Nuestro socio Miguel Marín, del Colegio de Pilotos, amable y oportunamente nos informa que el Colegio publicará unos posters alertando a la comunidad aeronáutica nacional sobre el "rollover" del GPS, a la medianoche (UTC) del 21 al 22 de agosto. El año pasado publicamos en el número de marzo del boletín impreso, un artículo sobre el asunto, el cual puede consultarse en http://www.femppa.org/femppa/jlp/h7/hangarsiete.html El problema es que los satélites GPS fueron originalmente diseñados con sólo diez posiciones en el contador binario de semanas del reloj-calendario, por lo que el máximo número de semanas que pueden contar es 1024 (2 elevado a la décima potencia), antes de reciclar (rollover) el contador a ceros. La semana uno del sistema GPS se inició a las 00 UTC del 6 de enero de 1980 y la semana 1024 terminará a las 2400 UTC del sábado 21 de agosto de 1999. ¿Qué pasará el 22 de agosto? que los satélites GPS "creerán" que es 6 de enero de 1980 y empezarán a transmitir a los receptores las posiciones en las que estuvieron en esa fecha y no las reales. Es de hacer notar que aunque por prudencia es conveniente verificar que nuestros equipos GPS funcionen correctamente después del "rollover", la mayoría no tendrá problema. Como regla general, los equipos fabricados en los últimos cinco años están programados para corregir el error y harán la transición de la semana 1024 correctamente. La mayoría de los fabricantes ha puesto en internet información sobre cada modelo. Una relación completa de fabricantes de GPA existe en Para aquellos interesados en leer el boletín de prensa de la Oficina del Espacio de los Estados Unidos, lo reproducimos a continuación (cortesía de Miguel Marín) Felices Vuelos.
Press Release from http://www.ifalpa.org/if_news/PresReleaseUSSC.htm Press Release from U.S. Space Command News Release 8-99 Year 2000 (Y2K) and End of Week (EWO) Compliance of GPS Receivers The Global Positioning System (GPS), made famous by Desert Storm, is an integral navigational tool for both military and civilian users because of its accuracy and flexibility. However, there are two upcoming events that may affect civil GPS users and government users of commercially procured receivers-the GPS End of Week (EOW) rollover and Year 2000 (Y2K) issues. The GPS EOW rollover happens every 20 years because GPS system time, counted in weeks, started counting on Jan 6, 1980. At midnight between Aug. 21 and 22, 1999 the GPS week will rollover from week 1023 to 0000. This is significant because it is the first EOW rollover since the GPS constellation was established and could be interpreted as an invalid date in GPS receivers that were not designed to meet GPS specifications. The GPS Y2K issue stems from the fact that many computer programs use a two-digit date field and assume that the year is 19XX. When the year 2000 occurs within the program, the two-digit date becomes "00" and could be interpreted as an invalid date. As with the EOW rollover, if receivers were manufactured according to GPS specifications, then this issue will not be a problem. The Department of Denfense is the service provider for GPS with direct control of the overall GPS service. The DoD's GPS Program Office has verified that all generations of GPS satellites and ground support systems are Y2K and EOW rollover compliant. This means that the GPS navigation signal will continue to be delivered during and after each of these events. The U.S. Air Force GPS Joint Program Office has conducted extensive testing of military receivers. The results of these tests may be viewed at the GPS JPO Y2K Web Site http://www.laafb.af.mil/SMC/CZ/homepage/y2000/index.html . Military users of commercial GPS receivers can also check the GPS JPO Y2K Web Site or contract receiver manufacturers to verify receiver EOW and Y2K compliance. End user systems are the receivers and applications that use GPS and have no controlling entity. It is these users that must verify that their receivers and applications, like electronic charting systems, will also work properly throughout these events. There are several initiatives in place to inform and educate civil users regarding GPS Y2K and EOW issues. However, it remains the responsibility of users to determine if their particular receivers and applications are Y2K and EOW compliant. The Department of Transportation is the primary interface for all civil GPS matters and created the Civil GPS Service interface Committee to meet this obligation. Since 1996, this committee has been actively informing the public about GPS Y2K and EOW issues. Relevant information, such as a list of receiver manufacturers and points
of contact for the public, is posted on the Coast Guard Navigation Center's
Web Site http://www.navcen.uscg.mil |
