Attitude Control
Attitude is controlled by the Attitude Control and Determination System (ADCS). Attitude information can be set as part of a window, or at run-time, in-orbit when there is an ADCS lease window, via the Satellite Bus API. The ADCS provides a way for the satellite to reorient itself, and report which way it is facing. Attitude information is always relative to an aperture/antenna. If none is provided then the X/S-BAND radio is assumed.
No other controls (e.g. thrusters or orbit changes) are available to users. Orbital station keeping is performed by Spire.
Setting ADCS on windows
If the user knows ahead of time what the area of interest is (e.g. tracking a point on earth or facing a fixed direction) then this information can be provided in adcs_config on the payload window. For example, to take a photo of a location on earth, the user would schedule an PAYLOAD_IPI window to have the the IPI aperture track that location:
{
"type": "PAYLOAD_IPI",
"parameters": {
"adcs_config": {
"mode": "TRACKING",
"aperture": "IPI",
"target_latitude_north": 25.5,
"target_longitude_east": -71.5
},
"user_command": { /* take photo */ }
}
}
}
The Tracking an Area Of Interest Tutorial demonstrates this.
Setting ADCS at Run-time
If the user plans to command the satellites attitude from the payload, a LEASE_ADCS window must be scheduled which allows a payload window to call the Satellite Bus API to control attitude in real-time. For example, this can be used by a user process running on a payload in-orbit that listens for ADS-B messages and directs a camera to take a photograph of the location reported within a specific ADS-B message. The location is not known at the time the window is scheduled, so the satellite must be commanded in real-time.
The Leasing ADCS for Realtime Control demonstrates this.