Iridium, labelling the Iridial constellation
Walter Nissen (wnissen@freenet.tlh.fl.us)
Wed, 10 Nov 1999 10:54:03 -0500 (EST)
I recently surfed by the VSOHP,
http://www2.satellite.eu.org/satintro.html, and stumbled across
a rich source of links concerning the Iridia, Lloyd Wood's
http://www.ee.surrey.ac.uk/Personal/L.Wood/constellations/iridium.html. 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.
Cheers.
Walter Nissen wnissen@tfn.net
-81.8637, 41.3735, 256m elevation
---
Did you know?:
"Ascending"
is an orbital mechanician's way of saying "moving from South to North".
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