ISS position and a spoofed radio signal on four maps
Hypothesis. The radio signals attributed to the International Space Station come from ground transmitters along its track, imitating a source that moves at the measured speed, {{V_SIG}} km/s.
Test. The station is placed where the published orbit puts it, which is where it is seen to pass at the predicted times (Spot the Station); its speed across each map follows from that map's distances. The spoofed signal is the source those transmitters imitate, moving along the same track at {{V_SIG}} km/s, lined up with the station at each northbound equator crossing, or at any moment with Line up signal now. A city turns red when the station is above its horizon and the signal is not, or the reverse.
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Signal
Lined up: each northbound equator crossing
Station, published-orbit position
Spoofed signal at the measured speed
Gap along the track
Above the horizon
City: station and signal in view
City: one without the other
Globe
Sphere, radius 6,371 km
Map speed
—
Speed change
—
Signal
—
Signal speed
—
Cities out of sync now
—
Map speed this orbit, km/s · dashed: measured
North-pole AE
Centred on the North Pole
Map speed
—
Speed change
—
Signal
—
Signal speed
—
Cities out of sync now
—
Map speed this orbit, km/s · dashed: measured
Dual-pole AE
Centred on 0°N 0°E
Map speed
—
Speed change
—
Signal
—
Signal speed
—
Cities out of sync now
—
Map speed this orbit, km/s · dashed: measured
Mercator
True on the equator, edges joined
Map speed
—
Speed change
—
Signal
—
Signal speed
—
Cities out of sync now
—
Map speed this orbit, km/s · dashed: measured
Result
On the globe the signal stays level with the station by construction: both come from the published orbit (numerically within {{GLOBE_DRIFT}} km over {{N_ORBITS}} orbits). On each flat map the station's track per orbit is longer than the {{SIG_TRACK}} km the signal covers in the same time: {{AE_TRACK}} km on the North-pole map, {{ME_TRACK}} km on Mercator and {{DP_TRACK}} km on the dual-pole map. One orbit after it is lined up, at whatever moment, the signal is {{AE_LAG1}} behind on the North-pole map, {{ME_LAG1}} on Mercator and {{DP_LAG1}} on the dual-pole map. Restarted level every minute instead, it is still up to {{AE_LAG60}} adrift on the North-pole map. The recordings show no such drift: in {{SN_N}} SatNOGS recordings of three passes on 3 October 2026, the S-curves are centred within {{SN_RMS}} s (rms per pass) of the closest approaches the published orbit predicts.
Other ways to send the signal
Corrected in real time (Real-time correction, above): transmitters that track the station and steer the signal to where it was a latency earlier keep it that latency behind. To stay with the station the signal must then cross the map at the map speed, up to {{AE_XSIG}} times the {{V_SIG}} km/s its Doppler shift shows on the North-pole map. The recordings allow neither: their S-curves are centred within {{SN_RMS}} s of the predicted closest approaches, and their shifts give {{REC_V_SOUTH}} km/s over South America and Australia, where the North-pole map needs {{REC_AE_SOUTH}} km/s.
Ground transmitters timed to the station can keep in step with it, but a transmitter sends one frequency to every receiver in range. At {{BURST_UTC}}, {{BURST_N}} receivers from Ireland to Belarus were recording the station's UHF signal at the same instant: {{BURST_UP}} heard it shifted up and {{BURST_DOWN}} down, from {{BURST_MIN}} to {{BURST_MAX}} kHz, each within about {{SN_OFFSET}} Hz of the shift the published orbit predicts for its own position. Imitating that takes a separate transmitter for each receiver, heard by no other. The signal also arrives from where the transmitter is, which a directional antenna or a pair of antennas measures, not from the station's place in the sky.
The station adjusting its own signal over a flat map: the signal then arrives from the right direction, and the station can give one receiver the shift the globe predicts, but every other receiver hears the correction meant for that one. Over the North-pole map, adjusted for VK4JBE in Brisbane two minutes before closest approach on its highest pass in this window, it is {{ONE_E100}} Hz off for a receiver 100 km east and {{ONE_N1000}} kHz off 1,000 km north (437.55 MHz). Unadjusted, its shift would show the map speed: {{REC_AE_SOUTH}} km/s where the recordings from South America and Australia show {{REC_V_SOUTH}} km/s, and {{REC_AE_EU}} km/s where those from Europe show {{REC_V_EU}} km/s.
Over {{N_ORBITS}} orbits
Globe
North-pole AE
Dual-pole AE
Mercator
Map speed, km/s
{{G_VR}}
{{AE_VR}}
{{DP_VR}}
{{ME_VR}}
Fastest ÷ slowest, each orbit
{{G_RATIO}}
{{AE_RATIO}}
{{DP_RATIO}}
{{ME_RATIO}}
Speed gained and lost per orbit, km/s
{{G_SWING}}
{{AE_SWING}}
{{DP_SWING}}
{{ME_SWING}}
Largest speed change along the track, g
{{G_AMAX}}
{{AE_AMAX}}
{{DP_AMAX}}
{{ME_AMAX}}
Station's track per orbit, map km
{{G_TRACK}}
{{AE_TRACK}}
{{DP_TRACK}}
{{ME_TRACK}}
Signal's distance per orbit, map km
{{G_TRACK}}
{{SIG_TRACK}}
{{SIG_TRACK}}
{{SIG_TRACK}}
Lag one orbit after lining up, any start
level
{{AE_LAG1}}
{{DP_LAG1}}
{{ME_LAG1}}
Gap one orbit after lining up, map km
{{GLOBE_DRIFT}}
{{AE_GAP1}}
{{DP_GAP1}}
{{ME_GAP1}}
Largest lag, restarted every minute
level
{{AE_LAG60}}
{{DP_LAG60}}
{{ME_LAG60}}
Method
Orbit
ISS (NORAD 25544) orbital elements from CelesTrak, epoch {{EPOCH_UTC}}; positions every second by SGP4 for {{N_ORBITS}} orbits from {{START_UTC}}. Period {{PERIOD}} min, mean altitude {{ALT}} km.
Measured speed
{{V_SIG}} km/s: the straight-line reading of the SatNOGS recordings, from the height of each S-curve with no map assumed (weighted mean of {{SN_N}} receivers). Over a plane this is the speed of a source in level flight and of the point beneath it; climbing or descending would make the source faster than the point beneath it, so level flight is the flat maps' best case. On the globe the same recordings fit the published orbit: {{V_ORBIT_RANGE}} km/s relative to the ground at {{ALT}} km, and {{GLOBE_V_RANGE}} km/s for the point beneath.
Map speed
Speed of the point beneath the station across the map, from positions 1 s apart, subdivided where a step exceeds 20 km on the map. Speed change: the rate of change of that speed over 10 s, along the track; turning adds to it. The ratio of fastest to slowest does not depend on the map's scale.
Signal
A source moving along the station's track on the map at {{V_SIG}} km/s from a moment when it is level with the station: each northbound equator crossing, or the moment chosen with Line up signal now, after which it runs without restarts. With Real-time correction the signal is instead placed where the station was the chosen latency earlier, so it moves at the map speed while its Doppler shift still shows {{V_SIG}} km/s. Signal speed: its speed across the map against the speed its Doppler shift shows. Lag: time since the station was at the signal's position. Gap: distance between them along the track, on the map. The one-orbit figures cover every start time at 1-min intervals over the {{N_ORBITS}} orbits.
In view
Within {{HORIZON_DEG}}° of arc ({{HORIZON_KM}} km) of the point beneath the station or the signal: the area over which the station is seen to rise and set, which is the horizon of a sphere at {{ALT}} km. Over a plane nothing would hide it: at {{ALT}} km it would stand {{EL_HORIZON}}° above the horizon at {{HORIZON_KM}} km and {{EL_10000}}° at 10,000 km. Cities: GeoNames, population one million or more, with places within 30 km of a larger one merged ({{N_CITIES}}).
Maps
As in the Cable Latency Survey, except that Mercator's east and west edges are joined so that the track continues across 180°. On the dual-pole map the speed has no upper limit near 0°N 180°E, where the map's rim divides the Pacific; this window's closest pass, {{DP_RIM}}° away, needs {{DP_VMAX}} km/s.