Wu YaJun

Relative position determination of a lunar rover using the biased differential phase delay of same-beam VLBI

When only data transmission signals with a bandwidth of 1 MHz exist in the rover, the position can be obtained using the differential group delay data of the same-beam very long baseline interferometry (VLBI). The relative position between a lunar rover and a lander can be determined with an error of several hundreds of meters. When the guidance information of the rover is used to determine relative position, the rover’s wheel skid behavior and integral movement may influence the accuracy of the determined position. This paper proposes a new method for accurately determining relative position. The differential group delay and biased differential phase delay are obtained from the same-beam VLBI observation, while the modified biased differential phase delay is obtained using the statistic mean value of the differential group delay and the biased phase delay as basis. The small bias in the modified biased phase delay is estimated together with other parameters when the relative position of the rover is calculated. The effectiveness of the proposed method is confirmed using the same-beam VLBI observation data of SELENE. The radio sources onboard the rover and the lander are designed for same-beam VLBI observations. The results of the simulations of the differential delay of the same-beam VLBI observation between the rover and the lander show that the differential delay is sensitive to relative position. An approach to solving the relative position and a strategy for tracking are also introduced. When the lunar topography data near the rover are used and the observations are scheduled properly, the determined relative position of the rover may be nearly as accurate as that solved using differential phase delay data.

Analysis of VLBI observation for Tianma radio telescope in Chang’E-3 orbit determination

天马望远镜(上海65 m射电望远镜)于2012年10月完成了第一阶段建设并具备了S/X, L, C波频段的VLBI观测能力. 2013年12月全程参加了嫦娥三号着陆器和月球车X频段的VLBI测定轨测定位任务. 在嫦娥三号中, 利用天马望远镜代替上海佘山25 m射电望远镜, 使中国VLBI观测网的灵敏度提高至1.67倍. 同时, 利用2比特采样代替嫦娥二号的1比特采样, 使灵敏度提高至1.38倍. 上述两项措施使定轨后的ΔDOR型VLBI时延残差由嫦娥二号时的1. 77 ns降至嫦娥三号时的0.67 ns, 着陆器和月球车同波束VLBI差分相时延随机误差降至0.011 ps rms. 本文在介绍天马望远镜及其X频段致冷接收和数据采集系统的基础上, 对其在嫦娥三号测定轨VLBI观测中的应用进行分析.

Mars rover positioning technology basedon same-beam VLBI

Position measurement of a Mars rover is important for engineering and scientific researches. This paper reports a method to carry out high precision positioning of the rover and orbit determination of the orbiter by using the same- beam VLBI between the rover and the orbiter and the orbiter’s ranging data. The calculation method of the differential phase delay and signal link of a Mars rover is analyzed. The measurement error of the differential phase delay caused by solar plasma, atmosphere, ionosphere and instruments is estimated to lower than 10 ps. As a successful example, in Chang’E-3, the differential phase delay data between the rover and lander are obtained with a random error of 1 ps, and the relative position of the rover is determined with an accuracy of 1 m by using the same beam VLBI, which demonstrates the effectiveness of the method. In the case of the Mars rover and the orbit, the simulation analysis results show that the Mars rover position can be determined with an error of hundreds of meters and the orbit of the orbiter can be determined with an error of tens of meters by using the orbiter ranging and the same-beam VLBI differential phase delay data.

VLBI phase delay and its application in orbit determination of spacecraft

As one of the key technologies for orbit determination, very long baseline interferometry (VLBI) will play an important role in deep space explorations. The traditional group delay of VLBI is affected by the signal to noise ratio (SNR). As the spacecraft going to outer space, the random error of group delay increases quickly because of the SNR getting worse and worse. In this paper, we introduce the phase delay whose random error is much smaller than that of group delay at the same SNR. We deduce the conditions and method to determine the phase ambiguity, and then give the formula of calculating phase delay. The phase delay is used to determine the orbit of Change 2 (CE2) satellite with Doppler/ranging data when it flies to the Sun-Earth Lagrangian point L2 which is 1 500 000 km away from the Earth. It proves that the phase delay is useful for orbit determination.