GNSS Satellite (GIOVE-A)

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Saturday, 26 January 2008

2008 An interesting year for GNSS!

The year 2008 promises to become a very interesting year for the Global Navigation Satellite Systemss (GNSS). You say why? Well let me explain.

Lets first have look at the dominating global satellite navigation system, the American NAVSTAR GPS (Global Positioning System). What makes 2008 special for 2008!? Well there are four launches planned. Most of them are really needed to ensure that the system remains complete. Currently there are 32 GPS satellite operational. This is actually the maximum number of PRN codes that were originally envisioned for GPS. However, from the 32 satellites 14 are relatively old Block IIA satellites. Most (if not all) of them have passed their design life time and thus they may fail any day. Therefore launching new satellites is not really a luxury but actually a most. The interesting part is that with the new launches the L2C capacity in orbit is enhanced and will allow a thorough use of it. Thus it will allow us to evaluate how much this signal can help to improve the quality of using GPS. The real highlight is that one of the launches will be the launch of the new GPS Block IIF satellite. This will be really interesting since it will be the first GPS satellite which emits signals on three frequencies. This will open up a whole new "world" to the users of the GPS constellation. I am really looking forward to working with the first data from this satellite and analyse the quality of the new signalis. The triple frequency will offer an exiting field for new usage of the GPS signal. The launch of this satellite is currently scheduled for August 2008. The other GPS launches are planned for March, June, and September.

Now to the Russian based system GLONASS. By the way the abreviation GLONASS comes from the Russion "Global'naya Navigatsionnaya Sputnikovaya Sistema" which may be translated as "Global Navigation Satellite System". Also for GLONASS 2008 holds quite some promise. After the two successful "triplet" launches in October and December 2007 the GLONASS system currently has 16 active satellites. The launch schedule for 2008 is not 100% clear (it is still difficult to get reliable information out of Russia). However, at least one additional triplet launch is planned but there are also indication that there will be two. The first triplet launch is scheduled for September. The second may be, as is almost a GLONASS tradition, around Christmas 2008. The most interesting fact for GLONASS is the planned launch of the first new GLONASS-K satellites. The GLONASS-K, is an entirely new model based on the non-pressurized platform, standardized to the specifications of the previous models' platform, Express-1000. Its main difference with the previous GLONASS satellites is that is much lighter (about half the weight!). This allows them to be launched (two at a time) with the Soyuz launcher which is much cheaper than the Proton launcher currently used (even if it launches three satellites at the same time). Furhtermore the design lifetime of the GLONASS-K satellites is much longer. There are rumours that the GLONASS-K will also transmit on three frequencies. But this is not very clear at the moment. In any case it will be interesting to see if Russia can keep up with their very ambitious plan of restoring GLONASS to full orbit constellation (FOC) by 2009. So far they have been doing very well and I am convinced that they will manage this. The only real threath to this goal would be significant politcal changes is Russia. Given the fact that Putin seems to have all well under control this threath does not seem to be very large. In any case it will be very interesting to receive the first GNSS data from this completely new satellite and see how both the data and the satellite will behave.

Next to GPS and GLONASS there are also developments on the European "front". As you may know Europe is in the process of building up its own Global Satellite Navigation System, called Galileo. A first test satellite, called GIOVE-A, is in orbit since two years and performing very well. In 2008 its "larger brother", called GIOVE-B, is scheduled for launch in April. The real "special" GIOVE-B offers is its on board clock. The on-board clock is the single most important instrument of any GNSS satellite. Therefore, all GNSS satellite use atomic clocks since those are the only ones which offer the required clock stability. And since the clock is so imporant typically 3 or 4 clocks are on-board for redundancy purposes. The new thing on GIOVE-B is that besides atomic clocks it will also have what is called a Hydrogen Maser on board. A H-maser on the long term is not as stable as an atomic clock but on the short term (12-48 hours) it is extremely stable. Thus the behavior of a H-maser clock can be predicted much betten than an atomic clock. And since the navigation messages as broadcasted by all GNSS systems are based on predictions the use of H-masers offers a significant accuracy improvement for the end-users (e.g. you and me with our cars navigation systems). So it will be very thrilling to see the behaviour of the H-maser in orbit. This is the first time such a clock is flown on a GNSS satellite! Furthermore, it will be very interesting to observe the GIOVE-B signals and validate if they can uphold the European Galileo promise of much improved signal quality compare to GPS and GLONASS. Furhtermore, there is also some rumour that the GIOVE-A2, a copy of the GIOVE-A, will be launched in November 2008. However, I believe that this will only happen if the GIOVE-B fails.

Furthermore, 2008 will certainly also show some new developments on the Chinese side of the GNSS world. The Chinese are quickly expanding their Beidou/Compass system. Currently I have very little knowledge on this system. I will dig into that during the year and "blog" about that later.

So I hope that you agree with me that 2008 holds a lot of GNSS promises! Maybe not all promises will be kept, but nevertheless even if 1 or 2 of these exiting events will come true the year will be very interesting!!

More on GNSS next month (or sooner if I can find the time).

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1 Comments:

Blogger Matteo Vannucchi said...

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11 March 2008 11:18

 

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