Author: Steven Phan
Introduction
A LEO satellite is a communications satellite that creates a communication channel between a source transmitter and a receiver at different locations on Earth.
According to the Internet Society, there is “considerable potential in the use of Low Earth Orbit (LEO) satellites for Internet access for unserved or under-served communities, especially where other ways of delivering Internet access are not viable”. Furthermore, there is also potential for LEO to provide “internet access to communities affected by natural or human disaster, and to increase the overall resilience of Internet connectivity”.
Source: Internet Society
How does this technology play a role in everyday life?
Starlink is an example of commercially available system built atop LEO satellites.
Figure 1: Four examples of starlink in use in rugged, rural or remote environments. Credit: 1 – Starlink, 2 – Clodagh Kilcoyne / Reuters, 3 – SpaceX, 4 – Dan Lin / Roadtrippers (From Top Left, Clockwise)
Apple Satellite Messaging is another example of a commercially available product that uses LEO.
Figure 2: Two examples of Apple Satellite Messaging as shown in Apple iPhone UI
Credit: Apple
How does it work?
There are three main components in a LEO satellite system:
1. Satellite Constellation: hundreds or thousands of satellites that are launched into orbit and typically arranged into different “shells” at different altitudes.
2. User Terminal: AKA ground terminal or simply an antenna or dish, this is how the users receive data from and transmit data to the satellites.
3. Ground stations: AKA gateways, these are the large antennas and facilities that connect the satellites to the rest of the Internet
Image 3: A diagram showing the flow of signals between Satellite Constellations, User Terminals and Ground Stations Credit: Steven Phan
Typical flow for a local device using a LEO system for internet connectivity:
- A web browser on the device will send a request to the local user terminal using standard protocols.
- The user terminal, acting as the browser’s internet gateway, connects to a LEO satellite and sends the request.
- The LEO satellite then sends the request to a ground station
- The ground station will send the request out on the Internet.
- When the response comes back to the ground station, the process will go in reverse, with the ground station sending to a satellite, and the satellite sending back to the user terminal which will send the info to the user’s device.
Because the LEO satellites are moving so quickly, the ground station may send the response back via a different satellite than the one used for the initial request. LEO ground terminals must be able to track and work with multiple LEO satellites within the LEO constellation.
For clarity, each LEO satellite network is often tied to a singular server provider For example, Apple is not using Starlink satellites and vice versa.
Source: Perspectives on LEO Satellites, Internet Society, 2022
The key development for Starlink and other LEO companies launching to the public was integrating inter-satellite laser links (ISLLs or ISLs). Known as “space lasers”, these links allow a data connection to hop from satellite to satellite until it reaches a satellite within range of a ground station. This allowed for users in regions without ground stations to still be able to connect to the internet via a LEO system. This substantially reduced the quantity of ground stations required for a LEO network to function.
Early versions of this technology required ground stations distributed at a high frequency regionally to ensure that user terminals and their respective satellite constellations could maintain connectivity to the broader internet.
Source: Achieving >99% Link Uptime on a fleet of 100G Space Laser Inter-Satellite Links in LEO, Society of Photo-Optical Instrumentation Engineers (SPIE), 2024. This conference presentation is from an engineer at SpaceX and is available through NYU Library.
LEO Satellite Constellations in Orbit
Figure 4: A diagram showing the 10000+ LEO satellites orbiting the earth in a giant mesh. Credit: Branch Education, How does Starlink Satellite Internet Work?
LEO Satellite constellations wrap the planet. As of November 2024, there are 6,764 Starlink satellites in orbit, of which 6,714 are working, according to Astronomer Jonathan McDowell who tracks the constellation on his website.
Statistic Source: Tereza Pultarova, Starlink satellites: Facts, tracking and impact on astronomy.
What came before LEO satellites?
Low Earth Orbit (LEO), in the context of satellites, is defined as one that orbits fewer than 500 miles from the surface of the earth, though most LEO satellites are positioned approximately 250 miles above the earth. For comparison, a typical satellite (ex. broadcasting television signals) orbits at about 22000 miles from Earth and is referred to as a geostationary satellite (GSO).
Source: Communications Satellite, Wikipedia
To contrast LEO satellites from their counterparts, GSO satellites are a subset of geosynchronous satellites that appear stationary in the sky from any fixed point on Earth because the satellite’s orbit matches the Earth’s orbit. Because they appear fixed in the sky, they allow for simple, fixed antennas on Earth to receive signals. The large distance also creates a significant delay in communication, rendering real-time two way communication impractical.
This delay is referred to as latency which is significantly reduced in LEO satellite systems.
Typical Broadcast Satellite Orbit
Figure 5: A diagram showing a typical GSO satellites orbiting the earth. It communicates the way that GSO satellites match the orbit speed of the planet. Credit: Geosyncronous satellite, Wikipedia
Policy, Regulation and the Future
As these systems develop around the world, new issues will continue to arise such as the impact of a huge number of satellites lining our skies. Astronomical organizations are currently raising serious concerns about the future of astronomy and our study of the cosmos.
Source: New York Times, How Astronomers Are Saving Astronomy From Satellites — For Now
Geopolitical borders also play a huge role in the development and rollout of LEO networks. In terms of communications licensing, all components of the system require spectrum frequency allocation and regulatory licensing approval before operating within a given country. Simply having satellites criss-crossing the skies of any one nation does not necessarily afford it’s citizens the right to access a network; physical ground stations and frequency licensing is an equally important factor in the equation.
Looking forward to the future, LEO networks have tremendous potential to expand internet access to underserved communities globally and may one day even pose a threat to traditional wired ISPs that have ruled our access to the internet since early days of the net.