# Problems receiving Iridium messages during the middle of the 'day' in the far North

I have some scientific instruments using Iridium modems for communication active at around or higher than 82°N. At the time of writing this message, we are in middle of August, i.e. the polar day still.

I observe that I have a very high level of messages dropout during the middle of the day, from 10am to 5pm. I have very few dropouts during the 'night', outside of this time. I am quite puzzled about this.

• Any idea why this may happen?

• Do you know if this has been observed before?

I have no reason to expect anything else than the pure RF communication to fail. Could it be that depending on the time, solar radiation / particles may disturb transmissions (the magnetosphere etc is well distorted by the solar wind right, so may this explain for the night vs day difference?)? Or should I blame it on the polar bears? ^^

• Polar bears. 10am to 5pm...business hours. Coincidence? I think not. Aug 20, 2020 at 20:38
• My first assumption would relate to the earth's magnetic field (a thing all by itself with respect to the poles) and then also the deformation of the van allen belts. Despite that the tilt is almost directly towards the sun (as you say, it's "day") think of the relative position during rotation with respect to the solar wind and the magnetic field, too. That's just me being a lay person. Have you contacted someone at JPL or NASA to ask? I'd start by seeking and then discussing this with an expert there or in academia. (I wouldn't blame the polar bears.)
– jonk
Aug 20, 2020 at 20:48
• eurekalert.org/pub_releases/2001-05/NS-Htga-1505101.php Aug 20, 2020 at 20:54
• Precipitation during the warmest hours? Aug 20, 2020 at 21:13
• Realistically you're going to have to take this up with the provider. It might be aspects of satellite orbits, or it might be overload from other user's patterns of usage. What it is not, is an electronic design question backed by sufficient supporting detail - if experiential knowledge of the system is key, this is the wrong venue for the question. Aug 20, 2020 at 22:15

Iridium has 100 minute polar cycle time. Rx’s must be aimed properly. look for the old satellites to have solar reflections follow the grid lines and aim between 2 lanes at the optimum elevation angle which is a tradeoff but might be off 90 deg. Try direction north of vertical.

Reflections may cause Rayleigh losses at low angles. therefore if you have poor reception, it will be rapid cycles between satellites but aim north and try to catch the converging longitudinal paths over the pole slightly off vertical.

how are the Northern Lights?

In the polar regions, Cross-seam inter-satellite link hand-offs would have to happen very rapidly and cope with large Doppler shifts; therefore, Iridium supports inter-satellite links only between satellites orbiting in the same direction or every 60 deg Longitude.

The constellation of 66 active satellites has six orbital planes spaced 30° apart, with 11 satellites in each plane.

Consult with service provider.

• Iridium terminals use omnidirectional quadrafilar helix antennas, or broad beam patches, so no need to aim them. Aug 21, 2020 at 6:23
• Also, I believe that given that there are 66 satellites in polar orbite, the coverage should be very good in the polar regions, right? :) Aug 21, 2020 at 6:40
• Quad helix ought to high gain narrow beam. But you are saying they are spacially offset? Every 30 deg longitude yet alternating directions and lane changing only in same direction. So from the ground every 60 deg over the poles Aug 21, 2020 at 6:49
• Smaller azimuth near poles short aperture time higher doppler so every 60 deg Aug 21, 2020 at 6:55
• +1 possibly of interest: What (actually) makes Iridium “the world's only truly global mobile satellite communications company”? and also Why do orbits in the Iridium constellation have an inclination of 86.4°? Welcome to Space!
– uhoh
Aug 21, 2020 at 7:22