Satellite InferenceAI Inference in OrbitGet in touch FROM REQUEST TO ANSWER / SI-P1 PATHFINDER
Someone asks what is happening in a place on Earth. The task has to reach the satellite, the satellite has to pass over the place, the data has to become an answer, and the answer has to come down. Here a payload hosted like SI-P1 flies a real orbit for a week over the published sites of real ground networks. The scenarios show what one ground station, an inclined host, a full queue or a relay link change; tap the globe to ask about anywhere.
01 / WHERE THE TIME GOES
A radar satellite at 525 km can image the Gulf of Guinea at 15° to 45° incidence on 0.71 passes a day, and the passes come in clusters. A request made at a random moment waits 45 hours on average for the next one, and up to 5 days. More satellites carrying the payload shorten that wait; a faster computer does not.
Svalbard and Troll give a sun-synchronous satellite 24 contacts a day, never more than 1.4 hours apart. A single station at 33° south gives 4, with gaps of up to 11.5 hours. Polar stations see a polar orbit on almost every revolution, yet neither sees a 53° orbit at all.
With the polar pair, the answer computed on board lands 18 minutes after the capture, most of it the flight from the area to the next station. Raw data takes 31 minutes more even when it goes first: 1.6 GB to send down, then processing on the ground, which you can change.
02 / WHAT COMPUTE ON BOARD CHANGES
With the illustrative sizes from our workload calculator, a 1,600 MB raw scene becomes an 18 MB package of detections and image chips. A day of polar contacts at 150 Mbit/s carries about 190 GB: 119 raw scenes, or 10,600 packages.
When the host's own data is already waiting on board, a raw scene queues behind it while the small package can go first. With 50 GB waiting, the raw-data answer arrives 7.7 hours after the one computed on board in the median case; with 200 GB, 25 hours. The chart under the simulator shows the whole curve.
If the host carries a low-rate relay link, a 50 kB alert of detections can leave minutes after processing: 6 minutes from capture to answer at 200 kbit/s with a 2-minute delay, both assumptions. The full package follows at the next contact; raw scenes are far too large for such a link.
03 / METHOD AND LIMITS
The host's orbit is propagated for two weeks with Earth's gravity to J4 (EGM96) and a fixed-step Runge–Kutta integrator; stations and areas sit on the WGS 84 ellipsoid and the Earth turns with mean sidereal time. Over two days and 69 station passes, contact start and end times agree with an independent calculation (a SciPy DOP853 orbit and Skyfield with the IAU 2000A Earth orientation model) to 0.36 s, and peak elevations to 0.03°; the Sun's elevation over the areas agrees with JPL's DE421 to 0.01°. Automated tests check these limits on every build.
Not modelled: drag, which would shift pass times by about 0.6 s after a day and 30 s after a week for a typical host (operators re-predict from fresh tracking every day); clouds over optical targets; other satellites competing for the same stations; the time a satellite needs to turn toward a target; link rates that change with elevation; and the host's own power, thermal and scheduling limits. Processing on board is pending measurement, and every size, rate and duration in the assumptions panel is illustrative and editable.
Station coordinates: Svalbard and Troll (KSAT) and Hartebeesthoek from Wikipedia; all other sites from SSC's published station list, to 0.01°. Downlink rate: X-band radios for small satellites that have already flown reach 150 Mbit/s (NASA, State-of-the-Art of Small Spacecraft Technology, 2024, Table 9-3). Earth imagery: NASA Blue Marble Next Generation and NASA Black Marble 2016. The SI-P1 pathfinder would fly in its host's orbit and use its host's ground segment; no station or relay service shown here is booked.