Download Low energy particle spectrometer for 3-axis stabilized spacecraft Yoshifumi Saito

An Introduction to Space Instrumentation,
Edited by K. Oyama and C. Z. Cheng, 193–202.
Low energy particle spectrometer for 3-axis stabilized spacecraft
Yoshifumi Saito
Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Chuo, Sagamihara, Kanagawa 252-5210, Japan
Most of the recent satellite-borne instrumentation for low energy charged particle measurement adopts tophat type electrostatic analyzers. Since the top-hat type electrostatic analyzers have wide field of view of 2π
radian with uniform transmission characteristics, they are suitable for low energy charged particle measurement
by spin-stabilized spacecraft. However, 3-axis stabilized spacecraft is favored in most of the planetary missions
due to the affinity with imaging instruments. Therefore, for the future planetary plasma observations, it is quite
important to develop lightweight, low-power consumption and compact low energy charged particle analyzers
for 3-axis stabilized spacecraft. In order to realize 3-D field of view on 3-axis stabilized spacecraft under limited
resources, ASKY-ESA (All SKY-ElectroStaitc Analyzer) was developed. ASKY-ESA consists of FOV (Field
Of View) scanning deflectors at the entrance and spherical/toroidal electrostatic deflectors inside. The FOV is
electrically scanned between +/−45 degrees around the center of the FOV, which is 45 degrees inclined from the
axis of symmetry. Since ASKY-ESA has hemi-spherical field of view, three-dimensional space is covered by two
ASKY-ESAs installed on spacecraft panels opposite to each other. ASKY-ESA is also suitable for low energy
charged particle measurement on a surface of airless heavenly bodies, for example, the Moon, Martian satellite
Phobos, and numerous small objects/asteroids.
Key words: Low energy charged particle, electrostatic analyzer, 3-axis stabilized spacecraft.
1.
Introduction to the Low Energy Particle Spec- craft can be used, it is easy to adopt option 1). However, it
trometer for 3-Axis Stabilized Spacecraft
is also true that there are some drawbacks. One of them is
1.1
Aim of the low energy particle spectrometer for 3axis stabilized spacecraft
Most of the recent satellite-borne instrumentation for low
energy charged particle measurement adopts top-hat type
electrostatic analyzers (Carlson et al., 1983; Young et al.,
1988). Since the top-hat type electrostatic analyzers have
wide field of view of 2π radian with uniform transmission
characteristics, they are suitable for low energy charged particle measurement by spin-stabilized spacecraft. However,
3-axis stabilized spacecraft is favored in most of the planetary missions due to the affinity with imaging instruments.
Therefore, for the future planetary plasma observations, it
is quite important to develop light-weight, low-power consumption and compact (requires as small area on the spacecraft as possible) low energy charged particle analyzers for
3-axis stabilized spacecraft. In order to realize 3-D field of
view on 3-axis stabilized spacecraft, there are three options
as follows: 1) using low energy particle spectrometers for
spin-stabilized spacecraft with rotation tables, 2) using multiple low energy particle spectrometers for spin-stabilized
spacecraft so that necessary angular directions are simultaneously observed, and 3) using one or two sensors that have
wide field of view. There are several examples of the option
1). CAPS on CASSINI (Young et al., 2004) uses a rotation
table that sweeps the field of view of the charged particle
analyzers with two-dimensional field of view. ASPERA3 on Mars Express (Barabash et al., 2006) and ASPERA4 on Venus Express also use rotation tables. Since welldeveloped electrostatic analyzers for spin-stabilized spacec TERRAPUB, 2013.
Copyright the limited scan speed of the mechanical rotation tables that
leads to the limited time resolution. Another drawback is
that the required power is larger than adopting option 3).
The option 2) is simple but it requires much more resources including power, mass and installation area on the
spacecraft than the other two options. The installation of
the sensors is difficult if three-dimensional space should be
covered with high angular resolution. Due to this reason,
there is no example that the option 2) is really used for covering three-dimensional field of view on a 3-axis-stabilized
spacecraft. Instead, the option 2) is planned to be used for
high time resolution measurements of low energy charged
particles on a spin-stabilized spacecraft (Saito et al., 2009).
Although the option 3) requires additional development
of the electrostatic deflectors and stepping high voltage
power supplies, it is a feasible option under limited resources. The low energy particle spectrometer for 3-axis
stabilized spacecraft described in this paper also adopts this
option 3). Most of the examples of option 3) that were developed before 2000s were for low energy charged particles
below 1 keV/q. DYMIO on MARS96 (Berthelier et al.,
1998) and FONEMA on MARS96 (Fedorov et al., 1998)
are the examples. FONEMA used hyperbolic mirror at the
entrance of the analyzer in order to cover hemi-spherical
field of view. Recently a couple of new instruments that
can be categorized into option 3) for low energy charged
particles over 1 keV/q are developed. FIPS on MESSENGER is an example that covers nearly hemi-spherical field
of view using novel electrostatic optics. PICAM on BepiColombo/MPO (Orsini et al., 2010) is a plasma camera
originally proposed by Vaisberg et al. (2005) that also can
cover hemi-spherical field of view by utilizing parabolic
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Fig. 1. An example of ASKY-ESA (MAP-PACE-ESA-S2 on Kaguya). Left hand side figure shows the outlook of the analyzer. A cross section of the
electron optics part is shown in the right hand side figure.
Fig. 2. Electrostatic potential distribution around the deflectors when +3200 V is applied to the upper (a) and lower (b) deflectors while the lower (a)
and upper (b) deflectors are grounded.
mirror at the entrance. Although it is not hemi-sphere, Ion
Mass Analyzer (IMA) that is a part of ASPERA-3 on Mars
Express (Barabash et al., 2006) and ASPERA-4 on Venus
Express can cover similar size of the solid angle. IMA has
a wide annular field of view centered by the annular 2π radian field of view of the standard top-hat type analyzer by
electrically scanning its field of view by +/−45 deg. The
latest example of option 3) is MAP-PACE on Japanese lunar
orbiter Kaguya (Saito et al., 2008a, 2010) that is described
in this paper in detail.
1.2 Principle of low energy particle spectrometer for
3-axis stabilized spacecraft
ASKY-ESA(All SKY-ElectroStaitc Analyzer) shown in
Fig. 1 is an example of low energy particle spectrometer for
3-axis stabilized spacecraft. ASKY-ESA belongs to the option 3) discussed in Subsection 1.1. It is MAP-PACE-ESAS2 on Kaguya. It consists of FOV (Field Of View) scanning
deflectors at the entrance and toroidal electrodes inside.
The FOV is electrically scanned between +/−45 degrees
around the center of the FOV, which is 45 degrees inclined
from the axis of symmetry. The three-dimensional electron
distribution function is observed with two ASKY-ESA sensors that are installed on the two panels of the spacecraft
opposite to each other. The curved upper and lower FOV
scanning deflectors are supplied with high voltages which
are swept between 0 V and +4 kV. The inner toroidal electrode is also supplied with a high voltage swept between 0
V and +3 kV simultaneously with the FOV scanning deflectors. The electrons that pass through the FOV scanning
deflectors enter into the toroidal deflectors. Only electrons
in a specific energy range can travel further down to the exit
of the toroidal deflectors. The electrons that pass through
the toroidal deflectors enter a Micro-Channel Plate (MCP)
and are intensified to detectable charge pulses. Between
the toroidal deflectors and MCP, there exists a slit and grid
supplied with a slightly negative voltage (−4.0 V) in order
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195
Fig. 3. An example of the electron trajectories when positive voltage is applied to the upper (a) and lower (b) deflectors, respectively. White lines show
the trajectories of the detected electrons. Color in the figure indicates the electrostatic potential.
to reject the secondary electrons that give spurious counts.
The charge pulses intensified by the MCP are received by a
one-dimensional circular resistive anode (Yokota and Saito,
2008). The positions where the charge pulses are detected
correspond to the incident azimuthal directions of the electrons.
2.
Instrument
2.1
Sensor, dimension, weight, favorable place to be
installed in rocket and satellite
The curved upper and lower FOV scanning deflectors of
ASKY-ESA is numerically designed so that hemi-sphere
can be covered with voltage as low as possible. In order to
prevent generating electron beams when illuminated by the
sunlight, positive voltage is applied to both upper and lower
deflectors. The shape of the curved upper and lower deflectors of MAP-PACE-ESA-S2 on Kaguya is proportional
to x 2.4 and x 2.9 , respectively, where x axis is the center of
the field of view. Figures 2(a) and (b) shows the potential
distribution around the deflectors when +3200 V is applied
to the upper/lower deflector while the lower/upper deflector is grounded. Figures 3(a) and (b) shows an example of
the electron trajectories when positive voltage is applied to
the upper/lower deflector, respectively. Figure 4 shows the
relation between Vdef /Vin and the incident angle of the electrons where Vdef is the voltage applied to the deflector and
Vin is the voltage applied to the inner sphere. The detailed
characteristics of ASKY-ESA including the design principle of the deflection system are reported by Yokota et al.
(2005).
The size of ASKY-ESA is different depending on the purpose of the analyzer. MAP-PACE-ESA-S1 that is the paired
analyzer with MAP-PACE-ESA-S2 (see Fig. 1) on Kaguya
is another example of ASKY-ESA. Although the outer size
of the analyzers ESA-S1 and ESA-S2 is the same, the gap
Fig. 4. Relation between Vdef /Vin and the incident angle of the electrons
where Vdef is the voltage applied to the deflector and Vin is the voltage
applied to the inner sphere. The data points show the deflection angle
averaged over all the azimuthal channels. The vertical line shows the
incident angle range covered by all the azimuthal channels.
between the toroidal deflectors of ESA-S1 is larger than that
of ESA-S2, the maximum energy and energy resolution of
ESA-S1 is lower than ESA-S2 while the g-factor of ESAS1 is larger than ESA-S2. Since ESA-S1 mainly observes
electrons from the Moon surface, larger geometrical factor
is necessary.
Figures 5 and 6 show other examples of ASKY-ESA:
MAP-PACE-IEA and MAP-PACE-IMA on Kaguya. IEA
and IMA are ion energy analyzer and ion energy mass an-
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Fig. 5. An example of ASKY-ESA (MAP-PACE-IEA on Kaguya).
Fig. 6. An example of ASKY-ESA (MAP-PACE-IMA on Kaguya).
alyzer, respectively. IMA consists of an energy analyzer,
which has a similar structure to the ESA shown in Fig. 1,
and an LEF (Linear Electric Field) TOF (Time Of Flight)
ion mass analyzer (McComas and Nordholt, 1990; Yokota
and Saito, 2005; Yokota et al., 2005). IEA consists only of
an energy analyzer that is the same as the energy analyzer
of IMA.
Since ASKY-ESA has hemi-spherical field of view,
three-dimensional space is covered by two ASKY-ESAs installed on spacecraft panels opposite to each other. Figure
7 shows an example of the ASKY-ESAs on a 3-axis stabilized spacecraft. ASKY-ESA is also suitable for plasma
measurements on a surface of airless heavenly bodies, for
example, the Moon, Martian satellite Phobos, and numerous small objects/asteroids. Only placing one ASKY-ESA
directly on a surface of the airless heavenly bodies, the necessary hemi-spherical field of view can be covered without
any additional rotation tables.
Tables 1 and 2 summarize the characteristics, size and
weight of the MAP-PACE electron and ion ASKY-ESA
sensors on Kaguya, respectively.
2.2 Electronics block diagram, command, timing signal from data processing unit
Figure 8 shows a functional block diagram of MAPPACE ASKY-ESA sensors on Kaguya. MAP is composed
of two subsystems MAP-PACE (Saito et al., 2008a, 2010)
and MAP-LMAG (Lunar MAGnetometer) (Shimizu et al.,
2008; Takahashi et al., 2009; Tsunakawa et al., 2010). In
order to minimize the mass and power, the control electronics for the MAP-PACE sensors and MAP-LMAG sensors
Y. SAITO: LOW ENERGY PARTICLE SPECTROMETER FOR 3-AXIS STABILIZED SPACECRAFT
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Fig. 7. An example of ASKY-ESA on a 3-axis stabilized spacecraft (Kaguya). A pair of ion ASKY-ESAs (MAP-PACE-IEA and MAP-PACE-IMA)
and a pair of electron ASKY-ESAs (MAP-PACE-ESA-S1 and MAP-PACE-ESA-S2) are on spacecraft panels opposite to each other.
Table 1. Characteristics of electron ASKY-ESA: MAP-PACE-ESA-S1 and S2 on Kaguya.
Energy range
Energy resolution
Energy sweep Step
Field of view
FOV sweep range
Angular resolution
g-factor (5◦ × 22.5◦ )
Time resolution
Analyzer type
Average radius
Gap
Eccentricity
Size
Weight
ESA-S1
6 eV–9 keV
15% (FWHM)
32
2π str.
45◦ ± 45◦ (Pol)
5◦ (Pol) × 8◦ (Az) (FWHM)
5.3 × 10−4 cm2 str keV/keV
(efficiency is not included)
1s
Toroidal analyzer
30 mm
5 mm
5 mm
170 mm × 170 mm × 249 mm
2.16 kg
are contained in one package, MAP-E (MAgnetic field and
Plasma experiment-Electronics). Detected electron/ion signals are pre-amplified and transmitted from each sensor to
MAP-E that includes a position detection circuit, TOF measurement circuit and count RAMs. MAP-E also controls
high voltage power supplies in each sensor head with analog signals. MAP-PACE sensors are controlled by a CPU
board called SI-OBC (Science Instrument-OnBoard Computer). MAP-E also consists of another CPU board called
TC-OBC (Telemetry Command-OnBoard Computer) that is
responsible for interfacing with spacecraft via a 1553B interface.
Figure 9 shows a more detailed block diagram of the
analyzer head part of MAP-PACE-ESA-S2 that includes
ESA-S2
9 eV–16 keV
10% (FWHM)
32
2π str. (<9 keV)
45◦ ± 45◦ (Pol)
5◦ (Pol) × 8◦ (Az) (FWHM)
1.2 × 10−4 cm2 str keV/keV
(efficiency is not included)
1s
Toroidal analyzer
30 mm
3 mm
5 mm
170 mm × 170 mm × 249 mm
2.16 kg
ASKY-ESA shown in Fig. 1, preamplifier and high voltage
power supply. Since circular 1-dimensional resistive anode (Yokota and Saito, 2008) is used for ESA-S2, the used
preamplifiers are two charge sensitive amplifiers (AMPTEK
A225). By comparing the charge ratio from the two terminals connected to the circular 1-dimensional resistive anode, the position of the incident charged particles can be
detected. Since several micro-seconds are necessary to detect the charge ratio, sum of the timing out signals from two
charge sensitive amplifiers is also counted as “event count”
when the pulse height is above the threshold level.
The sensor head of MAP-PACE-ESA-S2 can be controlled with high voltage control signals and two signals
“peak hold reset” and “strobe” that are used to control posi-
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Table 2. Characteristics of ion ASKY-ESA: MAP-PACE-IEA and IMA on Kaguya.
Energy range
Energy resolution
Energy sweep Step
Mass range
Mass resolution
Field of view
FOV sweep range
Angular resolution
g-factor (5◦ × 22.5◦ )
Time resolution
Analyzer type
Average radius
Gap
Size
Weight
IEA
7 eV/q–28 keV/q
5% (FWHM)
32
N.A.
N.A.
2π str. (<7 keV/q)
45◦ ± 45◦ (Pol)
5◦ (Pol) × 10◦ (Az) (FWHM)
2.1 × 10−4 (attn.: off) cm2 str keV/keV
3.8 × 10−6 (attn.: on) cm2 str keV/keV
(efficiency is not included)
1s
Spherical analyzer
55 mm
4 mm
220 mm × 400 mm × 307 mm
4.23 kg
IMA
7 eV/q–28 keV/q
5% (FWHM)
32
1–60
m/m ∼ 15
2π str. (<7 keV/q)
45◦ ± 45◦ (Pol)
5◦ (Pol) × 10◦ (Az) (FWHM)
4.5 × 10−4 cm2 str keV/keV
(efficiency is not included)
1s
Spherical analyzer
55 mm
4 mm
220 mm × 400 mm × 400 mm
6.55 kg
Fig. 8. Functional block diagram of MAP-PACE on Kaguya.
tion sensing preamplifier.
The raw bit rate of the MAP-PACE ASKY-ESA sensors
are shown in Table 3. Since the main purpose of MAPPACE-IEA is to measure solar wind ions, the necessary
angular resolution is high. The raw bit rate of ion energy
mass spectrometer MAP-PACE-IMA is much higher than
energy spectrometer due to the additional information of ion
species.
Since the telemetry rate (42 kbps) allocated to KaguyaMAP-PACE ASKY-ESA sensors was much lower than the
raw data rate, the onboard computer SI-OBC (see Fig. 8)
reduced the quantity of data in order that the data sent to
the ground would fit into the allocated telemetry rate. The
data processing for reducing the quantity of data includes
data compression, pitch angle sorting of electron data, integrating mass channels and angular sectors and selecting the
angular sampling points of the solar wind ions by tracking
solar wind direction. Arithmetic compression that is one
of the reversible data compression algorithms was used for
data compression.
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Fig. 9. Functional block diagram of ESA-S2.
Table 3. Raw bit rate of the Kaguya-MAP-PACE ASKY-ESA sensors.
Raw bit rate
Telemetry rate
2.3
ESA-S1
64 kbps (max)
(16 az * 8 pol *
32 energy * 16 bits/1 sec)
42 kbps
ESA-S2
64 kbps (max)
(16 az * 8 pol *
32 energy * 16 bits/1 sec)
42 kbps
Excellent part and disadvantages, and weak points
of the instrument
The major advantage of ASKY-ESA comparing the standard top-hat type electrostatic analyzer with +/−45 deg.
field of view scanning deflector is as follows: (1) it is easier to find the installation position on the spacecraft since
the latter analyzer has to be installed at the corner of the
spacecraft or on a extendable boom while the former analyzer can be installed on any spacecraft panels (2) it is also
possible to use ASKY-ESA on a surface of airless heavenly bodies. ASKY-ESA also has an advantage from the
viewpoint of the time resolution. While the time resolution of the standard top-hat type electrostatic analyzers for
spin-stabilized spacecraft is limited by the spin period of the
spacecraft unless multiple sensors are simultaneously used,
ASKY-ESA’s time resolution is determined by the speed of
the high voltage sweep that can be controlled by the instrument team only installing two ASKY-ESAs on either
a spin-stabilized spacecraft or 3-axis stabilized spacecraft,.
Although the counting statistics depending on the measured
ion/electron flux and the saturation of the detector limit the
actual time resolution, time resolution independent of the
spacecraft motion is a big advantage. Another advantage
is the equally weighted division of the hemi-spherical field
IEA
1 Mbps (max)
(64 az * 32 pol *
32 energy * 16 bits/1 sec)
42 kbps
IMA
16 Mbps (max)
(64 az * 32pol * 32 energy *
16 bits * 16 mass/1 sec)
42 kbps
of view. Although the standard top-hat type electrostatic
analyzers on a spin-stabilized spacecraft has much denser
angular coverage in the pole direction than the equatorial
direction with respect to the spin axis, ASKY-ESAs angular
coverage is nearly equal if the angular division in the polar
coordinate system with respect to the spin axis is equal.
In addition to the advantages shown above, there also exist some disadvantages. Since ASKY-ESA utilizes electrostatic deflectors to cover hemi-spherical FOV, the maximum
voltage of the stepper high voltage power supply limits the
maximum detectable energy. Although the FOV scanning
deflector is designed so that the deflection efficiency should
be as high as possible, about twice the maximum voltage
applied to the deflectors is the highest energy of the charged
particle when the field of view scanning range is +/−45
deg. Another disadvantage of the ASKY-ESA is the severe
requirements on the magnetic cleanliness and surface potential uniformity of the spacecraft. Since the orbit of the
electrons/ions coming from the horizontal direction to the
sensor passes close to the spacecraft body, they are easily
affected by the surface potential of the spacecraft and magnetic field around the spacecraft body. Sometimes the EMC
requirements of ASKY-ESA on the DC magnetic field are
severer than that of magnetometers. Since magnetometers
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Fig. 10. Ion populations on the dayside of the Moon. Panel (a) shows a summary of low-energy ion population on the dayside of the Moon. Panel (b) is
an omni-directional E-t spectrogram from IMA. The vertical scale is the energy of ions while the horizontal axis is time. The color of each bin depicts
the ion differential ion flux, in each energy bin at the time of observations. All the populations shown in Panel (a) can be found in Panel (b). Panels
(c) and (d) are altitude of Kaguya, magnetic field intensity and direction in the Geocentric Solar Ecliptic (GSE) polar coordinate system observed
by MAP-LMAG. Panels (e) and (f) show the solar zenith angle and latitudinal/longitudinal position of Kaguya in the Mean Earth/Polar Axis (ME)
coordinate system.
are usually separated from the spacecraft using extendable
mast or boom, magnetometer sensors can be far from the
magnetic field source on the spacecraft. However, the orbit
of the charged particle cannot be far from the spacecraft if
the ASKY-ESA is directly installed on a spacecraft panel.
Of course, if ASKY-ESA is installed at the corner of the
spacecraft, these requirements on the magnetic cleanliness
can be highly relaxed.
2.4 Results obtained so far by MAP-PACE on Kaguya
MAP-PACE on Japanese lunar orbiter Kaguya (Saito et
al., 2008a, 2010) is an example of the ASKY-ESA sensors.
MAP-PACE made observations of low energy charged particles around the Moon. Kaguya was inserted into a circular
lunar polar orbit of 100 km altitude and continued observation for nearly 1.5 years until it impacted the Moon on 10
June 2009. During the last 5 months, the orbit was lowered
to ∼50 km-altitude, and some orbits had further lower perilune altitude of ∼10 km. Besides the solar wind, MAPPACE-IMA (anti-moon looking ion analyzer) found four
clearly distinguishable ion populations on the dayside of the
Moon (see Fig. 10). 1) Solar wind protons backscattered at
the lunar surface (Saito et al., 2008b), 2) solar wind protons
reflected by magnetic anomalies on the lunar surface, 3) reflected/backscattered protons picked-up by the solar wind,
and 4) ions originating from the lunar surface/lunar exosphere (Yokota et al., 2009; Tanaka et al., 2009; Saito et
al., 2010).
Using low altitude data, MAP-PACE revealed the plasma
structure over lunar magnetic anomalies on the dayside of
the Moon. At ∼25 km altitude over magnetic anomalies
on the Moon, deceleration of the solar wind ions, acceleration of the solar wind electrons parallel to the magnetic
field, and heating of the ions reflected by magnetic anomalies were simultaneously observed. Deceleration of the solar wind ions was observed for both two major solar wind
ion compositions: protons and alpha particles. Deceleration of the solar wind had the same E/q (E: deceleration energy, q: charge) for both protons and alpha particles.
In addition, the acceleration energy of the electrons was almost the same as the deceleration energy of the ions. It
indicates the existence of anti-moonward electric field over
the magnetic anomaly above the altitude of Kaguya. On the
other hand, the reflected ions had lower energy than the incident solar wind ions. Since the kinetic energy of the ions
magnetically reflected by magnetic anomalies on the lunar
surface will not change, it suggests the existence of an additional non-adiabatic dissipative interaction between solar
wind ions and lunar magnetic anomalies below Kaguya.
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3.
Toward Future Improvements
3.1 Which part should be improved?
The MAP-PACE sensors on Kaguya that is an example of
the ASKY-ESA have several points that should be improved
for the future usage of the similar kind of the analyzers.
1) Although 1-dimensional circular resistive anode was
used for MAP-PACE sensors, it should be replaced by
delay-line anode (Saito et al., 2006) or discrete anode with
ASIC (Saito et al., 2009) that have much faster data processing speed. Besides the data processing speed, the resistive anode used for MAP-PACE had characteristics that
the position detection resolution was worse at the edge of
the anode than at the center of the anode. This lead to wide
blind angle around the edge of the anode.
2) The poles to support the spherical grid at the entrance
of the analyzer (see Figs. 1, 5 and 6) should be made as thin
as possible in order to minimize the blockage of the field of
view.
3) The field of view scanning deflectors of MAP-PACE
were made of aluminum alloy with mirror finished surface
in order to reflect back the incident solar UV. However,
the mirror finished aluminum alloy surface also scatters
incident charged particles with high efficiency. Since these
scattered particles can be noise counts, the deflectors should
be serrated and blackened in order to reduce the scattering.
3.2 Unsolved scientific subjects, and necessary improvement of the instruments
Since ASKY-ESA deflects the incident angular direction
of low energy charged particles, higher voltage is required
when charged particles with higher energy should be observed. Although the efficiency of the deflection depends
on the design of the field of view scanning deflectors, it is
not possible to deflect the incident particles of all the energy range covered by the spherical/toroidal electro-static
analyzer when the same high voltage level upper limit is applied. In case of the MAP-PACE-ESA-S2 on Kaguya spacecraft, the maximum energy that could cover 3-dimensional
field of view was 9 keV, while that of MAP-PACE-IEA
and MAP-PACE-IMA was 7 keV/q. Since the pickup ions
around the Moon sometimes have much higher energy than
this maximum energy, some of the phenomena related with
pick-up acceleration could not be resolved by MAP-PACE
observations. Development of new optics to cover hemispherical field of view or further improvement of the angular scanning deflector and high voltage power supply is
necessary to resolve this problem.
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Y. Saito (e-mail: [email protected])