ADVANCED ASTRIUM TECHNOLOGIES TO BE LAUNCHED ON ARTEMIS

ARTEMIS, the Advanced Relay and Technology MISsion satellite is due for launch from Kourou, French Guiana on Thursday 12 July 2001. It will carry a wide range of equipment designed and built on Astrium sites in Germany, the UK, and France including two Ion thrusters systems RITA developed at Astrium’s Ottobrunn plant and EITA, from the Portsmouth, UK site and SILEX (the Semiconductor-laser Inter-satellite Link Experiment) designed and built in Toulouse.

These Ion thruster systems will provide full orbital control of the satellite. Compared with conventional chemical engines, RITA (Radio-frequency Ion Thruster Assembly)is propelled by xenon, an inert gas that occurs naturally. Radio waves that are generated electrically excite the electrons in the xenon atoms so that they oscillate and leave the atoms, and in this way positively charge the gas. The remaining positively charged particles, the so-called ions, are discharged from the thruster at a speed of 40 km/s. This outlet speed is more than ten times higher than that of chemical thrusters with a resulting propellant utilisation that is ten times better. The degree of efficiency of ion thrusters is 70 per cent. In comparison, a car petrol engine just manages 30 per cent efficiency.

The two EITA (Electron-bombardment Ion Thruster Assembly) units complete the Astrium-developed Ion Propulsion Package (IPP). In the EITA system, developed by Astrium in the UK, ionisation of the xenon atoms is effected by thermal discharge as opposed to the radio waves used in the RITA system.

The SILEX (Semiconductor-laser Inter-satellite Link Experiment) system will enable real-time transmission of the images acquired by Spot 4's instruments, via Artemis, in geostationary orbit (GEO), to ground stations.

Other equipment supplied by Astrium includes:

The LNA/Diplexer (LDLN), which is a combined transmit receive diplexer with an integral low noise amplifier. The equipment comprises four identical units with the ability to handle very high power signals in the transmit path, whilst providing rejection of that very signal in the receive path. All units also had to accurately phase track, with each other, over the full temperature range and with input signal variation.

The Solid State Power Amplifiers (SSPAs), which were designed for high power, multi-carrier operation, building on the development undertaken for the Company’s Inmarsat 3 payload programme. The Navigational Amplifier (Nav Amp) was a later payload enhancement and represented a new generation of SSPA, which laid the foundations for the current Inmarsat 4 product.

The Frequency Generator Unit (FGU), which provides all the local oscillators for the payload in a single, complex integrated unit. All the synthesised oscillators are phase locked to very stable, reference crystal oscillators, which are part of the equipment, giving very stable, low phase noise signals in order to achieve the bit error rate requirement of the payload.

The Solar Array Drive Mechanisms, which were developed from those currently flying on all Astrium’s Eurostar communications satellites.

The Pointing Mechanisms for the EITA thrusters were supplied via Astrium Ottobrunn.

The Pointing Mechanism Electronics for the SILEX system.