Successful downlink communication test for ATV from ISS (Forwarded)

ESA News
http://www.esa.int

27 March 2006

Successful downlink communication test for ATV from ISS

Earlier this month, 352 kilometres above the Earth, over three orbital
passes, the proximity communication link -- indispensable for the first
Automated Transfer Vehicle (ATV) rendezvous with the International Space
Station (ISS) -- was able to transmit "loud and clear" signals from the
Station to two ground stations in Spain during a downlink test.

"The test went well despite a sandstorm at Maspalomas ground station on
Gran Canaria island in Spain. It proves that the ATV communication system,
designed for Proximity Operations between ISS and ATV, is working fine",
said Detlef Otto, who is in charge of the ATV communication system for ESA
and who directed the test.

The main hardware of this proximity communication system is a
self-contained electronic box, called the PCE, for Proximity Communication
Equipment. This 55-kg box, which looks like a mini-bar refrigerator with a
lot of cable connections, is already on board the ISS. For the downlink
test, the PCE, which has been inside the Russian Zvezda module since its
arrival with a Progress cargo spaceship in March 2005, transmitted through
the two dedicated antennas on the outside of the ISS. Even at a speed of
28 000 km/h, the signal was clearly acquired by two 15-metre S-band
parabolic antennas on Earth which played the role of the ATV receivers.

When the first ATV, called Jules Verne, is launched in to orbit next year,
and navigates autonomously towards the Station, the two-way proximity
communication radio link will be established between the ISS and ATV at a
distance of between 30 and 100 kilometres, just prior the rendezvous
operations. At the same time, a second communications system via TDRSS
(NASA Tracking and Data Relay Satellites System) will be used for
remote-commands and telemetry transmissions.

The two-way proximity communication is especially important for the Jules
Verne mission, which marks the first ever rendezvous and docking for a
European spacecraft. Jules Verne will demonstrate that it can
automatically -- and safely -- handle any contingency plans. This
demonstration flight must test and prove that the 20.7-tonne cargo ship
can interrupt the rendezvous -- at any time -- by stopping its motion and
flying away from the Station.

In the attached phase between ATV and ISS, the proximity link chains are
nominally powered off. At the end of the 6-month re-supply mission of ATV,
just before undocking, the TDRSS links are switched on again and at least
for the first ATV flight, the proximity communication link will also be
used for departure. Therefore, one day prior to undocking, it is again
necessary to re-install the PCE and check it out with the attached ATV.

The two 19-cm diameter reception antennas are already installed on the
first ATV, one directly mounted on the side of the European re-supply
spaceship, the other on a deployable boom. At ESA's test facilities in
Noordwijk, the Netherlands, Jules Verne -- which is about 98 percent
assembled -- is going through a challenging year long campaign of crucial
environmental and functional tests, ahead of the inaugural launch on an
Ariane 5 launcher scheduled for May 2007.

In September 2004, the Expedition 9 crew, ISS commander Gennady Padalka
and ISS Flight Engineer Mike Fincke, installed the first three antennas
during a five and a half hour spacewalk, to make ISS ready to communicate
with Jules Verne. These antennas allow S-band digital radio communication
at a rate of 20 kBaud between ATV and the Zvezda module, where the ATV
will dock, as part of ATV automatic rendezvous and docking procedures.

As soon as the radio communication link is established between the
unmanned ATV and ISS, selected ATV telemetry will be displayed to the
crew. The crewmembers are not involved in the auto-piloting of ATV, but
they will carefully monitor its performance from the Russian Zvezda
Service Module using a video camera and an independent range finder and
range rate measuring system.

Through the proximity communication link, they have the capability to
interrupt the approach -- at any moment -- if they consider their safety
is at stake. The astronauts could initiate the Collision Avoidance
Manoeuvre on their own to move the 20.7-tonne spaceship away from the
Station, in the remote case of a major anomaly or malfunction showing up
on their consoles. This communication link will be also crucial for the
relative Global Positioning navigation (GPS) in real time between the
navigating ATV and ISS to prepare for the later acquisition of high
precision optical link used at close distance (less than 300 m) for
relative navigation.

Tilting the whole ISS

For the test in early March, at each orbital pass over Spain the whole
183-tonne ISS had to be tilted by 90 degrees to have the Russian module
aft section -- where the transmitting antennas are located -- pointing
vertically towards the Earth over the ground station reception antennas.
Normally these antennas would point horizontally towards the approaching
ATV, but since during this test the two ground stations played the role of
ATV, the Stations antennas had to point downwards towards the Earth. The
whole test, which required the Station to be tilted back and forth three
times throughout the three orbits, used 40 kg of ISS onboard propellant to
rotate the Station back and forth.

"Completion of this test marks another very important milestone in
preparing the International Space Station for the arrival of Jules Verne.
Planning and preparing for this test took the cooperative efforts of
technical specialists from ESA, RSC-Energia and NASA. NASA welcomed the
opportunity to involve the ESA ATV team into ongoing ISS operations", said
Adam Baker, Operations Lead at NASA's International Liason Office at
Johnson Space Center (JSC), Houston.

The two astronauts on board the Space Station were not involved with the
test since the sequence was fully automatic and was initiated and
supervised remotely from the ground. But a few days earlier, Flight
Engineer Valery Tokarev had to retrieve the PCE box from storage on ISS,
install it in the Russian Zvezda module and connect it to the electric
circuitry of the Station. The whole operation, which will be repeated for
each ATV rendezvous, takes about one day of work for a crewmember. To
return the PCS to storage takes about half this time. At present, US
Commander Bill McArthur and Russian Flight Engineer Valery Tokarev make up
the 6-month Expedition 12 crew which is due to return to Earth early in
April 2006.

Two European Ground Stations

Four ESA engineers from European Space Operations Centre (ESOC) in
Darmstadt, Germany handled the communication test on the ground. Although
the commands to switch the PCE on and off were conducted via an on board
computer programme sent to the Station through the Russian Mission Control
Centre in Moscow , with the coordination of NASA's Mission Control Centre
in Houston who is responsible for the safety of the whole ISS. About 20
people located in the three centres and at the ground stations
participated in the communication test.

The test, which involved about a 10-minute radio transmission on each
orbital pass from the ISS to the ground stations, took place over the
Canary Islands and Madrid, Spain. Because of its East-West motion at the
speed of 28 000 km/h, the Station flew first over the Maspalomas station,
located in the southern part of the Gran Canaria island and then, over the
ESA Villafranca ground station, located approximately 31 km from the
centre of Madrid. During the three orbital passes over the two ground
stations, the total communication time reached 40 minutes.

Established in 1975, after an international agreement between ESA and the
Spanish government, Villafranca is part of the worldwide ESOC station
network. The Maspalomas station is part of the Instituto Nacional de
Tecnica Aerospacial (INTA). ESA is using this facility in cooperation with
INTA.

These two ground stations will again be used for each future ATV mission.
Five days before each ATV launch, a similar test will be conducted to
check if the PCE has been properly installed and is operational. This test
is part of the launch commit criteria. In other words, if the test reveals
that the PCE is not working properly, the ATV launch will have to be
postponed.

During the entire mission, another ATV communication system will process
telemetry and commands in both directions through the NASA Tracking and
Data Relay Satellites System, which is used for the International Space
Station. TDRSS communications will start after the launch, four minutes
before separation of ATV from the Ariane 5 launcher and continue up to the
rendezvous phase with ISS. ESA is also using Artemis, the European data
relay satellite, as a backup during ATV free-flight, and as the primary
communication system when docked to the Station.

The PCE was tested a first time in June 2005, but the test -- because of
its complexity involving two transmitters and two antennas over a 15
minute pass, and because of the interferences from a Progress spaceship
docked to the Station at that time -- did not show conclusively if the
system was working properly or not. Even after the present successful
result, the PCE will again be tested in orbit next year to check a new
software upgrade made in Russia by RSC-Energia.

Related articles

* 2006: a challenging year for Jules Verne
http://www.esa.int/esaHS/SEM0EPG23IE_iss_0.html
* ESA issues first Jules Verne payload list
http://www.esa.int/esaCP/SEM5ARZCU8E_index_0.html
* Safety and autonomy make the ATV unique
http://www.esa.int/esaHS/SEMSEV5Y3EE_iss_0.html
* First rendezvous simulation: a major step for ATV
http://www.esa.int/esaHS/SEM60A1P4HD_iss_0.html

Related links

* Human Spaceflight and Exploration
http://www.esa.int/esaHS/
* International Space Station
http://www.esa.int/esaHS/iss.html
* Automated Transfer Vehicle (ATV)
http://www.esa.int/spaceflight/atv

[NOTE: Images supporting this release are available at
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