Barycentric Ephemeris

这个项目的目标是为新的太阳系星历奠定基础。在第一个资助阶段，工作重点是观测数据的识别和获取，相关力模型的改进，以及相应的软件开发。关于力模型，这项工作最初集中在月球的振动运动，以及由于单个小行星或小行星群以“质量环”的形式产生的扰动效应。计划在第一阶段结束时实施质量环。关于力模型，将在第二阶段进行更新，其中包括改进的月球振动模型（PN3）。此外，我们将研究额外质量环的意义，例如，代表海王星外天体。TCB的明确可选使用计划用于我们的星历表的未来版本，这需要引入时间尺度一致的初始值和质量。此外，与TT时间尺度的关系对于数据缩减至关重要。到目前为止，在这一步中我们采用了平山的级数展开。为了能够与其他星历表进行直接比较，这种解析方法应由时间尺度差分TT-TDB微分方程与太阳系天体运动方程的同时数值积分来代替。通过与著名的星历表（DE， INPOP， EPM）进行交叉比较，我们将继续检查星历表的准确性。另一方面，我们将利用新的可用观测（DVLBI，盖亚）。这是第一次将动力学参考系（通过天体运动实现）与运动学参考系（通过D-VLBI和盖亚对恒星和太阳系天体的观测）牢固地联系在一起。盖亚宇宙飞船（PN4）计划的VLBI观测给出了所涉及参照系之间的直接关系。在纳入任何可用的观测数据后，将重新确定有关的太阳系参数。这需要为不同的观测类型制定合适的组合策略和仔细的加权方案，并为共同调整选择一组最优参数。此外，新的星历表将支持对基本物理参数的测试。星历计算的计算量大，应采用并行计算技术来解决。受益于我们的经验，将在第二个筹资期间加强这方面的努力。在软件实施方面，我们将要求合作机构附属的高性能计算机中心提供支持。我们的新星历表在研究小组内的用户将是来自PN2、PN3、PN4和PN5项目的同事。计划与外部用户进一步合作，例如DLR的小行星和彗星组。

The goal of this project is to lay the foundations for a new solar system ephemeris. In the first funding phase, the work focused on the identification and acquisition of observational data, the improvement of relevant force models,, and on the corresponding software development. Regarding the force model, the work initially concentrated on the librational motion of the Moon as well as on perturbing effects due to individual asteroids or asteroid populations, in the form of ¿mass rings¿. The implementation of a mass ring is planned by the end of the first phase. Concerning force modeling, updates shall be implemented in the second phase, which includes an improved lunar libration model (PN3). Furthermore, we will investigate the significance of additional mass rings, representing e.g., Trans-Neptunian Objects. The explicit optional use of TCB is planned for future versions of our ephemeris, which requires the introduction of time-scale-consistent initial values and masses. Moreover, a relation with the TT time scale is essential for data reduction. So far, in this step we adopted the series expansion of Hirayama. To enable direct comparisons with other ephemerides, this analytical approach shall be replaced by simultaneous numerical integration of the differential equation for the time-scale difference TT-TDB together with the equations of motion for the solar system bodies. The check of the accuracy of our ephemeris will continue via cross-comparisons with renowned ephemerides (DE, INPOP, EPM). On the other hand, we will exploit new available observations (DVLBI, Gaia). For the first time, these allow a firm tie of the dynamical reference frame (realized by the motion of celestial bodies) w.r.t. the kinematical reference frame (via D-VLBI and Gaia observations of stars and solar system objects). A direct relation between the involved reference frames is given by planned VLBI observations of the Gaia spacecraft (PN4). After inclusion of any available observational data, a re-determination of relevant solar system parameters will be performed. This requires the development of a suitable combination strategy and careful weighting scheme for different observation types, and the selection of an optimal set of parameters for a common adjustment. In addition, the new ephemeris will support tests on fundamental physics parameters. The high computational burden of the ephemeris calculation shall be met by parallel computing techniques. Benefitting from our experiences, efforts in this direction will be intensified in the second funding period. For the software implementation we will request support from highperformance computer centers affiliated with the partner institutions. Users of our new ephemeris within the research group will be the colleagues from the projects PN2, PN3, PN4, and PN5. Further collaborations are planned with external users, such as with the asteroid and comet group at DLR.