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Villafranca Satellite Tracking Station


MARECS Missions Description

The MARECS missions were designed with the objective to provide high quality full duplex, real-time voice, data and teleprinter services between ship earth stations and coast earth stations for a minimum life time of 5 years:

  • Telephone service with access to the international public telephone network capable of supporting facsimile and data transmission. The satellites have in-orbit capacity of approximately 60 voice channels.
  • Telex service with access to the international public telex network. The telex channels are accommodated in blocks of 20, each block using approximately the equivalent capacity of a single voice channel.
  • Handling of priority messages for the maritime distress and safety services.
  • Relaying of low bit rate distress messages.
  • Broadcast of messages such as weather forecast and national news summaries to groups of ships.

The two spacecrafts consist of a service module and a payload module and are three-axis stabilised. They are identical with the exception that MARECS-A is supplied with 10 solar array sections and MARECS-B2 with 12 sections.

The spacecrafts are approximately 2 m wide and 2.5 m high, with a 2 m L-Band dish antenna.The solar arrays extend between 14 m from tip to tip. Spacecraft mass at launch was 1015 Kg. The two satellites are positioned in a geosynchronous orbit.

The Shore to Ship link (Forward Link) through the satellites is established at C-Band for the up-path (6420.25-6425 MHz) and at L-Band for the down-path (1537.75 - 1542.5 MHz). The Ship to Shore Link (Return Link) is performed at L-Band for the up-path (1638.6 - 1644.5 MHz) and at C-Band for the down-path (4194.6 - 4200.5 MHz).

The Flight Control Centre is located at ESOC and the TT&C ground station working at C-Band at Villafranca. A back-up VHF TT&C station and telemetry reception in C-Band is located at Redu.

MARECS Missions History

MARECS-A was launched on December 19, 1981 and MARECS-B2 on November 9, 1984. Both satellites were leased to INMARSAT to provide maritime satellite communication services in the Atlantic Ocean Region (MARECS-A) and in the Pacific Ocean Region (MARECS-B2).

In 1986 INMARSAT requested to relocate the two MARECS satellites. Thus MARECS-B2 was moved from the Pacific Ocean Region (POR) to the Atlantic Ocean Region (AOR), whilst MARECS-A was moved to the POR to be used as in standby.

In 1991 MARECS-A was removed from INMARSAT services and relocated to 22.5╟ East due to an extended degradation of solar array sections and has since then been successfully used by ESA for land mobile experimental communications with the ground based PRODAT terminal being located at Villafranca and later at Lario (Italy).

Following a request of INMARSAT, MARECS-B2 was moved in 1990 to 55.5╟ West to cover a new region (AOR-West) with prime maritime communication services.

The new relocation was preceded by an extensive campaign of 28 manoeuvres compressing effectively three years of North-South station keeping into three months. 38 Kg hydrazine were expended in 33 hours of thruster firings, to impart a delta V of 132 m/sec.

Finally in 1992 INMARSAT requested to relocate MARECS-B2 to 15╟ West (AOR-East), where the satellite is being used since December 1992 in a dual satellite operations system.

The future prospects of the two satellite missions are primarily limited by the increasing degradation of the solar array sections.

Inmarsat 3's C-band (6.4/3.6 GHz)

Main transponders  
Backup transponders  
Power 15 W
Bandwidth 39 MHz
Coverage Global
EIRP max  
Polarization  

Inmarsat 3's L-band (1.6/1.5 GHz)

Main transponders  
Backup transponders  
Power 20 W
Bandwidth forward: 29 MHz, return: 39 MHz
Coverage & EIRP max Navigation beam: global
5 spots: 47.4 dBW
Global: 40.5 dBW
Polarization

Milstar 1 series

Specifications

Prime contractor Lockheed Martin
Platform  
Mass at launch ~4500 kg
Mass in orbit  
Dimension  
Solar array 8000 W
Stabilization  
DC power  
Design lifetime  

Payload

Low Data Rate payload (75 bps to 2400 bps):
EHF (44.5 GHz) uplink
SHF (20 GHz) downlink
4 UHF AFSATCOM transponders

The satellites also have a 60 GHz crosslink to enable it to communicate with other Milstars


Nato 4's UHF-band (250-315 MHz)

Main transponders
Backup transponders  
Power 25 W (TWTA)
Bandwidth 25 KHz
Coverage Europe
EIRP max

Nato 4's X-band

Main transponders
Backup transponders  
Power 40 W (TWTA)
Bandwidth 60 and 135 MHz
Coverage global
EIRP max  
Polarization

Skynet 4's (D, E, F) UHF-band (254-318 MHz)

Main transponders 2
Backup transponders  
Power 50 W
Bandwidth 25 KHz
Coverage Europe
EIRP max

UHF-band

Channels 39
Amplifiers 11
Power  
Bandwidth 21 x 5 KHz (narrow)
17 x 25 KHz (relay)
1 x 25 KHz (fleet)
total: 555 KHz
Coverage  
EIRP max  
Polarization  
Frequencies 240-270 MHz