Research And Simulation On Autonomous Orbit Determination For Navigation Satellites

Now navigation constellation system is a sort of very important strategic resource, a very important exhibition to show synthesis power of a country, a necessary strategy to take up stratagem plateau of military, communication and information technology.The orbit precision of navigation constellation is one of the most important factors to judge its quality. Satellite navigation system, which was delegated by GPS, its technology of precise orbit determination is rather mature, but heretofore is supplied by ground monitor scattered over the world. From eighties middle age of last century, American arm was beginning to research on autonomous navigation of GPS, and got a series of results. There are more than ten GPS BLOCK IIR satellites in the orbit with autonomous navigation function. With the construction and development of Chinese satellites navigation system, autonomous orbit determination of navigation satellites become the focus [Liu Jinnan, Zhang Wentao,2001]. The core of this paper makes some deeply research on autonomous orbit determination theory, calculation method.. data simulation, so as to realize to supply effective navigation in a long time. The main work and results are show as the following:1. The development history of satellites orbit determination technology is reviewed; the ground orbit determination technology and autonomous orbit determination technology of GPS satellites system are expounded. Constellation eddy error and integral clock error can not be eliminated by the methods of autonomous orbit determination, but their accumulations were decreased by effective filtering method, so as to ensure to supply independent navigation power.2. In order to realize the autonomous orbit determination of navigation satellites, the links are necessary between satellites. Usually the observations of radial distance and the rate of radial distance are used for autonomous orbit determination. The characteristic of possible used means such as laser ranging wireless ranging velocity determination are expounded. It is proved that observation between satellites should adopt microwave technology, and done by the means of passive, one-way, dual-frequency pseudo-code.3. Based on the characteristic of navigation satellites, observation mode and data processing method of autonomous orbit determination are put forwarded .which are independent mode, grouping mode, unification mode. Three mode all can realize the autonomous orbit determination function of navigation satellites, and have different command to data observation,data processing, communication between satellites.4. The error of navigation satellites signal during launching, transmitting and reception are mainly satellite clock error, satellite antenna phase bias error, troposphere error, ionosphere error, multi-path error and receiver noise. The satellite clock error can be eliminated by special filer; the satellite antenna phase bias error can be corrected by different satellite type; the troposphere delay error is different form its on the methods of ground orbit determination, only very delicately affect on the observation and can be ignored; The first order Taylor of ionosphere error can be eliminated by dual-frequency technology; the signal noise can be eliminated in filtering calculation; the multi-path error are often litter than the affection to the methods of ground orbit determination, and can be eliminated by both method of hardware and software.5. The theory and methods of autonomous orbit determination are systematic expounded. A series of reference system: time system, coordinates system and force mode system are expounded in detail, which compose of the base of autonomous orbit determination.6. The strictness function relationship between the observation of distance and velocity, dynamics equation and variational equation of satellites are established. The linearization of the observation equation between satellites is realized effectively. It is proved that when the precision of satellite approximate coordinate keeps in 100 meters and expand to the first Taylor, it can meet the requirement of linearization.7. In order to resolve large volume observation equation between satellites, quickly, overcome mode error and linearization error of autonomous orbit determination, prevent the filter divergence in normal equation resolution, so a adaptive static filtering method is put forwarded; This method ensure not divergence, easy to realization and have high estimation precision.8. Simulation research platform of autonomous orbit determination is constructed. Autonomousorbit determination program is developed by author, and is composed by below module: simulation modular of distance between satellites; filtering orbit determination modular of between satellites; analysis modular of numerical value result; orbit integration modular of many days' orbit.9. When research on orbit determination by utilizing distance between satellites, in order to get single day orbit form many days' observation data, we adopt the method of fitting many days' orbit, and the result accord to the IGS ultimate precise ephemeris, so proved that this method is correct.10. There is whole excursion between the original coordinate system and the other after autonomous orbit determination for navigation satellites. The distinct parameters between two coordinate systems are gained by Helmert transformation and statistics test. The meteyard whether or not the two coordinate frameworks are oneness is brought forward according to the criterion of navigation precision of American GPS.In the simulation of autonomous orbit determination for 60 days, three kinds of parameter are obtained by Helmert transformation. The displacing parameters and scale parameter are not distinct or smaller. But the rotational parameters are increased with time, nevertheless, smaller than the limit. The result of simulation indicates that the coordinate framework of autonomous orbit determination is same as the ITRF2000.The J2 of the earth gravitational field and motion of the sun and the moon result in the ascend rotation of navigation satellites and rotational parameters' augmentation. It made whole constellation turning [M.P. Ananda, H. Bernstein, K..E. Cuningham, 1990]. The autonomous orbit determination can't correct the constellation turn's error and obtain the earth rotation parameters: Polar Motion (PM) and Movement of UT1.11. A series of examination are designed based on research result above and by utilizing real observation data of GPS. All kinds of examination results are described in tabulation and figure, necessary analysis are done at the same time.Simulation examination conclude: the variance selection of observation; the selection of different apriori variance; sampling interval of distance between satellites and single day precision of autonomous orbit determination; 30 days autonomous orbit determination result based on IGS precise ephemeris as initial value; and 60 days autonomous orbit determination result based on broadcast ephemeris as initial value.When determine the orbit using broadcast ephemeris autonomously, statistical precision of allsatellites error are highly improved, single day orbit precision of all satellites are less than 1.0meter, the most orbit bias is 2 meters, which show that independent orbit determination precisionare better than 2.0 meters in the worst conditions.When determine the orbit based on IGS quick precise ephemeris autonomously, all the error ofeach coordinates axis component continue to increase with the time delay, which the precisiondescend 10 centimeter per 10 days.When determine the orbit autonomously using broadcast ephemeris as initial value, the orbitprecision of all satellites can keep a quite high quality after SO days, and have a same precisionwith the broadcast ephemeris. Orbit precision of all satellites has a drop tendency with the timedelay.Based on different examination, we can draw the conclusion: using the ranging technology between satellites, the autonomous orbit determination of navigation satellites system can keep high precision in the long time, and can realize the autonomously navigation service without?ground supply.The continued research contents are put forward at the end of the paper on the author's research experience.