GIOVE

GIOVE, or Galileo In-Orbit Validation Element, is the name for each satellite in a series being built for the European Space Agency (ESA) to test technology in orbit for the Galileo positioning system. [ [http://www.esa.int/esaCP/SEM10V638FE_index_0.html First Galileo satellites named 'GIOVE'] , ESA press release, 9 March 2005.]

Giove is the Italian word for "Jupiter". The name was chosen as a tribute to Galileo Galilei, who discovered the first four natural satellites of Jupiter, and later discovered that they could be used as a universal clock to obtain the longitude of a point on the Earth's surface.

The GIOVE satellites are exploited by the GIOVE Mission [ [http://www.esa.int/esaNA/SEMWL4N0LYE_index_0.html GIOVE mission core infrastructure] , ESA press release, 26 February 2007.] [ [http://www.esa.int/esaNA/SEMUGJRMTWE_galileo_0.html One year of Galileo signals; new website opens] , ESA press release, 12 January 2007.] (GIOVE-M) segment in the frame of the risk mitigation for the In Orbit Validation (IOV) of the Galileo positioning system.

Purpose

These validation satellites were previously known as the "Galileo System Testbed (GSTB) version 2 (GSTB-V2)". In 2004 the "Galileo System Test Bed Version 1 (GSTB-V1)" project validated the on-ground algorithms for Orbit Determination and Time Synchronization (OD&TS). This project, led by ESA and European Satellite Navigation Industries, has provided industry with fundamental knowledge to develop the mission segment of the Galileo positioning system. [ [http://www.esa.int/esaNA/SEM6KYP3K3E_index_0.html Galileo System Test Bed Version 1 experimentation is now complete] , ESA News release, 7 January 2005]

GIOVE satellites are transmitting multifrequency ranging signals equivalent to the signals of future Galileo: L1BC, L1A, E6BC, E6A, E5a, E5b. The main purpose of the GIOVE mission is to test and validate the reception and performance of novel code modulations designed for Galileo including new signals based on the use of the BOC (Binary Offset Carrier) technique, in particular the high-performance E5AltBOC signal.

It should be stressed that the role of GIOVE is purely to test transmission and reception of the new signals: these satellites can not be used for navigation even for testing.

Already launched satellites

GIOVE-A

Previously known as "GSTB-V2/A", this satellite was constructed by Surrey Satellite Technology Ltd (SSTL).

Its mission has the main goal of claiming the frequencies allocated to Galileo by the ITU. It has two independently-developed Galileo signal generation chains and also tests the design of two on-board rubidium atomic clocks and the orbital characteristics of the intermediate circular orbit for future satellites.

GIOVE-A is the first spacecraft whose design is based upon SSTL's new Geostationary Minisatellite Platform (GMP) satellite bus, intended for geostationary orbit. GIOVE-A is also SSTL's first satellite outside low Earth orbit, operating in medium Earth orbit), and is SSTL's first satellite to use deployable sun-tracking solar arrays. Previous SSTL satellites use body-mounted solar arrays, which generate less power per unit area as they do not face the sun directly.

Launched on 28 December 2005

It was launched at 05:19 UTC on December 28, 2005 on a Soyuz rocket from Baikonur Cosmodrome in Kazakhstan.

First Galileo transmissions

It began communicating as planned at 09:01 UTC while circling the Earth at a height of 23,222 km. The satellite successfully transmitted its first navigation signals at 17:25 GMT on 12 January 2006. These signals were received at Chilbolton Observatory in Hampshire, UK and the ESA Station at Redu in Belgium. Teams from SSTL and ESA have measured the signal generated by GIOVE-A to ensure it meets the frequency-filing allocation and reservation requirements for the International Telecommunication Union (ITU), a process that was required to be complete by June 2006.

Technical details

The GIOVE-A signal in space is fully representative of the Galileo signal from the point of view of frequencies and modulations, chip rates, and data rates. However, GIOVE-A can only transmit at two frequency bands at a time i.e. (L1+E5 or L1+E6).

GIOVE-A codes are different from Galileo codes. The GIOVE-A navigation message is not representative from the structure and contents viewpoint (demonstration only purpose). The generation of pseudorange measurements and detailed analysis of the tracking noise and multipath performance of GIOVE-A ranging signals have been performed with the use of the GETR (Galileo Experimental Test Receiver) designed by Septentrio [ [http://www.septentrio.com/papers/SimskySleewaegenMertensWillemsHollreiserF3iongnss2007.pdf A.Simsky et al. Multipath and Tracking Performance of Galileo Ranging Signals Transmitted by GIOVE-A] , Proceedings of ION GNSS 2007] .

There has been some public controversy about the open source nature of some of the Pseudo-Random Noise (PRN) codes. [ [http://www.engineeringbritain.com/space/archives/40-Unlocking-the-truth-behind-GIOVE-A-signals.html Unlocking the truth behind GIOVE-A signals] , SSTL press release, 18 July 2006.] In the early part of 2006, researchers at Cornell monitored the GIOVE-A signal and extracted the PRN codes. The methods used and the codes which were found were published in the June 2006 issue of "GPS World". ESA has now made the codes public. [ [http://www.esa.int/esaCP/SEM4EDN0LYE_index_0.html GIOVE-A navigation signal available to users] , ESA press release, 2 March 2007.]

GIOVE-B

GIOVE-B (previously called "GSTB-V2/B"), has a similar mission, but has greatly improved signal generation hardware.

It was originally built by satellite consortium European Satellite Navigation Industries, but following re-organization of the project in 2007, the satellite prime contractor responsibility was passed to Astrium.

GIOVE-B also has MEO environment characterization objectives, as well as signal-in-space and receiver experimentation objectives. GIOVE-B carries three atomic clocks: two rubidium standards and the first space-qualified passive hydrogen maser.

Launched on 27 April 2008

The launch has been delayed due to various technical problems, [ [http://dev.space.com/spacenews/satellitecomm/GioveB_090106.html Giove B Launch Slips to Early 2007] , Peter de Selding, Space News, 1 September 2006.] and took place on 27 April 2008 at 04:16 Baikonur time (22:16 UTC Saturday) aboard a Soyuz-FG/Fregat rocket provided by Starsem. The Fregat stage was ignited three times to place the satellite into orbit. [cite web |url=http://www.arianespace.com/site/news/releases/presrel08_04_27.html |title=Starsem successfully launches second Europe navigation satellite |publisher=Arianespace |date=2008-04-27] Giove-B reached its projected orbit after 02:00 UTC and successfully deployed its solar panels. [ [http://afp.google.com/article/ALeqM5jydCERiyJhe5puK-JKlQ-n6BqEtw afp.google.com, Second test satellite for Galileo launched, reaches orbit] ]

First Galileo navigation transmissions

GIOVE-B started transmitting navigation signals on May 07, 2008. The reception of the signals by GETR receivers and other means has been confirmed at a few ESA facilities [ [http://www.esa.int/SPECIALS/GIOVE-B_launch/SEMGVUZXUFF_0.html ESA - GIOVE-B launch - GIOVE-B transmitting its first signals ] ] .

Technical details

According to ESA, 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".

“"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 ESA 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.

To be launched : GIOVE-A2

With the delays of GIOVE-B, the European Space Agency has again contracted with SSTL for a second satellite, to ensure that the Galileo programme continues without any interruptions that could lead to loss of frequency allocations. [ [http://www.esa.int/esaCP/SEM8LNN0LYE_index_0.html GIOVE-A2 to secure the Galileo programme] , European Space Agency press release, 5 March 2007.]

References

External links

* [http://www.esa.int/SPECIALS/GIOVE-B_launch/index.html ESA GIOVE-B launch pages]
* [http://www.giove.esa.int/ GIOVE Mission Processing Centre website]
* [http://directory.eoportal.org/pres_GIOVEGalileoInOrbitValidationElement.html eoPortal description of GIOVE]
* [http://space.ballard.co.uk/ blog of GIOVE-A launch] and [http://www.ballard.co.uk/press_releases/company_releases.aspx?company=sstl press releases] from Ballard Communications Management, used by SSTL.
* [http://www.giove.esa.int/page_index.php?menu=705&page_id=73 Technical papers on GIOVE-A mission]