Subsea Cables vs Satellites: Which Is Better?

Subsea cables are better than satellites for international internet for the vast majority of traffic, carrying over 95% of intercontinental data, because they offer far higher capacity, lower latency, and lower cost per bit. Satellites excel in specific niches—remote areas, maritime, aviation, and broadcasting—but cannot match the sheer bandwidth and speed of fiber-optic cables for general internet use.

How Subsea Cables Work

Subsea cables are fiber-optic lines laid on the ocean floor, typically about the thickness of a garden hose. They use pulses of light to transmit data across continents at speeds approaching the speed of light in glass (about 200,000 km/s). Modern cables use multiple fiber pairs and dense wavelength-division multiplexing (DWDM) to send hundreds of separate light wavelengths per fiber, achieving capacities of tens of terabits per second per cable. For example, the MAREA cable, which connects Virginia, USA, to Bilbao, Spain, has a design capacity of 200 Tbps.

These cables are not just a single strand; they are layered with protective coatings, steel wire armor, and a waterproof copper sheath. In deep water, they lie directly on the seabed, but in shallow areas they are buried under the ocean floor to protect against anchors and fishing trawlers. The entire system is powered by high-voltage electricity sent from shore stations, with repeaters every 50–80 km to boost the optical signal.

How Satellites Provide Internet

Satellite internet works by beaming data from ground stations to satellites in orbit, which then relay it back to users. There are three main types of orbits:

• Geostationary (GEO): Satellites at ~35,786 km altitude that stay fixed over one spot. They cover large areas but have high latency (~600 ms round trip) and lower capacity.
• Medium Earth Orbit (MEO): Satellites at ~20,000 km, used mainly for navigation and some broadband, with latency around 150 ms.
• Low Earth Orbit (LEO): Satellites at 500–1,200 km, such as Starlink and OneWeb, that orbit quickly and provide latency as low as 20–40 ms, much closer to terrestrial fiber.

LEO constellations are the most promising for internet, but they require hundreds or thousands of satellites to maintain continuous coverage, and each satellite has limited bandwidth shared among users.

Key Comparison: Capacity, Latency, and Cost

The core differences come down to three metrics:

• Capacity: A single subsea cable can carry tens of terabits per second. The entire Starlink constellation, as of 2024, has a total capacity estimated at a few hundred terabits per second, but that is spread across the whole globe. For a single route, cables win by orders of magnitude.
• Latency: Light travels faster in a vacuum than in glass, but cables take a more direct path. For transatlantic traffic, a cable’s latency is about 60–70 ms, while a GEO satellite would be around 600 ms. LEO satellites can achieve ~40 ms, but they still require ground stations and often have longer routing paths.
• Cost per bit: Cables are extremely cost-efficient once installed, with an estimated cost of a few cents per gigabyte. Satellite bandwidth is much more expensive, often dollars per gigabyte, due to the cost of building and launching satellites.

When Satellites Are the Better Choice

Despite cables’ dominance, satellites are indispensable in specific situations:

• Remote and rural areas: Places without terrestrial infrastructure, like Antarctic research stations or isolated islands, rely on satellites for any connectivity.
• Maritime and aviation: Ships and aircraft use satellite links for navigation, communication, and passenger internet.
• Disaster recovery: When earthquakes or tsunamis sever cables, satellites can provide emergency connectivity.
• Broadcasting: Satellite TV and radio still use GEO satellites for one-to-many distribution.
• Backup and redundancy: Some organizations use satellite links as a failover when their primary cable connection fails.

Common Problems and Vulnerabilities

Both technologies have weaknesses. Subsea cables are vulnerable to:

• Physical damage: Anchors and fishing trawlers cause about two-thirds of cable faults. Earthquakes and underwater landslides can also break cables, as happened with the 2006 Hengchun earthquake that disrupted several cables in East Asia.
• Repair difficulty: Repairing a deep-sea cable requires a specialized ship that can take weeks to reach the site and days to fix the break.

Satellites face different issues:

• Space debris and collisions: LEO constellations increase collision risk, and a single satellite failure can create debris that threatens others.
• Weather interference: Heavy rain or snow can attenuate satellite signals (rain fade), especially at higher frequencies.
• Limited bandwidth per user: A satellite’s capacity is fixed and shared, so during peak times speeds can drop significantly.

Future Trends and Hybrid Approaches

The future is not either/or but a combination. Cable operators are constantly laying new cables to meet growing demand, while satellite companies are launching more LEO constellations. Some initiatives, like Google’s Project Taara, are even using free-space optical links (laser beams through the air) to complement cables in difficult terrain, but that is not a full replacement.

In practice, the internet backbone relies on cables, and satellites serve as an extension. For example, a rural user might connect via Starlink to a local gateway, which then connects to the global fiber backbone. This hybrid approach leverages the strengths of both: cables for high-capacity long-haul, satellites for last-mile coverage where cables are impractical.

Frequently Asked Questions

Do satellites have lower latency than subsea cables?

No, not for long distances. Subsea cables have lower latency than GEO satellites and are comparable to LEO satellites. For example, a transatlantic cable has about 65 ms latency, while GEO satellites have ~600 ms. LEO satellites can achieve ~40 ms, but they often route through multiple ground stations, adding delay. For most users, cable latency is better.

Why do we still need satellites if cables carry most traffic?

Because cables only reach places where they are physically laid. Satellites provide coverage over oceans, polar regions, and remote land areas where laying cables is impossible or uneconomical. They are also crucial for mobility (ships, planes) and for restoring connectivity after cable breaks.

Can a single cable break cut off a country’s internet?

Yes, if a country relies on one or few cables, a break can cause major outages. For example, in 2020, a cable cut in Mauritania disrupted internet for several African countries. That’s why many countries have multiple cable landings for redundancy, and why satellite links are used as backup in some cases.

Are subsea cables faster than satellites in terms of data speed?

Yes, in terms of raw capacity, cables are far faster. A single cable can carry tens of terabits per second, while a single satellite might offer a few gigabits per second. Even entire LEO constellations have total capacities in the hundreds of terabits per second, but that is shared globally, so individual users get less.

How long does it take to install a subsea cable vs a satellite?

Subsea cables take years to plan and lay—often 2–3 years from concept to operation. Satellites can be launched in months once built, but building a full constellation takes several years and many launches. For example, Starlink began launches in 2019 and took until 2023 to offer global coverage.

Which is more environmentally friendly?

Subsea cables have a lower environmental impact over their lifetime because they use less energy per bit and have no rocket launches. Satellites require fuel-intensive launches and have a shorter operational life (5–15 years), after which they must be deorbited, contributing to space debris. However, cables can disrupt seabed habitats during installation, though modern techniques minimize this.

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