The Direct Mode Data Message (DMDM) is contained in the DMSP RTD, RDS and SDS telemetries (see dmsp). It is encoded in the telemetry as 6-bit words representing letters from the following 64-character alphabet:
@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_!"#$%&'()*+,-./0123456789:;<=>?
The same DMDM message is continually being transmitted in the telemetry until it is updated by the DMSP operational centers. Each DMDM message is composed of 184 characters; for the RTD telemetry about one DMDM character is transmitted per OLS line and thus the entire message is transmitted about every 16 seconds.
The first 92 characters of this message are complete nodal/orbital data for the sending spacecraft. The second 92 characters contain "special messages." The eight forms of these special messages are described below:
Special Message Description
--------------- -----------
1 Textual Information
2 Partial Nodal Data for Other Satellites
3 Complete Nodal Data for Another Satellite
4 Pre/Post Satellite Launch Information
5 Orbital Information for Another Satellite
6 Data Programming Code
7 Transmitter Frequency Information
8 Extended (two-card) Orbital Information
The DMDM message is processed by extracting the raw DMDM message from the telemetry using the appropriate ingest function (rtdin or rdsin), and then formatting the message using getdmdm.
dmsp, ols, ssmi, getdmdm, rtdin, rdsin.
For more information see the document called "32 appendix 50 - ICD-CWD-3004 DMDM interface control document", which has excerpts from the MARK IV Operations Instructions Manual #EX96M-2.1, or the document described as "3.15 PROGRAM DESCRIPTION - ODMLOD.PR."
Last Update: $Date: 1999/05/10 21:16:28 $