ATV Automated Transfer Vehicle
ILA/Berlin, Bremen/Les Mureaux, 10 May 2004
The Automated Transfer Vehicle, (ATV), is one of Europe’s major contributions to the International Space Station (ISS). The ATV represents a logistics vehicle designed to ferry supplies to the International Space Station and, once docked, to raise its orbit. The first ATV is supposed be launched in 2005.
ATV: First European Automated Rendezvous in Space
The ATV is the first European vehicle developed by Europe that will carry out rendezvous and docking with a space station. After docking, it will become an integral part of the station, providing vital services for up to six months. It will be launched by Ariane 5. Developed for the European Space Agency, the ATV programme was confirmed by ESA member-states during the ministerial-level Council meeting in Toulouse in October 1995. The logistics services during these flights represent Europe's contribution "in kind" to the operating costs of the ISS.
The ATV programme comprises a space segment, including the vehicle itself, plus testing and integration facilities, and a ground segment, comprising the control centre, ground support equipment, simulators and other training systems. ESA is directly leading the development of the ground segment. It has placed French space agency CNES (Centre National d'Etudes Spatiales) in charge of development of the ATV control centre, based in Toulouse.
EADS SPACE Transportation is prime contractor for development and production of the ATV space segment. EADS SPACE Transportation Teams in Les Mureaux, near Paris are responsible for the development phase. The Bremen site (Germany) is in charge of ATV integration and Test.
Launch of the production phase will be approved by ESA members within the scope of ISS operations.
The ATV will provide support services as soon as it is docked to the Russian Zvezda service module, for up to six months. First and foremost, the ATV will provide propulsion support. Its propulsion system will be used by the ISS to correct its orbit and compensate for regular altitude losses. In addition, the ATV will enable the station to conduct debris avoidance manoeuvres if needed. Up to four tonnes of propellants in the ATV's tanks can be used for these purposes.
The ATV will also deliver several types of supplies to the station:
Up to 100 kilograms of air, oxygen or nitrogen, carried in high-pressure tanks and used to renew the station's atmosphere.
Up to 840 kg of drinking water for the crew.
Up to 840 kg of propellants for the station's own propulsion system. Different from the ATV's propellants, this fuel is carried and transferred using a purpose-built system.
Up to 5,500 kg of dry cargo items, in the form of bags, drawers or racks, in a pressurised module that enables unloading by the crew.
The ATV will carry a combination of these supplies for each flight, depending on the station's own needs and its own payload capacity. It's current configuration ensures a carrying capacity of more than nine tonnes of cargo and propellants thanks to a Ariane 5 launcher that is capable of boosting 20,5 tonnes into low Earth orbit. At the end of its mission, the ATV offloads solid waste and wastewater from the station, and burns up during its atmospheric reentry.
Preparation and integration
Each ATV mission is prepared and defined according to the station's operational needs. These requirements determine the launch date, payload and flight configuration.
Flight preparation guarantees that the spacecraft and control centre are fully operational, that the cargo is ready for loading that the Ariane 5 launch will be ready, and that the communications services via satellite are available. In addition, it guarantees that the station is ready to rendezvous with the ATV, and that all American and Russian station teams and ATV crew members are ready and have all the resources needed to carry out their missions.
Finally, to guarantee station and crew safety, operators and crews are given thorough training, and the vehicle, procedures and personnel are all certificated.
Following the flight preparation stage, the ATV is shipped to the Ariane 5 launch site in Kourou, French Guyana. At this point it is still in two parts: the service module (called “Spacecraft”) and the cargo carrier, already filled with the bags, drawers and racks that it will carry to the station. Concerning the first mission, the loading will be done exclusively in Kourou. Several additional payload elements can still be added at this point, at the end of the operation in Guyana, if necessary. Then final integration of the vehicle, loading with fuel, water and gases, and final verification tests take place. Following this, the ATV is mated to Ariane 5 and final launch preparation phase can start.
Each ATV flight includes five main phases:
* Launch by Ariane 5
* Orbital flight to match the station's orbit
* Rendezvous with the station and docking
* The "attached" phase, when the ATV is an integral part of the station
* Separation, deorbiting and atmospheric reentry
To ensure the successful completion of all these phases, the ATV is designed for highly automated operation, while still offering a large degree of operational flexibility. Safety and reliability are designed in.
Launch by Ariane 5
The ATV will be injected into the ISS’s orbit, inclined 51.6 degrees to the Equator. For the first two missions, the ATV will be launched by Ariane 5, featuring storable propellant upper stage (EPS).
About three minutes after lift-off, the fairing is ejected; seven minutes later the main cryogenic stage (EPC) separates, leaving the ATV attached to the upper stage. About 70 minutes after lift-off, the ATV, which onboard systems, especially propulsion, are activated, separates from the upper stage using the clamp band-based attachment and is injected on a viable and almost circular orbit at an altitude of 260 kilometres.
5-day orbital flight to hook up with the ISS
When it separates from the Ariane 5 upper stage, the ATV's navigation-flight control and propulsion systems are already activated, and the spacecraft points toward the Sun. Its solar panels are deployed, followed by the antenna for communications with the ISS. At this point, the ATV is in orbital configuration, with its solar panels following the Sun to supply the electrical power needed by onboard equipment. The thermal control system keeps equipment at the right temperature, and the ground communications system operating via the TDRS relay satellites is up and running.
The phase from initial orbital injection to docking can last up to five days. They consist in broughting gradually together the ATV and ISS orbits, using a combination of natural orbital drift and powered manoeuvring. It is also designed to bring the ATV and the station into orbits that go over Russian territory, so that the Moscow control centre can monitor the docking "live" for twenty minutes, via its own ground communications stations.
Throughout this phase, all ATV operations are controlled and monitored by the Mission Control Centre at CNES's Toulouse facility.
The ATV approaches the station and docks, slowly and safely
Approach and docking is carried out in several steps, under the combined authority of the station and ATV control centres. The number one priority throughout these operations is of course the safety of the crew and the station.
The station control centre authorises each step in the rendezvous; these steps are controlled by commands from the ATV control centre.
The station control centre of course handles ISS operations, especially by sending the command to align the docking port with the incoming ATV, and to activate all communications, control and monitoring systems needed for the approach and docking. In other words, the ATV moves closer and closer in predefined steps, each started upon commands sent by the ATV control centre based on authorisation by the station control centre. For each of these steps, the ATV performs automated manoeuvres.
Throughout the rendezvous phase, the ATV's behaviour and trajectory are closely monitored, not only by its own and the station's systems, but also by the ground control centres.
The ATV's onboard systems provide monitoring on several different levels, and can order a manoeuvre to avoid the station. There is also a dedicated emergency system on the ATV, which can trigger the station avoidance manoeuvre as a last resort.
At any given moment during the approach phase, based on detection by sensors or a decision by the station, its crew or the ATV control centre, the rendezvous operations can be suspended and resumed, or postponed, or even stopped entirely if it is considered that the station is in danger.
When the ATV arrives within 30 km of the ISS and six km below it, it sets up a direct microwave link with the station. This enables it to accurately calculate its position and speed in relation to the station, using GPS measurements from its own receiver and those sent by the station. The final rendezvous manoeuvres, calculated by the ATV and checked by the control centre, place the vehicle in the exact same orbit as the ISS, right behind it. The dedicated safety system on the ATV, which monitors the spacecraft's behaviour and can trigger and execute avoidance manoeuvres in an emergency, is armed by a command from the ground.
At a distance of 3,500 metres from the station, the ATV receives authorisation to continue its approach; if not, it can remain in position, pointing towards the Sun, while awaiting further instructions from the ground. At 250 metres, the ATV points its docking system and sensors directly towards the ISS, and uses its videometer for relative navigation. On receiving authorisation from the station, it continues its approach to 20 metres and begins to bring its attitude under control of the station. Then, receiving authorisation from the ground, it continues its approach up to 12 metres of the ISS and the crew is able to check by video that the spacecraft’s behaviour is normal. Finally, on authorisation of the crew and of the ground, it covers the last few metres at a relative speed of a few centimetres per second, bringing the ATV to within 10 centimetres of the station’s axis, and making first contact with the docking port.
The "attached" phase, when the ATV is an integral part of the station
As soon as its docking system touches the ISS, the ATV propulsion system provides the thrust needed to ensure its capture by the station's docking port. It then activates the automatic docking sequence, which will mechanically attach it to the station via a leaktight seal, and set up all electrical and fluid connections. At this point, the ATV is docked to the service module on the Russian part of the station (Zvezda). Following various checks, the crew opens the doors in the station and the ATV, and the latter is now an integral part of the orbital infrastructure. Once docked, the ATV provides services on request from ISS. The ATV can remain docked to the station or up to six months. When not in operation, it is placed in dormant mode, which means the vehicle keeps ready, but makes minimal use of resources. Once docked, the ATV operates very independently from the station. Its own solar arrays generally provide all the electrical power it needs. Its thermal control system is active and minimises the need for additional heating, and its onboard computer provides autonomous operating capability.
At any given moment, depending on its operational needs, the space station can activate the ATV. To do so, it sends a set of commands directly to the ATV, placing it in the required operating mode. This enables the station to use the ATV’s propulsion system, to transfer propellants and for the crew to carry out all cargo-related operations.
For the altitude reboost and attitude control manoeuvres, the ATV is reactivated by command from the station. These operations can last up to 12 hours. They comply with the ISS operations plan determined by the control centres in Moscow and Houston. For these operations, the ATV's propulsion system is controlled directly by the station's own navigation, guidance and flight control software. The ATV’s four 490-newton engines and the twelve 220-newton thrusters of its attitude control system provide orbital corrections. Attitude control manoeuvres use only the 220-N thrusters.
Transfer of the bags, drawers and racks is handled manually by two astronauts, who record each transfer in the station's inventory. Water, air, oxygen and nitrogen are transferred by the same way in the station.
The propellant transfer operations are also controlled directly by the ISS. They include line leak tightness checks, transfer of fluids and line venting. The propellant tanks located in the outside module of the ATV's payload carrier, hold 300 kg of fuel and 540 kg of oxidiser. The station sends the valve opening/closing commands to the ATV for refuelling operations, which can be carried out in several stages, during the entire period that the ATV is docked to the station.
Separation, deorbiting and atmospheric reentry
The ATV separates from the station, de-orbits and is destroyed during re-entry.
Before the ATV leaves the station, the crew loads it with solid waste and wastewater, then closes the access doors. The seal between the ATV and the station is depressurised. The ATV, which has already been activated and prepared for departure by its control centre, separates from the station and distances itself automatically, carefully and safely.
On command from the control centre, the ATV then automatically performs the manoeuvres needed to de-orbit. For safety reasons the ATV and everything inside burns up during a controlled re-entry in the atmosphere – over the Pacific Ocean.
Bremen/Les Mureaux, May 2004
Dr. Mathias Spude
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