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The Galileo Energetic Particles Detector


Galileo EPD Handbook


Chapter 1. Instrument Summary


Telemetry and Operation Changes


Source: Stephen Jaskulek, October 2, 1987



Prime/Unprime Selection


In the proposed new design for the CMS electronics, there are enough analog processing channels to allow the unprime and prime sides to operate simultaneously.  It is not clear whether the count rates in one will overwhelm the other in the PHA, however, or whether some unforeseen interaction will cause us a problem.  We are therefore trying to allow the new design to accommodate running either one side at a time, alternating sides, or both sides simultaneously.


In the old design, only the first two functions are supported.  It is important to realize that in the proposed new design, we are no longer just multiplexing viewing directions as we were previously.  Since the two CMS sensor heads will cover different energy ranges, we will receive only part of our total CMS energy range coverage at one time unless the two sides can run simultaneously.


Simultaneous operation will require the use of a second command line (in addition to the PRIME SELECT line) to decide which set of preamps should be processed.  The design will make use of the lines PRIME SELECT and PRIME ACTIVE (previously called TOVR ANALOG) to provide this flexibility.


As defined in the flight software, the purpose of TOVR ANALOG was to indicate when all TOF logic requirements should be overridden (ignored). Therefore, the old signal TOVR ANALOG was a logic high in the prime mode or anytime the TOF electronics was off.  It was a logic low only when the system was looking at the unprime side, the TOF circuitry was on, and the command TOVR AN was not active.  This operation closely follows that of the signal PRIME SELECT, except for the requirements dealing with the TOF status and the TOVR AN command.  We will now therefore use the control signal TOVR AN to decide when the prime side signals should be processed.


If the instrument is in the prime mode, has the TOF electronics off, or has explicitly commanded the line to a logic high with a ground command via the PRIME ACTIVE command, the prime signals will go through. The unprime side electronics will still be controlled by the inverted PRIME SELECT signal:  when PRIME SELECT is a logic high (prime side), the unprime and TOF data will not be processed, and when it is a low, the unprime side and TOF data will be processed.  Under "normal" operation, only PRIME SELECT NOT or PRIME ACTIVE will be logic high, so only one side will be on. If, however, we command the instrument to the unprime side (PRIME SELECT NOT is therefore high) and then send the command PRIME ON (thus also turning on the prime side), we can operate both sides simultaneously.


In addition, the Ja and Jb detectors were previously summed into the same preamp, and run simultaneously.  The latter was possible because the detectors were small (25 mm2 each), thereby keeping the capacitive noise on the preamps down. In the new design, it is the prime side detectors that will be summed together (since the Jb detector is now on the prime side, replacing Jc).  Since these detectors are larger (50 mm2 each), the capacitive noise will be higher.  It will therefore probably be necessary to operate only one of these detectors at a time.  This limitation should be acceptable.



Continue: Rate Channel Generation 


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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.