Iridium, Table of the Iridial Constellation

Walter Nissen (
Fri, 15 Oct 1999 11:34:37 -0400 (EDT)

Below is a tabular display of the Iridial constellation, principally to
facilitate visual observation.

At the top of the table you will find a rectangle of 66 objects which form
the working array.  A total of 90 objects have been orbited, including 2
Sim objects which are (always?) faint because they lack the mirror-like
surfaces of the operating Iridia.  The 66 objects are in 6 regular
undecagons (11-sided regular polygons).  The planes containing objects
going in the same direction, ascending or descending, are separated by
about 31.58 degrees, though this is not indicated in the table.  The
planes in which objects go in opposite directions are separated by about
22.10 degrees.  In the table, the six planes are designated P0 thru P5 and
these correspond to planes numbered 1 thru 6 in some other sources.  The
Earth carries you (unless you are reading this from a spacecraft or are
near one of the poles) under the planes in consecutive order beginning
with P0 and ending with P5.  All of these objects are going the same
direction, ascending or descending.  Then the direction reverses and you
go under the planes again in the same order.

The objects within a given plane are numbered 0 thru 9 and A,
consecutively, in the order in which they pass by.  The table also shows
the number used by OIG for the object.  Note that some of these numbers
from OIG are the same as those used by others for different objects, thus
making them all but useless to identify a particular object.  However the
P-designations are not ambiguous, to the very best of my knowledge.  Thus,
if Ir P50 39 has just passed by, then in about 9.1 minutes, Ir P51 80 will
pass by going the same direction and a little bit to the West of the track
of Ir P50.  With the P-designations, this deduction is simple.  Best of
luck using the numbers you find elsewhere.  Fortunately, the table allows
you to translate.  Within the rectangle, an R follows the P-number of an
object which replaces an object which formerly occupied the same position
in the array.  This practice prevents ambiguity.

The remaining 90 - 2 - 66 = 22 objects are shown below the rectangle.
Some objects may be on standby, to be used in the event one of the
operating objects fails.  These are designated with B, C, D, etc.  Some
objects have failed and are flashing, apparently because they are
tumbling.  These are designated S, T, U, etc.  The objects which have
moved out of plane are shown in the table offset to the left, with
arrows marking some which have moved substantially.

The full table is pretty long to post here very often, so just the most
interesting part is shown below.

If you see behavior inconsistent with this explanation, your report will
be welcome here, and when confirmed, will indicate a need to update the

Thanks are due to many people for information and inspiration, Rob Matson,
Mike McCants, Ron Lee, Alan Pickup, John Gardner come prominently to mind,
and to Jim Varney for publicly expressing his appreciation.


Walter Nissen         
-81.8637, 41.3735, 256m elevation


    P00  64     P10  24*    P20  32     P30   5     P40  10*    P50  39
    P01  65     P11  47     P21  33     P31   6     P41   9*    P51  80
    P02  66     P12R 11A    P22  57     P32   7     P42  52*    P52  17
    P03  67     P13  49     P23  58     P33   8     P43  12     P53  15
    P04  68     P14  26     P24  59     P34   4     P44  13     P54  81
    P05  74     P15R  3     P25  60     P35  35*    P45R 83     P55  38
    P06  72     P16  22     P26  55     P36  61     P46  16     P56  41
    P07R 75     P17  23     P27  28     P37  19     P47  53*    P57  43
    P08  70     P18  76     P28  29     P38  34     P48  56     P58  20*
    P09  62     P19  25     P29  30     P39  37*    P49  50*    P59  42
    P0A  63     P1A  45     P2A  31     P3A  36     P4A  54*    P5A  40

    P0 C 73     P1 B 69                 P3 B 51     P4 B 86     P5 B 77
    P0 D 14A    P1 D 20A                            P4 C 84     P5 C 82
    P0 E 21A    P1 S 46*                            P4 S 11     P5 S 18*
                P1 T 71                             P4 T 14     P5 T 44
            P1 U 48                    P4 U 85         P5 U 21 <------<
                      P2 S 27 <---<             P5 V 79 <-------------<
                                P4 ?? 2 <-----------------<

*   numbers have been confused, resolution uncertain

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