Galileo HIC Instrument Packet File (IPF) Overview
Instrument Packet Files are Data Management Team (DMT) products that include engineering and/or science data packets which have been checked for quality, quantity, and continuity (QQC). During Phase II, quick-look versions of the Galileo instrument packet files (QIPF) are generated and delivered via FTP to the Galileo Science Vax Cluster (GLLSVC). Galileo Heavy Ion Counter IPFs are stored here until they are downloaded by FTP to our workstations here at Caltech for analysis.
An overview of how HIC IPFs are processed from raw binary data to finalized, Heavy Ion Counter data products (including rate plots and histograms) is available here.
Generation of an IPF
In the process of downlinking IPF data, a variety of header information is appended to the engineering and science data. The following summarizes the generation of an IPF into its final form:
- Each HIC packet sent by the Galileo spacecraft contains data plus a packet header. These packets are assembled by the Command Data Subsystem (CDS) into Virtual Channel Data Units (VCDU), which are downlinked to the ground in an encoded telemetry frame (four VCDUs per frame).
- Once telemetered to the ground, the VCDUs are decoded and disassembled by the Multimission Ground Data System (MGDS). Each packet is arranged into a Standard Formatted Data Unit (SFDU) with a header that includes an MGDS packet sequence number, Record Creation Time, Earth Received Time (ERT), Spacecraft Event Time (SCET), and Spacecraft Clock Time (SCLK).
- The Data Management Team then performs an advanced quality, quantity, and continuity (AQQC) check on the SFDU, appends an IPF header, and delivers the finished IPF to the Galileo Science VAX Cluster. The final structure of the IPF is represented below (diagram courtesy of Betsy Wilson and JPL):
Instrument Packet File Header
The following table outlines the structure of the 352-bit long IPF header.
Description of Items
Application IDs are unique to each instrument and its data packet formats. Application IDs for the Heavy Ion Counter vary according to the time format of the telemetered data as summarized by the following table:
APID Number HIC Data Type Description 2 (02h) HIC 1 HIC recorded, playback data from DMS recorder 43 (2bh) HIC 2 HIC Real-time data 22 (16h) HIC 3 HIC recorded, "real-time" data
- Start SCLK:
The spacecraft clock reading of th first packet in the file. This can also be extracted from bytes 32-37 of the tertiary SFDU packet header of the first packet (48 bits long).
- End SCLK:
The spacecraft clock value of the last packet in the file.
- Start SCET:
The Spacecraft Event Time of the first packet in the file. This value can also be extracted from bytes 38-43 of the SFDU tertiary header of the first packet (48 bits long).
- End SCET:
The Spacecraft Event Time of the last packet in the file.
- Start ERT:
The Earth Received Time of the first packet in the file. This value can also be extracted from bytes 10-15 (48 bits) of the SFDU secondary header of the first packet. This value may vary and only indicates when the data was received on Earth.
- End ERT:
The Earth Received Time of the last packet in the file.
- Packet Count:
The total number of packets in this IPF, given as an integer between 1-65536.
- File Creation Year:
The year in which this IPF was created, given as the year's last two digits.
- File Creation Day of Year:
The day of the year this file was created, ranging from 1-365.
- File Size:
The total number of bytes of this IPF, including the header information. The values for file size may be up to 16,777,216 bytes.
This document is based upon the information furnished by Betsy Wilson and the Galileo Software Interface Specification for Phase II IPFs. The original documentation from which this is based is available here.
Last Revision: Tuesday 22 April, 1997