This week is poised to set a new milestone in the GPS history. The launch of the first GPS block IIF satellite is scheduled for Thursday May 20. You may ask "why is this special". Well firstly because this is only the fourth type of GPS satellite to be launched. It all started with the block I test satellite from which only 10 were operated. Those were followed by only 9 block II satellites and 19 block IIA satellites. The block II and IIA were very similar satellites. The current constellation consists mainly out of the 12 block IIR (R for Replenishment) and 8 IIR-M (M for Modernised) satellites which build the third generation of GPS satellites. One of the IIR-M (SVN49/PRN01) is still unhealthy due to the issues with its signal caused by its experimental triple frequency, see our past reports on this issue.

The first block IIF (F for Follow-On or Future) we originally supposed to be launched in 2000. However, due to the much longer lifetime of the GPS block II satellites the launch date was moved backwards. In recent year’s problems in the development caused significant additional delays which even impaired the GPS constellation. There were concrete fears that the GPS constellation could drop below the required number of 24 healthy satellites. A successful launch of this first IIF satellite will put an end to these worries and will pave the way for a further shining GPS future.

As PosiTim we will anxiously await the first triple frequency signals from this satellite in the scope of our work at the navigation support office (OPS-GN) at the European Space Operations Centre (ESOC) of the European Space Agency (ESA). We hope to analyse this data as soon as they become available from the tracking network of the International GNSS Service (IGS). We hope to be able to report soon on the quality of the signals of this satellite. A second important aspect will be to study the in orbit behaviour of this satellite. As the shape and dimensions are completely different from the previous GPS generation the orbit model may be somewhat different. In order to achieve the highest possible accuracies it will be important to have a very good understanding of the orbit model.

The additional third frequency on this new GPS satellite generation will open up completely new capabilities in the scientific GNSS world. One interesting example is the application of triple carrier ambiguity resolution (TCAR) which a very promising technique for high accuracy GNSS solutions.

We hope to be back soon with a very positive report on this new satellite and with that a new era in GPS!

Labels: GPS, IIF, TCAR