The mapping phase is a key stage of the Tianwen-1 orbiter. It has the longest exploration time and gathers abundant radio tracking data via the Chinese deep space network. Thus, it also provides opportunities for radi...The mapping phase is a key stage of the Tianwen-1 orbiter. It has the longest exploration time and gathers abundant radio tracking data via the Chinese deep space network. Thus, it also provides opportunities for radio science research topics such as the Mars gravity field model, ephemeris, and radio occultation experiments. At this stage, the need for imaging takes the highest priority, leading to frequent attitude adjustments for the spacecraft, which presents challenges for Precise Orbit Determination (POD). To improve the accuracy of the spacecraft’s orbit, this study analyzes the effects of arc length, the empirical acceleration, and the solar radiation pressure parameters on POD, considering the limited number of radio tracking observations. For one-day arcs, the POD is not able to adequately account for wheel off-loading and a few unknown forces with limited observations, but reasonable fitting is performed for the wheel off-loading occurring during tracking periods or the gap between two tracking periods. When extending the POD arc to three days, the estimated empirical acceleration can be well-fitted and reflects the aggregation feature, but the solar radiation pressure parameter has little impact on POD results. The root mean square of two-way range-rate residuals after POD is about 0.18-0.35 mm/s;the orbital position accuracy of 60% of the arcs is better than 100 m.展开更多
On September 20 th, 2015, twenty satellites were successfully deployed into a near-polar circular orbit at 520 km altitude by the Chinese CZ-6 test rocket, which was launched from the Tai Yuan Satellite Launch Center....On September 20 th, 2015, twenty satellites were successfully deployed into a near-polar circular orbit at 520 km altitude by the Chinese CZ-6 test rocket, which was launched from the Tai Yuan Satellite Launch Center. Among these satellites, a set of 4 Cube Sats conform the atmospheric density detection and precise orbit determination(APOD) mission, which is projected for atmospheric density estimation from in-situ detection and precise orbit products. The APOD satellites are manufactured by China Spacesat Co. Ltd. and the payload instruments include an atmospheric density detector(ADD), a dual-frequency dualmode global navigation satellite system(GNSS) receiver(GPS and Beidou), a satellite laser ranging(SLR) reflector, and an S/Xband very long baseline interferometry(VLBI) beacon. In this paper, we compare the GNSS precise orbit products with colocated SLR observations, and the 3 D orbit accuracy shows better than 10 cm RMS. These results reveal the great potential of the onboard micro-electro-mechanical system(MEMS) GNSS receiver. After calibrating ADD density estimates with precise orbit products, the accuracy of our density products can reach about 10% with respect to the background density. Density estimates from APOD are of a great importance for scientific studies on upper atmosphere variations and useful for model data assimilation.展开更多
In view of the requirements of Tianwen-1 missions on precision orbit determination and scientific application,this paper proposes a high-precision open-loop velocity measurement method based on ground-based radio.At f...In view of the requirements of Tianwen-1 missions on precision orbit determination and scientific application,this paper proposes a high-precision open-loop velocity measurement method based on ground-based radio.At first,relying on space–ground TT&C resources of the Tianwen-1 probe,the paper designs an open-loop velocity measurement strategy based on China’s deep-space network.Then,it proposes a core algorithm of open-loop velocity measurement based on local cross-correlation reconstruction to obtain instantaneous Doppler frequency observables.This algorithm is characterized by a high ability to avoid phase lock loss,convenient and efficient implementation,and flexible parameter configuration and is suitable for high-precision velocity measurement in the case of high dynamics and low signal-to-noise ratios.On this basis,the similarity and difference of velocity observables between open-loop and baseband velocity measurements are analyzed comparatively.Finally,on the basis of the open-loop velocity measurement method,the paper carries out tests on high precision orbit determination with independent support of velocity measurement,as well as on Mars radio occultation.According to the research results,the accuracy of open-loop velocity measurement can reach 0.05 mm/s(in 1-s integration time),which is 2 to 3 times better than that of baseband velocity measurement.Open-loop velocity measurement can independently support orbit determination accuracy of 50 m of the Tianwen-1 probe and effectively support autonomous retrieval of Martian ionospheric electron density profiles.Thus,this method can be effectively applied to future missions of deep-space exploration and research of planetary radio science.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12203002 and 42241116)National Key R&D Program of China(No.2022YFF0503202).
文摘The mapping phase is a key stage of the Tianwen-1 orbiter. It has the longest exploration time and gathers abundant radio tracking data via the Chinese deep space network. Thus, it also provides opportunities for radio science research topics such as the Mars gravity field model, ephemeris, and radio occultation experiments. At this stage, the need for imaging takes the highest priority, leading to frequent attitude adjustments for the spacecraft, which presents challenges for Precise Orbit Determination (POD). To improve the accuracy of the spacecraft’s orbit, this study analyzes the effects of arc length, the empirical acceleration, and the solar radiation pressure parameters on POD, considering the limited number of radio tracking observations. For one-day arcs, the POD is not able to adequately account for wheel off-loading and a few unknown forces with limited observations, but reasonable fitting is performed for the wheel off-loading occurring during tracking periods or the gap between two tracking periods. When extending the POD arc to three days, the estimated empirical acceleration can be well-fitted and reflects the aggregation feature, but the solar radiation pressure parameter has little impact on POD results. The root mean square of two-way range-rate residuals after POD is about 0.18-0.35 mm/s;the orbital position accuracy of 60% of the arcs is better than 100 m.
基金supported by the National Natural Science Foundation of China(Grant Nos.41874183,41474131&41604131)
文摘On September 20 th, 2015, twenty satellites were successfully deployed into a near-polar circular orbit at 520 km altitude by the Chinese CZ-6 test rocket, which was launched from the Tai Yuan Satellite Launch Center. Among these satellites, a set of 4 Cube Sats conform the atmospheric density detection and precise orbit determination(APOD) mission, which is projected for atmospheric density estimation from in-situ detection and precise orbit products. The APOD satellites are manufactured by China Spacesat Co. Ltd. and the payload instruments include an atmospheric density detector(ADD), a dual-frequency dualmode global navigation satellite system(GNSS) receiver(GPS and Beidou), a satellite laser ranging(SLR) reflector, and an S/Xband very long baseline interferometry(VLBI) beacon. In this paper, we compare the GNSS precise orbit products with colocated SLR observations, and the 3 D orbit accuracy shows better than 10 cm RMS. These results reveal the great potential of the onboard micro-electro-mechanical system(MEMS) GNSS receiver. After calibrating ADD density estimates with precise orbit products, the accuracy of our density products can reach about 10% with respect to the background density. Density estimates from APOD are of a great importance for scientific studies on upper atmosphere variations and useful for model data assimilation.
基金supported by the National Natural Science Foundation of China(nos.11973015 and 12373082)Civil Aerospace Research Project of China(no.D020309)National Key Laboratory of Aerospace Flight Dynamics(no.KGJ6142210220106).
文摘In view of the requirements of Tianwen-1 missions on precision orbit determination and scientific application,this paper proposes a high-precision open-loop velocity measurement method based on ground-based radio.At first,relying on space–ground TT&C resources of the Tianwen-1 probe,the paper designs an open-loop velocity measurement strategy based on China’s deep-space network.Then,it proposes a core algorithm of open-loop velocity measurement based on local cross-correlation reconstruction to obtain instantaneous Doppler frequency observables.This algorithm is characterized by a high ability to avoid phase lock loss,convenient and efficient implementation,and flexible parameter configuration and is suitable for high-precision velocity measurement in the case of high dynamics and low signal-to-noise ratios.On this basis,the similarity and difference of velocity observables between open-loop and baseband velocity measurements are analyzed comparatively.Finally,on the basis of the open-loop velocity measurement method,the paper carries out tests on high precision orbit determination with independent support of velocity measurement,as well as on Mars radio occultation.According to the research results,the accuracy of open-loop velocity measurement can reach 0.05 mm/s(in 1-s integration time),which is 2 to 3 times better than that of baseband velocity measurement.Open-loop velocity measurement can independently support orbit determination accuracy of 50 m of the Tianwen-1 probe and effectively support autonomous retrieval of Martian ionospheric electron density profiles.Thus,this method can be effectively applied to future missions of deep-space exploration and research of planetary radio science.
