Overview - ISO 11104:2011 (Time code formats)
ISO 11104:2011 specifies standardized time code formats for use in space data and information transfer systems. Adopted from CCSDS 301.0-B-4, the standard defines a small set of recommended time codes (one unsegmented and three segmented) that use the international standard second as the fundamental unit and a defined epoch as the start point. ISO 11104:2011 covers format, field structure and identification (P‑Field and T‑Field) for interoperable time tagging in cross‑agency data interchange. It explicitly does not address timing performance (stability, precision, accuracy).
Key topics and requirements
- Standard time code types:
- CCSDS Unsegmented Time Code (CUC) - a pure binary count from an epoch
- CCSDS Day Segmented Time Code (CDS)
- CCSDS Calendar Segmented Time Code (CCS)
- CCSDS ASCII Calendar Segmented Time Code (ASCII)
- Field definitions:
- P‑Field (Time Code Preamble Field) - identifies the specific time code format (may be explicit or implicit)
- T‑Field (Time Specification Field) - carries the time value (time units and fractional units)
- Segmented vs. unsegmented:
- Unsegmented codes are single binary counts of seconds and fractions.
- Segmented codes accumulate counts in cascaded counters (modulo bases) such as days, hours, seconds, etc.
- Scope limitations:
- ISO 11104:2011 does not specify timing accuracy, stability, or precision metrics.
- Security considerations:
- The CCSDS-derived publication includes a security section discussing potential threats and the consequences of not applying appropriate time‑code security.
- Informative annexes:
- Guidance on counter ranges, rationale, glossary, and conversions (e.g., between TAI and UTC) are included as informative material.
Applications and users
Who uses ISO 11104:2011:
- Space agencies and mission operators (NASA, ESA, JAXA, etc.)
- Spacecraft avionics and telemetry engineers
- Ground systems and mission operations centers
- Standards developers and integrators working on cross‑agency data interchange
Practical applications:
- Time‑stamping telemetry, science data and event logs for spacecraft and ground systems
- Ensuring interoperability of time tags between agencies and international missions
- Defining consistent epoch and format for archived data products and collaborative analysis
- Implementing deterministic time fields in packetized telemetry and mission data formats
Related standards
- CCSDS 301.0-B-4 (Time code formats) - the CCSDS Recommended Standard upon which ISO 11104:2011 is based
- ISO/TC 20/SC 13 - the ISO technical committee/subcommittee responsible for space data standards
Keywords: ISO 11104:2011, time code formats, CCSDS, CUC, CDS, CCS, space data, epoch, time tagging, spacecraft telemetry, P‑Field, T‑Field.
