This document discusses the Iridium satellite system. It provides information on: - The original proposal for 77 satellites that was later reduced to 66 satellites placed in low Earth orbit. - The classification of different types of orbits including low Earth orbit, medium Earth orbit, and geostationary Earth orbit. - The architecture of the Iridium system including the arrangement of the 66 satellites in six orbital planes and 11 satellites per plane. - How the Iridium system works to route phone calls between satellites and gateways to provide global coverage.

1. Name:- HARSHIT SINGH
Roll No:- 1709731903
Year:- 4th (A)
DEPARTMENT OF ELECTRONIC AND
COMMUNICATION ENGINEERING
Logo of
AKTU
IRIDIUM SATELLITE

2. CONTENTS
 Introduction
 Classification of orbits
 Iridium system architecture
 Arrangement of iridium satellite
 Working of iridium satellite
 Advantage & Disadvantage
 Application
 Conclusion
 References

3. 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.
 The only satellite system with true pole-to-pole coverage.
 66 low earth orbiting (LEO) satellites with 14 spares.
 It has onboard satellite switching technology which allows it to service large areas with
fewer gateways.
 Since it was originally designed as a voice only system it provides a low data rate
of 2.4 kbps.
 An artificial body placed in orbit round the earth or another planet in order to collect
information or for communication.

4. CLASSIFICATION OF ORBITS
LOW EARTH ORBIT ( LEO) :-
 Low Earth Orbit satellites have a small area of coverage. They are positioned in an orbit
approximately 3000km from the surface of the earth.
 They complete one orbit every 90 minutes.
 The large majority of satellites are in low earth orbit.
 The Iridium system utilizes LEO satellites.
 The satellite in LEO orbit is visible to a point on the earth for a very short time.
MEDIUM EARTH ORBIT ( MEO) :-
 Medium Earth Orbit satellites have orbital altitudes between 3,000 and 30,000 km.
 They are commonly used in navigation systems such as GPS.

5. Geostationary Earth Orbit (GEO):-
 Geostationary Earth Orbit satellites are positioned over the equator. The orbital altitude is
around 30,000-40,000 km.
 They complete one orbit every 24 hours. This causes the satellite to appear stationary with
respect to point on the earth, allowing one satellite to provide continual coverage to given
area on the earth's surface
 One GEO satellite can cover approximately 1/3 of the world’s surface.
 They are commonly used in communication systems
Fig 1 : iridium constellation [1]

6. Fig 3 :Iridium satellite network [3]Fig 2 : Satellite orbit structure [2]

7. IRIDIUM SYSTEM ARCHITECTURE
The iridium uses GSM-based telephony architecture to provide a digitally switched telephony
architecture network and global roaming feature is assigned in to the system . Each subscriber is
assigned a personal phone no and will receive only one bill no matter in what country or area they
use the telephone.
Fig 5 : Iridium system architecture [5]Fig 4 : Iridium interface center [4]

8. ARRANGEMENT OF IRIDIUM SATELLITE
 The 66 satellite are grouped in six orbital
plane ,11 active satellite in each plane.
 The satellite has a circular orbit at an
altitude of 783 km from earth surface.
Satellite Type LEO
Satellite altitude 780 km
Angle of inclination 86.4
Average satellite view
time
9-10 minutes
Access scheme FDMA and TDMA
Maximum number of
located users
80 users in a radius of
318 km
Theoretical throughput 2.4 Kbps
Table 1 : Background iridium [7]Fig 6 : Block diagram[6]

9. WORKING OF IRIDIUM SATELLITE
 When an IRIDIUM telephone is activated, the nearest satellite - in conjunction with the iridium
network - automatically determines account validity and the location of the user.
 The subscriber selects among cellular or satellite transmission alternatives, depending
on compatibility and system availability, to dispatch a call.
 If the subscriber's local cellular system is unavailable, the telephone communicates directly
with a satellite overhead. The call then is transferred from satellite to satellite through the
network to its destination, either to another IRIDIUM telephone or to an IRIDIUM ground
station. IRIDIUM system gateways interconnect the satellite network with land-based fixed or
wireless infrastructures worldwide.
 The receiving antenna is small enough to fit on a hand-held telephone. The small,
lightweight IRIDIUM satellites are electronically interconnected to provide continuous
worldwide coverage. Intersatellite and ground control links take place in the Ka-band
frequencies. Telephone and messaging communications take place in the L-band frequencies.

10. ADVANTAGE
 Short propagation delays (10-15msec).
 Low transmission power required .
 Low price for satellite and equipment.
DISADVANTAGE
 Small coverage spot.
 High system complexity.
 Greater no of satellites for coverage.
Fig 7: Air navigation [8]
Fig 8 : iridium next satellite [9]

11. APPLICATON
 Earth quake and tsunami alert through ISS.
 Disaster early morning.
 Mobile communication.
 Air Navigation .
 Medical purpose.
Fig 9 : Earthquake and Tsunami [10]

12. CONCLUSION
Iridium is currently developing, and is expected to launch during 2016 and 2017, Iridium NEXT, a
second-generation worldwide network of telecommunications satellites consisting of 66 satellites,
with six in-orbit and nine on ground spares. These satellites will incorporate features such as data
transmission which were not emphasized in the original design. The original plan was to begin
launching new satellites in 2014. Satellites will incorporate additional payload for Air on, Inc. and
perhaps cameras and sensors in collaboration with some customers and partners. Iridium can
also be used to provide a data link to other satellites in space, enabling command and control of
other space assets regardless of the position of ground stations and gateways will provide L-
band data speeds of up to 1.5 M bit/s and high-speed Ka-Band service of up to 8 M bit/s.

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