Instrument Information |
|
IDENTIFIER | urn:nasa:pds:context:instrument:suisei.esp::1.0 |
NAME |
SOLAR-WIND EXPERIMENT |
TYPE |
PARTICLE DETECTOR |
DESCRIPTION |
Instrument Overview =================== The objective of this experiment is to measure the three-dimensional velocity distributions of the solar-wind ions and electrons in the energy range from 30 eV up to 16 keV within +/- 30deg of the ecliptic plane. During the cometary encounter, the interaction of the solar wind with the cometary ionosphere will be investigated, paying particular attention to the mass loading of the solar wind by cometary ions, to the existence, location and strength of the upstream shock transition and of (possibly) backscattered particles from the shock and other,unexpected, plasma populations. Data will be collected on such solar-wind phenomena as the halo and core distributions of electrons, variations in the flow velocity, and the He++/He+ ratio in relation to solar rotation and longitude. The instrument consists of one sensor for electrons and one for positive ions. As shown in Figure 3, each sensor consists of a fan-shaped collimator, a 270deg spherical electrostatic analyzer, and a Micro-Channel Plate (MCP) detector with five discrete anodes. The collimator's field of view is 5deg in azimuth and 60deg in polar angle respectively, the latter being centered perpendicular to the spacecraft spin axis and thus in the ecliptic plane. The 270deg spherical analyzer has a better-defined response in energy-angle space than a quadrispherical analyzer. After leaving the analyzer, particles are post-accelerated by a potential of 250 V for electron and 2500 - 3500 V for ion analysis. A Z-type three-stacked MCP detector is used to obtain a saturated pulse-height distribution over a wide dynamic range of counting rates. The anodes of each MCP are split into five sections in order to provide a five-point angular distribution with a 12deg resolution in the polar direction. The output pulses from each MCP anode are amplified, shaped and accumulated in 19-bit counters. The contents of the counter are compressed into 8 bits and stored temporarily in the PAM buffer memory. The instrument's angular distribution in the azimuthal direction, obtained by the spacecraft spin, is 5.625deg within +/- 22.5deg of the solar direction and 22.5deg in the remaining spin phase. The instrument has four modes of energy scanning (Table below). In each mode the energy is scanned in steps as E(n)=30 exp (0.0066n), where E(n) is the energy of the n-th step and n=n(1), . . . . .,n(2). Details of the energy scanning, which is synchronized to the spin phase, are shown for the E1-mode in Figure 5. During each spacecraft spin four energy steps are scanned periodically in every 22.5deg interval, i.e. the step is changed every 1.40625deg around the solar direction and 5.625deg over the remaining azimuthal directions. Consequently, it takes 24 spacecraft spins in the E1-mode to cover the complete energy range in 96 steps. At high bit rate (2048 bit/s), three-dimensional velocity distributions will be obtained for both electrons and ions. These data, produced during one spin, will be transmitted in 10 PCM frames (5 s) during the next spin interval. At low bit rate (64 bit/s), two-dimensional distributions will be obtained for electrons and ions by summing the counts from each anode. The energy scanning will be carried out over 16 spin periods once every 512 s, required to transmit these data. The ESP instrument will be operated during the Halley-encounter phase as well as during the cruise and post-encounter phases, but only while Planet-A is in its high-spin-rate mode (nominally 6.3 rpm). ----------------------------------------------------------------------- Table 2. Energy scanning modes of Planet-A Solar-Wind Plasma Experiment Time for one Total no. complete Mode n(1) n(2) delta n of steps Energy range (eV) sequence* (s) ----------------------------------------------------------------------- E1 0 95 1 96 30 ~ 15800 228.6 E2 O 63 1 64 30 ~ 1920 152.4 E3 32 95 1 64 250 ~ 15800 152.4 E4 1 95 2 48 34 ~ 15800 114.3 ----------------------------------------------------------------------- n(1) = lowest step number delta n = step interval n(2) = highest step number * = times refer to high bit rate; always 512 s at low bit rate |
MODEL IDENTIFIER | |
NAIF INSTRUMENT IDENTIFIER |
not applicable |
SERIAL NUMBER |
not applicable |
REFERENCES |
Reinhard, R and B. Battrick (eds), 'Space Missions to Halley's Comet', European
Space Agency ESA SP-1066, ESA Pub Div, Moordwijk, Netherlands, 1986. 'Encounters with Comet Halley, The first results', Nature, Volume 321, No. 6067, 15 May 1986. |