> ## Documentation Index > Fetch the complete documentation index at: https://docs.valar.space/llms.txt > Use this file to discover all available pages before exploring further. # Spacecraft Schedule File (SSF) > Read, validate, and exchange flat KVN-encoded spacecraft activity schedules covering ground passes, eclipses, apsides, node crossings, and SAA transits > For the complete documentation index, see [llms.txt](/llms.txt). The Spacecraft Schedule File (SSF) is a flat ASCII text format that lists every operationally relevant activity for a spacecraft over a chosen window — ground station passes, eclipse entries and exits, apsis crossings, node crossings, and South Atlantic Anomaly (SAA) transits — in a single chronologically sorted document. The format is derived from the CCSDS 902.1 Simple Schedule data model and uses Keyword-Value Notation (KVN) so the file is readable by humans and trivially parsed by downstream tooling. VALAR emits SSF files from the **Export Schedule** dialog on the [Burn Plan Timeline](/features/burn-plan) and the passes timeline. ## Key Components An SSF file is composed of three KVN blocks separated by blank lines: * **Header Block**: format version, free-form comments, generation timestamp, originator * **Schedule Metadata Block**: spacecraft identifier and the inclusive UTC window the schedule covers * **Activity Blocks**: one block per activity, sorted ascending by start epoch, each containing the activity type, start and (when applicable) stop epochs, and any type-specific metadata keywords ## Header Block The Header Block opens the file and identifies the document and its origin. | Keyword | Description | Example | | - | - | - | | **CCSDS\_SSF\_VERS** | The format version. Always `1.0` for VALAR-emitted files. | `1.0` | | **COMMENT** | Optional free-form comment lines. Multiple `COMMENT` lines may appear. | `Generated for operations handover` | | **CREATION\_DATE** | UTC timestamp at which the file was generated, in ISO-8601 format. | `2026-04-13T08:00:00.000Z` | | **ORIGINATOR** | The system or organization that produced the file. Always `VALAR` for VALAR-emitted files. | `VALAR` | VALAR also writes operational `COMMENT` lines that record how a schedule was produced. When a spacecraft's orbital events were computed from a lower-accuracy public [TLE](/file-formats/tle) (see [Orbit age](/features/orbit-age#degraded-level)), the file carries `COMMENT Orbital events derived from public TLE - indicative timing`, so a downstream reader treats their exact timing as indicative. When no fresh orbit was available at all, the file instead carries `COMMENT Orbital events unavailable - no fresh state vector`. ## Schedule Metadata Block The Schedule Metadata Block follows the Header and frames the activities that follow with the spacecraft and time window they belong to. | Keyword | Description | Example | | - | - | - | | **SPACECRAFT\_ID** | The spacecraft this schedule belongs to. | `MATTIA` | | **SCHEDULE\_START** | Inclusive start of the schedule window in UTC ISO-8601. | `2026-04-13T00:00:00Z` | | **SCHEDULE\_STOP** | Inclusive end of the schedule window in UTC ISO-8601. | `2026-04-15T00:00:00Z` | ## Activity Blocks Each activity is its own block containing `ACTIVITY_TYPE`, `ACTIVITY_START`, an optional `ACTIVITY_STOP`, and any type-specific metadata. | Keyword | Description | | - | - | | **ACTIVITY\_TYPE** | The activity category (see [Activity Types](#activity-types) below). | | **ACTIVITY\_START** | UTC start epoch of the activity in ISO-8601. | | **ACTIVITY\_STOP** | UTC stop epoch of the activity in ISO-8601. **Optional** — see below. | | Type-specific metadata | Additional keywords that depend on `ACTIVITY_TYPE` (for example `DURATION_S` on `SAA_ENTRY`). | **Sorting invariant.** Activities appear in ascending order by their `ACTIVITY_START` epoch regardless of type. A ground pass and an eclipse entry that fall in the same minute are interleaved by start time, not grouped by category. **Optional `ACTIVITY_STOP`.** The `ACTIVITY_STOP` keyword is present for activities that have a duration (ground passes, umbra and penumbra bands, SAA transits) and is omitted for instantaneous events (apsis crossings, node crossings, and `SAA_EXIT`). When `ACTIVITY_STOP` is omitted you can treat the activity as a single-epoch marker at `ACTIVITY_START`. ## Activity Types The `ACTIVITY_TYPE` keyword takes one of exactly 11 case-sensitive values: | Type | Description | Has `ACTIVITY_STOP`? | | - | - | - | | **GROUND\_PASS** | Ground station visibility pass (AOS to LOS). | Yes | | **PENUMBRA\_ENTRY** | Spacecraft enters Earth's penumbra (partial shadow). | Yes | | **UMBRA\_ENTRY** | Spacecraft enters Earth's umbra (full shadow). | Yes | | **UMBRA\_EXIT** | Spacecraft exits Earth's umbra. | Yes | | **PENUMBRA\_EXIT** | Spacecraft exits Earth's penumbra. | Yes | | **SAA\_ENTRY** | Spacecraft enters the South Atlantic Anomaly. Carries the band transit duration as the `DURATION_S` metadata keyword and a synthesized `ACTIVITY_STOP`. | Yes | | **SAA\_EXIT** | Spacecraft exits the South Atlantic Anomaly. Point event; carries no metadata. The transit duration is recorded on the paired `SAA_ENTRY` activity. | No | | **PERIAPSIS** | Spacecraft reaches closest approach to Earth. | No | | **APOAPSIS** | Spacecraft reaches farthest point from Earth. | No | | **ASCENDING\_NODE** | Spacecraft crosses the equatorial plane heading north. | No | | **DESCENDING\_NODE** | Spacecraft crosses the equatorial plane heading south. | No | ## KVN Encoding SSF uses a fixed Keyword-Value Notation: * Each keyword occupies a 24-character left-justified column followed by `= ` and the value. * Values are plain ASCII text encoded as UTF-8. There is no quoting or escaping. * Blocks are separated by a single blank line. * Within an activity block, type-specific metadata keywords appear in alphabetical order after `ACTIVITY_START` and `ACTIVITY_STOP`. ## Common Use Cases * **Operations scheduling**: Hand a single file to flight controllers covering every contact, eclipse, and high-radiation transit for the upcoming window. * **Automated handover**: Feed the schedule into ground-segment automation to pre-arm tracking, payload, and safe-mode logic at the right times. * **Downstream tooling**: Consume the schedule from third-party planning tools or in-house scripts using any KVN parser without bespoke schema work. Complete definition of the Simple Schedule data model is available in the [CCSDS 902.1-B-1 Simple Schedule](https://public.ccsds.org/Pubs/902x1b1.pdf) recommendation. ## Worked Example The example below shows a 2-day schedule for a single LEO spacecraft. It contains four representative activity blocks: a ground pass with an explicit stop, an umbra entry band, an instantaneous periapsis crossing, and an SAA entry carrying its `DURATION_S` metadata. ``` CCSDS_SSF_VERS = 1.0 COMMENT Generated for operations handover CREATION_DATE = 2026-04-13T08:00:00.000Z ORIGINATOR = VALAR SPACECRAFT_ID = MATTIA SCHEDULE_START = 2026-04-13T00:00:00Z SCHEDULE_STOP = 2026-04-15T00:00:00Z ACTIVITY_TYPE = GROUND_PASS ACTIVITY_START = 2026-04-13T03:42:18Z ACTIVITY_STOP = 2026-04-13T03:51:04Z GROUND_STATION_ID = SVALBARD-01 MAX_ELEVATION_DEG = 72.4 ACTIVITY_TYPE = UMBRA_ENTRY ACTIVITY_START = 2026-04-13T04:18:32Z ACTIVITY_STOP = 2026-04-13T04:53:11Z ACTIVITY_TYPE = PERIAPSIS ACTIVITY_START = 2026-04-13T05:11:47Z ACTIVITY_TYPE = SAA_ENTRY ACTIVITY_START = 2026-04-13T06:24:09Z ACTIVITY_STOP = 2026-04-13T06:32:48Z DURATION_S = 519.0 ``` ## Related Pages * [Burn Plan Timeline](/features/burn-plan): The page where the **Export Schedule** dialog produces `.ssf` files for a chosen spacecraft and window. * [OEM (Orbit Ephemeris Message)](/file-formats/oem): Time-series state vectors for the same spacecraft, complementary to a schedule. * [OPM (Orbit Parameter Message)](/file-formats/opm): Single-epoch state vector exchange. * [TDM (Tracking Data Message)](/file-formats/tdm): Raw tracking observations from ground sensors. 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