A Revised Sensitivity Model for Cassini INMS: Results at Titan
A Revised Sensitivity Model for Cassini INMS: Results at Titan
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DOI：
10.1007/s11214-014-0133-8
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发表时间：
2015-01
影响因子：
10.3
通讯作者：
B. Teolis;H. Niemann;J. Waite;D. Gell;R. Perryman;W. Kasprzak;K. Mandt;R. Yelle;A. Lee;F. Pelletier;G. Miller;D. Young;J. Bell;B. Magee;E. Patrick;J. Grimes;G. Fletcher;V. Vuitton
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文献类型：
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作者：
B. Teolis;H. Niemann;J. Waite;D. Gell;R. Perryman;W. Kasprzak;K. Mandt;R. Yelle;A. Lee;F. Pelletier;G. Miller;D. Young;J. Bell;B. Magee;E. Patrick;J. Grimes;G. Fletcher;V. Vuitton
卡西尼号离子中性质谱仪(INMS)在卡西尼号任务上空与大约100个土卫六相遇时测量到的离子密度是中性的，离子密度比其他几个航天器系统的估计值低约2到3倍，包括姿态和关节控制系统以及导航系统。本文提出了一种新的INMS仪器灵敏度模型，该模型通过重新分析(1)中性气体通过仪器的捕获和传输，以及(2)探测器在发射前测试期间的增益降低而得到。通过修正原始校准模型对气体从仪器泄漏到太空的低估，并根据增益变化进行调整，新模型使INMS密度与其他卡西尼号系统更接近。相应地，由于INMS通风口和前室到闭合源管的影响，INMS离子密度向上修正了1.55±21%的恒定探测器灵敏度修正系数，而中性灵敏度与仪器指向方向有复杂的关系。在靶上指向的特殊情况下，中性密度向上修正了2.2±23%的恒定系数。这里给出的修正的中性和离子灵敏度适用于以前在土卫六、土卫二和土星系统其他地方发表的所有INMS结果。新的模型给出了高冲角下的可靠密度，在某些情况下超过90度，从而扩大了可用于提取INMS密度的土卫六飞行的列表。我们应用该模型从几个离星的土卫六上获得了准确的密度，这些土卫六给出了不寻常的中性密度与海拔高度的剖面，或者用原始的定标得到了不合理的高密度。
Cassini Ion Neutral Mass Spectrometer (INMS) measurements from roughly a hundred Titan encounters over the Cassini mission yield neutral and ion densities systematically lower, by factors approximately 2 to 3, than estimates from several other spacecraft systems, including the Attitude and Articulation Control System, and Navigation system. In this paper we present a new INMS instrument sensitivity model, obtained by re-analyzing (1) the capture and transmission of neutral gas through the instrument, and (2) the detector gain reduction during pre-launch testing. By correcting for an under-estimation of gas leakage out of the instrument into space by the original calibration model, and adjusting for the gain change, the new model brings INMS densities into much closer agreement with the other Cassini systems. Accordingly, the INMS ion densities are revised upward by a constant detector sensitivity correction factor of 1.55±21 %, while the neutral sensitivities have a complex instrument pointing direction dependence, due (mostly) to the effect of the INMS vent and antechamber-to-closed source tube. In the special case of on-ram pointing the neutral densities are revised upward by a constant factor of 2.2±23 %. The corrected neutral and ion sensitivities given here are applicable to all previously published INMS results at Titan, Enceladus and elsewhere in the Saturn system. The new model gives reliable densities at high ram angles, in some cases above 90 degrees, thereby expanding the list of Titan flybys from which INMS densities may be extracted. We apply the model to obtain accurate densities from several off-ram Titan flybys which gave unusual neutral density vs. altitude profiles, or unreasonably high densities, with the original calibration.