## 4 Discussions and Conclusions  
The KOD method using the LEO satellite onboard single-frequency GNSS observations is a cost-effective solution for future commercial aerospace applications. In this study, the improved data processing strategy of GPS/BDS-combined single-frequency KOD is proposed for the LEO satellite using the sun-pointing attitude mode. The satellite attitude impact on the GNSS observations is analyzed, and results show the theoretical C/N0 of the tracked signals and the noise characteristics change as the antenna radiation pattern rotates. To process this situation, an observation weighting model based on the C/N0 characteristic and exponential function is developed. The coefficients of this weighting model can be estimated and then applied in the real LEO KOD. Experiments show that this weighting model is suitable for processing the GPS/BDS observations from the LEO satellite with the sun-pointing attitude mode.  
The real-time single-frequency cycle slip detection algorithm with the capacity of handling receive clock jump is developed for improving the single-frequency carrier phase preprocessing. This method is designed to compute the phase acceleration jump based on a linear model and employs a robust approach in the estimation of the receiver clock jump. The cycle slip and clock jump can be identified, respectively. Moreover, cycle slips/outliers can be further discriminated using two adjacent detection results. This algorithm is independent of the clock steering events and can reasonably detect cycle slips in the GPS/BDS data preprocessing of the LEO satellite.  
The GPS/BDS-combined single-frequency KOD results of the Luojia-1A satellite show that the above improved data-processing strategy is suitable for LEO satellites with the sun-pointing attitude mode. Considering the unique feature of the Luojia-1A sun-pointing satellite attitude mode, incorporating low-elevation observations can improve data availability and orbit accuracy. The number of valid epochs and the PDOP values are improved by 12.9% and 37.5%, respectively, when using observations from satellites between \(-10^{\circ}\) and \(5^{\circ}\) elevation. As a result, the orbital RMS accuracy of the GPS/BDS-combined single-frequency KOD can be improved by 22.1%, 16.4%, and 6.5% in the radial, along-track, and cross-track directions, respectively. The contribution of the BDS observations is also analyzed for the Luojia-1A KOD based on the processing strategy. Compared with the GPS-only case, the orbital RMS accuracy of the GPS/BDS combination solution is improved up to 28.8%. The benefit of combining GPS/BDS observations in LEO KOD is demonstrated with the onboard GNSS data from the Luojia-1A satellite.  
**Author Contributions:** [PERSON] designed the experiment and wrote the manuscript. [PERSON] edited this manuscript. [PERSON], [PERSON], [PERSON] and [PERSON] helped to improve the manuscript. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Program of the National Natural Science Foundation of China (Nos. 41904038, 42074036, 41704002, and 91638203) and the China Postdoctoral Science Foundation (No. 2019M662713), and LIESMARS Special Research Funding.  
The GNSS precise satellite orbit and clock products provided by the Crustal Dynamics Data Information System (CDDIS) (Greenbelt, MD, USA) are available at [[ftp://cddis.gsfc.nasa.gov/gps/products/mgex](ftp://cddis.gsfc.nasa.gov/gps/products/mgex)]([ftp://cddis.gsfc.nasa.gov/gps/products/mgex](ftp://cddis.gsfc.nasa.gov/gps/products/mgex)). Luojia-1A onboard GNSS data on the re-sults of this study are currently not in the public domain and therefore cannot be accessed online. Data requests can be sent to the corresponding authors in case of specific interests.  
The authors thank the reviewers for their beneficial comments and suggestions.  
The authors declare no conflict of interest.