The Galileo Energetic Particles Detector
From Space Science Reviews
Space Science Reviews Article: LEMMS
The Low Energy Magnetospheric Measurements System
The LEMMS telescopes are designed to measure low to medium energy ion and electron
fluxes with wide dynamic range and high angular (<20 deg) and temporal (1/3 to 4/3 s)
resolution. As stated previously, a full 4pi coverage of the unit sphere is obtained by
the use of a stepping platform in conjunction with satellite spin.
The LEMMS detector head is a double-ended telescope containing eight heavily shielded
silicon solid state surface barrier totally depleted detectors providing measurements of
electrons from 15 keV to > 11 MeV, and ios from 22 keV to eV to ~55 MeV, in 32 rate
channels.
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Detail of the EPD LEMMS detector head. |
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Graphical summary of EPD energy and species rate channel coverage. Additional high energy resolution and detailed species identification are obtained from pulse height analysis data gathered simultaneously with the rate channel data show. |
LEMMS Channel Descriptions
Channel Species Energy Range Geometric Factor Name (MeV) (cm**2 sr) -------------------------------------------------------------------------------- A0 Z >= 1 0.022- 0.042 0.006 A1 Z >= 1 0.042- 0.065 0.006 A2 Z >= 1 0.065- 0.120 0.006 A3 Z >= 1 0.120- 0.280 0.006 A4 Z >= 1 0.280- 0.515 0.006 A5 Z >= 1 0.515- 0.825 0.006 A6 Z >= 1 0.825- 1.68 0.006 A7 Z >= 1 1.68 - 3.20 0.006 A8 Z >= 2 3.50 - 12.4 0.006 B0 Z = 1 3.20 - 10.1 0.006 B1 electrons ~1.5 - 10.5 0.006 B2 Z = 2 16.0 -100. 0.006 DC0 Z >= 1 14.5 - 33.5 0.5 DC1 Z >= 1 51. - 59. 0.5 DC2 electrons >~ 2. 0.5 DC3 electrons >~11. 0.5 E0 electrons 0.015- 0.029 0.006* E1 electrons 0.029- 0.042 0.020* E2 electrons 0.042- 0.055 0.030* E3 electrons 0.055- 0.093 0.033* F0 electrons 0.093- 0.188 0.028* F1 electrons 0.174- 0.304 0.007* F2 electrons 0.304- 0.527 0.016* F3 electrons 0.527- 0.884 0.018* AS singles all counts 0.006 in detector BS singles all counts 0.006 in detector CS singles all counts 0.5 in detector DS singles all counts 0.5 in detector EB1 background sidewise penetrators EB2 background E1E2 coincidences FB1 background Sidewise penetrators FB2 background F1F2 coincidences * Geometric factor determined from table in paper by Y. Wu, T.P. Armstrong.
The geometric factor of the collimator and magnetic optics system has been analyzed by extensive computer modeling (Wu and Armstrong, 1988). The energy dependent aperature-integrated geometry factors for detectors E1 and F1 are shown here.
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Response of the EPD LEMMS low energy electron detectors. The geometric factor, as calculated from a detailed simulation shown as a function of energy. |
A diagram of the LEMMS analog electronics is included next. The unbuffered preamp
tail-pulse output signals are sent down the polytwist wiring harness to three LEMMS analog
boards, where the signals are amplified and shaped. All signal processing in the LEMMS
channels is done in the linear domain. Comparator-like discriminator circuits assigned to
each of the eight channels fire whe pre-defined threshold levels are exceeded.
The resulting discriminator outputs are sent to the rate logic electronics, where
combinatorial logic is used to define 32 rate channels (event bins).
LEMMS data also are processed through a pulse height analyzer (PHA) that produces 13
46-channel energy spectra per major frame.
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Block diagram of LEMMS analog electronics. |
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Updated 8/23/19, Cameron Crane
QUICK FACTS
Mission Duration: Galileo was planned to have a mission duration of around 8 years, but was kept in operation for 13 years, 11 months, and 3 days, until it was destroyed in a controlled impact with Jupiter on September 21, 2003.
Destination: Galileo's destination was Jupiter and its moons, which it orbitted for 7 years, 9 months, and 13 days.