A7.4 EDR Processing

EDRGEN shall extract science, science instrument housekeeping, and spacecraft engineering data from each minor frame of the Science Data Format. EDRGEN shall then build individual experiment data records by collecting all the minor frames of data of a given type corresponding to 8 major frames ("formats") or 256 minor frames (except 4 major frames/128 minor frames for STO). These data, combined with the time of the first minor frame in the record, the corresponding spacecraft event time, data presence indicator flags, GCF error flags, and other related parameters (reference Sections A7.1 and A7.2) are written as one experiment data record. An accumulation of summary data shall be performed and a copy of the complete summary for a given period shall be provided to the PI with the EDR tape.

A7.4.1 Spacecraft Clocks and Counters

The on-board spacecraft clock (SCLK) is a 32-bit counter that increments once every 2 seconds. When the spacecraft is telemetering science data to Earth, the SCLK is output in the telemetry once every 32 minor frames (1 major frame). Thus, for science data, the relationship between data rate, number of minor frames (MF), time, and SCLK is as follows:

Table A7-4 EDR Clocks and Counters

The engineering-only major frame consists of a pair of minor frames. When the spacecraft is telemetering engineering-only data to Earth, the SCLK is output in the telemetry once every major frame, in words 64-67 of the first, or even, minor frame. Thus, for engineering-only data, the relationship between data rate, number of minor frames (MF), time, and SCLK is as follows:

Table A7-5 Relationship between data rate, number of minor frames, time, and SCLK

In addition, Word 63 of each minor frame (science or engineering-only) contains an 8-bit counter that counts from 0-31 in the case of science data and 0-1 in the case of engineering-only data, and is used to synchronize ground decommutation. Word 127 of each of minor frame contains a 5-bit auxiliary MF counter counting 0-31 for science data and 0-1 for engineering-only data, and is used to identify major frame boundaries in real time as well as playback.

A7.4.2 Science Data Extraction Procedure

The reference to "N" seconds in points 2 and 3 below refer to the table of the previous section.

The extraction procedure is applicable to all real-time science records. All science records correspond to an N second ULS telemetry major frame. Experiment data will be extracted from the telemetry formats using SCLK count, ERT, and the minor frame counters to control the extraction process. The following criteria are to be applied to SCLK count and the minor frame counters for each telemetry minor frame, in order to extract the experiment and engineering data.

1. Start of a new major frame: If the current real-time minor frame counter is zero, the minor frame contains the SCLK count. Save this new SCLK Count and the current ERT as references. Start building a new EDR record with the current minor frame.

2. Subsequent minor frames of the same major frame: If the current real-time minor frame counter is not zero and the ERT of the current minor frame is greater than the ERT of the previous minor frame "0" by less than N seconds, then continue building the current EDR record. If the current real-time minor frame counter indicates a skip greater than one count, locate the data by the real-time minor frame counter, update the current EDR record, and flag the filler blocks.

3. Subsequent minor frames of different records: If the current real-time minor frame counter is not zero and the ERT of the current minor frame is greater than the ERT of the previous minor frame by 8N seconds (4N for STO records) or more, then flag the remainder of the current EDR record with filler and output the current EDR record. Begin updating a new EDR record with the current minor frame and flag any filler as needed.

4. Real-time minor frame counter regression: If the current non-zero real-time minor frame counter indicates a decrement, flag the remainder of the current EDR record with filler and output the EDR record. Begin updating a new EDR record with the current minor frame; flag filler data blocks as needed.

Interspersed playback data extraction is handled in similar fashion. After real-time and playback data are separated, the extraction procedure is the same as for real-time telemetry. However, the auxiliary minor frame counter is used to identify minor frame order.

Telemetry Bit Rate Change. When the telemetry bit rate changes, the current EDR record shall be closed out and completed with filler bits to maintain standard record lengths. A new EDR record shall be started with the first telemetry frame at the new bit rate. The data shall be positioned in the output record according to SCLK values, preceded by filler data if required.

Next: A7.5 Lanzerotti (LAN) Experiment

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