Back for a while

[_richardMdBorn]

I gave my talk last week on the invention of GPS to about 150 aerospace engineers. It went well though I'm not used to speaking with a microphone.

[_Gazelam]

Question for you.

I recently heard that the entire GPS infrastructure could be down within the next two to three years unless some important upgrades are made. I also heard that by the current timetable they are not going to make it.

Care to comment? enquireing minds want to know.

Gaz

[_richardMdBorn]

Question for you.

I recently heard that the entire GPS infrastructure could be down within the next two to three years unless some important upgrades are made. I also heard that by the current timetable they are not going to make it.

Care to comment? enquireing minds want to know.

Gaz

Hi Gaz,

That's a good question which has been much discussed recently. Some background may be helpful. There were four constellation studies done for TIMATION, the Navy's predecessor system to GPS. The Navy proposed a 3 x 9 configuration (3 planes with 9 satellites in a plane) at 8 hour orbits. When the Air Force took over the program, it was changed to 3 x 8 at 12 hour orbits. Later, the 24 satellite configuration was reduced to 18 which is barely adequate and then back to 24 satellites. It also was changed from 3 planes to 6.

I'm far from an expert on the current system since I've been focusing on the 1960s and 1970s. This opinion seems reasonable:

What the GAO found was that “some military operations and some civilian users could be adversely affected.” That’s hardly the “collapse” that some media outlets described. In fact, the core of the report indicates that there is an 80% chance that the system will not have the full complement of 24 operational satellites at some point between 2010 and 2014. Yet as long as Air Force Space Command maintains more than 30 operational satellites—and even has four non-operational on-orbit spares—the possibility of a real system degradation, excluding the unlikely scenario where the system is attacked, is pretty low.

http://www.thespacereview.com/article/1381/1

[_JohnStuartMill]

It'll also be interesting to see how much of a burden the EU will bear with their Galileo satellite navigation system when it becomes operational (supposedly in the next few years). Will the U.S. cut back on its GPS infrastructure investments if the Europeans make the system largely redundant? Will we pour more money in it to retain our military advantage along that dimension? Will we try to dovetail the two systems together, if that's technically feasible?

Interesting stuff.

[_richardMdBorn]

It'll also be interesting to see how much of a burden the EU will bear with their Galileo satellite navigation system when it becomes operational (supposedly in the next few years). Will the U.S. cut back on its GPS infrastructure investments if the Europeans make the system largely redundant? Will we pour more money in it to retain our military advantage along that dimension? Will we try to dovetail the two systems together, if that's technically feasible?

Interesting stuff.

Good observation JSM. There has already been much discussion about combining various GNSS systems. See for example:

Precise Point Positioning (PPP) is an emerging technology by using a standalone-receiver to determine absolute position of a point accurately. It uses precise orbit and clock products from IGS community, and takes all the errors correction of single-way carrier phase observables into consideration. Presently, Most of the researchers has focused on PPP with single GPS system, numerous literature shows that, mm´s to cm´s accuracy in static positioning with enough observation session length, and cm´s to dm´s
accuracy in kinematic positioning could be achieved with PPP method. However, Compared with single GPS System, integrations of multiple GNSS systems shows more advantages in a number of aspects including positioning continuity, availability, reliability, precision, efficiency etc. With the progressively recovery of the GLONASS System of Russia and the formal operation of IGLOS-PP, the GLONASS System is becoming a part of the IGS Service. There are now four IGS analysis centers, i.e. CODE?IAC?BKG and ESA/ESOC, who are supplying GLONASS precise ephemeris. Among them, IAC and ESOC could also supplies precise satellite clock correction products. As a result, GPS and GLONASS combination in PPP show us great potential. The combination of GPS and GLONASS could improve geometry strength, and ensure the positioning availability of 100% in most cases, which will satisfy the users who operate in the area with signal blockage. During practical data acquisition , users cannot be guaranteed to track enough satellites continuously in many cases. For example, users can only track less satellites in downtown (with high buildings blocking), vegetation-covered areas?and many other blind areas such as underground passages. Sometimes the tracked satellites are not enough to fix the location. In these circumstances, if users could combine GLONASS satellites in view, it will strengthen the geometry of the GPS satellites.

The paper provides detailed mathematical models of Precise Point Positioning based on combination of GPS and GLONASS observation. The GLONASS has different time system, coordinate system and frequency compared with the GPS, and every single GLONASS satellite has a individual frequency.

http://www.ion.org/meetings/abstract.cfm?meetingID=25&pid=566&t=E&s=3

[_Gazelam]

Rich,

Thanks for the reply. Very informative.

Gaz