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TLE and Satellite Data
Pi-Sat depends on two satellite data sources:
- TLE data for orbital prediction
- transponder/profile data for frequency planning and display
These are separate problems and are handled separately.
Pi-Sat supports multiple TLE URLs in configuration. All configured sources are downloaded and merged into one cache.
When the same NORAD ID appears in multiple TLE sources:
- Pi-Sat compares the TLE epoch
- the newest entry wins
- older duplicates are discarded
This avoids relying on source ordering and makes multi-source TLE usage practical.
Pi-Sat writes merged TLE data to a local cache file. That cached file is what the orbital engine uses during normal runtime.
This gives the app a stable local orbital data source even when a remote TLE source is temporarily unavailable.
At service start, Pi-Sat attempts to refresh TLE data. If download fails but an existing cache is present, the app can continue using the existing cache.
Pi-Sat refreshes TLE/pass data:
- at service start
- every 6 hours
- on manual demand from the UI
The settings UI provides a force-update action for TLE data. This is useful when:
- sources were changed
- a source recovered from failure
- the operator wants an immediate reload rather than waiting for the scheduler
Transponder data is handled separately from TLE data. Pi-Sat refreshes transponder profiles for tracked satellites and stores them with the satellite profile data.
Pi-Sat refreshes transponder/profile data:
- at service start
- nightly at local midnight
- on manual demand
TLE data answers:
- where the satellite is
- when it rises and sets
- what Doppler should be
Transponder/profile data answers:
- what frequencies and modes to use
- whether the profile is RX-only or RX/TX
- how offsets map between downlink and uplink
Both are required for a usable satellite control surface, but like the rest of this project, I try to keep things separate where possible to avoid complexity.