jgg     2013 33 (6):  107-111    ISSN: 0412-1961  CN: 21-1139/TG SIMPLIFICATION OF JPL’S DE AND ITS APPLICATION ON  AUTONOMOUS ORBIT DETERMINATION OF GLOBAL  NAVIGATION CONSTELLATION School of Geodesy and Geomatics, Wuhan University, Wuhan 430079 Received: 2013-04-12  Revised: null  Online: 2013-12-13 Supporting info