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ATV Automated Transfer VehicleILA/Berlin



 
 
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Old May 10th 04, 02:38 PM
Jacques van Oene
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Default ATV Automated Transfer VehicleILA/Berlin

ATV Automated Transfer VehicleILA/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 SpaceThe 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 MissionThe 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.
MISSION SCENARIO

Preparation and integrationEach 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 5The 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 ISSWhen 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 safelyApproach 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 stationAs 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 reentryThe 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


--
---------------------------

Jacques :-)

www.spacepatches.info



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