Satellite Phone Purchase > Mobal Satellite Expert

Inmarsat vs Iridium - Which service is best for me?

Purchasing a satellite phone is a big decision, and it is important that you are making the correct choice. I hope that after reading my helpful guide you'll feel confident making the correct purchase.

Before you make any decision on which satellite phone to choose it is important that you understand the significant differences between how the two satellite systems operate. Don't be fooled into comparing just the features and specs of the phone handsets themselves. These handset features are likely to be far less relevant to you than the significant operational differences described below:

Inmarsat's satellite coverage is provided by just three satellites. These orbit the earth at very high altitudes (over 22,000 miles, incredibly). This height achieves what is known as a 'geostationary orbit', meaning that the satellites appear to remain fixed in the same position in the sky all the time. In contrast, Iridium's coverage is provided by over 66 satellites, which zoom around the earth in multiple orbits at a much lower level (485 miles). At this lower orbit the satellites are constantly moving in the sky (each will take 10-15 minutes to pass from horizon to horizon, with one passing overhead every seven minutes or so).

With either system, if you have a clear line of sight to any one of the satellites then you will be able to make and receive calls. If, however, your view to the satellite is obscured (by nearby buildings, trees, mountains etc.) then you will not get a signal at all, and you will not be able to use your phone. Therefore, because Inmarsat's satellites are in a fixed position, that means that if you can't "see" the satellite from where you are then you can't use your phone - simple as. You will have to move yourself to a different location where a clear line of sight to the satellite is available.

With Iridium, however, even if your view to the satellite is currently obscured, it's only a matter of time before the next one comes into view and you can make your call.

With Iridium, the satellites move to you, but with Inmarsat you must move to the satellites. Obviously this is a big convenience advantage to the Iridium service, but conversely this movement of the Iridium satellites will inevitably lead to some variability of the signal strength, and occasional dropped calls. With Inmarsat, as long as you maintain a clear line of sight to the satellite then your signal strength is assured, and dropped calls are much more unlikely. This can be a particular benefit if you wish to perform data transfer, as a more consistent connection is required.

To confuse things further, another significant difference is that Inmarsat's satellites orbit the Equator, while Iridium's orbit the Poles. This might not sound significant, but it does mean that the further you travel from the Equator, the more increasingly difficult it will become to achieve that all-important line of sight to the Inmarsat satellites. In equatorial regions Inmarsat's satellites will be very high in the sky, thus very easy to connect to; but the further north or south you travel, the lower the satellites will be in the sky, and thus the harder it will be to be confident of getting a clear line of sight to the satellites. Moreover, as you approach the polar regions the Inmarsat satellites will be so low in the sky that it will not be possible to connect to them at all. With Iridium, the satellites will always be passing overhead, wherever you are in the world, so coverage is always assured, even at extreme latitudes.

In summary then...

Inmarsat

Pros	Cons
Cheaper than Iridium (hardware, monthly costs, and calls). Less dropped calls. Better for data (because connection is less likely to be disrupted).	Doesn't work everywhere (only where you have a clear line of sight in the direction of the satellite). Less convenient (you must 'move to the satellite', it won't 'move to you'!). Won't work at the Poles.

Iridium

Pros	Cons
Works everywhere (multiple, roving satellites). More convenient (the satellites will 'move to to you'). Even works at the Poles.	More expensive than Inmarsat (hardware, monthly costs, and calls). Higher chance of dropped calls. More difficult to maintain a reliable data connection.