Solar Wind Spectrometer

The solar wind spectrometer, designed to measure protons and electrons at the lunar surface, was part of the Apollo 15
ALSEP package left on the Moon. It consisted of seven modulated Faraday cups opened toward different, but slightly overlapping,
portions of the lunar sky. The instrument was used to observe the directional intensities of the electron (6-1480 eV) and positive
ion (30-10400 eV) components of the solar wind and magnetotail plasma that strike the surface of the Moon. The scientific objectives
of the Apollo 15 Solar Wind Spectrometer Experiment were to measure electron charge fluxes at the lunar surface, study the
interaction of the solar wind with the local magnetic field, determine if lunar limb shocks can be detected at dawn or dusk, measure
solar wind conditions, make simultaneous comparisons with Apollo 12 data, and study time-dependent phenomena.

Each Faraday cup had a circular opening, five circular grids, and a circular collector. The five circular grids were an aperture
grid, a modulator grid, a screen grid, a screen plate, and a suppressor grid. These served to apply an AC modulating field to
incoming particles and screen the modulating field from the sensitive preamplifiers. Sensor covers were over each cup to protect
against dust during the EVA's and lunar module ascent. Charged particles entered the cup and a current amplifier determined the
resultant current flow. Energy spectra of positively and negatively charged particles were obtained by applying fixed sequences of
square-wave AC retarding potentials to a modular grid and measuring the resultant changes in current. One cup was oriented vertically
and the other six cups surrounded it symmetrically facing 60 degrees off vertical. The electronics were in a temperature-controlled
container below the sensor assembly attached to a radiator. The instrument had deployed dimensions of 30.5 x 28.2 x 34.5 cm, a mass
of 5.7 kg, used 12.5 W total power, and had an average data rate of 66.2 bits/sec.

A sequence of plasma measurements was made every 28.1 seconds, consisting of 14 energy steps spaced a factor of square root of 2
apart for positive ions and 7 steps a factor of 2 apart for electrons. Flux rates of 2.5E6 to 2.5E11 particles cm^-2 sec^-1 could be
measured. A large number of internal calibrations are provided. The instrument as deployed had the east-west axis of the instrument
approximately 1 degree south of east, a 2 degree slope to the east and a 2.5 degree slope to the north. These were well within the 5
degree specifications for the instrument. The ALSEP central station was located at 26.1341 N latitude, 3.6298 E longitude. The solar
wind spectrometer was situated 4 meters north of the central station.

The instrument was deployed on 31 July 1971 and turned on with the sensor covers in place to provide background data at 19:37:10 UT.
The covers were removed by command from Earth on 2 August 1971 at 18:07:32 UT, approximately one hour after lunar module ascent. The
experiment performed well until November 5, 1971, when intermittent modulation dropping in proton channels 13 and 14 occurred. This
intermittent, though scientifically usable, behavior continued until June 30, 1972, when the intrument experienced loss of science
and engineering data. Analysis indicated that high-voltage arcing was occurring in the instrument electronics. To prevent the
additional power consumption this entailed, the instrument was put into standby mode indefinitely. Tests were done periodically but
no change in status was detected, and the solar wind spectrometer was permanently commanded off on 14 June 1974.

该太阳风光谱仪，用于测量月球表面的质子和电子，是阿波罗15号任务ALSEP（月球科学实验设备）包的一部分。该仪由七个调制法拉第杯组成，这些杯面向月球天空的不同、但略有重叠的部分。该仪器被用于观测电子（6-1480电子伏特）和正离子（30-10400电子伏特）组成的太阳风和磁尾等离子体撞击月球表面的方向性强度。阿波罗15号太阳风光谱仪实验的科学目标包括测量月球表面的电子电荷通量、研究太阳风与局部磁场的相互作用、确定月球边缘冲击是否可以在黎明或黄昏时检测到、测量太阳风条件、与阿波罗12号数据进行同时比较以及研究时间依赖现象。

每个法拉第杯都有一个圆形开口、五个圆形网格和一个圆形收集器。这五个圆形网格包括一个孔径网格、一个调制网格、一个屏幕网格、一个屏幕板和一个抑制网格。这些网格的作用是施加交流调制场于入射粒子，并屏蔽调制场，以保护敏感的前置放大器。每个杯上都有一个传感器盖，以防止在舱外活动期间和月球模块上升时尘埃侵入。带电粒子进入杯中，电流放大器确定结果电流。通过对模块网格施加固定的方波交流延迟电压序列，并测量电流的变化，获得了正负带电粒子的能量谱。一个杯垂直放置，其他六个杯以对称方式围绕它，面向垂直方向偏离60度。电子设备位于传感器组件下方、连接到散热器上的温度控制容器中。该仪器的展开尺寸为30.5 x 28.2 x 34.5厘米，质量为5.7千克，总功率为12.5瓦，平均数据速率为66.2比特/秒。

每28.1秒进行一次等离子体测量序列，包括14个能量步骤，对于正离子而言，这些步骤之间的间距是2的平方根的因子；对于电子而言，有7个步骤，间距是2的因子。可以测量2.5E6到2.5E11个粒子每平方厘米每秒的通量率。提供了大量的内部校准。部署的仪器中，仪器的东-西轴大约在东边1度南边，向东有2度的倾斜，向北有2.5度的倾斜。这些都在仪器的5度规格范围内。ALSEP中央站位于26.1341北纬，3.6298东经。太阳风光谱仪位于中央站北方4米处。

该仪器于1971年7月31日部署，并在传感器盖放置的情况下启动，以在19:37:10 UTC提供背景数据。地球命令于1971年8月2日18:07:32 UTC移除盖子，大约在月球模块上升后一个小时。实验在1971年11月5日之前表现良好，当时在质子通道13和14发生了间歇性调制下降。这种间歇性的行为，尽管在科学上可使用，但一直持续到1972年6月30日，当时仪器经历了科学和工程数据的丢失。分析表明，仪器电子设备中发生了高压电弧。为了防止由此产生的额外功耗，仪器被无限期地置于待机模式。定期进行了测试，但没有检测到状态的变化，太阳风光谱仪于1974年6月14日永久关闭。