UoSAT SPACECRAFT DATA SHEET

                        UNIVERSITY OF SURREY
                      Guildford, Surrey GU2 5XH
                 Tel: 0483-509143    FAX: 0483-34139

           WOD ON THE UOSAT-3 PACSAT COMMUNICATIONS EXPERIMENT

The PCE can conduct Whole Orbit Data surveys much like those supported by 
previous UoSAT onboard computers, but with some enhancements.  The PCE 
Housekeeping Integration Task can sample up to 3 WOD surveys simultaneously, 
and the sample rate of a survey can be any value from 1 second upward.

The PCE stores WOD and other information in an internal solid-state file 
store. WOD surveys are stored in binary files with Standard PACSAT File 
Headers (described in a separate document called PACSAT File Header 
Definition).  As indicated in that document, the <file_type> in the header of 
a UoSAT-format WOD file is 3.

WOD files in the PCE file store are named using the following convention:

wdMMDDNN

wd - indicates that the file is a whole-orbit data file.
MM - is replaced by a two digit month number, starting with 01 for January.
DD - is replaced by a two digit day of the month.
NN - is replaced by a two digit survey number, starting each day at 0.

For example, the first whole orbit data survey taken on the 3rd of February 
will be in file a file named "wd020300".

WOD files can be downloaded using the UoSAT-3 file server or received 
passively using the PACSAT Broadcast Protocol.  These procedures are described 
in two documents: PACSAT Broadcast Protocol and PACSAT Protocol: File Transfer 
Level 0.

BINARY FILE FORMAT

Once a WOD file has been downloaded and its PACSAT file header removed, the 
file body contains a WOD survey in the standard binary format defined below.  

(Data structures are described in a C-like syntax defined in the document 
PACSAT Data Specification Standards.)

All multi-byte values are stored least significant byte first.

'long' is 4 bytes
'int'  is 2 bytes
'char' is 1 byte

WOD files begin with a WOD_HEADER structure.  

WOD_HEADER {
  unsigned long start_time;
  unsigned long end_time;
  int sample_period;
  unsigned char number_of_channels;
}

The header is followed by the channel numbers, each one stored as an unsigned 
char (e.g. a single byte).  

<start_time> is the start time of the WOD survey, an unsigned 32-bit binary 
integer counting the number of seconds since Jan 1 1970.

<end_time> is the ending time of the WOD survey, time encoded as above.

<sample_period>  is the number of seconds between samples in the survey.

<number_of_channels> is an 8-bit unsigned binary integer telling how many 
channels were in the survey.

The following <number_of_channels> bytes are the channel numbers themselves.

This header is followed by the data samples from the survey.  Each data sample 
contains <number_of_channels> channel values.  The channel values are stored 
as unsigned 16-bit integers.  Within each sample the channel values are in the 
same order as specified in the WOD_HEADER.  That is, if the wod header says 
that channels 12, 13 and 22 are being sampled, each sample in the file will be 
three 16-bit integer values, the first from channel 12, the second from 
channel 13 and the third from channel 22.

For example, here is the beginning of a survey taken on the UO-14 simulator, 
where the actual telemetry values have been replaced by their channel numbers 
(e.g. reading telemetry channel 1 always returns 1).

The survey started at 0x26495e00, ended at 0x26495e78, was sampled every 
0x0001 seconds, contained 0x04 channels and those channels were channels 01 02 
03 and 04.  The first two samples from the survey are then included.

00 5E 49 26 78 5E 49 26 01 00 04 01 02 03 04 01
00 02 00 03 00 04 00 01 00 02 00 03 00 04 00