A4.5 CDF Data Record Format Specifications

A4.5.1 Data Overview

The CDF generation software (CDFGEN) accepts experiment data in the form of EDR type records from the MDR file. Experiment data are processed through algorithms developed by Principal Investigators and output as individual science records. No synchronization between experiments is possible because of the wide variation in timing between the individual instruments; however, all records will be in SCET order within each CDF file.

Filler and spare bits in the CDF formats shall be binary zeroes unless otherwise noted.

The following subsections define CDF processing, record build-up, and the CDF data block formats for each instrument.

A4.5.2 CDF Processing

CDFGEN shall provide processing of control parameters that govern the production of Common Data File records such as start/stop time, algorithms to be used, and data types to be included. CDFGEN shall then retrieve the appropriate records from the MDR file and present them one at a time to the individual CDF algorithms. When an algorithm has an output result from its processing, CDFGEN shall take the result and produce a record as defined in the following subsections. A copy of the summary information for a given period shall be provided to each Investigator along with the CDF tape.

Spacecraft Clocks and Counters. The on-board spacecraft clock (SCLK) is a 32-bit counter that increments once every two seconds. However, the SCLK is output in the telemetry only once every 32 minor frames (1 major frame). Thus the relationship between data rate, number of minor frames (MF), time, and SCLK increment is as follows:

Data Rate
1024 bps
512
256
128

#MF
32
32
32
32

#Seconds (N)
32
64
128
256

SCLK Incr
16
32
64
128

In addition, word 63 in each minor frame contains an 8-bit counter that counts from 0-31 and is used to synchronize ground decommutation. Word 127 of each minor frame contains a 5-bit auxiliary MF counter counting from 0 to 31 and is used to identify major frame boundaries in real time as well as playback. These values are used by the Data Records System to insert a SCLK for each minor frame, if possible.

Extraction Procedure. Real time and playback data for each experiment are already merged in spacecraft event time order prior to their introduction to the CDF processors. Only one sampling rate has been defined for each experiment algorithm, independent of telemetry downlink rates. All processing shall be based upon spacecraft event time. CDFGEN shall be responsible for interpreting data presence indicators in the EDR records in order to detect missing frames of data.

• A4.5.3 File 1
• A4.5.4 File 2

Non-participants: GRU, HUS, GWE, SCE