employed in satellite systems to cover areas that may not be easily reachable or adequately covered by satellites in standard geostationary orbits. By adjusting the inclination of the orbit, an IGSO satellite can provide coverage to higher latitudes or specific regions on Earth that might be inaccessible from equatorial geostationary orbits.

Key parameters for an Inclined Geosynchronous Orbit (IGSO)

Characteristics of Inclined Geo-Synchronous Orbit

• Inclination Angle: The defining characteristic of IGSO is the inclination angle, denoting the angle between the orbital plane and the equatorial plane. Unlike GEO satellites with zero inclination, IGSO satellites have non-zero inclination angles, introducing a twist to their orbital behavior.
• Orbital Period: Inclined Geosynchronous Orbit still maintains a 24-hour orbital period,  ensuring synchronization with the Earth's rotation. This synchronization allows the satellite to appear stationary over a specific longitudinal point despite its inclination.
• Coverage Area: The coverage area of IGSO satellites extends beyond the equator, reaching higher latitudes due to their inclined path. This expanded coverage can be advantageous for specific applications, especially in regions where traditional GEO coverage may be limited.

Applications of Inclined Geosynchronous Orbit (IGSO)

• Communication: IGSO can be strategically employed in communication satellites to enhance coverage for higher latitudes, providing improved connectivity in regions that may experience challenges with standard GEO satellites.
• Satellite Downlink Beam Coverage: In IGSO, when NSSK is relaxed, the satellite's inclination gradually increases, impacting the downlink beam coverage. The communication satellite's onboard antenna exhibits a figure-8-like orbit pattern. As the inclination changes, periodic alterations occur in the edge of the antenna beam coverage, especially in the polar region. Continuous adjustments of pointing equipment, both in software and hardware, are required to overcome these coverage changes and maintain effective communication.
• Satellite Tracking Antenna for Ground Station: Ground stations tracking SIGSO satellites face challenges in adjusting their antennas due to varying azimuth and elevation angles. The automatic gain control (AGC) system monitors signal levels, adjusting the antenna to track the satellite. Alternatively, program-controlled mathematical calculations can be used to determine the pointing angles to the satellite, providing a method to adjust the antenna. The tracking range of azimuth and elevation angles is crucial for efficient communication.
• Polarisation Loss: Antenna polarization becomes a critical consideration for linear polarization antennas on SIGSO communication satellites. Polarisation mismatch can result in significant signal attenuation. It is essential to address this issue to ensure optimal communication performance.
• Earth Observation: Inclined Geosynchronous orbit is valuable for Earth observation missions. The inclination allows satellites to observe a broader range of latitudes, facilitating more comprehensive monitoring and data collection.
• Navigation Systems: IGSO satellites can contribute to global navigation systems, offering coverage in areas that may be less efficiently served by equatorial GEO satellites.
• Doppler Frequency Drift: In IGSO, the Doppler frequency shift caused by the relative velocity between the Earth and the satellite introduces a noticeable drift. This shift impacts navigation functions, particularly in Carrier Phase Navigation (CAPS). Velocity measurements in navigation applications are influenced by the Doppler frequency drift, necessitating the use of frequency pre-bias techniques to counter the shift.