Orbit and Positioning Accuracy for New Generation Beidou Satellites during the Earth Eclipsing Period

Abstract

The Beidou System (BDS) started functioning at the end of 2012. The Yaw-Steering (YS) attitude mode for Inclined Geosynchronous Orbit (IGSO) and Medium Earth Orbit (MEO) satellites in BDS ensures that the solar panels face the Sun. The orbit radial accuracies for IGSO/MEO satellites are 0·5 m and the User Equivalent Range Errors (UERE) are 1·5 m in YS mode. BDS-2 satellites adopt Orbit-Normal (ON) mode to meet the power supply and thermal control requirements of the satellite during deep Earth eclipse periods. In ON mode, long-term orbit ephemeris accuracy monitoring in the Operational Control System (OCS) of BDS indicates that the orbit accuracies for IGSO/MEOs are reduced to a few hundreds of metres, seriously affecting the positioning accuracy and navigation service capability of the BDS system. Solar Radiation Pressure (SRP) is difficult to model in ON mode. Continuous Yaw-Steering (CYS) mode is available for new generation Beidou satellites launched since 2015. The orbit accuracies for these new generation Beidou (BDS-3) satellites were estimated based on BDS monitoring station data and SRP models including ECOM 9/5/3. The evaluation method consisted of four steps, namely, orbit internal consistency analysis, UERE calculation, Satellite Laser Ranging (SLR) data fitting Root Mean Square (RMS) determinations and positioning performance analysis; the data gathering period lasted for more than 60 days and included two CYS periods and one ON period. The experiments showed that the orbit accuracy of the radial component in CYS mode for the BDS-3 satellites degrades by 2 to 3 cm and positioning accuracy degrades only by 1 cm over that in YS mode which is just a small reduction in accuracy compared with the decimetre-level BDS orbit accuracy and the metre-level single point positioning accuracy with BDS pseudorange data. This overcomes declining orbit and positioning accuracy issues in ON mode for BDS-2 satellites. Other results also show that the reliability of BDS has been improved.

Precise orbit determination for BDS satellites

“…For BDS-2 IGSO and MEO satellites, the Yaw-Steering (YS) and ON modes are adopted. The transformation from YS to ON occurs when the absolute value of β angle is less than 4° and the absolute value of yaw angle ( ψ angle) is no greater than 5° (Li et al, 2018), while the conditions for switching from ON to YS are |β| > 4 • and |ψ| < 5 • . They present the yaw angles during the attitude switch period from the telemetry data for C08, C11 and C12 satellites, and the sudden rump-up and rump-down jumps instead of smooth switch can be clearly observed at the attitude switch points.…”

“…With the Revise Kinematic Precise Point Positioning (RKPPP) approach proposed by Dilssner et al (2011), the yaw angles were estimated with ground L-band measurements Dai et al, 2015). Almost the same conditions as Li et al (2018) are derived by Dai et al (2015). However, by assuming that the attitude mode will switch when the yaw angle is closest to the required orientation, Guo et al (2017) derived the conditions for yaw attitude switch when µ = 90 • and |β| closest to 4°, where µ is the orbital angle.…”

Impacts of Arc Length and ECOM Solar Radiation Pressure Models on BDS-3 Orbit Prediction

“…For the BDS-2 satellite, studies have shown that its orbit determination accuracy will decrease significantly during the eclipse period [20], but there are few studies analyzing the orbit prediction accuracy of the BDS-3 satellite during the eclipse season. Therefore, in the following section, this study explores the orbit prediction accuracy of the BDS-3 satellite during the eclipse season.…”

“…The reason may be due to the advanced attitude control mode of the BDS-3 satellites. In addition to the yaw-steering (YS) mode, the BDS-3 MEO/IGSO satellites adopt the continuous yaw steering (CYS) attitude mode in eclipse seasons [20]. The CYS mode not only meets the requirements of the power supply and thermal control of the BDS-3 MEO/IGSO satellites but also avoids rapid yaw slews near the sun-spacecraft-Earth geometries.…”

“…The CYS mode includes two periods of midnight-turn maneuver and noon-turn maneuver. Midnight-turn maneuver and noon-turn maneuver are activated when the β angle is between −3 • and +3 • , and the sun's azimuth angle |α| (defined by the angle between Earth-satellite vector and Earth-"noon" vector on the orbit plane) is ≤10 • or |α ± 180 • | ≤ 10 • [20]. As for the CYS mode, the solar sensor can no longer control the yaw's attitude, and the BDS-3 MEO/IGSO satellites start to yaw with estimated hardware yaw rates in order to make the yaw angle transform 180 • .…”