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GALILEO

The Galileo Energetic Particles Detector

 

Galileo EPD Handbook

 

Chapter 1. Instrument Summary

 

Telemetry and Operation Changes (continued)

 

Rate Channel Telemetry

 

As discussed earlier, we must somehow compress the new rate channel data into the existing CMS telemetry structure.  This includes not only changing the order in which we read the existing accumulator channels, but also adding the two previously unused accumulators.  Both the normal CMS rate channels and the multiplexed singles rates will be affected.

 

Luckily, our existing data system telemetry software was written to allow this sort of operation in flight.  The software runs the accumulator servicing via a table stored in memory.  To change the servicing sequence, we must merely generate a different table in memory, and have the program jump there instead of using the former table address.

 

The singles rates are a little more complicated, due to the fact that different channels were sent down depending on which side of the telescope was being processed.  The present commutation scheme is:

 

S/B J/J' Format SB0 SB1 SB2 SB3 SB4 SB5 SB6
0 0 L AS BS CS DS EB1 EB2 FB2
0 1 L AS BS CS DS EB1 EB2 FB2
1 0 J AS LS JaS JcS KS JbS FB1
1 1 J' AS BS Ja'S Jc'S K'S EB2 FB1

 

The singles/background flag (S/B) toggles in value every other logical record (4/3 seconds).  If we are in either the prime or unprime modes, the format "J' " or "J" would be selected, respectively, thus resulting in a pattern of ..L,J',L,J',L.. or ..L,J,L,J,L.. .In the alternating mode, the sequence would be ..L,J,J',L,J,J'.. .Therefore, we are in the "L" format every other 4/3 seconds, or every third 4/3 seconds, depending on whether we are alternating the J/J' flag.

 

If we hope to operate the two sides simultaneously, we must insure that a singles/background format contains information on both sensors, since we will not be toggling the J/J' flag. In addition, we must also fit in the data from those two new accumulator channels.  What we propose is that there only be two singles/background formats defined: L and C (LEMMS and CMS). The C format will replace both the J and J' formats; both the J and J' table address pointers will point to the C table.  The new singles/background table will appear as follows:

 

S/B J/J' Format SB0 SB1 SB2 SB3 SB4 SB5 SB6
0 0 L AS BS CS DS EB1 EB2 FB2
0 1 L AS BS CS DS EB1 EB2 FB2
1 0 C TACs STARTs Ja'S KtS K'S Jb'S FB1
1 1 C TACs STARTs Ja'S KtS K'S Jb'S FB1

 

The two extra accumulators would be included in the telemetry stream by multiplexing four rate channels into two telemetry slots.  Rather than using the J/J' flag to do the multiplexing, however, we will use the S/B flag.  This means that every "full" CMS rate channel will be included in both the L and the C formats.  The remaining four channels will be included in only one of the formats; thus they will not be cleared each logical record as the singles/background rates are. This results in lower time resolution, but continuous coverage for these four channels.

 

Based upon their expected low count rate, we have decided to multiplex the CH5 and TH1 channels into the slot previously used only for the CH5 channel. The A singles rate, AS, previously received full coverage, despite being a singles/background rate, since it appeared in each of the L, J' and J formats.  It will now be multiplexed, via the S/B flag, with the TAC singles rate.  In effect, we are moving the CH5, TH1 and TAC channels into the S/B commutation algorithm.

 

Calibrator Operation

 

The EPD inflight calibrator circuit is used to provide test stimuli to various analog channels in both CMS and LEMMS. As presently designed, the calibrator does not exercise the TOF electronics.  In the proposed design, the TOF will be an essential channel, rather than an additional channel, so it will be added to the calibrator system.  Likewise, the Jc analog channel will now be carrying Kt information, so the Kt discriminators will also have to be calibrated.  Table 10 shows the proposed servicing routine for the calibrator system.

 

It is difficult to estimate exactly where the discriminators will be set in the new design, so the proper choice of attenuation decades is difficult. Therefore, the discriminator/calibration slot assignments are tentative (although we are assigning some channels to more than one decade where possible).

 

TABLE 10. NEW CALIBRATION CHANNEL ASSIGNMENTS

 

CMD INDEX DISC LEVEL
ATTEN=1000
F450 80 K0 12%
F451 81 K0 88%
F452 82 KT0 12%
F453 83 KT0 88%
F454 84 KT1 12%
F455 85 KT1 88%
F456 86 M0 12%
F457 87 M0 88%
F458 88 M1 12%
F459 89 M1 88%
F45A 90 JA0 12%
F45B 91 JA0 88%
F45C 92 JA0 12%
F45D 93 JA0 88%
F45E 94 M0 12%
F45F 95 M0 88%
ATTEN=100
F460 96 KT1 12%
F461 97 KT1 88%
F462 98 K2 12%
F463 99 K2 88%
F464 100 JA1 12%
F465 101 JA1 88%
F466 102 KT2 12%
F467 103 KT2 88%
F468 104 KT3 12%
F469 105 KT3 88%
F46A 106 M1 12%
F46B 107 M1 88%
F46C 108 M2 12%
F46D 109 M2 88%
F46E 110 JA1 12%
F46F 111 JA1 88%
ATTEN=10
F470 112 KT3 12%
F471 113 KT3 88%
F472 114 KT4 12%
F473 115 KT4 88%
F474 116 JA3 12%
F475 117 JA3 88%
F476 118 JA4 12%
F477 119 JA4 88%
F478 120 K5 12%
F47 121 K5 88%
F47 122 K4 12%
F47 123 K4 88%
F47 124 M2 12%
F47 125 M2 88%
F47 126 M3 12%
F47 127 M3 88%

 

 

Next: Command Changes

 

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Updated 8/23/19, Cameron Crane

QUICK FACTS

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.