ISS And Space Environment Interactions Without Operating Plasma Contactor
ISS And Space Environment Interactions Without Operating Plasma Contactor
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不操作等离子接触器的国际空间站和空间环境相互作用
DOI：
10.2514/6.2001-401
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发表时间：
2001
期刊：
影响因子：
--
通讯作者：
C. Pankop
中科院分区：
文献类型：
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作者：
M. Carruth, Jr.;T. Schneider;M. Mccollum;M. Finckenor;R. Suggs;D. Ferguson;I. Katz;R. Mikatarian;J. Alred;C. Pankop
国际空间站（ISS）将是发射入轨的最大、功率最高的航天器。因此，其电力系统的设计与以往的系统有显著不同。太阳能电池阵将在160伏电压下运行，配电电压将为120伏。空间站结构与太阳能电池阵的负极相连，所以在适当的情况下，有可能使国际空间站的电位变得很负。国际空间站上增加了一个等离子体接触器，用于控制空间站结构相对于周围等离子体的电位。国际空间站的要求是，空间站结构相对于当地等离子体的电位正负不超过40伏。使用如此高电压的电力系统运行大型结构会有什么影响呢？在国际空间站上应用等离子体接触器可控制结构与当地等离子体之间的电位，防止不良影响。可以想象，可能会出现等离子体接触器无法工作的情况。这可能是由于电力不足、在某些组装过程中需要关闭它、在更换之前两个等离子体接触器都失去功能以及类似的情况。进行了一项研究，以了解等离子体接触器正常工作的重要性，以及在国际空间站出现不可接受的性能下降之前它可能会停止工作多长时间。在设计需求的推动下，航天器相互作用效应的细节才会被研究。国际空间站也是如此。如果允许结构处于很高的负电位，撞击的离子会溅射暴露的导体，这会使主表面性能下降，并且由于溅射材料还会产生污染。已知在相对于周围等离子体呈负电位的太阳能电池阵上会发生电弧现象。这也会产生电磁干扰和电压瞬变。国际空间站暴露在太空的大部分结构和压力舱表面是阳极氧化的铝。阳极氧化层很薄，以提供所需的太阳吸收率和发射率。在国际空间站结构可能带大量负电（占电池阵电压的很大比例）的情况下，这一层的介电强度很低，可能会发生介电击穿（电弧）。结构中电容性储存的能量可传递给电弧。这种能量传递的机制以及有多少能量可用尚未完全量化。有人提出疑问，由于太阳能电池阵从当地等离子体收集电流，是否可能产生持续的电弧。据推测，即使没有发生介电击穿，微流星体和太空碎片的撞击也可能穿透国际空间站上的薄介电层，并由于撞击产生的密集当地等离子体所提供的耦合而引发电弧。这在马歇尔航天飞行中心（MSFC）和奥本大学联合进行的实验中得到了证实。实验使用了一个带有模拟电离层等离子体的靶室、一块带偏压的阳极氧化铝板和一个1微法的电容器。然后用加速到轨道速度的75微米颗粒撞击铝板。在较高电压下电弧放电能够持续，但似乎存在一个阈值，低于该阈值则不会引发放电。大多数没有暴露的电力系统的物体在电学上会接近当地等离子体电位浮动。航天飞机、进行舱外活动的宇航员以及类似物体都是如此。国际空间站的结构可能处于很大的负电压。因此，在对接、安装外部设备箱和设备以及宇航员与空间站结构接触时，电容性储存的能量可能会转移。本研究评估了这种情况可能发生的条件以及产生的影响。此外，进行舱外活动的宇航员可能会在电弧附近。对这种情况的所有安全方面，包括充电、电弧部位的熔融颗粒以及电磁干扰都进行了评估。本文将报告这项针对4A配置的研究的全部结果，该研究计划于2000年11月完成。诸如电弧、碎片引发的电弧、持续电弧、溅射、溅射和电弧产生的污染、对接相互作用以及宇航员安全问题等相互作用都将得到讨论。
The International Space Station (ISS) will be the largest, highest power spacecraft placed in orbit. Because of this the design of the electrical power system diverged markedly from previous systems. The solar arrays will operate at 160 V and the power distribution voltage will be 120 V. The structure is grounded to the negative side of the solar arrays so under the right circumstances it is possible to drive the ISS potential very negative. A plasma contactor has been added to the ISS to provide control of the ISS structure potential relative to the ambient plasma. The ISS requirement is that the ISS structure not be greater than 40 V positive or negative of local plasma. What are the ramifications of operating large structures with such high voltage power systems? The application of a plasma contactor on ISS controls the potential between the structure and the local plasma, preventing degrading effects. It is conceivable that there can be situations where the plasma contactor might be non-functional. This might be due to lack of power, the need to turn it off during some of the build-up sequences, the loss of functionality for both plasma contactors before a replacement can be installed, similar circumstances. A study was undertaken to understand how important it is to have the contactor functioning and how long it might be off before unacceptable degradation to ISS could occur. The details of interaction effects on spacecraft have not been addressed until driven by design. This was true for ISS. If the structure is allowed to float highly negative impinging ions can sputter exposed conductors which can degrade the primary surface and also generate contamination due to the sputtered material. Arcing has been known to occur on solar arrays that float negative of the ambient plasma. This can also generate electromagnetic interference and voltage transients. Much of the ISS structure and pressure module surfaces exposed to space is anodized aluminum. The anodization thickness is very thin to provide the required solar absorptance and emittance. For conditions where ISS structure can charge negative a large percentage of the array voltage, the dielectric strength of this layer is low, and dielectric breakdown (arcing) can occur. The energy stored capacitively in the structure can be delivered to the arc. The mechanisms by which this energy is delivered and how much of the energy is available hasn't been fully quantified. Questions have been raised regarding the possibility of whether a sustained arc might result due to current collected by the solar arrays from local plasma. It was postulated that even if dielectric breakdown didn't occur, impacts due to micrometeoroids and space debris could penetrate thin layers of dielectric on ISS and initiate an arc due to the coupling provided by the dense local plasma produced by the impact. This was proven in experiments conducted jointly by MSFC and Auburn University. A target chamber with a simulated ionospheric plasma and a biased, anodized aluminum plate and a 1-microfarad capacitor was used. The plate was then impacted by 75-micron particles accelerated to orbital velocity. Arc discharges were sustained for higher voltages but a threshold appears below which no discharge was initiated. Most items without an exposed power system will float electrically near the local plasma potential. This is true of the Space Shuttle, an Astronaut on EVA, and similar items. The structure of ISS might be at a large negative voltage. Therefore, capacitively stored energy can be transferred during docking, installing external boxes and equipment and Astronaut contact with ISS structure. The circumstances of when this can happen and the resulting effects are evaluated in this study. Also, a crewmember on EVA might be in the vicinity of an arc. All safety aspects of such an encounter including charging, molten particles from the arc site and EMI have been evaluated. This paper will report on the total results of this study focussed on the 4A configuration, scheduled to be complete in November, 2000. Interactions such as arcing, debris induced arcs, sustained arcs, sputtering, contamination from sputtering and arcing, docking interactions and Astronaut safety issues will all be addressed.