How does the Iridium satellite constellation work?

While it lasted it worked very well.

There were 11 polar low-earth orbits; in each 7 satellites were placed at equal intervals, so all of them moved at the same inter-satellite ditances. At poles, where orbits overlapped, it was designed so that each orbit is separated in height (by distributing each of the 11having perigees at different, equally distributed latitudes). Thus, there were 77; and the elemnt '77' in periodic table is 'Iridium'; that is why the name. But later, it was modified with 6 satellites each in the 11 orbits.

Then the particular satellite that happens to be overhead of the transmitting radio, picks up the signal (in 'packets'), then efficiently convey it by relaying from satellite to satellite till the satellite covering the geographical location of intended recipient radio. Because they are all in LEO (low-Earth Orbit about 400km above groung), the latency (the time taken by the electricalmagnetic signals, at the speed of light; almost following the great circle distance between those two points) is not noticeable, unlike the Geo-stationary satellites placed at 33,000 km disatnce (electromagnetic signals cover it in 0.11 seconds, one way) if it is directly above, that is not the usual case. Two points diametrically opposite on earth ( antipodes) are at a distance of 12,550 km that is the maximum.

It needed lot of highly sophisticated software (no 'bugs' can be tolerated) running into reams of paper (hardware to boot, too) and cost of launching all those satellites in precise orbits just to say 'Papa! how are you?'. Iridium satellites sense international borders and switch as enter a non-member countries. During 'Kargil' war, the TV channels in India got 'real' time coverage from the near zone of war front from 'Iridium'; the satellites switched off in Pakistan, a non-member of Iridium.

How much did it cost, paying all those high-paid dozens of software programmers, electronics %26amp; communication experts and workers! Its way too expensive and could not sustain. The consumer wanted all these at affordable (cheap) cost that we have now!

After it declared 'bankrupt', it looks like American armed forces acquired it very cheaply.How does the Iridium satellite constellation work?Rather well, actually. Contact is established through an uplink and the system scans for the intended receiver. Then the nearest satellite to the receiver is used for downlink contact and a 2-way is established.



Doug