确定航天器在轨双行根数(Two Line Elements,TLEs)是进行轨道预报的前提,文章以航天器双行根数为状态变量,以飞行位置和速度为测量变量,提出基于无迹卡尔曼滤波(Unscented Kalman Filter,UKF)的航天器双行根数转换方法.仿真结果表明:方法有效可行,能快速转换得到双行根数.当测量噪声位置误差为10 m时,转换得到的双行根数精度均达到了其标准格式精度;使用UKF转换的双行根数进行轨道预报,预报时长取一天,位置和速度的预报值与STK仿真值之间的误差分别在10 m和0.008 m/s以内.在大测量噪声和大初始误差条件下,UKF仍能转换得到满足精度要求的双行根数.

火箭子级这类较大外形的残骸,不同的姿态影响其受到的气动力,进而影响残骸的质心运动.在质心运动的基础上,对残骸的姿态运动进行了分析与建模,提出火箭子级残骸六自由度落点预报方法.通过数值仿真,将某次任务火箭一子级残骸的落点预报值与真实落点坐标进行了对比,结果显示:射向偏差1.2km,横向偏差0.1km,两部分偏差均在2km以内,将理论落区的搜索范围缩小了约90％,表明该预报方法可增强搜索的针对性并提高搜索效率.

In order to improve the ranging accuracy between satellites and increase the available bandwidth of systems in the simulation and tests,a design algorithm for high-accuracy fractional delay filter based on the boundary fitting Remez algorithm was proposed.The proposed algorithm used the polynomial approximation thought of Farrow structure to fit the impulse response boundary coefficients of the filter designed by Remez algorithm,and achieved fractional delay filters through the polyphase decomposition.The proposed algorithm achieved continuous impulse response boundary when high-order filters was used,while the group delay error was reduced and the accuracy was improved.The simulation results show that the proposed algorithm improves the accuracy of fractional delay filters a little,doubles the available bandwidth and reduces the number of multipliers need to be used.

To meet the needs of image stabilization system of domestic solar observatory imaging instrument,a position sensitive detector( PSD)-based electronics system design for high-precision sun sensor is proposed.Concrete measures are put forward to improve the sensitivity and reduce system noise. At presemt,level of the system noise is lower than 4 n A,and has high resolving power of 0. 3″ in center area of working scope,can cooperate with tip-tilt mirror to make up this system image stabilization system,which serve for Kua Fu and SPORT project and other solar imaging instruments which has high resolution imaging demand.

Search for Terrestrial Exo-Planet (STEP)[1] was originally proposed in 2013 by the National Space Science Center, Chinese Academy of Sciences, which is currently being under background engineering study phase in China. The STEP mission is a space astrometry telescope working at visible light wavelengths. The STEP aims at the nearby terrestrial planets detection through micro-arcsecond-level astrometry. Determination of the separation between star images on a detector with high precision is very important for astrometric exoplanets detection through the observation of star wobbles due to planets. The requirement of centroiding accuracy for STEP is 1e-5 pixel. A centroiding experiment have been carried out on a metrology testbed in open laboratory. In this paper, we present the preliminary results of determining the separations between star images. Without calibration of pixel positions and intra-pixel response, we have demonstrated that the standard deviation of differential centroiding is below 7.4e-3 pixel by the algorithm of linear corrected photon weighted means(LCPWM)[2,3]. For comparison, the photon weighted means(PWM) and Gauss fitting are also used in the data reduction. These results pave the way for the geometrical calibration and the intra-pixel quantum efficiency(QE) calibration of detector array equipment for micro-pixel accuracy centroiding.

Search for Terrestrial Exo-Planest (hereafter STEP) mission is a latest advanced research project in Chinese Strategic Pioneer Program (SPP) on Space Science. STEP aims at the nearby earth-alike planets detection, comprehensive research on the planetary system and some astrometry research with 1 micro-arcsecond precision in the space, which will get the fruitful achievements in the exo-planetary and astrometry research fields. STEP will take the Space Astrometry technique in the optical band. The FOV is 0.44 degree, based on 1.2 m primary and focus length is 50 m. The special metrology technique will be taken to reach 0.5 ∼ 1 uas astrometry precision, which will be ideal for terrestrial exo-planets detection.

PSR J0218+4232 is a millisecond pulsar (MSP) with a flux density ∼0.9 mJy at 1.4 GHz. It is very bright in the high-energy X-ray and γ-ray domains. We conducted an astrometric program using the European VLBI Network (EVN) at 1.6 GHz to measure its proper motion and parallax. A model-independent distance would also help constrain its γ-ray luminosity. We achieved a detection of signal-to-noise ratio S/N >37 for the weak pulsar in all five epochs. Using an extragalactic radio source lying 20 arcmin away from the pulsar, we estimate the pulsar's proper motion to be μαcos δ = 5.35 ± 0.05 mas yr−1 and μδ = −3.74 ± 0.12 mas yr−1, and a parallax of π = 0.16 ± 0.09 mas. The very long baseline interferometry (VLBI) proper motion has significantly improved upon the estimates from long-term pulsar timing observations. The VLBI parallax provides the first model-independent distance constraints: kpc, with a corresponding 3σ lower-limit of d = 2.3 kpc. This is the first pulsar trigonometric parallax measurement based solely on EVN observations. Using the derived distance, we believe that PSR J0218+4232 is the most energetic γ-ray MSP known to date. The luminosity based on even our 3σ lower-limit distance is high enough to pose challenges to the conventional outer gap and slot gap models.

Pulsed gamma-ray emission from millisecond pulsars (MSPs) has been detected by the sensitive Fermi space telescope, which sheds light on studies of the emission region and its mechanism. In particular, the specific patterns of radio and gamma-ray emission from PSR J0101-6422 challenge the popular pulsar models, e.g., outer gap and two-pole caustic models. Using the three-dimensional annular gap model, we have jointly simulated radio and gamma-ray light curves for three representative MSPs (PSR J0034-0534, PSR J0101-6422, and PSR J0437-4715) with distinct radio phase lags, and present the best simulated results for these MSPs, particularly for PSR J0101-6422 with complex radio and gamma-ray pulse profiles, and for PSR J0437-4715 with a radio interpulse. We have found that both the gamma-ray and radio emission originate from the annular gap region located in only one magnetic pole, and the radio emission region is not primarily lower than the gamma-ray region in most cases. In addition, the annular gap model with a small magnetic inclination angle instead of an "orthogonal rotator" can account for the MSPs' radio interpulse with a large phase separation from the main pulse. The annular gap model is a self-consistent model not only for young pulsars but also MSPs, and multi-wavelength light curves can be fundamentally explained using this model.

We demonstrate how observations of pulsars can be used to help navigate a spacecraft travelling in the solar system. We make use of archival observations of millisecond pulsars from the Parkes radio telescope in order to demonstrate the effectiveness of the method and highlight issues, such as pulsar spin irregularities, which need to be accounted for. We show that observations of four millisecond pulsars every seven days using a realistic X-ray telescope on the spacecraft throughout a journey from Earth to Mars can lead to position determinations better than ∼20km and velocity measurements with a precision of ∼0.1ms−1.

A study on the two-band observations of the millisecond pulsar J0437- 4715 is carried out based on the radio data of the Parkes Observatory of Australia and the X-ray data obtained with the ASM (All Sky Monitor) in the RXTE (Rossi X-ray Timing Explorer). For the radio observations of J0437-4715 the software TEMPO2 is applied to the calibration of the timing data of different terminal systems, thereby improving the accuracy of the timing model. By taking advantage of the all-weather observations of the ASM in the RXTE, the study of the medium- and long-term light variations of the pulsar J0437-4715 at the X-ray wavelengths is carried out by means of structure function, and it is found that this pulsar has a 620 d light period in the X-ray waveband.

Using observations of pulsars from the Parkes Pulsar Timing Array (PPTA) project we develop the first pulsar-based time-scale that has a precision comparable to the uncertainties in International Atomic Time-scales (TAI). Our ensemble of pulsars provides an Ensemble Pulsar Scale (EPS) analogous to the free atomic time-scale Echelle Atomique Libre. The EPS can be used to detect fluctuations in atomic time-scales and therefore can lead to a new realization of Terrestrial Time, TT(PPTA11). We successfully follow features known to affect the frequency of the TAI, and we find marginally significant differences between TT(PPTA11) and TT(BIPM11). We discuss the various phenomena that lead to a correlated signal in the pulsar timing residuals and therefore limit the stability of the pulsar time-scale.

AbstractAn Ensemble Pulsar Time Scale (EPT) is derived based on the Pulsar Timing Array. It is interesting to compare the EPT with the TT terrestrial time scale, and get many new realization on the pulsar time scale and the algorithm. Some future interesting applications of the EPT are described and discussed.

X-ray detector is a key element of pulsar navigation system. The requirements of the detector for X-ray pulsar navigation are analyzed, and an X-ray detector based MCP is proposed. The detector consists of photocathode, dual MCP and front-end electronics. The detector sensitivity and temporal resolution are two important parameters for the navigation. The sensitivity of detector with and without CsI reflection photocathode are calibrated with AXUV100G Si-PN standard detector, CsI reflection photocathode can increase the detector sensitivity to 5000A/W which is 10 times of bare MCP. The temporal resolutions of the detector and the electronic are measured, and the results show that the total temporal resolution is less than 20ns.

Based on the knownstability algorithm σZ of pulsar time,the method of dealing with pulsar time with gaps of long time spans has been advanced,and the result of stability has been showed with related discussion taking PARKES' observation data of the typical pulsar J1857+0943 as example.The fit process of the timing software Tempo2 in getting the minimum time residuals was briefly introduced,making the simulated data as input,the analysis and discussion about the disposal of pulsar time scales with Tempo2 has been provided.At last,the application of timing data with gap in the algorithm of ensemble pulsar time was complemented.

Pulsars have very high rotational stability,which allow them to be applied for autonomous navigation in space.Selecting a set of X-ray pulsar sources for autonomous navigation is a very important work.X-ray pulsar flux density,position and rotational parameter precision are very important to navigation.This paper describes the assembled X-ray pulsar navigation sources catalogue in detail,X-ray pulsar can be grouped in three different families according to the powering source:accretion-powered pulsars(APSRs),rotation-powered pulsars(RPSRs) and anomalous X-ray pulsars(AXPs).By analyzing their characteristics,APSRs and AXPs are not suitable candidates. RPSRs possess the most advantageous characteristics for navigation.We gather all RPSRs into one collective set.Totally,34 RPSRs have been detected with the X-ray pulse profiles,including 10 millisecond pulsars,which could form the basis of navigation system.In addition,32 other sources have only been detected with X-ray radiation,which may need high sensitivity X-ray detector to detect the pulse profiles.Then,we provide briefly discussion on the RPSRs,including their properties at radio and X-ray band,which allows the analysis of each source for its potential as a candidate for navigation purpose.Finally,we present a set of pulsars which may be suitable for China X-ray navigation experiment in the future.

The applications of pulsar timing to several important aspects are introduced and a skeletal definition of the pulsar time scale is given. By taking advantage of the observational timing data of millisecond pulsars obtained at the Parkes Astronomical Observatory, Australia, the ensemble pulsar time based on 4 millisecond pulsars is built up, the comparison of its stability σz, with that of the atomic time is made, and finally a few of important factors which affect the ensemble pulsar time, as well as their influences on the pulsar timing accuracy and application are analyzed.

Pulsar navigation is a promising new technique for space exploration because of its autonomous and deep space capability. Since the baseline of pulsar navigation approach is to observe the X rays (0.2 similar to 20keV) emitted from pulsars, a compact high temporal resolution X-ray detector is needed. In this paper an micro-channel plate(MCP) photon counting detector sensitive to X-rays is proposed. The detection system consists of a CsI photocathode, a 50mm diameter micro-channel plate (MCP) stack, a collection anode, a preamplifier, a constant fraction discriminator(CFD) and data acquisition(DAQ). The incident X-rays photons are absorbed by CsI and converted to photoelectrons, the electrons are multiplied by MCP and collected by the anode. Anode output signal is a fast pulse which need to be amplified by preamplifier and then fed to CFD circuit and DAQ for a precise timing. The total temporal resolution(Delta T) of the entire detection system could be determined by Delta t(D), the intrinsic temporal resolution of cathode-MCP-anode, and Delta t(E) the resolution of electronic system including preamplifier and CFD. The resolution of the detection system is tested to be 18.4ns in experiment.

1 课题意义 随着卫星导航、飞行器编队等航天活动的深入开展,对星座自主时间同步和自主定轨产生了重大需求.在这种需求背景下,本课题开展星间双向时间同步方法的研究,并开展星座自主时间同步和定轨的仿真计算和分析.本课题研究成果对于发展我国卫星导航系统具有重要参考意义.

We show how pulsar observations may be used to construct a time standard that is independent of terrestrial time standards. The pulsar time scale provides a method to determine the stability of terrestrial time standards over years to decades. Here, we summarise the method, provide initial results and discuss the possibilities and limitations of our pulsar time scale.

This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy