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Pulsar time has different physical mechanisms from atomic time, and these two time-scales are complementary in terms of stability performance. The joint timekeeping of pulsar and atomic time is currently an important application direction. Our research utilizes a wavelet analysis method to perform multiscale analysis of time signals in both the time and frequency domains, and assigns corresponding weights to different frequency bands for synthesis, which solves the problem of balancing long- and short-term stability in unified weighted synthesis. In this paper, a joint time-scale APT (atomic pulsar time) is obtained by a fusion of pulsar ensemble time (EPT) and atomic time TA(NTSC) (AT) based on wavelet analysis. The results show that APT effectively integrates the stability advantages of both EPT and AT, and the short-term stability of APT at 0.4 yr is consistent with that of AT, reaching 5.6 × 10−15 as evaluated by σ z variance. The stability of APT remains consistent with EPT after 3.2 yr, and the long-term stability at 13.1 yr is close to 1.3 × 10−16, perfectly retaining the excellent long-term stability characteristics of pulsar time. The root mean square of APT's clock difference relative to TT(BIPM) is much lower than that of TA(NTSC). Moreover, we propose ways to improve the stability of APT through experimental comparisons. The results indicate that APT has the potential to serve as a reference for steering UTC(NTSC) in the future, improving the long-term timekeeping capability of local atomic time in China, thereby comprehensively improving the stability and reliability of China's time reference. [ABSTRACT FROM AUTHOR]

China will launch in the forthcoming years a sample return mission called ZhengHe, to asteroid 469219 Kamo'oalewa (provisional designation 2016HO3) and comet 133P/Elst-Pizarro. The mission will consist of an orbiter and a nano-lander. One of ZhengHe's investigations is the radio science experiment, whose main objective is the asteroid GM estimate. In this paper, we conduct full numerical simulations of the radio science experiment using the wudogs software package, developed by Wuhan University. In addition to two-way Doppler measurements, we also include one-way on-board distance measurements. A list of parameters including the spacecraft initial conditions and the global asteroid GM are solved using a weighted least-squares fit. The simulation results indicate that the GM solution is very sensitive to the ephemeris error. We need an accuracy within 2 km on the ephemeris of the asteroid to achieve a reliable estimate of GM. [ABSTRACT FROM AUTHOR]

Using orbital integrations of particles ejected from Comet Halley's passages between 1404 and 240 BC, the authors investigate possible outbursts of the Orionids (twin shower of the Eta Aquariids) that may have been observed in the Western hemisphere. In an earlier orbital integration study, the authors determined there was a high probability linking probable outbursts of the Eta Aquariid meteor shower with certain events recorded in inscriptions during the Maya Classic Period, AD 250–900. This prior examination was the first scientific inquiry of its kind into ancient meteor outbursts possibly recorded in the Western hemisphere where previously no pre-Columbian observations had existed. In the current paper, the aim is to describe orbital dynamics of rare but probable Orionid outbursts that would have occurred on or near applicable dates recorded in the Classic Maya inscriptions. Specifically, significant probable outbursts are found in AD 417 and 585 out of 30 possible target years. The driving mechanisms for outbursts in those two years are Jovian 1:6 and 1:7 mean motion resonances acting to maintain compact structures within the Orionid stream for over 1 kyr. Furthermore, an Orionid outburst in AD 585 recorded by China is confirmed. [ABSTRACT FROM AUTHOR]