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GMU - ECE 739, Fall 2003 - Satellite Communications Class: Nov-24-2003
(C) Leila Z. Ribeiro, 2003 1
ECE 739 – Fall 2003
Satellite Communications
Lecture 12
Non-Geostationary Orbits (NGSO)Dr. Leila Z. RibeiroNovember 24, 2003
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Agenda
• Design considerations• Case studies
– MSS: Mobile Satellite Systems:• Iridium (Big LEO)• Globalstar (Big LEO)• ICO Global (MEO)• Ellipso (MEO)
– Store-and-Forward Services:• ORBCOMM (Little LEO)
– Broadband (Internet/Multimedia):• Skybridge• Teledesic
Design Considerations
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Brief History
• Early satellites (since Sputnik, 1957) were all LEO
• 1963 first GEO (Geostationary) satellite• For about next three decades, the vast
majority of communication satellite systems were GEO (also called GSO = Geostationary Satellite Orbit)
• Non-GSO systems proposed in early 1990s
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Advantages of LEO and MEO
• Can provide true global coverage
• Lower path loss (allows hand-held terminals)
• Low-to-medium propagation delay (5-100 ms) from transmitter to receiver
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Disadvantages of LEO and MEO (1)
• Larger number of satellites are needed• Satellite visibility of 10-180 minutes
(requires inter-beam and inter-satellite handover) complex architecture
• Signal strength not constant, due to varying range and elevation angle
• Intense Doppler effects• Interference (hard to predict)
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Disadvantages of LEO and MEO (2)
• Large number of eclipses, requiring battery cycles (shorter life cycle)
• Higher number of satellites increases debris• Technology still developing (higher risk)• Initial deployment requires multiple launches
before operation starts (upfront investment)• Challenging to maintain and replenish network
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Disadvantages Outnumber Advantages:So Why Use LEOs ?
• Mobile communications is a huge and rich market,LEO’s lower path loss may help meet the challenge of global personal communications.
• Lower propagation delay is key for real-time communications
• Lower coverage footprints allow higher frequency-reuse, more efficient spectrum utilization, (factor of approximately 4 to 1)
• OBP development supports network complexity• Distributed architecture increases reliability
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NGSO Categories
• Little LEO System: Low bit rates non-real-time services, such as messages (<4 kbps)
– ORBCOMM• Big LEO Systems: Real-tima medium bit rate
interactive services (1-10kbps), such as voice– Iridium, Globalstar
• MEO Systems: Real-time medium/high rates– ICO Global System, Ellipso
• Broadband LEO: Broadband services such as high-speed internet (16 kbps to 1 Gbps)
– Teledesic, Skybridge10
Examples of NGSO Systems
System Category Store-and Forward MSS MSS MSS MSS Broadband BroadbandOrbit Category Little LEO Big-LEO Big-LEO MEO MEO Big-LEO Big-LEO
System Orbcomm Iridium Globalstar Ellipso New-Ico SkyBridge Teledesic
Service Types messaging,
paging, e-mail
Voice, data, fax, paging,
messaging
Voice, data, fax, paging,
messaging
Voice, data, fax, paging,
messaging
Voice, data, fax, paging,
messaging
Internet Access, Voice, Data,
Video, Videoconferencing
Internet Access, Voice, Data,
Video, Videoconferencing
Voice/Data (kbps) 2.4 kbps uplink
4.8 kbps downlink 2.4 2.4 to 7.2 0.3 to 9.6 2.42,000 uplink
20,000 downlink2,000 uplink
64,000 downlink
Orbit Altitude (km) 775 780 14148050, 6149/8050,
633/7605 10390 1469 1375
Orbit Type (s) Circular, Inclined Circular Polar Circular Inclined
Circular (1), Elliptical (2), Sun-Synchronous (2) Circular inclined Circular Inclined Circular polar
Orbit Planes 4 -> 5 6 6 1 -> 3 -> 5 2 20 12
Satellites per Plane 4x8 + 1x4 11 8
1x7 (circular)+2x3 (elliptical) + 2x5
(sun-synchronous) 5 4 24
Number of Satellites 48 66 48 23 10 80 288Earth Stations 10 200 TBD
Beams/Satellite 1 48 16 61 163 ~50 64Footprint diameter (km) 3000 1412
Mobile Uplink (MHz) 148-150 MHz1616-1626.5 (L-
band)1610-1626.5 (L-
band) 1.610 - 1.621 GHz 1.6 GHz
Mobile Downlink (MHz) 137-138 MHz1616-1626.5 (L-
band)2483.5-2500.0 (S-
band) 1.610 - 1.621 GHz 2 GHz
Feeder Uplink (GHz) 148-150 MHz27.5-30.0 (Ka-
band)5.091-5.250 (C-
band) probably C-band C-band 2.75-14.5 (Ku-band28600-29100 (Ka-
band)Feeder Downlink (GHz) 137-138 MHz band) band) probably C-band C-Band 0.7-12.75 (Ku-band band)
Connectivity Ground-Relay ISL Ground-relay Ground-relay Ground-relay Ground-Relay ISLService Date 1996 1998 2000 Unknown Late 2003 2001 2004
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Summary of Mobile Satellite System Orbits
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Van Allen Radiation Belts
• Two Van Allen radiation belts•1,500 km (approx.)
•15,000 km (approx.)
• LEO systems “bottled in” by lower belt
• MEO systems have wider choices
• GEO systems have only one choice
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Important Design Considerations
• Service area• Geographical distribution of traffic within the area• Global or regional operation• Geometrical vs. RF coverage• Spectrum reuse: coverage area divided into smaller
sets which are each covered by a spot beam• Dynamic variations of coverage footprint makes
use of software essential
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Example of Coverage from a LEO System (1)
24 satellites: 4 orbital planes, 6 satellites/plane
Copyrighted. Reproduce
with permission
only (Maral, 1991).
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Orbital path of satellite
Movement of the coverage area under the satellite
Earth
Track of sub-satellite-satellite point along the
surface of the Earth
Example of Coverage from a LEO System (2)
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Frequency Re-Use
Spectrum A
Spectrum B
Spectrum C
Instantaneous Coverage Region
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Terminal Requirements
• Size of terminals limited due to transportability reasons
• Transmitting power limited by radiation safety reasons; typical power (0.25 - 0.5 Watts)
• Battery life and size limited by terminal cost• Design of satellite G/T ratio depends on the
terminal EIRP (to close the uplink)• Design of satellite EIRP depends on mobile G/T
ratio (to close the downlink)18
Network Architectures:Non-Real Time Systems
• Non-real time services: Includes services such as messaging, that can tolerate some delayExample: ORBCOMM
– Uses store-and-forward method– Number of satellites depends on tolerable delay
• Satellite-based store-and-forward– Messages stored at satellite, delivered when satellite coverage area is
over destination terminal
• Earth station-based store-and-forward– Messages received at satellite immediately transmitted to relay station,
which chooses best route (satellites) to direct the message; stored at ground terminal
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Network Architectures:Real Time Systems (1)
• Include services such as voice and video conference• Messages routed from source to destination via inter-
satellite links (ISL). Example: Iridium– Routing protocols:
• Centralized: Central site maintains database with current location of all satellites and users; continually updated, lots of signaling for each connection
• Distributed: Each satellite keeps its own database; more complex on-board schemes
• Flooding: Each message contains destination header; message is forwarded by all receiving nodes to all visible nodes, unless by the destination; resource inefficient
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Network Architectures:Real Time Systems (2)
• Connectivity via ground-relays: Messages received at satellite are immediately transmitted to a relay ground station, which routes it via satellite hops or terrestrial means to another relay station until the message is delivered to destination. Example: Globalstar, Ellipso, New Ico
• Connectivity via geostationary satellites: Inter-satellite links use GEOs as repeaters
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Connectivity via Inter-Satellite Link
SourceDestination
Satellite 1Time T0
Satellite 2Time T1
Satellite 3Time T2
ISL ISL
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Connectivity via Ground Relays
SourceDestination
Satellite 1Time T0
Satellite 2Time T1
Satellite 3Time T2
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Mobility Management
• Mobile Switch Center (MSC)– Interfaces with public networks and performs switching
• Home Location Register (HLR)– Database containing location and other information, such as
billing, about each mobile associated to that network as its “home” area
• Visitor Location Register (VLR)– Database that registers all mobiles belonging to other areas
that are currently visiting the network where the VLR belongs– Sends messages to the mobile’s HLR so the latter always has
an updated location for all mobiles belonging to it
Case Studies
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Outline
• Iridium
• Globalstar
• ICO Global
• Ellipso
• ORBCOMM
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Iridium Overview (1)
• First into the ring
• Not affiliated with current satellite systems
• Very comfortable with advanced technology
• Saw potential match between urban and rural needs
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Iridium Overview (2)
• No competitors other than GSO entities
• Target was hand-held user
• Delay was not the design focus
• Power budget led to LEO selection28
An Aside: Delay
• Common misconception is that delay will kill GEO systems
• One way delay from GEO ≈ 250 ms
• One way delay from Iridium satellite is from 160 ms to 260 ms
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• TDMA frame length of 90 ms
• 2.4 kbit/s vocoders
• ISL cross-link issues
• Gateway distances
An Aside: Principle Factors in Delay
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Iridium System Details
• 66 satellites• 689 kg per satellite• 6 polar orbital planes• 780 km orbit height• 100.5 min. orbital period• 48 spot beams• Lifetime 5 - 8 years
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Iridium Constellation
Source: Source: www.geom.umn.edu/~worfolk/SaViwww.geom.umn.edu/~worfolk/SaVi
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Iridium Satellite
Copyrighted. Reproduce with permission only.
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Iridium Link Parameters
• Handset frequency: 1.6 GHz• ISL frequency: 23 GHz• Gateway frequency: Ka Band• Handset margin: 16 dB (average)• Multiple access: FDMA/TDMA• Modulation: QPSK• Transmission rate: 2.4 kbit/s• Traffic: Voice/fax/data
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Three Iridium Launchers
• DELTA II (5 Iridium satellites per launch; 11 launches = 55 satellites)
• PROTON (7 Iridium satellites per launch; 3 launches = 21 satellites)
• LONG MARCH 2C (2 Iridium satellites per launch; 5 launches = 10 satellites)
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Iridium Launch Campaign (1)
1 May 5, 1997 Delta 2 5 satellites 14 May 2, 1998 L. March 2 satellites2 June 18, 1997 Proton 7 satellites 15 May 2, 1998 Delta 2 5 satellites3 July 9, 1997 Delta 2 5 satellites 16 Aug. 20, 1998 L. March 2 satellites4 Aug. 20, 1997 Delta 2 5 satellites 17 Sept. 8, 1998 Delta 2 5 satellites5 Sept. 13, 1997 Proton 7 satellites 18 Nov. 6, 1998 Delta 2 5 satellites6 Sept. 26, 1997 Delta 2 5 satellites 19 Dec. 19, 1998 L. March 2 satellites7 Nov. 8, 1997 Delta 2 5 satellites8 Dec. 8, 1997 L March 2 satellites9 Dec. 20, 1997 Delta 2 5 satellites10 Feb. 18, 1998 Delta 2 5 satellites11 Mar. 25, 1998 L. March 2 satellites12 Mar. 29, 1998 Delta 2 5 satellites13 Apr. 6, 1998 Proton 7 satellites
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• Between 7 and 12 in-orbit failures
• Majority of failures appear to be bus and ISL-related
• Now at least 74 operating satellites in orbit
• Constellation completed
Iridium Launch Campaign (2)
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Iridium System Testing
• Beta testing began 23 September 1998
• Commercial paging and communications
• Services began 1 November 1998 with a call by Al Gore from the Rose Garden
• All 12 gateways operational
• Last gateway (China) completing testing
• 5000 handsets shipped by Motorola
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Iridium Costs
• Left to individual gateway operators to set charges
• Prices for air-time are between $1.50 and $10.00 per min.
• Demand reported to be “high” but availability of handsets for commercial operations was limited
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Iridium Handsets (1)
• Motorola satellite series 9500• 2.7 X 2.4 X 7.6 inches, 8.5 inch antenna• $3,400 average street value• All calls are international; precede all
numbers by 00• 100 name international directory, four-line
display assists caller• 16 hours standby/2 hours talk
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Placing an Iridium Call
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Iridium Handsets (2)
• Raft of accessories– Desktop and solar chargers– Auxiliary, mobile, & mast antennas– RS-232 adapters for computers to handle data
traffic (late 2001)
BUT……….42
Iridium Filed For Chapter 11August 1999
• Despite:– Incredible run of successful launches– Licensing issues proceeded as planned– Iridium licensed to operate in more than 29 countries
and signed on more than 60 ‘roaming’ and ‘service’ providers; all 13 Gateway facilities built……..
• User acceptance was very poor due to costs and quality
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Iridium Quality Issues (1)
• Initial Grade of Service (GOS) was 30% (typical cellular systems are 2%)
• Managed to get GOS < 10%• Dropped call ratio was reducing, but was
still higher than expected• Paging exceeded expectations
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Iridium Quality Issues (2):Grade of Service (GOS)
• The maximum supported traffic can be smaller than the traffic offered, it is possible that the system fails to assign channels when an user attempts to make a call
• The probability of this type of failure is referred as blocking or Grade of Service(GOS)
Investors pulled the plug on cash-flow issues
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Iridium: Facts (1)
• Original concept in 1987• Iridium LLC established: 1991• Overall cost of the system: $5 billion
Business case calculated at 600,000 to break even
• Beginning of operation: October 1998
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Iridium: Facts (2)
• August 1999: Filed for bankruptcy protection• March 2000: Stopped operation with about 55,000
subscribers• December 2000:
– Sold to a group of investors for $25 million– Creation of Iridium Satellite LLC: focus on government
services and niche industrial markets– Signed contract with DoD for $72 million for 2 years
unlimited service– Used as backup communications at US embassies
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Iridium Today
• Owned by Iridium Satellite LLC• Operated by Boeing• Delivers communications services
applications such as heavy construction, defense/military, emergency services, maritime, mining, forestry, oil and gas and aviation.
• Iridium currently provides services to the United States Department of Defense and launched commercial service in March 2001.
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Globalstar (1)
• Started late• Closely affiliated with satellite system
operators• While comfortable with advanced
technology, needed to catch up• Saw match between current business and
new opportunity
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Globalstar (2)
• Started with Iridium in its sights
• Needed to “design down” that system for potentially more rapid implementation
• Wanted hand-held user market which also led to LEO choice
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Globalstar (3)
• Went for system design that included Governments
• Decided to provide system as a “common carrier” with Government institutions acting as service providers
• Design did not require ISLs
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Globalstar System Details
• 48 satellites• 390 kg per satellite• 6, 52 deg. inclined planes• 1414 km orbit height• 114 min. orbital period• 16 spot beams• Lifetime - 7.5 years
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Globalstar Link Parameters
• Handset frequency: 1.6 GHz uplink, 2.5 GHz downlink
• Gateway frequency: C band• Handset link margin is about 5 dB• Multiple access: CDMA• Transmission rate: 7.2 kbps max.• Traffic: Voice/fax/data
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Three Globalstar Launchers
• DELTA II (4 Globalstar satellites per launch; 2 launches planned = 8 satellites)
• ZENIT (12 Globalstar satellites per launch; 3 launches planned = 36 satellites)
• SOYUZ (4 Globalstar satellites per launch; 3 launches planned = 12 satellites)
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Globalstar Status
• Constellation of 48 complete• Four ground stations completed (France, S.
Korea, USA, Australia)• Franchises set up with > 100 local service
providers, covering 88% of the world’s population
• Service provided to China, Russia, U.S., Middle East, Brazil and maritime zones by 2001
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Globalstar Costs
• Sells air-time at “wholesale” rates as a “common carrier”
• Firm numbers quoted from Russian partner at $1.50 per min. and, based on information from Airtouch, costs will be between $1 and $1.20 per min.
• Have also seen <$ 0.55 quoted
BUT……….56
Globalstar Issues
• Filed for Chapter 11 Feb. 2002• Restructured to recover from bankruptcy in
second quarter 2002• Overhead costs too high => suffered $3.8
billion loss in 2000 and $600 million loss in 2001
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Globalstar Today
• Court approves in 21-Nov. 2003 the acquisition of Globalstar by Thermo Capital PartnersTransaction
• $43 million acquisition plan expected to close in early 2004 and would give Thermo an 81.25% ownership of a new company that would take control of Globalstar's assets and operations
• The remaining 18.75% of the equity interests in the new company would be available to Globalstarfor distribution to its creditors.
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ICO Global
• Late in starting - took very deliberate design approach
• Spun-off from Inmarsat so basically owned by government
• Very uncomfortable with advanced technology due to ownership heritage
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ICO Global
• Started with GEO heritage
• Wanted to include maritime element
• Forced into compromise solution of MEO (double hop calls still have less delay than GEO single-hop)
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ICO Global
• Since owned by 44 nations who were part of Inmarsat, went for inclusive approach
• MEO compromise required an adventurous antenna design to provide enough power into the hand-held unit; the antenna was the pacing item
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ICO Global System Details
• 10 satellites• 2750 kg per satellite• 2, 45 deg. orbital planes• 10355 km orbit height• Approx. 6 hour orbital period• 163 spot beams• Lifetime 12 years
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ICO Global Beam Coverage
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ICO Global Link Parameters
• Handset frequency: 1.6/2 GHz• Gateway frequency: C band• Handset margin: 8 dB min.• Multiple Access: FDMA/TDMA• Transmission rate: 2.4 kbit/s• Traffic: voice/fax/data
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ICO Global Launchers
• Four launchers are used with one spacecraft per rocket
• 1 ATLAS IIAS
• 3 PROTONs
• 3 ZENITs (with sea launches ) ##
• 5 DELTA IIIs
## Joint Boeing/Hughes undertaking with ZENIT
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ICO Global Launch And Satellite Status
• First ICO spacecraft has completed integration at Hughes
• First launch delayed more than a year (could be sea launch or an Atlas IIAS)
• With 6 satellites in orbit (3 per plane) interim service started
• Full service was planned for mid-2002 when 10 satellites in place (5 per plane)
BUT………. 66
ICO Global Problems
• Economic crash of Iridium scared the market• ICO Global could not attract investors when it
tried to raise cash• Went into Chapter 11 in Aug. 1999• Long-time CEO resigned• Looked at a reduced fleet
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ICO Global Status
• ICO-Teledesic Global Limited acquired ICO Global in May 2000 after bankruptcy in August 1999
• First satellite launched in 2001 with expected constellation of 10 satellites and 2 spares operating at 10390 km
• Service expected to start in late 2003
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• Up to individual country/operator to set charges (as with Inmarsat)
• Assumed that the costs will be “competitive” with other services available in the country of service (<$1.50 per minute has been quoted)
ICO Global Airtime Costs
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Ellipso (1)
• Started late• Not closely affiliated with satellite system
operators• Not a “deep pocket” company• Investigated market and targeted specific
customers• Saw need for an incremental approach
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Ellipso (2)
• Low cost “bent-pipe” satellites
• MEO orbit selection minimizes number of gateways => ground cost minimized
• Phased deployment => revenues generated with only 4 satellites
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Ellipso (3)
• Identified two key world population demographics– Very few people live below 40 S and so can
reach majority of world from equatorial orbit– But majority of “developed world” landmass
and people in northern hemisphere live above ~40 N
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• Went for two completely different architectures– Ellipso-Concordia (equatorial sub-constellation
of initially 6, then 10, satellites. First 6 satellites are in circular orbit, next 4 are in slightly elliptical orbits)
– Ellipso-Borealis (2, inclined elliptical orbits with 4 satellites-per-plane with the perigee always in the south)
Ellipso (4)
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• 6, then 14, then 18 satellites• 650 kg per satellite• 0 deg. and 2 x 116 deg., latter are sun-
synchronous• 8060 km (0 deg.) AND 520 / 7,849 km
(sun-synchronous)• ~ 3 hour orbital periods• 61 spot beams• 5 - 7 year lifetime
Ellipso System Details
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Ellipso Orbits
Concordia
Borealis Borealis
Earth
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Ellipso Link Parameters
• Handset frequency: 1.610 - 1.621 GHz for services in 5 MHz segments
• Gateway (unknown but probably C-band)• Multiple access: CDMA• Transmission Rate: 300 - 9600 bps• Traffic: Voice/fax/data
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• Launchers to be used are not known
• Due to mass of Ellipso satellites (650 kg) they will probably need a launcher of the Delta II class
• Multiple satellites per launch are planned
Ellipso Launchers
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• Incremental growth rate and focused customer base will give lowest potential costs of any system
• Will “make money” with just 1,000,000 subscribers
• Aiming at fixed as well as mobile; Fixed costs could be < $0.12 per min.
Ellipso Costs
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Ellipso Remaining Issues
• Yet to set up launch services contracts (apparently)
• Landing rights/service issues are not yet fully public
• If both of these prove to be satisfactory and normal launch success is obtained, the system looks set
• Expansion into 2 GHz frequency band filed with FCC
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ORBCOMM (1)
• A different approach/service• Targets low data rate/ paging services• Very low cost approach ($330 million vs.
$5 billion of Iridium)• Saw market opportunity for distributed low-
rate links
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ORBCOMM (2)
• Started with blank sheet• No other competitors• Target was to bring information from disbursed
units into a central office for analysis; grew to voice
• Ultra-low cost approach led to LEO selection• Went for low-cost global coverage• “Store-and-forward” option removed need for
multiple gateways or inter-satellite-links• Went for “temperate” market first; global later
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ORBCOMM System Details
• 36 satellites• 40 kg per satellite• 4, 45 deg. orbital planes (32 S/C); 1, 72 deg.
plane (4 S/C)• 775 km orbit height• 100 min. orbital period• Single beam coverages
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ORBCOMM System Details
• Terminal frequency: 148 MHz uplink; 137 MHz downlink (VHF)
• Multiple Access: IP packet network• Transmission rate: Message size typically 6
- 250 bytes at rates up to 4.8 kbit/s• Traffic: Data/Paging/Voice(?)
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ORBCOMM Launchers
• Two launchers are used• PEGASUS XL (8 ORBCOMM satellites per launch; 4
launches planned = 32 satellites)
• TAURUS (2 ORBCOMM satellites per launch; 2 launches planned = 4 satellites) ##
## Land-launched version of the air-launched Pegasus, for higher inclined orbits
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ORBCOMM Launch Status
• 30 successfully in orbit (first LEO system to have a revenue stream)
• Constellation is now complete
• Marketing an e-mail system using a hand-held GSC 100 system that with 50 inch telescoping antenna
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ORBCOMM Operation Status
• System is currently earning revenues from paging, remote sensing, and position location services
• Depending on the definition of (fully) operational, ORBCOMM could claim to be the first LEO system to go into commercial service
• Small-to-large company conversion in less than two years
• Other than that, given good satellite reliability, the system is set to go
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SkyBridge
• Focus on Internet Multimedia Applications
• System is “Globalstar-like”, I.e:
- Inclined orbits at about same height (1469 km).
- No intersatellite links, satellites are “bent-pipe”, terrestrial based switching.
But:
-Frequencies above 10 GHz (Ku-band)
-Established minimum limit of 10 degrees elevation angle to protect re-use of Ku band GEO systems.
-Forced the number of gateways to 200 and satellites to 80
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Teledesic
• Focus is “Internet-in-the-Sky”
• System is “Iridium-like”, I.e:
- Polar orbits (12 planes, 24 satellites per plane)
- Connectivity through intersatellite links, using onboard processing.
But:
-Frequencies are in Ka-band: more critical rain attenuation.
-Established minimum limit of 40 degrees elevation angle to avoid rain impact.
-These conditions forced the number of satellites to 840. Original height was then changed from 700 to 1400km, reducing constellation to 288 satellites.