Fundamental Technologies

Galileo Spacecraft Pages

Rationale for EPD LGA Format

Source: E. Roelof, May 11, 1993

Basic Angular Sampling:

Maximum resolution (14 bins) MP: 1+2 and 6 (both 2-sectored); 3, 4, and 5 (4-sectored)
Intermediate resolution (6 bins) MP: 1+2 and 6 (both un-sectored); 3+4+5 (4-sectored)
No angular resolution (1 bin) MP: 1+2+3+4+5+6 (un-sectored)

Note: These sampling schemes have un-sectored "polar caps" along the spin and anti-spin directions that cover 15% of the sphere. Solar x-rays/EUV are likely to contaminate the first motor position (MP1), but probably not MP2. Sector centers must be offset 45 degrees from planetary axis.

Rate Channels: Ions

Ion rate channels have much higher sensitivity to <1 MeV protons than the TOF proton channels. However, their angular distributions (particularly in convective flows) will be dominated by the presence of minor ions (e.g., O and S). Consequently, fine angular information is essential only at the lowest energies.

A0 (6 bins)Detector A noisy, so it is risky to assign maximum angular resolution to A0.
A1-2 (16 bins)Lowest energy "reliable" ion channels.  Highest angular resolution essential for extracting protons at energies below TP1 from convective distributions, because proton flows can differ from minor ion flows extrapolated from  TO1-2 and TS1-2.
A3-6 (6 bins)Partial angular coverage to facilitate cross-calibration with TP1-3. Overlaps TP1-3 and mixes ions covered by TA1-2, TO1-3, TS1-2. Because of low secondary electron production efficiencies in TP1 (<20%) through TP3 (1%), these rate channels will have higher count rates, but will be a mixture of protons and heavies.
A7 (1 bin)Proton response 1.68-3.20 MeV, but also contains CNO and S (covered by TO3-4 and TS2 channels).
A8 (1 bin)Minor ions (Z2) 3.5-12.4 MeV total energy.
B0 (6 bins)Highest energy 2-parameter protons (3.2-10 MeV). Unlike TP3, efficiency is known and much higher (100%). Aside from Jovian protons, anisotropy may be very important in analyzing solar/interplanetary protons entering Jovian magnetotail, thus indicating topology of open field lines.
B1 (1 bin)Highest energy 2-parameter alphas (4.0-25 MeV/nuc)
DC0-1 (1 bin)Highest energy ions (14.5-59 MeV), partially obscured 180 end, bi-directional
AS-DS (1 bin)Singles

Rate Channels: Electrons

Electron dynamics are a fundamental physical puzzle at Jupiter. Ulysses measured extreme electron pitch-angle anisotropies (with a strong bi-directional component) at mid-latitudes in the dusk sector.  Their behavior in the midnight-dawn sector at low latitudes must be determined by Galileo.

E0 (16 bins)Lowest energy (15-29 keV, b=0.3) electron channel. Extreme anisotropies (unidirectional, bi-directional) possible, especially near midnight.
E1 (6 bins)Different spectra in different directions is diagnostic of different electron populations and/or source regions.
E2-3, F0-1
(1 bin)
Electron spectra tend to vary smoothly in any given direction.
F2 (16 bins)304-527 keV streaming may differ from 15-29 keV (E0)
F3 (6 bins)527-884 keV.  Same reason as E1.
B1 (6 bins)Highest energy (>1.5 MeV) electrons measured by unobstructed 0 end.  Stream essential to analyzing "clock" phenomena.  Anisotropy also useful for identifying open magnetotail field lines during solar electron events.
DC2-3 (1 bin)Highest energy electrons, (>2 MeV) partially obscured 180 end, bi-directional.
EB1-2, FB1-2 (1 bin) Background.

TOF Channels

"Pure" ion anisotropies offer the best diagnostic of convection. Essential for removing minor ion contributions to rate channels in order to estimate proton contribution. Necessary for estimating densities and temperatures of CNO and S. Helium important as solar wind source tracer. The general approach is to have the best (16 bins) angular resolution at lowest energy for species and next best (6 bins) for next higher energy channel. This gives 20 measurements to determine flow velocity, temperature, and field-aligned anisotropy (in convective frame).

TP1 (16 bins) Protons (efficiency <20%)
TP2 (6 bins) Protons (efficiency low; needs cross-calibration with ion rates)
TP3 (6 bins) Low rates due to low electron production efficiency for start (0.54-1.25 MeV)
TA1 (16 bins) Alphas for solar wind source strength estimate
TA2 (6 bins)  
TO1 (16 bins) CNO
TO2-3 (6 bins)  
TO4 (1 bin) Directional information least important for this highest energy CNO channel
TS1 (16 bins) Intermediate nuclei (Na, S)
TS2 (6 bins)  
TS3 (1 bin)  
TH1 (1 bin) Iron (20-200 keV/nuc). Rates too low for pitch angle dynamics.
TACS, KTS (6 bins) Singles (angular information for instrument diagnostics)
STARTS (16 bins) Start singles (angular information for instrument diagnostics)

Figures

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Updated 5/27/04, T. Hunt-Ward
tizby@ftecs.com