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The Galileo Energetic Particles Detector


Galileo EPD Handbook


Chapter 2. EPD Software


EPD SBAND Mission Software Requirements (continued)

Source: S. Jaskulek, various dates


CDS-Produced EPD Telemetry Record (continued)





Figure 3. EPD3 RRCC Mode Packet Header


Field Name Data Offset Field Size Content/Description
Time Include Flag 0 1 +1, always
APID 1 7 =1A hex
Packet Size 8 9 =76, 152, or 228
Packet Sequence # 17 7 0-127
Packet Time 24 32 R-R-R-mf
EPD Minor Frame Data Packet 56 608 76-Byte EPD Record
EPD Minor Frame Data Packet 664 608 76-Byte EPD Record
EPD Minor Frame Data Packet 1272 608 76-Byte EPD Record


Time Included - This bit indicates if the time filed contains information. For the Record Rate Change Coverage data, time is always included.


Application ID - This 7-bit field generated by the CDS for all packets, and is used to identify the source of the data.


Size - This 9-bit field indicates the number of data bytes included in the packet.


Sequential Number - This 7-bit counter is incremented for each new EPD packet created.


Time - This 32-bit value will contain time reference data whenever the "Time Incl." flag is set. The format is "R-R-R-mf." This is the 24 least significant bits of the S/C RIM counter + spacecraft minor frame clock.


A more complete description of the header contents is contained in GLL-3-280, Rev. D, Appendix D.




Each rate channel bin is represented by a 9 bit number. The format of the bins in the telemetry packets is shown below:


Figure 4a. EPD2, Map1 Rate Packet Data Format


Field Name Data Offset Field Size Content/Description
Low Resolution Channels 0 1386 A0, A3, A4, A5, A6, A7, A8, E0, E2, E3, F0, F1, AS, TP3, TA1, TA2, TO3, TO4, TS2, TH1, TACS, KTS
Omni Channels 1386 288 F3, B0, B1, B2, DC0, DC1, DC2, DC3, BS, CS, DS, EB1, EB2, FB1, FB2, TS3
High Resolution Channels 1674 1530 A1, A2, E1, F2, TP1, TP2, TO1, TO2, TS1, STARTS


Figure 4b. EPD2, MAP2 Rate Packet Data Format


Field Name Data Offset Field Size Content/Description
Low Resolution Channels 0 1449 AO, A6, A7, A8, E0, E2, E3, F0, F1, F3, B0, B1, B2, BS,  EB1, FB1, TP3, TA2, TO4, TS3, TH1, TACS, KTS
Omni Channels 1449 162 DC0, DC1, DC2, DC3, AS, CS, DS, EB2, FB2
High Resolution Channels 1611 2448 A1, A2, A3, A4, A5, E1, F2, TP1, TP2, TA1, TO1, TO2, TO3, TS1, TS2, STARTS


Note: These tables were revised to match the actual CDS readout pattern (vs. what the EPD had originally requested; 2/6/96).




This area contains the information necessary to monitor the health of the instrument. All of the information in this field will be collected and formatted by the EPD and provided to the CDS for direct inclusion in the telemetry packet. There are several types of information included here (1 byte each):


  1. HV Monitor - This byte is copied from the EPD analog housekeeping subcommutated data. It represents the measured output level of the high voltage supply. The binary to engineering unit conversion is the same as is used for the subcom HV monitor value. This value is included in the S/C engineering channels as S-1673; it does not appear as part of the EPD telemetry record.
  2. Subcom Index - This byte identifies which subcom parameter is reported in the Subcom Value byte. Value will range from 0 to 91; these values correspond directly with the MOD91 subcom-based housekeeping used in the HGA and record mode software.
  3. Subcom Value - This value contains a subcommutated byte from the original EPD subcom array. A (new) command option will provide the ability to freeze the subcom on a particular parameter.
  4. Opcode - This byte contains the opcode of the last command executed by the EPD. This is the same status channel as is reported in the HGA and record mode software.
  5. CMS PHA Block Entry Pointer - This 5-bit pointer indicates where in the CMS PHA readout sequence the data was taken (see below for details). The pointer will be maintained by the EPD software and passed to the CDS.
  6. Status Bits - This is a collection of bits from the instrument:
    MSB [1] Motor Scan Error Flag
    [1] Combined Error Flag {Power Monitor Flag + Bus Adapter Parity Error Flag + Resync Flag]}
    [1] Subcom mode {0=rotating, 1=fixed} Note: This is a new PhaseII feature.
    [1] Motor Direction Flag [0=CCS, 1=CW] {sampled at the beginning of each new science record}
    [1] Motor Centerline {sampled at the end of each science record}
    LSB [3] Motor Position {sampled at the end of each science record}


When the 10 bps telemetry rate is being used, the motor will complete 3 complete cycles per science record. This provides uneven coverage to the end sectors, but this can be compensated for on the ground if the motor stepping pattern used in each science record is known.  The motor direction flag will be used by the ground processing sofware to determine if the stepping pattern is {0-5, 6-1, 0-5} or {6-1, 0-5, 6-1}.





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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.