Calling from the Moon

History of Communication Satellites in a Nutshell

These days we can call up someone in the remotest parts of Antartica and have a conversation as though they were right next to us. However, without the nifty technology that is the ‘Satellite’, none of this would be possible.

They were first mentioned by Arthur C. Clarke (author of ‘2001: A Space Odyssey’) in his article ‘Wireless World’ written in 1945, where he described the transmission of TV programmes from manned satellites in 24-hour orbit around Earth; and then later looked at in detail by John R. Pierce in 1951-2, paving the way to the first communication satellite to be launched in 1957: Sputnik 1.

Sputnik 1 Replica. Credit: NSSDC, NASA

Following this, many more innovations came and with this, many more communication satellites. From Telstar 1 in 1962 which transmitted the first satellite TV (including images of the Eiffel Tower and Statue of Liberty, since it was sent from Brittany to Maine in north east USA); to e-BIRD: a broadband satellite which provided signal to parts of Europe with none.

As well as their many innovations of everything from what they could transmit to where in Earth’s orbit they were (more on that later), communication satellites have also famously been getting smaller; a lot smaller. The small light (from 1 to 10kg) nanosats have become very popular in recent years: ever since the first six in June 2003, they’ve been providing an affordable way to collect data and send it back to Earth, needing little fuel to send them into Space and little material to make them.

Another miniaturising innovation is the the smallsat: a satellite class slightly bigger than the nanosat at less than 180kg. They have been especially popular as communication satellites; most notably with Starlink and OneWeb. Aside from the disruption of Earth-based astronomy, their focus is on fast global broadband, reaching places that couldn’t get an internet connection before using much cheaper methods than older broadband satellites to provide more universal coverage [1][2][3][4][5][6][7].

Model of OneWeb Satellite. Credit: NASA/Kim Shiflett

Where are they?

The simple answer is, of course, in orbit around Earth. However, Earth’s orbit is a very big place, so there are various common orbit types: Geostationary Orbit (GEO), Low Earth Orbit (LEO), Medium Earth Orbit (MEO), Polar Orbit and Sun-Synchronous Orbit (SSO), Transfer Orbits and Geostationary Transfer Orbits (GTO) and the Lagrange Points (L-points) [8].

First, let’s look at GEO: 35,786km above Earth and travelling west to east to follow the rotation of the Earth along the equator, thereby staying above the same place on Earth at all times. They can serve large sections of Earth with constant coverage, and so ensure that area always gets coverage (for relaying signals, for instance) or is continually monitored (like with weather satellites) [8].

LEO is, as the name suggests, low: less than 1000km high to be specific, following any plane (angle of orbit) they want, meaning there’s lots more space for satellites. This makes them fantastic for imagery satellites, but not so for satellite communications, since they’re travelling so fast, orbiting 16 times a day. However, mega-constellations like those of Starlink and OneWeb are in LEO, so how? It’s down to the fact they work together to cover the whole Earth at once, seamlessly changing the satellite in use after the previous one used is out of range. All this makes it extremely popular, whilst also creating a mine field of space debris [8][9].

And where does our prized GPS fit into all this? Well, GPS satellites (along with other navigation satellites such as ESA’s Galileo system) orbit in MEO, found between LEO and GEO. They have the advantages of a lower time to send signals than in GEO, a larger footprint across Earth than LEO, and the option of going in any plane around Earth [8][10].

Like LEO, SSO orbits at a similar altitude (600-800km) and does what it says on the tin: it orbits so, relative to the Sun, it’s fixed in the same position all the time, flying over certain locations at the same time each day and going over the North and South Poles within 20-30 degrees. This is helpful in seeing changes over time at certain places [8].

Scale diagram of where the orbits around Earth are.

Credit: Rrakanishu, CC BY-SA 4.0