Pam. Abusali et al., AUTONOMOUS NAVIGATION OF GLOBAL POSITIONING SYSTEM SATELLITES USING CROSS-LINK MEASUREMENTS, Journal of guidance, control, and dynamics, 21(2), 1998, pp. 321-327
The Global Positioning System (GPS) Block IIR satellites, which will r
eplace the current Block II/IIIA satellites, will have satellite-to-sa
tellite communication capabilities that will allow intersatellite rang
ing between the Block IIR satellites. The cross-link pseudorange measu
rements will be used by onboard computers to update the stored navigat
ion messages, which are based on trajectories predicted over an extend
ed period of time, by ground-based processing of tracking data, During
normal operations, the cross-link pseudorange measurements will provi
de improved satellite states, which then can be broadcast to the users
, One of the error sources in the updated navigation messages, which c
annot be corrected by cross-link measurements, is found in the Earth o
rientation parameter (EOP) errors, ks a consequence, as the age of the
Earth rotation parameter increases, the performance of the autonomous
navigation system will degrade, The effect of this error source on th
e Block II GPS autonomous navigation accuracy is described. This work
is based on simulated cross-link pseudorange measurements. Realistic f
orce, measurement, and reference frame models are used in the analysis
to account for additional major error sources. Cross-link measurement
s for a period of one day, generated at the end of each of three diffe
rent prediction intervals, are used to update the predicted trajectory
. The estimated solutions then are compared to true solutions to evalu
ate the effect of prediction errors. With the current EOP prediction e
rrors, the user range errors (URE), computed from improved trajectorie
s and clock differences for a 90-day prediction, exceed 9 m, and for a
130-day prediction, they exceed 17 m. Finally, results of processing
measurements from ground stations, instead of cross links, are discuss
ed wherein the URE for the 180-day prediction case are shown to be abo
ut 3.1 m.