Iridium : observing project , Iridial constellation

From: Walter Nissen (
Date: Sat May 28 2005 - 21:36:28 EDT

  • Next message: Steve Newcomb: "Re: Iridium : observing project , Iridial constellation"

    Greetings, all,
    I'd like to point out that for mid-northern observers, the next month or
    so is optimal for observing multiple glints and the
    fine-structure of glints from the Iridial constellation.
    (Far to the north
    (hi, Bjoern)
    this project is better in the "shoulder" seasons around the
    June solstice or maybe there is a wholly different approach needed to
    observe the multiple planes visible from polar regions.)
    Anyway, for mid-northern observers there will be nights when it is
    possible to observe all of the objects in a plane.
    There are 11 operational objects in each of the 6 planes.
    One of them in each visible plane passes by every 9m 7s.
    It may be possible to observe all 11 of the objects in a plane twice in
    a night, all 22 observations coming on successive passes.
    I think my "record" is 13 consecutive operational objects
    (i.e., 2 of them twice).
    An easy question to answer for some latitudes is
    "How many planes are simultaneously visible?".
    I think a more challenging question is
    "How far North do you have to be to see more planes simultaneously?".
    A program like Rob Matson's IRIDFLAR or web site like
    can help you observe the bright glints which can be as bright as an
    eye-popping magnitude -8.
    I routinely run an ancient version of IRIDFLAR down to mag 6, which
    shows many more events.
    On 2005-05-05, it showed Iridium P3 B 51 and Iridium P35 35/37 glinting
    only 5 seconds apart.
    (Note use of an ISO 8601-compliant date format).
    I endeavored to follow Ir P35 because it's in the operational array,
    but, sure enough, after a while Ir P3 B appeared and the 2 objects
    looked remarkably like a NOSS pair.
    In my binoculars, with a 10 degree field of view, they were easy to
    follow together.
    Here's another easy question:
    "How much later did Ir P38 34 wander by?".
    Here's what I recorded in my log:
    Iridium P38 34
    12 located mag 4 or 5           38 16.75
    13 glint mag 4?                 39 40.19                2 39 35.76
    14 down to mag 5?               39 52.12
    15 glint mag 4 or 5             40  5.08                2 40   .65
    16 down to mag 5?                  15.59
    17 lost mag 6? suddenly         40 41.87
    The left column is the number of the split in the stop watch.
    I was late picking this one up.
    I should have been out looking for it a minute or so earlier.
    I try to record each time the object brightens to or dims to mag 5.
    Between events 13 and 15, this one didn't sink below mag 5 or so, so
    there was no event to time as "up to mag 5".
    The third column is the split time from the stop watch.
    The fourth column is the UTC, after correcting for the fact the watch
    was 2h 0m 4.43s slow from UTC, or something like that; the radio
    reception was horrible.
    There has to be a better way to fetch time using the Net, but I haven't
    found it yet.
    The output from IRIDFLAR reports only the brightest events.
    Most of them, like this one, for Ir P38, may not show up.
    That's ok, they come by every 9m 7s.
    Did I say "one"?  I suppose this was 2 events, there being 2 glints,
    although I managed to put 6 events into the watch.
    I have observed some triple and quadruple glints.
    What will you observe?
    Below is a diagram showing the current status of the Iridial
    constellation, using what are believed to be the only known unambiguous
    names for these satellites.
    There are 11 operating satellites in each of 6 planes,
    designated P0 through P5.
    The objects are numbered 0 through A in each plane.
    The objects follow one another across the sky in numerical order; so do
    the planes.
    An R, Q, etc., is appended to a satellite which has replaced another.
    Each plane used to seem to have at least one spare satellite, designated
    B, C, etc.
    Many failed satellites are designated S, T, etc.
    Horizontal positioning of the name indicates its placement within or
    between planes.
    As pointed out by Mike McCants, it seems that Ir P46 16 has failed, or,
    at least, has been removed from the operational array.
    Thus, it has been redesignated as P4 X.
    With the redeployment of P4 B 86, the only spare in P4, now redesignated
    P46R, it appears that P4 is now without any spare.
    Perhaps this means that there will be a launch soon, or that one of the
    spares in P2 or P3 will be redeployed into P4.
    Walter Nissen         
    -81.8637, 41.3735, 256m elevation
                    Configuration of the Iridial Constellation
        P00  64     P10  46*    P20  32     P30   5     P40R 84     P50  39
        P01  65     P11  47     P21  33     P31   6     P41  10*    P51  80
        P02  66     P12R 20*    P22  57     P32   7     P42  54*    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  37*    P45R 83     P55R 82
        P06  72     P16  22     P26  55     P36  61     P46R 86     P56  41
        P07R 75     P17  23     P27  28     P37  19     P47  50*    P57  43
        P08  70     P18  76     P28  29     P38  34     P48  56     P58  18*
        P09  62     P19  25     P29R 31     P39  35*    P49  52*    P59  42
        P0A  63     P1A  45     P2AR 30     P3A  36     P4A  53*    P5A  40
        P0 D 14*    P1 D 11*    P2 B 90     P3 B 51      P4 S 911   P5 B 77
        P0 E 21*  P1 S 24*      P2 C 91     P3 C 97   P4 T 914     P5 S 920
      P0 S 73      P1 T 71      P2 D 94     P3 D 98     P4 X 16    P5 T 44
                    P1 V 69     P2 E 95                             P5 W 38
                                P2 F 96
                            P5 U 921 <------------------------------------<
             (P4 W has precessed nearly full circle)         P4 W  2
    *   numbers have been confused (also 9nn numbers), be sure to use P-number
    the 2 simulator objects are not included
    the 5 decayed objects are not included
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