Broadband from space: Will it work this time?

Does the recent launch of early Starlink satellites by Elon Musk's revolutionary company SpaceX herald a new age of space-based broadband - or will the new low-orbit ventures fail like their predecessors?

It's one of the rules of the telecomms world: satellites aren't great for carrying internet traffic.

The reasons for this are several. Firstly, satellites in low orbit only have line of sight across a relatively small part of the Earth's surface. This means that the lower the orbit, the more satellites you need to achieve global coverage. But satellites are expensive things, so the existing low orbit, two-way communications constellations are still high enough to keep the numbers reasonable: examples include Iridium, with 66 spacecraft in operation, Globalstar with 24 and ORBCOMM with 31.

These satellites are still low enough that reasonably compact user equipment with simple antennas can connect with them. The trouble is that they offer only sharply limited bandwith. Iridium and Globalstar can carry voice or narrrowband data only. ORBCOMM users are usually restricted to sending short data bursts every few minutes and ORBCOMM is mainly used for machine-to-machine (M2M) applications.

As a business, low orbit satcomms isn't the goldmine that some of its advocates suggested it would be back in the 1990s. The unforeseen popularity and ease of international roaming using ordinary mobile phones robbed it of many customers. Iridium, ORBCOMM and Globalstar have all been through bankruptcy and restructuring. Nowadays, with broadband data service more and more important, it's clear that narrowband platforms like these cannot meet many users' needs.

If you want to feast on space data, you'll need a dish

It's always been possible to achieve greater bandwidth by the use of a dish antenna pointed at a satellite, but with an ordinary dish this means that the satellite needs to be sitting still in the sky. The only way to achieve this is to put the satellite much higher up, in geostationary orbit 36,000 km above the Equator, such that it circles the planet in exactly 24 hours. As the planet itself is turning at the same rate, from the surface a geostationary satellite sits dead still in the sky and it is a simple matter to train a rooftop dish on it.

Geostationary works excellently for one-way omnicast applications like television, where a single satellite can cover a large area of the planet below with HD programming. It can also be used to provide broadband internet download to a limited number of dishes on the surface, and such services are on offer. Upload via the satellite is quite possible, but it requires special transmission equipment. In some cases the upstream connection is actually provided by surface channels - as where a home user receives broadband downloads via rooftop satellite dish, but upload traffic reaches the internet via narrowband landline DSL. Most home users don't need much upload bandwidth.

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