By continuing to use this site, you agree to the use of cookies. You can find out more by following this link Accept & Close ›
Space Blog

Retired GIOVE-A could help GPS reach even higher heights

In June 2012, the SSTL-built GIOVE-A satellite was retired after an impressive 6 years of service broadcasting prototype Galileo signals.
But that wasn’t the end for the plucky satellite. Not content with paving the way for European GNSS, engineers at SSTL- with the support of the European Space Agency- included an experimental receiver called SGR-GEO on GIOVE-A to look into extending the reach of the existing US GNSS system- GPS- in space.

Although GPS is commonplace on satellites in Low Earth Orbit (LEO) to determine orbit position, velocity and time, there are technical challenges preventing the service reaching satellites further away from Earth. The problem is, spacecraft higher than LEO are often also orbiting higher than the GPS constellation. This means that they can only receive a few signals that “spill over” from the far side of the Earth, so the GPS signals are weak and a position fix can’t always be attained.

The SGR-GEO was specially developed to be able to receive these weak signals. It has a high-gain antenna and a precise oven-controlled clock that helped it to achieve a position fix at 23,300km altitude; the first time a civilian satellite has achieved a position fix outside the GPS orbit. The receiver will also demonstrate longer integration tracking loop algorithms to allow reception of weak signals, and an orbit estimator intended to allow a near continuous position output throughout the orbit.
Apart from the spill-over signals, the SGR-GEO receiver on GIOVE-A is also acquiring side lobes from the GPS transmit antennas at higher signal strengths than expected. These signals of opportunity help to improve the availability of the useable measurements for navigation.

A first look at some of the results is given in the figure above. This shows a view of GPS signals tracked by the receiver over several days using standard tracking loops (software controlled delay-lock loops). The majority of the signals are in the first ring surrounding the Earth – these are signals that have travelled past the Earth from the main lobe of the transmit antenna. Outside that ring, there are some more signals – these are emitted by the first side-lobe of the GPS transmit antennas. Beyond that, there are five signals that have been acquired from the second sidelobe, and are spread out as far as 45 degrees away from the Earth.

When using the weak signal tracking loops, it is expected that even more signals will be acquired from first and second sidelobes, increasing the availability of GPS signals and improving the positioning geometry to give a better position accuracy.

The first position fix above GPS orbit is potentially an exciting problem-solver. It is allowing SSTL to collect data from the SGR-GEO receiver that could help GPS extend its reach further than LEO to Geostationary (GEO) and beyond - all through the use of more sensitive and smart receivers.





12 December 20120 Comments1 Comment

Back to Blog

Blog post currently doesn't have any comments.
 Security code

About This Blog

SSTL's lowdown on cost effective space technology, small satellites, space science and interplanetary exploration.

Post Archive

October 2017(1)
May 2017(1)
January 2017(2)
October 2016(3)
September 2016(1)
July 2016(1)
June 2016(1)
April 2016(1)
March 2016(4)
February 2016(3)
December 2015(2)
November 2015(3)
October 2015(3)
July 2015(1)
May 2015(0)
May 2015(1)
April 2015(1)
March 2015(2)
February 2015(2)
January 2015(2)
December 2014(1)
November 2014(2)
October 2014(2)
September 2014(1)
July 2014(2)
June 2014(3)
May 2014(1)
April 2014(1)
March 2014(1)
February 2014(2)
January 2014(2)
November 2013(3)
October 2013(2)
September 2013(2)
July 2013(3)
June 2013(2)
May 2013(2)
April 2013(4)
March 2013(1)
February 2013(3)
January 2013(5)
December 2012(6)
November 2012(5)
October 2012(4)
September 2012(4)
August 2012(1)
July 2012(6)
June 2012(1)
May 2012(2)
April 2012(5)
March 2012(3)
February 2012(3)
January 2012(1)
December 2011(1)
November 2011(4)
October 2011(5)
September 2011(4)
August 2011(3)
July 2011(4)
June 2011(6)
May 2011(3)
April 2011(1)
March 2011(3)
February 2011(2)
January 2011(3)
December 2010(2)
November 2010(1)
October 2010(2)
September 2010(4)
August 2010(4)
July 2010(2)
June 2010(2)
May 2010(2)
April 2010(4)
March 2010(4)
February 2010(4)
January 2010(3)
December 2009(2)
November 2009(5)
October 2009(2)
September 2009(6)
August 2009(4)
July 2009(3)
June 2009(1)
May 2009(2)
March 2009(2)
February 2009(5)
January 2009(2)
December 2008(3)
November 2008(6)
October 2008(5)
September 2008(3)
August 2008(5)
June 2008(1)
May 2008(3)
April 2008(5)
March 2008(1)
February 2008(1)
January 2008(3)
December 2007(3)
November 2007(6)
October 2007(3)
September 2007(3)
August 2007(1)
July 2007(1)
June 2007(2)
May 2007(2)
April 2007(1)
January 2007(3)
December 2006(1)
September 2006(1)
May 2006(2)
January 2006(1)
December 2005(7)

Show/Hide All

If you like Space Blog, why not subscribe by RSS by clicking the subscribe button, or to recieve updates by email click the subscribe by email button.

*Comments Policy
SSTL reserves the right not to publish comments if they are deemed inappropriate.