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Successful
downlink communication test for ATV from ISS
27 March 2006
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On 8 March 2006,
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) planned for next year - was
able to transmit "loud and clear" signals from the
Station to two ground stations in Spain during a downlink
test. This ground track graphic shows how the ISS passed over
Gran Canaria and Madrid.
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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.
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When the first
ATV, called Jules Verne, is launched in to orbit next year,
and navigates autonomously towards the Station, a 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. Two
dedicated antennas on the outside of the ISS will be used to
establish the communication link.
Credits: NASA
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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
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The ESA ground
station at Maspalomas, Canary Islands, is located in the
southern part of the Gran Canaria island on the campus of the
Instituto Nacional de Tecnica Aerospacial (INTA). The antenna
is operated by INTA in cooperation with Ingenieria y
Servicios Aerospatiales (INSA).
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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
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Artist's
impression of the Automated Transfer Vehicle approaching the
International Space Station. In combination with ESA's new
Ariane 5, the 20.5 t, 8.5 m-long Automated Transfer Vehicle
(ATV) will enable Europe to transport cargo to the
International Space Station. This new vehicle, scheduled for
its initial test flight in September 2004, can carry 9 tonnes
of scientific equipment, general supplies, water, oxygen and
propellant. Up to 4 t can be propellant for ATV's own engines
to reboost the Station at regular intervals as atmospheric
drag reduces the orbit. Developed under Aerospatialess prime
contractorship, an ATV will be launched on average every 15
months as a means of ESA contributing to the Station's
operating costs. It can remain docked for up to 6 months,
during which time it will be loaded with Station waste before
being undocked and flown into Earth's atmosphere to burn up.
Credits: ESA-D.Ducros
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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.
Source
/ Credit: ESA
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