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NASA Software Evaluates GPS Satellite Geometry to Aid Navigation Controllers
August 15, 2011

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Innovators at NASA's Johnson Space Center have developed a software program that evaluates global positioning system (GPS) satellite geometry for a given Earth-fixed location or trajectory. The GPS Satellite Geometry Analysis Tool (GPSGEM) provides a listing of all GPS satellites in view and can extrapolate a vehicle's trajectory if one or two satellites are removed. The tool provides navigation controllers with insight into expected performance of the GPS constellation and allows an assessment of the implications to onboard navigation performance for the ascent abort and entry phases of flight. With GPSGEM output, analysts can assess whether GPS constellation geometry is robust enough to support vehicle GPS receiver state solutions and/or accurate enough for a safe landing even if one or two satellites fail.


  • Predictive: Projects geometric dilution of precision (GDOP) along a trajectory, assuming satellite failures
  • Efficient: Aggregates results over any desired time interval; reports any continuous periods with poor geometry


  • Real-time use in NASA's Mission Control Center
  • Commercial air traffic control operations

Licensing and Partnering Opportunity

This technology is being made available through JSC's Technology Transfer and Commercialization Office, which seeks to transfer technology into and out of NASA to benefit the space program and U.S. industry. NASA invites companies to consider licensing this technology for commercial applications.

Contact Information

If you would like more information about this technology or about NASA's technology transfer program, please contact:

Technology Transfer and Commercialization Office
NASA's Johnson Space Center
Phone: 281-483-3809
E-mail: jsc-techtran@mail.nasa.gov

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Page Last Updated: January 16th, 2014
Page Editor: NASA Administrator