FLUG REVUE November 2004: European ATV readied for ISS mission

ATV READY FOR ISS MISSION

By Matthias Gründer

The Automated Transfer Vehicle (ATV) is one of the most important European contributions to the International Space Station. The ATV will be used not only to supply the astronauts on board the ISS, but also to correct its trajectory as necessary. The first ATV launch is planned for 2005.

ATV

The ESA Ministerial Council's decision to go ahead with the ATV programme in October 1995 gave the European space industry a substantial amount of work. It was not just a matter of developing and building the actual launch vehicle, but also the test equipment, control centre, ground networks, simulators and training facilities that went with it. ESA also placed a contract with the French space organisation CNES in Toulouse for the construction of an ATV control centre.

EADS SPACE Transportation is the prime contractor for development, integration and testing of the space vehicle. The development work was carried out in the French location of Les Mureaux, near Paris, while the production phase, including testing, was completed in Bremen.

The ATV will be the first space vehicle built in Europe that is capable of carrying out rendezvous and docking manoeuvres with a space station. Current plans envisage that six such space vehicles will be launched for rendezvous with the ISS, carrying fuel, drinking water, conventional cargo and experiments.

Each of the ATVs will be used not only to transport consumable materials, but also to supply propulsive support for reboost manoeuvres. The latter will entail correcting the orbit of the entire ISS complex to compensate for recurring losses of altitude. In addition, with the aid of the onboard engines it will be possible to carry out any evasive manoeuvres that might be necessary to avoid debris that is flying around in space.

The cargo ship is divided into three sections:

a pressurised cargo section for 5,500kg of experiments or solid supplies and materials, which has a Russian-designed docking unit with a hatch through which, once a hermetic seal to the ISS has been accomplished, the astronauts can enter, or rather, “float into”, the module;

a tank section accommodating compressed gas cylinders containing up to 100kg of air, oxygen and nitrogen, with 840 litre water tanks and fuel tanks with a capacity of 840kg;

and finally, a propulsion section containing the onboard engines, the steering system and the onboard energy supply in the form of four retractable solar panels.

ISS REQUIREMENTS WILL DETERMINE PRECISE PAYLOAD COMPOSITION

On each of its flights, the ATV will transport a mixture of these items, the precise composition to be determined by the ISS's operational requirements. At present it is assumed that each mission will carry about nine tonnes of freight and fuel, so that transportation of the spacecraft by the European heavy-lift launcher Ariane 5 should present no problems, as this can carry payloads of up to 20.5 tonnes into low earth orbit.

Each of the six flights will be defined and its logistics prepared according to the actual requirements. Mission preparations will include loading the cargo, controlling the communications links and carrying out all the tests. Integration of the propulsion unit and cargo module will be conducted in Kourou, and apart from on the first flight it is planned to always fully load the cargo module.

Taking into account the ISS orbit and the specific location of the ISS above the surface of the earth, the space launch vehicle, with the ATV on board, will be launched with an angle of inclination of 51.6º to the Equator. On the first two missions, Ariane 5G will be deployed with the EPS upper stage; after that the restartable cryogenic upper stage will be used. About 70 minutes after lift-off, the engines and onboard systems will be activated by telemetry and the ATV will separate from the upper stage, following which the spacecraft will pursue a roughly circular trajectory at an altitude of about 260km.

The ATV's navigation and attitude control systems will send instructions to the onboard engines to ensure that the vehicle is pointed at the sun, following which the solar panels will unfold and the communication link with the ISS will be established. Because the ATV and the ISS are on different trajectories, the approach could take up to five days. After numerous corrective manoeuvres, the two should then meet above Russian territory, so that the control centre in Moscow can monitor the docking operation. This assumes that the ATV will dock with the rear of the Zvezda service module. Meanwhile, the manoeuvre itself will be monitored and controlled from the control centre in Toulouse.

At the same time, Mission Control in Houston, Texas will also be involved in the manoeuvre and will be responsible for ensuring that the Space Station is aligned with the axis of approach of the ATV and for activation of the communications and control systems. Every individual step in the approach will be predefined, and the corresponding manoeuvres will be executed fully automated. In case of emergency, an avoiding manoeuvre will be initiated via a specific safety system. It will be possible for any of the manoeuvres to be deferred, postponed or even aborted by a decision from either the crew or the ground station.

30km away and about 6km below the ISS trajectory, a direct radio link will be established, so that the position and relative speed can be accurately determined. The next few manoeuvres will then bring the transport vehicle up to a position right behind the ISS, and the docking system and sensors will align themselves at a distance of only 250m. The approach will continue in slow motion until the crew are able to check using video images whether the alignment is optimal. The final rapprochement will proceed centimetre by centimetre until the gap has been reduced to only ten centimetres. One last boost, and the docking system will lock into place.

Once all the mechanical and electrical connections are in place and testing has been carried out to ensure a hermetic seal, the crew will now be able to open the hatch and enter the pressurised section of the ATV. For the next six months they will then have an extra room at their disposal. This they will gradually unload, while simultaneously refilling it with used materials and rubbish. Over this period the ATV will be in an autonomous rest mode, during which its power supply and thermal controls will function independently of the ISS's own systems. Each mission will end in a colourful way, as the ATV will burn up in the earth's atmosphere Meanwhile, however, the first transfer vehicle, which has been named the “Jules Verne”, is ready and waiting on the launchpad.

From page 72 of FLUG REVUE 11/2004

Last updated 13 October 2004

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