Over the past couple weeks I was involved in a really interesting project which involved testing of GNSS hardware within the Rotterdam World Gateway (RWG). It was a really amazing learning opportunity. Within the up coming weeks, I'll write a few blog posts that highlights some of my experiences within the facility. In the mean while, here is a nice video that highlights their opening ceremony, September 2015
Accurately detecting an eclipsing satellite may not be as easy as I thought. This would be an evolving blog post. I will update as I learn more about the calculations involved. An eclipse is an event that occurs when an object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer. During an eclipse there are three main phases the object can experience. These phases include:
GNSS satellites has two eclipse seasons per year, each lasting for approximately every seven weeks (IGS, 2009). GNSS satellites only experiences an umbra and penumbra. The satellite isn’t far enough from the earth to experience an antumbra. During an eclipse the GPS position quality degrades. A major source of this degradation is the mismodeling of the yaw attitude of those GPS satellites that are in eclipsing orbits. The yaw attitude of GPS satellites is essentially random during an eclipse and for up to 30 minutes past exiting from shadow. Furthermore, commonly used models of the noon turn can be inaccurate for a period of up to 30 minutes. This leads to both measurement and dynamic errors. Errors in the radio metric measurements are introduced because the transmitter phase center and the carrier phase wind-up are mismodeled. This measurement error can be as large as 1 wavelength. Errors in the satellite dynamics are introduced because the direction of the solar pressure force is mismodeled during the 30-minute recovery period after exiting the shadow and during the noon turn (Bar-Server Y, 1994). Therefore, when the satellite enters an eclipse, the solar radiation pressure is zero (umbra) or changing (penumbra), thermal re-radiation force changes as S/C temperature drops down and dolar sensors can no longer control the attitude
Problem with GPS satellite timing signal triggered alarms across the continent and caused an unknown number of outages, including the disruption of some features of critical infrastructure. The GPS problem was caused by an error in ground software uploaded January 26 as system operators removed space vehicle number (SVN) 23 from service. The long-planned deactivation of SVN 23, the oldest of the GPS satellites, clears the way for a new satellite, the last GPS Block IIF, which is to be launched February 4. The software problem, however, threw GPS's coordinated universal time (UTC) timing message off by 13 microseconds, which affected the timing data on legacy L-band signals and the time provided by GPS timing receivers, said 50th Space Wing spokesman James Hodges. The problem did not appear to have affected the GPS systems's ability to provide positioning and navigation service.
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