The Galileo Energetic Particles Detector
Galileo EPD Handbook
Appendices
Appendix B. SEDR Files (continued)
Source: J. F. Schmidling, JPL 625-610, SIS 224-09, Phase 2 Rev., 6/21/85
4. Detailed Interface Specifications (continued)
SEDR Data Block Formats. The full complement of SEDR parameters shall be contained in two separate data blocks of SEDR parameters: 1) Interplanetary Cruise (IC) SEDR Data Block which is present on both GSOC and JPL SEDRs, and 2) Jupiter Orbital Operations (JO) SEDR Data Block which is present only on JPL SEDRs. Basically the IC sub-block contains solar system state vectors, ranges, angles, etc., between the spacecraft and earth, sun and Jupiter. The JO sub-block contains the above geometries between the spacecraft and Jupiter and the Galilean satellites.
The format and detailed contents of the IC block are presented in Table 3, while the JO block is specified in Table 4. Figures 7 through 11 provide a graphical representation of the contents of the IC block
Usage of the File
The following paragraphs provide the user with the exact definition of how to interpret the floating point quantities contained in the SEDR data block formats. These data blocks consist entirely of 32 bit floating point quantities in VAX format. The definition of this format is provided in the following figure and its supporting text. This format, of course, is automatically interpreted correctly if these word formats are read and processed by an VAX or VAX compatible computer.
| bytes → |
-------2------- |
-------1------- |
|
| bits → | 15 | 14 7 | 6 0 |
| VAX floating point word |
SIGN | EXP | FRACTION |
| FRACTION | |||
| bits → |
31 24 |
23 16 |
|
| bytes → | ------4------ | ------3------ | |
where
| SIGN | indicates the sign of the quantity represented by the floating point word. If SIGN=0, the quantity is positive. If SIGN=1, the quantity is negative. |
| CHAR | indicates the location of the binary point of the FRACTION portion of the word. This value is normalized to a decimal value of 128 such that EXP - 128 (decimal) locates the binary point to the right when positive and to the left when negative. |
| FRACTION | contains the normalized significant bits of the quantity with the high order one (1) bit hidden between bits 6 and 7. |
Although the above figure describes the 32 bit format of the VAX floating point words, it does not represent the order in which the 4 8-bit bytes of the words are output to the SEDR file. The bytes are written to the file in ascending order (1 through 4) with the following VAX bit order:
| Byte 1 → | VAX Bits 7 - 0 |
| Byte 2 → | VAX Bits 15 - 8 |
| Byte 3 → | VAX Bits 23 - 16 |
| Byte 4 → | VAX Bits 31 - 24 |
Once the sign, exponent and fraction have been evaluated, the following equation could be used to evaluate these floating point quantities:
VALUE = (1 - 2*SIGN) * FRACTION * (2 ** (EXP - 128) )
Note: All values and arithmetic operations are decimal and FRACTION must be evaluated with the hidden order bit included with the binary point located to the left of the hidden bit.
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Updated 8/23/19, Cameron Crane
QUICK FACTS
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.