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The Galileo Energetic Particles Detector


Galileo EPD Handbook


Chapter 1. Instrument Summary


Overview of Rework


Source: Stephen Jaskulek, October 2, 1987


The following is a brief listing of all the anticipated rework to the flight EPD instrument.



Data System


The data system will probably receive two additional RAM chips to help increase the amount of RAM available for patches. All the RAM on the board (16 chips) must be replaced with new TCC244 chips anyway (general JPL RAM directive). This will require two new wire runs to act as chip enable signals for the new memory devices. In addition, one wire run will be moved to an adjacent pin on the CMD B line.


Bus Adapter


If there are space and parts available, we may build a "watchdog" timer circuit on this board.


Low Voltage Power Converter


Assuming we no longer need it, the K detector bias "piggyback" board will be removed from the converter shield exterior. We will need to rewire the relay K71 so that it switches the spacecraft ±15 volt bus rather than the ±3 volt supplies.  We plan on maintaining the ±3 volt secondary windings in the converter, but we will eliminate the dummy loads used to maintain regulation on the buses when TOF power was off.  A simple 4.3 volt zenor diode circuit will be added to each output to prevent switching transients from causing excessive fluxuation on the lines. (The -3 volts is used on the rate logic timing hybrids and the +3 volts is used on the motor encoder LEDs.)


The command line going to the K70 and K71 relays (presently switching the TOF power) will be separated into two lines.  The ±6 volts will still be switched by the TOF On/Off commands.  The high voltage power will be commanded by the JA00 On/Off commands (see tables 11 and 12).


Motor Controller


Both of the RAM chips on the board must be replaced with new TCC244 chips (general JPL RAM directive). A spare 1852 output line will be utilized for strobing the high voltage reference latch; it is already wired to the board connector.




The gain on the TOF and old Jc channels will have to be adjusted via tailor points to account for the new signal levels being generated in the TOF sensor.  In addition, we will have to add a latch to the board to catch the K0 discriminator signal. This signal will replace the output "J SELECT" coming from the ROM (that line will be cut). A circuit that previously used K0 to indicate whether an event was active will be replaced by "K0 or KT0 or TAC" (this is generated on the new CMS rate logic board).


If we wish to try generating a TOF spectrum, it will probably be necessary to make additional changes to this board (perhaps a couple cuts and 8 jumpers).


LEMMS Analog Boards (3)


Other than routine discriminator tailoring, these boards should remain unchanged unless we replace the LEMMS preamplifiers.  If this is done, all the discriminators will probably have to be adjusted.


Motor Driver


No changes are anticipated on this board unless it is determined that the capacitors are aging and need replacement to maintain the design specification of 0.013 Farads total capacitance.  (Might it be desirable or possible to add additional capacitance at this time?)


TOF Analog Electronics


This circuitry will be completely replaced with new circuitry being developed and built by APL/MPAE.  Unlike the previous TOF design, this circuitry will not produce an analog output pulse unless there is a valid start/stop pair (i.e., the JKTm function is performed on the TAC board). This should eliminate the singles events from reaching the TOF log amplifiers, thus increasing the practical TOF channel rate capabilities.  The new circuitry will not product a JKTm or PUR signal, but will generate singles counts on valid TAC events and STARTS (MCP1 signals).





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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.