With the release of the new Iridium Extreme and the increasing sales of the Isatphone Pro within our business I felt that it was important to outline to new satellite phone users the differences between the two services from Iridium and Inmarsat. Choosing the right service is as important as selecting the best satellite phone for you and 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.
For a summary of the pro’s and cons visit my page Iridium vs Inmarsat
I hope this has been helpful for you, any questions just ask them in the comments section.