This document specifies two standard message formats for use in transferring spacecraft attitude information between space agencies: the Attitude Parameter Message (APM) and the Attitude Ephemeris Message (AEM).  Such exchanges are used for:

- preflight planning for tracking or attitude estimation support;

- scheduling attitude and data processing support;

- carrying out attitude operations;

- performing attitude comparisons;

- carrying out attitude propagations and/or sensor predictions;

- testing to initialize sub-system simulators (communications, power, etc.).

This document includes sets of requirements and criteria that the message formats have been designed to meet.  For exchanges where these requirements do not capture the needs of the participating agencies, another mechanism may be selected.