GNSS Satellite (GIOVE-A)

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Saturday, 22 November 2008

Galileo Status

Short update on the Galileo, or rather Giove, status. Both Giove-A and Giove-B are in good health and cycling the Earth. The 13 Galileo Experimental Sensor Stations (GESS) are tracking the satellite signals. The GESS track Giove-A using 2 channels and Giove-B using 5 channels. This is due to the limit of 7 Galileo (Giove) tracking channels in the GESS hardware, these are truly experimental receivers.


Giove-A, launched in December 2005, is meanwhile passed its design lifetime but still going strong. Giove-B is performing very well. Especially its on-board passive hydrogen maser (PHM) is performing extremly well. Even much better then its specifications. This is a very important result for two reasons. First of all this is the first time such a clock is flown in space. Secondly, this type of clocks holds a promise of significantly improving the navigation quality of the GNSS systems. The main limiting factor today in GNSS navigation solutions is the quality of the predicted clocks. This PHM will allow clock predictions that may be one order of magnitude better than todays atomic clocks. A real break trought for GNSS!

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Monday, 12 May 2008

GIOVE-B is transmitting

After its successful launch on 27 April, GIOVE-B has began transmitting navigation signals on May 7. 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. These GIOVE-B signals, locked on-board to its 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 worldwide.

With GIOVE-B broadcasting its highly accurate signal in space using is extremely stable clock 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. I am looking forward to the first microwave obeservations (in the RINEX format) from the 13 world wide distributed Galileo Experimental Sensor Stations (GESS) to study the quality of the signals in comparison with GPS and GIOVE-A. In addition this should give us information regarding the stability and behaviour of the on-board clock.

As soon as I have some results I will inform you here (after ESA approval of course).

For more information look here:
http://www.esa.int/esaNA/SEMGVUZXUFF_index_0.html

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Sunday, 27 April 2008

Giove-B a major step forwards for Galileo

Today, 27-April-2008, Giove-B was launched succesfully!

You can watch the launch at:
http://www.videocorner.tv/giove-b/popup.html

The Giove-B satellite, which weight is only 500 kg, was lofted into a medium altitude orbit around the earth by a Soyuz/Fregat rocket departing from the Baikonur cosmodrome in Kazakhstan by launch operator Starsem. Lift-off occurred at 04:16 local time on 27 April (00:16 Central European Summer Time). The Fregat upper stage performed a series of manoeuvres to reach a circular orbit at an altitude of about 23,200 km, inclined at 56 degrees to the Equator, before safely delivering the satellite into orbit some 3 hours and 45 minutes later. The two solar panels that generate electricity to power the spacecraft deployed correctly and were fully operational by 05:28 CEST.

Giove-B will continue the demonstration of critical technologies for the navigation payload of the future operational Galileo satellites. Like Giove-A, Giove-B carries two redundant small-size rubidium atomic clocks, each with a stability of 10 nanoseconds per day. But it also features an even more accurate payload: the Passive Hydrogen Maser (PHM), with stability better than 1 nanosecond per day. The first of its kind ever to be launched into space, this is now the most stable clock operating in earth orbit.

GIOVE-B also incorporates a radiation-monitoring payload to characterise the space environment at the altitude of the Galileo constellation, as well as a laser retroreflector for high-accuracy laser ranging. Signal generation units will provide representative Galileo signals on three separate frequencies broadcast via an L-band phase array antenna designed to entirely cover the visible earth below the satellite. The satellite is now under the control of Telespazio's spacecraft operations centre in Fucino, Italy, and in-orbit checking-out of the satellite has begun.

The next step in the Galileo programme will be the launch of the first four operational satellites, to validate the basic Galileo space and related ground segment, by 2010. Once that In-Orbit Validation (IOV) phase is completed, the remaining satellites will be launched and deployed to reach the Full Operational Capability (FOC), a constellation of 30 identical satellites.

Galileo will be Europe's very own global navigation satellite system, providing a highly accurate, guaranteed global positioning service under civil control. It will be interoperable with the US Global Positioning System (GPS) and Russia's GLONASS, the two other global satellite navigation systems. Galileo will deliver real-time positioning accuracy down to the metre range with unrivalled integrity. Numerous applications are planned for Galileo, including positioning and derived value-added services for transport by road, rail, air and sea, fisheries and agriculture, oil-prospecting, civil protection, building, public works and telecommunications.

I am looking forward to the first real observations from Giove-B and to compute its first accurate orbit and especially accurate clock corrections. The passive hydrogen maser is the real "special" that Giove-B offers. Accurate clocks in space may offer a substantial benefit in all areas of GNSS. For the work I do, high precission GNSS at the mm level, I hope that the accurate Galileo clocks will offer an accuracy improvement of a factor of at least two, maybe more....

As soon as I have some first results I will post a new Blog here.

For more general info on Giove-B and Galileo have a look at:
http://www.esa.int/esaNA/galileo.html

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Saturday, 29 March 2008

GPS, GLONASS, and GALILEO status

So it has been a while since my last post... Just too busy at work to get any new BLOG entry. However, on the GNSS front several things have happened.

First of all yet another GPS satellite has been launched successfully on March 15. Meanwhile this satelite, GPS-48 with PRN number 07, is already transmitting its signals. It is still set unhealty so most navigation devices will not yet use it but the International GNSS Service (http://igs.org) is producing accurate orbits and clocks for this satellite. The launch of first GPS IIF is no longer planned for 2008 but shifted to 2009. However, the next GPS satellite due for launch, in June 2008, will be able to transmit on three frequencies. This as proof of concept for the GPS IIF satellites. This will be really exiting since it will bring us a complete new set of signals.

GLONASS now has 16 active satellites. Unfortunately the global tracking network still has many gabs and several of the receivers still have problems tracking the satellites with zero and/or negative frequency numbers. Nevertheless, GLONASS is in a much better state then ever in the last decade. With 6 more satellites scheduled for launch this year the future really looks bright. Hopefully the tracking equipment will improve. This will be a important task for Trimble, TPS, JPS, and Co. Also the global tracking network should improve. This is an important task for the IGS.

Last but not least GALILEO. GIOVE-B is getting ready for launch. ESA has set up a special web site for this major event GIOVE-B launch . The launch is scheduled for April 27, less then 1 month from now! As I wrote in my previous BLOG the exiting thing of GIOVE-B is the extremly stable clock, the Hydrogen Maser. This should improve the clock quality for the navigation and other real-time users. For the high accuracy domain it should enable a very significant reduction of the number of estimated clock parameters. This should give an accuracy improvemente comparable, if not more, to integer ambiguity resolution. Furthermore, with GIOVE-A and GIOVE-B in orbit at the same time it will give to opportunity to study how well integer ambiguity resolution may be performed when using the Galileo signals! I am really looking forward of working with the GIOVE-A and B data and especially looking forward at exploiting all the opportunities offered by the new signals and the H-Maser.

Please feel free to comment on this text and join me next time on this BLOG!

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