GPS geometry dictates that a minimum of 24 satellites is necessary to provide complete global coverage.  Properly configured within the GPS constellation, more satellites would mean improved coverage and ostensibly greater accuracy.  Although the United States currently has 30 satellites in orbit, several of these are riding shotgun with older satellites and serving strictly in an auxiliary capacity, so the working constellation has remained steady at 24.  However, things are about to change dramatically.  

On January 11, 2010, following extensive feasibility studies, the U.S. Strategic Command (USSTRATCOM) announced that three of the augmentation satellites would be moved to new locations within the GPS constellation, thus effectively increasing the number of individually positioned satellites from 24 to 27.  The main thrust of the reconfiguration is to increase coverage in previously degraded areas, such as the mountainous regions of Afghanistan, for military purposes.  However, the changes will benefit civilian and commercial users as well. 

The new “Expandable 24” configuration will take approximately two years to implement fully, but the first satellite is already on the move.  Space Vehicle Number (SVN) 24 began its journey on January 13 and should arrive in its new position sometime in January 2011.  The other two satellites have shorter journeys ahead of them.  SVN 49 will begin its journey on January 21 and is expected to be in its new position by May 2010.  SVN 26 will being its journey on February 8 and should also be in its new position sometime in May 2010. 

From the mountainous regions of Afghanistan to the urban canyons of the United States, GPS users should begin to notice gradual improvements in GPS coverage over the next two years as the number of satellites visible from any location on earth begins to increase.   I find it especially intriguing that two of the three satellites being moved are expected to be in place in May 2010, exactly 10 years after Selective Availability (SA) officially ended and GPS first became readily available to non-military users.

SVN 24, a GPS IIA satellite similar to the one in this image, is currently on the move to provide enhanced GPS coverage to users worldwide. The satellite is expected to arrive in its new location within the GPS constellation sometime in January 2011. (Public domain image courtesy of http://pnt.gov/public/images/.)

The European Commission has awarded a contract for the first 14 satellites in the burgeoning Galileo constellation.  The first satellite is scheduled for delivery in July 2012, with one satellite every 1.5 months thereafter until the last satellite is delivered in March 2014.  Additional contracts were awarded for system support services and launch services. 

Bringing the Galileo constellation closer to reality will require the collective efforts of several nations in and beyond the European Union.  Companies in Germany (OHB System AG) and the United Kingdom (Surrey Satellite Technology Limited) will be providing the satellite components, an Italian company (Thales Alenia Space) will provide the system support services, and a French company (Arianespace) will provide launch services that will use both French Ariane-5 and Russian Soyuz launchers.

The announcement was made on January 7, 2010, and contracts are expected to be signed within the next few weeks.  The European Commission anticipates initial navigation system services by early 2014.  The final completion date of the 30-satellite constellation has not been announced.

In my last blog post, I reported on issues with the existing GPS constellation that may cause signal disruptions, performance degradation and a decline in positioning accuracy for GPS users worldwide.  A desire for independence, as well as concerns about United States control over system access and an aging satellite infrastructure have prompted other nations to develop their own Global Navigation Satellite Systems (GNSS) that could compete with and/or complement the existing GPS constellation. 

The Galileo constellation, sponsored by the European Union (EU) and European Space Agency (ESA), was originally slated for full operation by the end of 2009.  Though test satellites have been launched to verify orbits and time synchronization for the new constellation, delays in planning and lack of funds have postponed the first operational satellites from being launched until sometime in late 2010.  The projected number of satellites in the Galileo constellation has already been reduced from 28 to 22 initially, due to cost overruns.

Russia’s GLONASS was fully operational back in 1995, but lack of funding due to the collapse of the Soviet Union eventually caused the system to fall into disrepair.  A new commitment in 2001, including the announcement of a partnership with India, has put the program back on track, though still far behind its target date of restoring full world coverage by the end of 2009.  Even after placing 3 new satellites in orbit in December 2009, GLONASS has only 19 working satellites in its constellation, which guarantees coverage only within Russian territory.  A total of 24 satellites are needed to provide global coverage. 

After initially expressing interest in assisting the EU with its Galileo constellation, the Chinese government is planning its own Compass constellation that will expand the existing Beidou Navigation System from regional China-only coverage to worldwide coverage.  The target completion date is 2015.  However, there were positioning issues with the first 2 satellites in 2009 that may ultimately delay or even prevent the Compass constellation from becoming a reality.  

The Quasi-Zenith Satellite System (QZSS) is a proposed three-satellite system that would provide enhanced GPS coverage within Japan.  The first satellite is scheduled for launch sometime in mid-2010.  Full operation is anticipated by 2013.  However, funding for the second and third satellites in the system is not expected until 2011 at the earliest, since it is contingent on the successful launch and operation of the first satellite.  QZSS is intended to enhance rather than replace GPS, and is expected to provide improved reliability and usability to the entire South East Asian region. 

The Indian Regional Navigational Satellite System (IRNSS) is a regional satellite system being developed by the Indian Space Research Organisation.  A seven-satellite system is scheduled for completion by 2012, and will provide accurate coverage of India and a 2,000-kilometer perimeter around its borders.  All space, ground and user components will be made in India. 

As the United States moves to modernize its own aging GPS constellation in 2010 and beyond, interoperability with one or more of the new constellations will ultimately become possible.  GPS receivers with dual capabilities will be able to get more accurate readings, and the addition of new satellites to any of these alternate constellations will provide needed back-up to the United States as its older satellites fail.  I will be looking skyward in 2010 to monitor these conditions and providing periodic updates on each constellation as news becomes available.

Artist’s rendering of a GPS III-A satellite, part of the U.S. modernization of the existing GPS constellation. (Public domain image courtesy of http://pnt.gov/public/images/.)