What Orbits Are Best for Satellites?

Satellites are indispensable tools that power everything from global communication to environmental monitoring. One of the most critical decisions in satellite design and mission planning is choosing the orbit. The orbit determines a satellite's coverage area, resolution, and operational capabilities. But not all orbits are created equal—different missions require different orbital characteristics. This article explores the various types of orbits, their characteristics, and which ones are most suitable for specific satellite applications.

1. Low Earth Orbit (LEO)

Characteristics:

  • Altitude: 160–2,000 km (99–1,243 miles) above Earth

  • Orbital Period: 90–120 minutes

  • Coverage: Limited to specific regions at any given time; multiple satellites needed for global coverage

Advantages:

  1. High Resolution: Proximity to Earth enables detailed imaging and high data resolution, making LEO an ideal platform for Earth observation satellites.

  2. Low Latency: Short distances ensure minimal signal delay, which is crucial for real-time applications such as broadband internet.

  3. Cost-Effective Launches: Lower altitudes reduce the energy requirements of launch vehicles, thereby minimising costs.

Applications:

  • Earth observation (e.g., weather monitoring, environmental studies)

  • Broadband internet constellations (e.g., Starlink, OneWeb)

  • Scientific research (e.g., International Space Station)

Best for: Satellites that require high-resolution data, low latency, or shorter mission lifespans.

2. Medium Earth Orbit (MEO)

Characteristics:

  • Altitude: 2,000–35,786 km (1,243–22,236 miles)

  • Orbital Period: 2–12 hours

  • Coverage: Wider than LEO; fewer satellites needed for regional or global coverage

Advantages:

  1. Extended Coverage: Satellites in MEO can cover larger areas than those in LEO, making them suitable for regional navigation and communication systems.

  2. Longer Lifespan: Reduced atmospheric drag compared to LEO extends satellite operational life. Atmospheric drag is the force exerted on a satellite by the Earth's atmosphere, which can slow down the satellite's speed and lead to a decrease in its altitude over time.

Applications:

  • Navigation systems (e.g., GPS, Galileo, GLONASS)

  • Communication networks requiring moderate latency

Best for: Navigation satellites and medium-latency communication systems.

3. Geostationary Orbit (GEO)

Characteristics:

  • Altitude: 35,786 km (22,236 miles) above the equator

  • Orbital Period: 24 hours, matching Earth’s rotation

  • Coverage: Continuous observation of a fixed region on Earth

Advantages:

  1. Constant Coverage: A satellite in GEO remains fixed relative to a specific point on Earth, enabling continuous monitoring or communication.

  2. Wide Area Coverage: A single satellite can cover nearly a third of the Earth's surface, reducing the need for multiple satellites.

  3. Established Infrastructure: Ground-based systems for GEO satellites are well-developed.

Applications:

  • Weather monitoring (e.g., GOES satellites)

  • Television broadcasting

  • Long-distance communication

Best for: Applications requiring constant, wide-area coverage with minimal satellite infrastructure.

4. Highly Elliptical Orbits (HEO)

Characteristics:

  • Altitude: 500–50,000 km (311–31,068 miles) above Earth, varying wildly between perigee (closest point) and apogee (farthest point)

  • Orbital Period: 12–24 hours

  • Coverage: Extended dwell times over high latitudes

Advantages:

  1. Polar Region Coverage: HEO is particularly useful for monitoring regions near the poles, which are underserved by GEO satellites.

  2. Long Dwell Times: Satellites spend significant time near apogee, allowing prolonged observations over specific areas.

Applications:

  • Polar communications (e.g., Molniya orbits used by Russia)

  • Space science missions studying Earth's magnetosphere

Best for: Missions targeting polar regions or requiring extended observation times over specific locations.

5. Sun-Synchronous Orbit (SSO)

Characteristics:

  • Altitude: 600–800 km (373–497 miles)

  • Orbital Period: Approximately 90–100 minutes

  • Coverage: Near-global, with consistent lighting conditions for imaging

Advantages:

  1. Consistent Lighting: The orbit ensures that satellites pass over specific locations at the same local solar time, providing consistent illumination conditions for imaging.

  2. Global Reach: Sun-synchronous orbits are designed for near-complete Earth coverage over time.

Applications:

  • Earth observation (e.g., remote sensing, climate monitoring)

  • Environmental studies

  • Military reconnaissance

Best suited for: Imaging and observation satellites that require consistent lighting conditions.

7. Lunar and Interplanetary Orbits

Characteristics:

  • Altitude: Varies depending on mission objectives

  • Coverage: Focused on celestial bodies other than Earth

Advantages:

  • Mission-Specific Designs: These orbits are tailored to study specific celestial bodies or facilitate interplanetary travel.

  • Scientific Exploration: Enables detailed study of moons, planets, and other space phenomena.

Applications:

  • Lunar exploration (e.g., Lunar Reconnaissance Orbiter)

  • Mars missions (e.g., Mars Reconnaissance Orbiter)

Best for: Space exploration and studying other celestial bodies.

6. Polar Orbit

Characteristics:

  • Altitude: 200–1,000 km (124–621 miles)

  • Orbital Period: 90–120 minutes

  • Coverage: Entire Earth, as the satellite passes over both poles

Advantages:

  1. Global Coverage: Each orbit enables the satellite to cover a new swath of the Earth, allowing for full global coverage over time.

  2. Versatility: Polar orbits are suited for both civilian and military applications.

Applications:

  • Weather satellites

  • Reconnaissance

  • Mapping and geospatial studies

Best suited for Missions requiring comprehensive global coverage, particularly for environmental and security purposes.

Factors Influencing Orbit Selection

Mission Objective

The satellite's mission dictates the type of orbit it is placed in. For example:

  • Earth observation missions favour LEO for high-resolution imaging.

  • Communication systems often rely on GEO or MEO for consistent and broad coverage.

Cost

LEO satellites are less expensive to launch due to their lower altitude requirements, whereas GEO satellites require more powerful rockets, thereby increasing costs.

Regulatory Considerations

Certain orbits, such as GEO, are heavily regulated to prevent overcrowding and interference.

Technological Limitations

The satellite's onboard systems, including power, propulsion, and communication capabilities, can limit the range of suitable orbits.

Conclusion

The "best" orbit for a satellite depends entirely on its mission requirements, budget, and operational goals. While LEO offers high-resolution imaging and low latency, GEO provides unparalleled continuous coverage for communication and broadcasting. Specialised orbits, such as HEO and SSO, serve niche purposes, including polar monitoring and consistent lighting for imaging.

By understanding the advantages and limitations of each orbit type, satellite designers and operators can make informed decisions to optimise performance and achieve mission success. As space technology evolves, the diversity and capabilities of satellite orbits will continue to expand, opening new frontiers for exploration and innovation.