GIOVE-B Transmitting
Its First Signals
(7 May 2008) Following a successful
launch on 27 April, GIOVE-B began transmitting navigation signals
today.
This is a truly historic step for satellite navigation
since GIOVE-B is now, for the first time, transmitting the GPS-Galileo common
signal using a specific optimised waveform, MBOC (multiplexed binary offset
carrier), in accordance with the agreement drawn up in July 2007 by the EU and
the US for their respective systems, Galileo and the future GPS III.
A screen in the control room displays the spectra of signals received from GIOVE-B shortly after the spacecraft began transmitting navigation signals. (courtesy: ESA)
These GIOVE-B signals, locked on-board to a
highly stable Passive Hydrogen Maser clock, will provide higher accuracy in
challenging environments where multipath and interference are present, and
deeper penetration for indoor navigation. It demonstrates that Galileo and GPS
are truly compatible and interoperable and that positioning services will
benefit all users world-wide.
"Now with GIOVE-B broadcasting its highly
accurate signal in space we have a true representation of what Galileo will
offer to provide the most advanced satellite positioning services, while
ensuring compatibility and interoperability with GPS", said Galileo Project
Manager, Javier Benedicto.
After launch, early orbit operations and
platform commissioning, GIOVE-B's navigation payload was switched on and signal
transmission commenced on 7 May and the quality of these signals is now being
checked. Several facilities are involved in this process, including the GIOVE-B
Control Centre at Telespazio's facilities in Fucino, Italy, the Galileo
Processing Centre at ESA's European Space Research and Technology Centre
(ESTEC), in the Netherlands, the ESA ground station at Redu, Belgium, and the
Rutherford Appleton Laboratory (RAL) Chilbolton Observatory in the United
Kingdom.
Chilbolton's 25-metre antenna makes it possible to analyse the
characteristics of GIOVE-B signals with great accuracy and verify that they
conform to the Galileo system's design specification. Each time the satellite
is visible from Redu and Chilbolton, the large antennas are activated and track
the satellite. GIOVE-B is orbiting at an altitude of 23 173 kilometres, making
a complete journey around the Earth in 14 hours and 3 minutes.
The
quality of the signals transmitted by GIOVE-B will have an important influence
on the accuracy of the positioning information that will be provided by the
user receivers on the ground. Onboard, GIOVE-B carries a passive hydrogen maser
atomic clock, which is expected to deliver unprecedented stability
performance.
The signal quality can be affected by the environment of
the satellite in its orbit and by the propagation path of the signals
travelling from space to ground. Additionally, the satellite signals must not
create interference with services operating in adjacent frequency bands, and
this is also being checked.
Galileo teams within ESA and industry have
the means to observe and record the spectrum of the signals transmitted by
GIOVE-B in real time. Several measurements are performed relating to
transmitted signal power, centre frequency and bandwidth, as well as the format
of the navigation signals generated on board. This allows the analysis of the
satellite transmissions in the three frequency bands reserved for
it.
The GIOVE-B mission also represents an opportunity for validating
in-orbit critical satellite technologies, characterising the Medium Earth Orbit
(MEO) radiation environment, and to test a key element of the future Galileo
system - the user receivers.
(source: ESA)
