GPS World, February 2018

1150 1200 1250 1300 1350 1400 1450 1500 1550 1600 0 10 20 30 FIGURE 4 Normalized power spectra of QZS 2 and QZS 4 measured with DLRs 30 meter high gain antenna on July 18 2017 and Nov 7 2017 respectively 360 315 270 225 up to 100 seconds For longer periods the QZS 2 clock seems to perform slightly better However this effect is probably related to the number of stations contributing to the clock solutions of the individual satellites which differs by a factor of more than two For comparison purposes the Allan deviation of two Galileo rubidium clocks GAL 101 and GAL 204 and a Galileo passive hydrogen maser PHM GAL 207 are plotted in the bottom panel of Figure 6 Whereas the performance of the QZSS and Galileo rubidium clocks is very similar the Galileo PHM is more stable by a factor of two to five over all integration periods CONCLUSIONS With the launch of the third IGSO spacecraf t and the f i rst GEO spacecraft the QZSS constellation has re ache d a four satel l i te configuration which is required for the provision of operational augmentation services QZS 3 and QZS 4 were declared useable for PNT SLAS and CLAS trial services on Dec 18 2017 and Jan 12 2018 respectively Inclusion in the operational QZSS constellation is expected for 2018 and this will provide continuous visibility of three satellites in the service area An expansion to a constellation of seven satellites is planned for 2023 including a Public Regulated Service for authorized users 48 GPS WORLD WWW GPSWORLD COM FEBRUARY 2018 10 11 10 12 10 13 10 14 10 15 QZS 1 QZS 2 QZS 4 101 102 103 104 105 Integration period seconds Allan deviation GAL 101 GAL 204 GAL 207 10 11 10 12 10 13 10 14 10 15 101 102 103 104 105 Integration period seconds Allan deviation FIGURE 6 Modified Allan deviations of the QZSS IGSO rubidium clocks Galileo rubidium clocks GAL 101 and GAL 204 and a Galileo passive hydrogen maser GAL 207 MANUFACTURERS Data used in this article was collected using Javad GNSS www javad com Delta G3TH Trimble www trimble com NetR9 and Septentrio www septentrio com PolaRx4 and PolaRx5 receivers Authors PETER STEIGENBERGER STEFFEN THOELERT ANDRÉ HAUSCHILD and OLIVER MONTENBRUCK are from the German Aerospace Center DLR RICHARD B LANGLEY is from the University of New Brunswick and authors the monthly Innovation column for GPS World magazine FIGURE 5 Nominal yaw steering attitude blue and estimated attitude red of QZS 4 for Dec 9 2017 β 11 MORE ONLINE Further Reading For references related to this article and bonus text go to gpsworld com and click on More in the navigation bar then on Innovation Frequency MHz Received normalized power dB 40 L5 L6 L2 L1 QZS 2 QZS 4 0 6 12 18 24 180 Time hours Yaw angle degrees Nominal Estimated