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arXiv 1004.3610astro-ph.EP
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维斯塔黎明的动力环境

The Dynamical Environment of Dawn at Vesta

Pasquale Tricarico, Mark V. Sykes

摘要:

黎明号是美国宇航局第一个在主带中两个最大的小行星谷神星和灶神星附近运行的任务。这种双交会任务是通过使用小推力太阳能电力推进实现的。黎明号将于2011年抵达灶神星,并将在其附近运营约一年。灶神星的质量和非球形的形状,加上它的旋转周期,对主要依赖于小推力推进的航天器提出了非常有趣的挑战。灶神星高阶引力项的细节要等到黎明号抵达灶神星后才能确定,但很明显,它们对黎明号运行的影响为NASA迄今为止的任务创造了最复杂的运行环境。引力摄动引起黎明号轨道半径的振荡,发现在黎明号轨道周期和灶神星自转周期之间的1:1共振附近(大约在520 ~ 580 km轨道半径之间),航天器有可能被捕获,而在适当的轨道相位处的推力可以使这种共振捕获逃脱。在通过1:1共振后,重力扰动最终将低空操作的最小半径限制在400公里左右,以安全地防止表面撞击。最低的实际轨道是可取的,以便最大限度地提高伽玛射线和中子探测器的信噪比和空间分辨率,并通过黎明号分幅照相机和可见光红光测绘分光计提供最高的空间分辨率观测。黎明的动力学行为的范围广泛的灶神星重力模型的背景下建模。这些模型中的许多在黎明号的高海拔测绘轨道上是可以分辨的,其余的在黎明号的低海拔测绘轨道上被分辨出来,从而提供了对灶神星内部结构的深入了解。

英文摘要:

Dawn is the first NASA mission to operate in the vicinity of the two most massive asteroids in the main belt, Ceres and Vesta. This double-rendezvous mission is enabled by the use of low-thrust solar electric propulsion. Dawn will arrive at Vesta in 2011 and will operate in its vicinity for approximately one year. Vesta's mass and non-spherical shape, coupled with its rotational period, presents very interesting challenges to a spacecraft that depends principally upon low-thrust propulsion for trajectory-changing maneuvers. The details of Vesta's high-order gravitational terms will not be determined until after Dawn's arrival at Vesta, but it is clear that their effect on Dawn operations creates the most complex operational environment for a NASA mission to date. Gravitational perturbations give rise to oscillations in Dawn's orbital radius, and it is found that trapping of the spacecraft is possible near the 1:1 resonance between Dawn's orbital period and Vesta's rotational period, located approximately between 520 and 580 km orbital radius.This resonant trapping can be escaped by thrusting at the appropriate orbital phase. Having passed through the 1:1 resonance, gravitational perturbations ultimately limit the minimum radius for low-altitude operations to about 400 km,in order to safely prevent surface impact. The lowest practical orbit is desirable in order to maximize signal-to-noise and spatial resolution of the Gamma-Ray and Neutron Detector and to provide the highest spatial resolution observations by Dawn's Framing Camera and Visible InfraRed mapping spectrometer. Dawn dynamical behavior is modeled in the context of a wide range of Vesta gravity models. Many of these models are distinguishable during Dawn's High Altitude Mapping Orbit and the remainder are resolved during Dawn's Low Altitude Mapping Orbit, providing insight into Vesta's interior structure.

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