近二十年来，轨道在1000km以下的低轨卫星由于其特殊的应用和科研需要得到了迅速的发展，在很多领域发挥了重大的作用。随着GPS技术的开发和利用，利用星载GPS接收机为低轨卫星提供了一种相对经济、精确、快速有效的定轨途径。

对于目前大部分国内的星载GPS用户来说，一般采用单频GPS接收机，同时，大部分航天器有实时或准实时定轨的需求。本文研究目标是基于星载单频GPS对低轨卫星进行绝对定轨基础上，分析影响绝对定轨精度的各项误差和探讨相关改正方案以提高定轨精度，最后对轨道进行拟合和短时间预报。本文研究主要内容如下：

（1）基于星载单频GPS对低轨卫星进行绝对定轨和误差分析

     介绍基于星载单频GPS对低轨卫星进行绝对定轨的观测方程并线性化，分析影响定轨精度的各项误差。编写程序实现星载GPS绝对定轨方案，通过算例分析绝对定轨精度。

（2）星载单频GPS电离层误差分析和改正方案探讨

     介绍几种适合低轨卫星电离层误差改正模型和方法，通过算例感性认识空中电离层延迟大小，并分析电离层误差对定轨精度的影响。 

（3）星载单频GPS相位平滑伪距及周跳探测和修复问题探讨

     介绍相位平滑伪距的基本原理和方法，同时就相位中的周跳探测和修复问题作相关探讨，通过算例分析相位平滑伪距对提高伪距绝对定轨精度的影响。

（4）低轨卫星轨道拟合和预报

     利用较为简单方便的数学方法对低轨卫星离散轨道进行拟合，并作短期预报

In the past 20 years，the LEO satellites which orbit below 1000 km have witnessed speedy growth because of these special applications and scientific research needs, they play a major role in many areas. With the development of GPS technology, it provides a relatively economic, accurate, fast and effective way to the LEO satellites orbit determination based on GPS receivers. 

    The most of domestic on-board GPS users are generally use single-frequency GPS receivers, at the same time, most of spacecrafts demand real-time orbit determination. The paper research into single point orbiting means, analyze some errors which have an impact on accuracy of orbit determination and discuss some correction means to improve orbit deyermination accuracy, and fitting and forcasting LEO satellites orbit finally. The main contents of the paper are:

(1)Single point orbiting of the LEO satellites based on on-board GPS receivers and discussion of errors correction means. 

    Introuduced the observation equation of single point orbiting based on on-board single-frequency GPS and make it linear, analyzed some errors which have an impact on accuracy of orbit determination. Single point orbiting solution is realized by programming and analyized accuary of the solution from examples.

 (2)Analysis of on-board single-frequency GPS ionospheric effects and discussion of corrections means

    Introduced some models and means for correcting ionospheric effects which suit for single-frequency and high speed dynamic GPS receivers. Realized the size of ionospheric effects in the air and discussed its impact on orbit determination accuary from examples.  

(3)Discussion of GPS phase smoothing pseudo-range and cycle-slip detection based on spaceborne single-frequency GPS receiver

    Introduced the basic principle of phase smoothing pseudo-range technology and discussed means of cycle slip detection and correction, and analyzed impact on improving orbit determination accury of phase smoothing pseudo-range technology.

(4) LEO satellites orbit fittling and forecasting 

Fitting LEO satellites orbits and forecasting the orbits for a short time by simple geometric means.

Key words: on-board single-frequency GPS; LEO satellites; orbit determination; single point orbiting; error correction; ionospheric effects; phase smoothing pseudo-range; cycle- slip detection and correction; orbit fitting; orbit forecasting星载单频GPS;低轨卫星;定轨;绝对定轨;误差改正;电离层误差;相位平滑伪距;周跳探测和修复;轨道拟合;轨道预报on-board single-frequency GPS;LEO satellites;orbit determination;single point orbiting;error correction;ionospheric effects;phase smoothing pseudo-range;cycle- slip detection and correction;orbit fitting;orbit forecasting