But a European industrial space group, partly funded by the European Space Agency, is challenging the notion that old satellites must be retired. The company, Orbital Recovery, has recently signed for its first satellite-servicing mission. EuroNews 'Space' magazine has been talking to some of the actors of the very innovative "Space Tug" project.

"Worldwide, around 20 satellites are launched every year into the geostationary orbit at 36,000 km, in fixed positions with regard to the Earth below," explains ESA's Jorgen Sandberg. "These are not only commercial craft, but also military or governmental. They all have a lifetime of 10 to 15 years, so that means at least 200 satellites present in this orbit today."

Most spacecraft are launched and positioned with great accuracy. But there have been failures and ingenious missions to retrieve satellites, such as ESA's Artemis and Hipparcos, which had not reached their target orbits. NASA's Solar Max was also rescued by space-walking astronauts.

In four years time, a better solution will be available. It is today taking shape at Leiden in the Netherlands, in the clean rooms of the Dutch Space company which is the prime contractor for the CX-OLEV (or ConeXpress Orbital Life Extension Vehicule).

An impressive team of European space companies are involved including SENER, Spain, the Swedish Space Corporation, and Kayser Threde of Germany.

The principle is to use the volume within the satellite adaptor that carries the lower-placed passenger in an Ariane-5 dual launch. These truncated-cone structures are lost and eventually burn up after a satellite's release.

"The idea of using the payload adaptor of the Ariane rocket is not really new," says Dutch Space's project manager Han Scholten. "The problem was always that the volume was too small to take enough fuel to take this structure to the geostationary orbit. The enabling technology has been electric propulsion, the use of ion plasma thrusters."

The SMART-1 satellite, today orbiting the Moon, is ESA's latest example of electric propulsion which uses solar power and xenon gas to provide sufficient thrust over time to position satellites.

"After a geostationary satellite's ten years in orbit, it will have consumed practically all its propellant, it will not be able to maintain its fixed position and will start drifting," explains Han Scholten. "If nothing is done it might even collide with another spacecraft."

"This is where our CX-OLEV comes in, attaching itself to the satellite and providing with its thrusters the necessary orbital control to keep its correct position."

After a standard Ariane 5 geostationary launch, the CX-OLEV vehicle will deploy its solar array, and over a period of several months will use its electric thrusters to spiral up to the geostationary orbit. There it will rendezvous with its target satellite and dock with it.

A key element of the vehicle is its docking technology, licensed from the German space agency DLR. "A few years ago, DLR developed a mechanism which allows docking inside the engine nozzle of a large satellite," continues Han Scholten.

"The CX-OLEV pushes the capture tool inside the nozzle and latches in its throat. It is just a mechanical coupling, there is no electrical connection. The client satellite continues to communicate normally with the ground, and only uses CX-OLEV for its attitude and orbit control."

Extending the life of telecommunication satellites which often cost some 300 million euros to build and launch is economically advantageous. Resorting to a CX-OLEV mission, at an all-inclusive price of around 60 million euro, will prolong their operations for up to ten years.

Alternatively, the 'space tug' could be used for rescue missions, to store a satellite near the geostationary orbit for contingency purposes, or even to remove no-longer operational craft, propelling them to the so-called "graveyard orbit" 300 km higher up.

The CX-OLEV programme is supported in the framework of ESA's ARTES-4 public-private partnership (PPP) initiative.

"This venture is fully in line with the ARTES-4 objectives," says Jorgen Sandberg. "A number of new technologies have to be developed. Many elements have not been made before in the framework of ESA programmes, and have not been done before by European industry. That is why we are supporting it."

The project expects that Arianespace will have 4 opportunities per year to fly CX-OLEV, making use of around 1400 kg of unused mass capability. Last month, Orbital Recovery announced that it signed a reservation for a 2008 launch for its first, as yet unnamed, client.

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