================================================================================ PDS Galileo Instrument Template ================================================================================ /* Template: Instrument Template Rev: 1993-09-24 */ /* Note: Complete one template for each instrument. Identify each */ /* instrument reference by repeating the 3 lines for the */ /* INSTRUMENT_REFERENCE_INFO object. Also complete a separate */ /* REFERENCE template for each new reference submitted to PDS. */ /* Hierarchy: INSTRUMENT */ /* INSTRUMENT_INFORMATION */ /* INSTRUMENT_REFERENCE_INFO */ OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = GO INSTRUMENT_ID = EPD OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = "ENERGETIC PARTICLES DETECTOR" INSTRUMENT_TYPE = "ENERGETIC PARTICLES DETECTOR" INSTRUMENT_DESC = " The Galileo Energetic Particles Detector is fully described by Williams et al [WILLIAMSETAL1992]. INTRODUCTION Jupiter possesses the largest planetary magnetosphere in the solar system. It is the largest in spatial dimension, has the highest trapped particle energies and intensities, has the greatest compositional variety in its major particle populations, displays the largest co-rotational effects and has the largest number of moons within the magnetosphere that provide both strong sources for and losses of the observed particle populations. These characteristics, uncovered by the Pioneer and Voyager flybys demand an instrument design capable of accommodating the great range in parametric values established by these extremes. Within the Jovian magnetosphere, the energetic (>=20 keV) particle populations play an important dual role. First, they represent a major factor in determining the size, shape, and dynamics of the system. For example, observations of energetic particle intensities and corresponding energy densities show that these populations are important in (1) standing off the solar wind and thereby determining magnetopause position; (2) determining the general magnetic field configuration in the evening magnetosphere and (3) establishing the bulk of the ring current responsible for the magnetodisk configuration of the middle-Jovian magnetosphere. Secondly the energetic particles play an important diagnostic role in the determination of energization, transport, and loss processes active in the Jovian magnetosphere. In this role they also provide a remote sensing capability for identifying magnetospheric structures through finite gyroradius effects and for diagnosing remote processes through field-aligned flow, E x B drift, and magnetic drift effects. The Galileo EPD will provide major extensions to the Jovian energetic particle data base obtained from the Pioneer and Voyager flybys. For example: (1) Galileo will be placed into a highly elliptical orbit around Jupiter. The nominal two-year mission lifetime will allow both a direct measure of time variations in the Jovian magnetosphere and a significantly larger spatial sample of the system than has been possible with the previous flybys. (2) The nominal mission includes several close ( < 1000km) flybys of the Galilean satellites thereby providing the best opportunity to date to observe details of the satellite/magnetospheric interactions. (3) The EPD provides the first 4-pi steradian angular coverage for Jovian energetic particles, thereby assuring that the necessary energetic particle measurements will be obtained independent of satellite orientation and magnetic field direction. (4) The low-energy thresholds of the EPD effectively close the energy gap between plasma and energetic particle measurements that has existed in previous observations and assures that processes thought to operate in that gap will be tested by direct observation. For example, it has been suggested that the particles powering Jovian aurora are ions of energies <=100 keV/nucl, a composition energy range to be measured by Galileo instrumentation at Jupiter. EPD OVERVIEW The EPD instrument is the result of a joint effort between The Johns Hopkins University Applied Physics Laboratory (JHU/APL), The Max-Planck-Institute fur Aeronomie (MPAe) and The National Oceanic and Atmospheric Administration Space Environment Laboratory (NOAA/SEL). Proposed in 1976 with initial funds received in late 1977, the EPD was launched onboard the Galileo spacecraft on October 12, 1989. The MPAe was responsible for the detector heads and three analog circuit boards associated with those heads. The NOAA/SEL was responsible for the original time-of-flight (TOF) circuitry. The TOF circuitry employed in the upgraded TOF detector actually flown (and described in the composition measurement system, CMS, section) was the joint responsibility of MPAe and JHU/APL. The JHU/APL was responsible for all remaining electronics, the scanning motor, the data system, instrument power, structure test, instrument integration, and spacecraft integration. Calibrations were performed by JHU/APL and MPAe. The general characteristics of the EPD are listed in the following table: ----------------------------------------------------------------------- Galileo Energetic Particle Detector (EPD) characteristics ----------------------------------------------------------------------- Mass: 10.5kg Power: 6W electronics; 4W heaters Bit rate: 912bps Size: 19.5cm x 27cm x 36.1cm Two bi-directional telescopes mounted on stepper platform 4pi steradian coverage with 52 to 420 samples every 7 S/C spins (~140s) Geometric factors: 6E-03 - 5E-01 cm^2/ster, dependent on detector head Time resolution: 0.33-2.67 s dependant on rate channel Magnetic deflection, deltaE x E, and time-of-flight systems Energy coverage: (Mev/nucl) 0.02-55 Z>=1 0.025-15.5 Helium 0.012-10.7 Oxygen 0.01-13 Sulfur 0.01-15 Iron 0.015-11 Electrons 64 rate channels plus pulse height analysis ------------------------------------------------------------------------ The two bi-directional solid-state detector telescopes are the Low Energy Magnetospheric Measurement System (LEMMS) and the Composition Measurement System (CMS). These detector heads are mounted on a platform and rotated by a stepper motor contained in the main electronics box. The combination of the satellite spin and the stepper motor rotation (nominally stepping to the next position after each spacecraft spin) provides 4 pi steradian coverage of the unit sphere. The 0 degree ends of the two telescopes have a clear field of view over the unit sphere and also can be positioned behind a foreground shield/source holder for background measurements and in-flight calibrations. The 180 degree ends experience obscuration effects in motor positions 4, 5, and 6 caused by the magnetometer boom and foreground shield. The zero degree end of the LEMMS unit uses magnetic deflection to separate electrons from ions and provides, from detectors A and B, total-ion energy above ~20keV and from detectors E1, E2 and F1, F2 electron spectra above ~15keV. The 180 degree end of LEMMS uses absorbers in combination with detectors C and D to provide measurements of ions >~16Mev and electrons >~2Mev. The zero degree end of the CMS telescope employs a time-of-flight (TOF) versus total energy technique to measure elemental energy spectra above ~10keV/nucl for helium through iron. A sweeping magnet in the entrance collimator prevents electrons with energies <~256keV from entering the system. TOF start and stop pulses are generated as the incoming ions pass, respectively, through a thin entrance foil and impinge on the detector KT. Electrons released form the foil and the detector are accelerated and deflected through a series of grids and are detected by the microchannel places, MCP1 and MCP2. The time difference between the start pulse, MCP1, and the stop pulse, MCP2, is then obtained, along with the ion total energy from KT. Knowing the ion total energy and its travel time through the system (which gives its velocity), the ion mass is determined. The 180 degree end of the CMS telescope measures the ion energy loss, deltaE, as the ions pass through detectors Ja and Jb and the ion residual energy E=E(total) - deltaE, as they impact detectors Ka and Kb. The resulting deltaE and E measurement provides a measure of ion composition for energies >~200keV/nucl. The planned norman mode of EPD operation is to have both the telescopes powered and to step the stepper platform once each satellite spin. This will yield a 4-pi scan of the unit sphere approximately every 140s. Many other scanning modes are available and will be used for special circumstances. For example, during satellite encounters, the EPD will be configured to scan particular directions such as the expected direction of the magnetic flux tube, the direction of the Galilean satellite wakes as they travel through the Jovian magnetosphere, and the direction of the E x B drift paths. The following table contains the channel energy ranges and geometric factors for the detectors on the LEMMS telescope. 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 [WUARMSTRONG87]. The following table contains the channel energy ranges and geometric factors for the detectors on the CMS telescope. Channel Species Energy Range Geometric Factor Name (MeV nucl^-1) (cm**2 sr) ------------------------------------------------------------------------ TOF x E ------------------------------------------------------------------------ TP1 protons 0.08-0.22 0.007 TP2 protons 0.22-0.54 0.007 TP3 protons 0.54-1.25 0.007 TA1 alphas 0.027-0.155 0.007 TA2 alphas 0.155-1.00 0.007 TO1 medium nuclei 0.012-0.026 0.007 TO2 medium nuclei 0.026-0.051 0.007 TO3 medium nuclei 0.051-0.112 0.007 TO4 medium nuclei 0.112-0.562 0.007 TS1 intermediate 0.016-0.030 0.007 TS2 intermediate 0.030-0.062 0.007 TS3 intermediate 0.062-0.31 0.007 TH1 heavy nuclei 0.02 -0.20 0.007 TACS singles STARTS rates KtS ------------------------------------------------------------------------ Delta E x E ------------------------------------------------------------------------ CA1 alphas 0.17- 0.49 CA3 alphas 0.49- 0.68 CA4 alphas 0.68- 1.4 CM1 medium nuclei 0.16- 0.55 CM3 medium nuclei 0.55- 1.1 CM4 medium nuclei 1.1 - 2.9 CM5 medium nuclei 2.9 -10.7 CN0 intermediate 1.0 - 2.2 CN1 intermediate 2.2 -11.7 CH1 heavy nuclei 0.22- 0.33 CH3 heavy nuclei 0.33- 0.67 CH4 heavy nuclei 0.67- 1.3 CH5 heavy nuclei 1.3 -15.0 JaS singles rates JbS singles rates KS singles rates END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "WILLIAMSETAL1992" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "WUARMSTRONG87" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT