Paris, 24 March 1998
Scheduled for launch in late 1999/early 2000 on a Japanese H2A launcher, in the framework of a co-operation agreement with the Japanese space agency NASDA, ARTEMIS is being developed for ESA by a European industrial consortium led by Alenia Aerospazio (Italy).
Communications with mobiles
Not so long ago, mobile communication systems were mostly used by police forces, ambulance services or taxi companies. Today, mobile phones have become a reality for the man in the street and the market is literally exploding. It is estimated that there could be 20 million individual users in Europe by the turn of the century.
In terms of cost, capacity and spectrum efficiency alone, satellite systems cannot compete directly with cellular systems. However, satellites can provide a wider coverage, which is of particular interest in areas of low population where cellular systems are uneconomic.
ESA is focusing on the development of a pan-European satellite system for land mobiles - cars, trucks and trains - and ARTEMIS will serve this purpose.
To provide services between mobiles and fixed partners located throughout Western Europe and neighbouring regions - the Mediterranean Basin, the Middle East and Russia up to the Urals -, ARTEMIS embarks a new-generation land mobile transmission system.
Dubbed LLM (L-band Land Mobile), the system provides great versatility thanks to its three spot beams. It will carry up to 400 bi-directional user links channels. To make best use of onboard power and capacity, LLM has been designed with a high degree of flexibility in mind. The allocation of bandwidth, power and frequencies to the four beams can be modified in response to changing traffic patterns. The LLM payload is fully compatible with the EMS payload already developed by ESA and flown onboard ASI's Italsat-2 ka-band telecommunication satellite, in August 1996.
Earth observation satellites, for instance, cannot send their data to just one Earth station, because they fly at low altitude of about 800 km. As they scan the Earth's surface, they disappear behind the horizon after a few minutes at the most. The data must therefore be stored in on-board memories - which are far from fail-safe - or else transmitted to a large number of distributed Earth stations, which are costly to operate.
From its vantage point in geostationary orbit at 36 000 km above the Earth, ARTEMIS can be in constant communication with satellites in low-Earth orbit for long periods of each orbit, and can beam data from those satellites directly to users in Europe.
To demonstrate the reception of data from other satellites and their onward transmission to users in Europe, ARTEMIS will carry an advanced radio data-relay payload and a revolutionary laser data-relay payload called SILEX (Semiconductor Laser Inter-satellite Link Experiment). SILEX is the world's first civil inter-satellite data relay system using lasers as carriers for the signal transmission.
Using laser communications, very high data rates can be achieved via small terminals on Low Earth orbit satellites. Initially, SILEX will receive remote sensing data from the French SPOT-4 satellite to be launched in March 1998, beaming it to user ground stations in Europe. Fully bi-directional, SILEX can also relay commands from the control centre of a low Earth orbiting spacecraft via ARTEMIS.
The radio data-relay payload SKDR (S/Ka-band Data Relay) features the use of two frequencies for relaying data at low, medium or high rates - again both way. The first users of SKDR include ESA's environmental ENVISAT-1 satellite scheduled for launch in 1999.
Under an agreement with NASDA, the Japanese space agency, the ARTEMIS satellite will also serve several Japanese spacecraft and the Japanese module of the International Space Station.
Since the introduction of satellite navigation in the '70s, using data transmitted by Earth orbiting spacecraft, millions of small, portable receivers capable of receiving the satellite signals are being used to pinpoint the location of aircraft, ships, trucks to an accuracy of meters.
To help Europe meet the growing demand for accurate navigation services, ARTEMIS will carry a transponder which will from part of a European system aimed at improving the accuracy provided by the existing American GPS and Russian GLONASS systems.
ARTEMIS will herald the beginning of new generations of technology and communications services. Service providers will benefit from the experience gained with operations in mobile communications ; satellite manufacturers will expand their technological capabilities and hence their competitiveness in the world market and Europe will be in a better position to reap the benefits of its investment in Earth Observation from space, because ARTEMIS will help bring data direct to the user, which is where it is needed.
Communications is one of the sectors of space activity of a truly commercial nature. With ARTEMIS, Europe is setting the scene for the next decade.
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