Tim Furniss/LONDON
The European Space Agency's (ESA) Artemis project is now well on its way after cost and technical problems combined to delay the satellite, which had been originally due to be in orbit now. The flight model has been completed by Alenia Spazio in Rome and will soon be shipped to ESA's European Space Research and Technology Centre in the Netherlands for pre-launch testing.
The Artemis will demonstrate new civil telecommunications services in what ESA describes as "cutting edge technology for a unique mission".
Operating from 16.4° in geostationary orbit (GEO), the satellite will test high data-rate satellite to satellite communications, using S- and Ka- band frequencies and a revolutionary optical frequency laser link, the Semiconductor Intersatellite Link Experiment (SILEX).
The craft will show how a satellite in GEO can receive data directly from other satellites - such as Earth observation satellites in low Earth orbit (LEO) - and transmit onward, avoiding the need for those satellites to store data for a later dump when in line with a tracking station.
The SILEX payload on the Artemis will be used to receive data from a similar payload on the recently launched Spot 4 remote sensing satellite. The Japanese Optical Inter-Orbit Communications Engineering Test Satellite, scheduled for launch in 2000, will be another user of the optical system.
Data relay will also be provided to and from the Artemis in the S-band and Ka-band frequencies and will be used for data collection from ESA's LEO-orbiting Envisat polar platform and Japan's Advanced Earth Observation Satellite 2.
Ka-band satellite to satellite datalinks were demonstrated for the first time by Europe between ESA's Eureca free flying satellite, deployed from and retrieved by the Space Shuttle in August 1992 and June 1993, and the agency's Olympus communications satellite.
Affordable L-band wide-coverage voice and data mobile communications will also be demonstrated. The L-band spectrum is a scarce resource and the Artemis will overcome this limitation by using a mix of three spot beams and one wide beam to enable bandwidth and power to be configured dynamically. This means it will always fit exactly the constantly evolving or changing communications traffic, offering the maximum number of digital or voice channels.
The Artemis' 400 two-way voice-channel European Land Mobile system will complement the 450-channel European Mobile System operating on Italy's Italsat F2 satellite.
A navigation transponder is the third demonstration payload. This will be used as an element of the European satellite navigation system being implemented to augment and improve the US Navstar global positioning system (GPS) and Russian Glonass system. The combined use of GPS positioning data and the pan-European mobile communications capabilities of Artemis will offer more efficient transport management, says ESA.
The Artemis is based on the Alenia Italsat communications spacecraft bus and weighs 3,100kg. It measures 2.95 x 2.85 x 4.60m, with two solar arrays providing 2.75kW of power. As part of its technological demonstration objectives, it will use two redundant ion thruster systems from Daimler-Benz Aerospace and Matra Marconi Space for north-south stationkeeping, as well as conventional chemical systems.
A cost overrun, from the estimated ECU 665 million ($715 million) in 1992 to more than ECU 800 million in 1996, and technical problems, delayed the Artemis and caused the budget-starved ESA to offer Japan 40% of the use of the Artemis in return for its free launch on a Japanese H2 in 1999, now due on the uprated H2 Alpha Plus and delayed to February 2000.
The Artemis was to have been the precursor to an ESA fleet of data relay satellites which have been cancelled because of budget cuts. To compensate, Japan's planned fleet of data relay satellites could operate with the Artemis as a possible future alternative to the USA's Tracking and Data Relay Satellite System.
Source: Flight International
