Mobile satellite communications is based around mobile/cell phone technology which is now well established and works on your yacht just like a terrestrial mobile phone.

Signals to and from satellites are very weak and a clear path is required for reliable communications with the satellite. Most satellite phones have pop up antennas to clear the head of the caller. If putting satellite onboard a yacht do consider using an external satellite antenna.

Satellite phones offer a wide range of services including SMS, phone calls internet accress, email. Do consider that you may not be able to talk to other vessels or rescue services on the high seas. Therefore mobile satellite communications should not be considered as a replacement for conventional marine VHF or SSB communications. Satellite facts :-

• Life times - Satellites have a limited life time, dependent on fuel and orbit.
  • Satellites burn fuel to keep in the correct orbit. Low orbiting satellites are being pulled back toward the earth by gravity and hence have a short life time, 10 years. Higher orbiting geostationary satellites last about 15 years before running out of fuel and drift out into space.
• Number of calls - The satellite is basically a telephone exchange, it can only handle a limited number of calls.
  • Low orbiting satellites handle between 1700 to 2500 calls per satellite. Higher orbiting satellites can see more of the earth's surface and hence designed to handle a high number of calls, between 5000 to 25000 calls per satellite.
• Coverage - Depends on technology deployed.
  • Bent pipe technology is the most common due to low cost and small size. This is when all calls are passed to a ground station for processing. On low orbiting satellites, if the satellite cannot see a ground station then it cannot connect calls.
  • Interlink satellite technology uses larger and more expensive satellites. This is when satellite can transfer calls between themselves without going via a ground station.
• Mobility - You do need an antenna above deck to receive and make calls.
  • The low transmit power from your satellite phone needs to travel a long way. Low orbiting satellites are in the region of 500 miles above your head and move quickly across the sky. Geostationary satellites are some 22000 miles above the equator and you need a clear path between you and the satellite for your signal to reach it.
• Reliability - In the main good, but like any other mobile phone technology do expect to lose/drop calls.
• Systems cost - It is very expensive to put satellites up there and maintain them.
  • Satellites are designed to be reliable, you cannot send a man up there to fix them when they go wrong. Launch costs are high and each payload carries between 3 to 6 communication size satellites.

Mobile satellite systems available are:-

• Iridium - Offers global coverage and email. The lifetime of this system is now becoming an issue with end of service by 2014. Replacement system called Iridium Next is in develpment.
• Globalstar - Anything but global! Poor global ocean region coverage, email and data service. Second generation satelllites are being launched from 2010.
• Thuraya - European, Middle East and Far East coverage, emails anddata services for instant satellite access to the Internet.
• Inmarsat - A service targeted towards the marine users offering good ocean region coverage and with telephone and data with fast broadband internet access.
  • Inmarsat - C slow but reliable 600 bits per second data only service.
  • Fleet broadband with antenna from 33 to 80 cms and broadband speeds from 150 kbps to 500 kbps. The bigger antenna is used for faster data.

Satellite phone call charges :-
Telephone call cost range from $0.30 to $2.00 per minute and even more on some systems.
Beware of call costs to your satellite phone from shore, it is usually cheaper to make the call than to receive a call!
Data charges are very expencive, Inmarsat FleetBroadband charge around $12 per Mbit or $12000 per Gbit!
Also inter satellite calls between different satellite networks are expensive.

Satellite Data via satellite phone systems. For speech, a narrow bandwidth of only 2400 Hz is required. Some early satellite phone systems (Iridium and Globalstar) were only designed to handle voice communications which uses a very narrow bandwidth.

The narrow band restricts the amount of data which can be sent, data rates range from 2.4 k bits to 9.6 k bits per second depending on the service provider.

For satellite phones systesm for yachts click here

For low cost communications, do consider terrestrial SSB and SSB email