SimTX API/Packets/PassPredictionRequest

PassPredictionRequest

Frame	ClientFrame, field 41
Member	passes
Direction	Client → server
Session	Control
Roles	ROLE_CONTROL.
Permission	None. The satellite and an observer station must be visible to the session.
Answered by	PassPredictionResponse or Error
Answers
Defined in	control.proto

PassPredictionRequest asks the server when a satellite will be above an observer's horizon within a time window. It needs the server feature passes. The observer is one of your ground stations (or a PUBLIC one) or an arbitrary position.

Definition

message PassPredictionRequest {
  int64 request_id = 1;
  bytes satellite_id = 2;
  oneof observer_site {
    bytes observer_station_id = 3;
    GeoPoint observer = 4;
  }
  int64 from_ms = 5;
  int64 to_ms = 6;             // at most 7 days after from_ms
  double min_elevation_deg = 7;
  double frequency_hz = 8;     // for max Doppler; 0 = skip
}

Fields

#	Field	Type	Description
1	request_id	int64	Nonzero; echoed in the PassPredictionResponse or Error.
2	satellite_id	bytes	16-byte UUID of the satellite.
3	observer_station_id	bytes	Member of oneof observer_site. A ground station to observe from.
4	observer	GeoPoint	Member of oneof observer_site. An arbitrary observer position.
5	from_ms	int64	Start of the window, Unix ms of simulation time.
6	to_ms	int64	End of the window, Unix ms. At most 7 days after from_ms.
7	min_elevation_deg	double	Elevation threshold for acquisition and loss of signal, degrees.
8	frequency_hz	double	Carrier frequency for max_doppler_hz, Hz. 0 skips the Doppler computation.

Behaviour

• Exactly one of observer_station_id and observer. An observer station must be a ground station that currently has a live session on that server and is PUBLIC or your own; otherwise the request is answered with Error NOT_FOUND (Unknown observer station on this server; send the observer location instead).
• The window may be at most 7 days long, between the years 1970 and 2200.
• Elevations are geometric (no refraction), on the 6,371 km sphere. See Passes for the algorithm.
• Passes that overlap the window are clipped to it, and to a deorbiting satellite's reentry. An always-visible geostationary satellite gives one window-long pass; a never-visible one gives none.
• Satellite failures are answered with Error as for EphemerisRequest.
• Heavy request.

Examples

Complete frames, including the varint length prefix.

pass_request_station_observer (client to server, 74 bytes):

49                            frame length 73
CA 02 46                      passes (PassPredictionRequest), 70 bytes
  08 16                       request_id = 22
  12 10 99 99 99 99 …         satellite_id = 99999999-8888-4777-8666-555555555555
  1A 10 11 11 11 11 …         observer_station_id = 11111111-2222-4333-8444-555555555555
  28 80 94 83 B9 97 34        from_ms = 1793000000000
  30 80 CC 9C E2 97 34        to_ms = 1793086400000
  39 00 00 00 00 00 00 24 40  min_elevation_deg = 10.0
  41 00 00 00 60 19 EF B9 41  frequency_hz = 435100000.0

pass_request_point_observer (client to server, 67 bytes):

42                              frame length 66
CA 02 3F                        passes (PassPredictionRequest), 63 bytes
  08 17                         request_id = 23
  12 10 99 99 99 99 …           satellite_id = 99999999-8888-4777-8666-555555555555
  22 1B                         observer (GeoPoint), 27 bytes
    09 00 00 00 00 00 C0 47 40  latitude_deg = 47.5
    11 00 00 00 00 00 00 33 40  longitude_deg = 19.0
    19 00 00 00 00 00 00 5E 40  altitude_meters = 120.0
  28 80 94 83 B9 97 34          from_ms = 1793000000000
  30 80 CC 9C E2 97 34          to_ms = 1793086400000

See also

• Passes
• PassPredictionResponse