Introduction• Initial proposal called for 77 satellites in

the constellation

• Iridium name was derived from the element Iridium having atomic no. 77

• Later studies indicated that only 66 satellites were adequate

Disadvantages of GEO:• The first and foremost limitation of GEO

satellites is round trip latency • The second limitation of GEO schemes is cost.

Because the orbit is 36,000 km above the equator, you need to use a big satellite with powerful transmitters, high performance receivers and large antennas

• Increasing complexity the potential for hardware failure increases

• poor performance in the polar regions

• Low earth orbit (LEO) is used for iridium

Advantages of LEO:• LEO model satellites are placed into a

circular inclined orbit several hundred kilometres above the earth's surface

• This model are very low launch costs per satellite

• Modest demands on antenna, receiver and transmitter performance

• Very low propagation latency times.

Disadvantages of LEO

• Global coverage will require many satellites

• Cannot build a LEO constellation to cover one part of the world alone

• The limited life of the satellites

Arrangement of iridium satellites• The 66 satellites are grouped in six orbitals

planes,11 active satellites in each plane• The satellite has a circular orbit at an altitude of

783km from the earth surface• The distance between the corotating planes is

31.6° and counterrotating plane is 22°

History• Iridium communications service was launched

on November 1, 1998 and went into bankruptcy on August 13, 1999

• The first Iridium call was made by then-Vice President of the United States Al Gore

• Motorola provided the technology and major financial backing.

Downfall• Insufficient demand for the service, coupled

with a massive initial capital cost • The increased coverage of terrestrial cellular

networks (e.g. GSM) and the rise of roaming agreements

• The cost of service was also prohibitive for many users

• The bulkiness and expense of the handheld devices

• Mismanagement has also been cited as a major factor

Present status• Iridium Satellite LLC claims to have 203,000

subscribers as of June 30, 2007 • Revenue for the second quarter of 2007 was

$66.7 million with EBITDA of $20.2 million • Used extensively by the U.S. Department of

Defense • Total bandwidth is 28.8 kbit/s, making real

time e-mail conversations finally possible.• Iridium operates at 2200 to 3800 baud• Iridium claims data rates up to 10 kilobits per

seconds for their 'direct internet' service

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