Iridium, labelling the Iridial constellation

Walter Nissen (
Wed, 10 Nov 1999 10:54:03 -0500 (EST)

I recently surfed by the VSOHP,, and stumbled across
a rich source of links concerning the Iridia, Lloyd Wood's  I
take note of 2 images of the Iridial constellation, one at the top of that
page and one at the bottom.  Both of these images are double, each having
a hidden image below available for the clicking.  I write here below only
of the unhidden image at the bottom of his page.  This image,
IMG SRC="SaVi/iridium66-coverage.gif", labelled there as "Iridium's
satellite footprints at a moment in time", is a colorful image of the
surface coverage afforded by the constellation.

But I write not of the footprints, but of the 66 objects which afford this
coverage, each from her outpost more than 700 km above the surface of our
Earth.  And I ask this question:  Which satellite corresponds to each
footprint?  An answer may be found in the table of the Iridial
constellation which I have posted occasionally here.  It is convenient to
modify the usual presentation slightly to construct an array of labels for
the image.

In the image, portions of the surface which are within the footprint of a
single object are colored light orange.  When more than one object is
visible from a portion of the surface, then the coloration is darker
orange.  The image has two prominent, dark orange "seams" running
vertically, one about 1/4 of the way from the left margin and one about
1/4 of the way from the right margin, leaving about half the image in the
middle between the 2 vertical seams.  These "seams" correspond to the
space, of 22.1 degrees, between the planes of objects which move in
opposite directions, providing more dark orange overlap, than is provided
by the larger angles between the planes of objects moving in the same
direction.  At the center of the image, covering half the image, is a
large subset of the constellation.

Within this central half of the image, the planes are, vertically from
left to right, planes P0, P1, P2, P3, P4 and P5.  If we imagine that,
within this central half, the objects are all ascending, moving from South
toward the North, and that the light orange portion at the lower left is
that covered by Ir P00, then the footprints of the objects P10, P20, P30,
P40 and P50 form a main diagonal running from lower left to upper right
across the central half of the image.  Immediately below that diagonal,
the footprints of objects P11, P21, P31, P41, and P51 are prominently
shown, with the footprint of P01 being obscured among others at the bottom
by "South polar congestion".

Here are the 66 objects arrayed so as to show their spatial relationships
as they are when at somewhat low latitudes and, hence, so as to label the
central half of the image.

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

    P00  64

    P01  65

I repeated a couple of objects at the bottom to reinforce the fact that
these are arrayed in a "perpetual" cylinder, albeit a cylinder squeezed in
the polar regions, and more, but that is a topic for another day.

The top part of the labels shown here can label the objects in the lower
right of the central half of the image.  The bottom part shown here will
then label the upper left of the central half of the image.


Walter Nissen         
-81.8637, 41.3735, 256m elevation


Did you know?:
is an orbital mechanician's way of saying "moving from South to North".

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