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The Galileo Energetic Particles Detector


Galileo EPD Handbook


Chapter 1. Instrument Summary


Hardware Changes (continued)


Convert HV Reference Digital/Analog Conversion


The actual digital to analog conversion is performed on the new high voltage power supply. The 4 bits of data from the microprocessor are latched into a CD4052 by the clock signal generated on the motor controller board.


The 4 bits of digital information will be converted to an analog voltage by a pair of Harris 8:1 analog multiplexers, a resistor divider ladder, and an LM108-based buffer amplifier.  The 5.12 volt reference generated on the bus adapter (for the housekeeping ADC) will also be used here as the reference.


Switch High Voltage Input Power


The spacecraft ±15 volt supplies will be used as the input to the high voltage converter.  This voltage will be switched via the EPD power converter relay (K71) presently switching the ±3 volts used by the TOF.  Rather than using the "TOF ON" command to actuate the relay, however, we will use the command line presently used for "JA00 ON/OFF." This will separate the control functions of the TOF electronics and the high voltage supply, and allow us to continue using the E0 - E3 macro commands without worrying about the HV levels.  The supply will receive power through the one relay (current ratings are more than adequate).


In addition to these measures, we should install a high voltage arming connector on the exterior of the instrument.  The connector will pull down a logic signal to ground (or the 5.12 volt reference on the Harris muxs).  While this will provide additional protection for the HV supplies, it may introduce unwanted thermal leak paths through the blanket.  The placement and/or necessity of this arming connector requires further consideration.


Switch TOF Input Power


The TOF electronics power (±6 volts) will be switched through relay K71, as in the old design.  The dummy load on the ±6 volts will remain in the converter design to help maintain regulation when the TAC board is off.


The ±3 volt dummy load resistors will be removed since the EPD no longer will require significant power on the ±3 volt lines.  The only loads left on these lines will be the EME0263 hybrids on the rate logic (-3 volts) and the motor encoder assembly (+3 volts).  A 4.3 volt zenor will be connected in the power converter across each 3 volt power bus to prevent excessive switching transients from reaching these loads.


High Voltage Output Analog Monitor


The HV supply will produce an analog output voltage which is between 0 and -2.86 volts.  This voltage will be monitored via the -3 volt housekeeping multiplexer input on the calibrator board.  Since very little -3 volts is required in the new design, and the regulation is not critical, the lack of visibility on the -3 volt level should not be a problem.


Polytwist Wire Allocation


There are a number of new signals that must run through the polytwist.  Luckily, a number of spares are available to accommodate this need.  A list of the polytwist lines affected by the proposed design changes is shown in Table 9.




Polytwist Wire Run # Previous Function Previous Routing New Function New Routing Comments
115 +3V TOF [J37.46,J15.11] +15VSW
[J37.46,J93.8] Relay K71 will be controlled by a new command bit previously used by JA00.
85 -3V TOF [J37.43, J15.14 -15VSW
101 +6V TOF [J37.50,J15.13] +6V TOF [J37.50,J15.13] Relay K70 will continue to operate off the TOF ON/OFF command.
102 -6V TOF [J37.48,J15.5] -6V TOF [J37.48,J15.5]  
51 Spare (LEMMS Tel) [J42.32,P4.24] HV Ref Latch Strobe [J46.37,P93.1]  
88 150 K bias [J37.35,J15.8] 5.12 volt ref [J37.35,P93.12]  
100 Prime select [J49.46,J14.35] Prime Select unchanged Now controls only the unprime side multiplexers TAC inhibit. Supports simul. operation of prime & unprime sides.
48 Spare (GND) --- HV Ref Data 0 [J48.3,P93.6] Non P17/18 - Use P18.4 for feedthrough.
49 TOF - Box (GND) --- HV Ref Data 1 [J49.27,P93.13] Non P17/18 - Use P18.5 for feedthrough.
21 Spare (LEMMS) [J36.42/R16,J4.2] HV Ref Data 2 [J49.28,P93.4]  
2 Spare (LEMMS) [J42.32/R15,J4.2] HV Ref Data 3 [J49.30,P93.5]  
78 Spare An. Filter [J34,J14.12] Spare (unchanged}   Presently with shorting plug
79 Spare GND [J34sh,J14.31] Spare (unchanged)   Presently with shorting plug
97 CMD B [J49.38,J14.33] Prime Active line [J49.37,J14.33] Previously called TOVR AN; CMD B moved to adjacent pin on P49.39, and TOVR moved to P49.37 & connected via J49.39 to J49.38.
98 CMD C [J14.15,J49.40] CMD B' unchanged Jc' chain now used for Jb'
114 +3V TOF [J37.45,J15.1] Prime Select [J49.46,J15.1] Same as PT100, but going to the TAC as an inhibit (2 wires easier than rewiring).
86 -3V TOF [J37.44,J15.6] HV analog monitor [J43.25,P93.11]  
91 JKtm [J39.38,J15.4] TAC Event unchanged  
92 JKtm GND [J15.12] TAC Event GND unchanged
93 PUR [J15.10] START Event unchanged  
94 PUR GND [J15.3] START Event GND unchanged  
63 JB Analog Signal [J14.22,J29] KT Analog Signal unchanged Plugs into P30
64 JB Signal GND [J14.4,J29sh] KT Signal GND unchanged Plugs into P30
66 JC Analog Signal [J14.5,J30] JB' Analog Signal unchanged Plugs into P29
67 JC Signal GND [J14.24,J30sh] JB' Signal GND unchanged Plugs into P29
75 L Analog Signal [J14.8,J33] TCAL Analog Signal unchanged Plugs into P33, which now sums with TAC (P32) after C23 & R59
76 L Signal GND [J14.27,J33sh] TCAL Signal GND unchanged  
72 TOF Signal [J32,J15.2] TOF (TAC An.) Sig unchanged  
73 TOF Signal GND [J32sh,J15.9] TOF (TAC An.) GND unchanged  


Note: Twisted pairs are highlighted in grey or yellow.



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Updated 8/23/19, Cameron Crane


Manufacturer: The Galileo Spacecraft was manufactured by the Jet Propulsion Laboratory, Messerschmitt-Bölkow-Blohm, General Electric, and the Hughes Aircraft Company.

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.