PPAS entries for SPOT (93- 61 A) and Ir 20 (97- 34 C)

Kurt Jonckheere (kjonckheere@mail.unicall.be)
Wed, 1 Jul 1998 18:03:16 +0200

hello all,

within a week or so, I will create the next update to our database of
Photometric Periods of Artificial Satellites (PPAS).  So please send
your observations of flashing objects to the following address :
ppas@lists.satellite.eu.org

Determining the flashing period of a rocket is most of the time not that
very difficult as rockets are cylinders that are mostly tumbling 
end-over-end and thus having a regular flash pattern.

As clearly stated by the following observation of Walter Nissen,
for payloads it is sometimes more difficult to obtain a good period from
a number of timings of brightness maxima.  This is of course caused
by the fact that payloads might have a number of reflecting surfaces
(solar panels + other reflective areas like antennas, booms, ...),
that are - too make it more difficult - oriented in different ways.
So during some time of the pass one sees a reflection of surface1,
some time later together with surface2, then surface1 goes away and
reflection from another surface3 start and so on... (just a small
example)

So during one pass one can see all kind of reflections from different
origin, making it difficult to determine the exact rotation speed.

Sometimes it can help to record the brightness and the flatness-
sharpness of the flashes.
Also looking to a small part of the pass can help because during
a small amount of time conditions are 'nearly' the same and reflections
can come from the same areas.

In the remarks column, some further explanation can be given :
ssm : some secundary maxima, irr : irregular, ...

Walter wrote about SPOT and IR 20 (aka 18):

1)
>> Observed SPOT 3 (93 061A, #22823) tonight (6/17 evening). It 

>As in the case of 24871, I solicit suggestions about how to prepare this 
>for PPAS. (see below)

The observations indicated by q "*" are probably caused by the same
reflecting surface, although there is indeed the small anomaly (10.4)
Leaving this one out and starting from split 5 to 18 we get :
93- 61 A 98-06-18  2:46:05.2 WN   57.0  .6   5   11.4

Another surface seems to give flashes about 5 seconds later than
the 'main' surface :  split 1,3,6,9,12 also giving a period of :
45.8 / 4 = 11.45 seconds

>   y m d  h 
>19980618 02 UTC 
> 
>   UTC     lap   split 
>  m  s 
>44 46.46          0.00   0   * 
>44 51.03   4.57   4.57   1             - 
>44 57.91   6.88  11.45   2   *  11.45 
>45  2.43   4.52  15.97   3             11.40 
>45  5.30   2.87  18.84   4                    - 
>45  8.16   2.86  21.70   5   *  10.35 
>45 13.80   5.64  27.34   6             11.37 
>45 19.30   5.50  32.84   7   *  11.14 
>45 21.26   1.96  34.80   8 
>45 25.56   4.30  39.10   9             11.76 
>45 28.22   2.66  41.76  10                    22.92 
>45 30.76   2.54  44.30  11   *  11.46 
>45 36.82   6.06  50.36  12             11.26 
>45 39.73   2.91  53.27  13                    11.51 
>45 42.07   2.34  55.61  14   *  11.31 
>45 53.77  11.70  67.31  15   *  11.70 
>46  0.38   6.61  73.92  16                    20.65 
>46  2.55   2.17  76.09  17 
>46  5.17   2.62  78.71  18   *  11.40 
>46 11.03   5.86  84.57  19                    10.65 

2)
>Before I launch into my OBS, I want to point out, to beginners and those 
>who have hesitated to become involved with precise OBS, that all of the 
>below was done with an inexpensive stopwatch (albeit one with 100 
>splits/laps) and an inexpensive shortwave radio.  If you want to skip the 
>radio, if you are in the CONUS (continental US), you can pay $.50 to call 
I just like to add that to make measurements of the flashing period it is
even not really necessary to have the exact time of the last flash,
although it is of course helpful when trying to analyse the data, e.g.
to calculate the rotation axis.

>I would be happy to produce one or more PPAS-format reports of this OBS, 
>if someone would suggest the most desirable way(s) to do that.  I know how 
>to report when the timings are consistent, but confusion confuses me. 
> 
>Could the interval of 1.53 s between splits #44 and #45 be a synodic 
>anomaly, such as Bart and Patrick Wils have written about?  If you think 
>24871 is a polished cylinder and look only at splits #35 thru #50, would 
>you have to think so?  Of course, it's not a cylinder, but ... 
I guess that it might be a 'synodic anomaly', but for these Iridiums
which are very different of a cylinder I suppose that some of these
anomalies are just caused by the taking over of regular flashes for one
reflecting surface by another one due to the change of the geometry of
the satellite to the observer and sun.
These Iridiums have quite a few reflecting areas like the MMAs 
(main mission antennas), a solar panel or that battery thing 
Paul Maley wrote about recently.

To make one or more entries for the PPAS, I would suggest to take 
out the regular parts of the data, which would give something like :
                                    0
> 2 51 53.00    2 51 53.49      .81 1
> 2 51 53.96    2 51 54.45      .96 2
> 2 51 54.83    2 51 55.32      .87 3
> 2 51 55.80    2 51 56.29      .97 
> 2 51 56.77    2 51 57.26      .97 
> 2 51 57.80    2 51 58.29     1.03 
> 2 51 58.74    2 51 59.23      .94 
> 2 51 59.71    2 51 60.20      .97 
> 2 52  0.69    2 52  1.18      .98 
> 2 52  1.56    2 52  2.05      .87 
> 2 52  2.51    2 52  3.00      .95 
> 2 52  3.49    2 52  3.98      .98 
> 2 52  4.42    2 52  4.91      .93 
> 2 52  5.36    2 52  5.85      .94 
> 2 52  6.44    2 52  6.93     1.08 
> 2 52  7.49    2 52  7.98     1.05 
> 2 52  8.40    2 52  8.89      .91 
> 2 52  9.41    2 52  9.90     1.01 
> 2 52 10.56    2 52 11.05     1.15 
> 2 52 11.72    2 52 12.21     1.16 
> 2 52 12.50    2 52 12.99      .78 21
> 2 52 13.44    2 52 13.93      .94 22
> 2 52 14.31    2 52 14.80      .87 23
> 2 52 15.26    2 52 15.75      .95 24
> 2 52 16.25    2 52 16.74      .99 
We can do some small 'consistency check' : between 0 and 22,
1 and 23, 2 and 24 we get 21.3, 21.3, 21.3
Also in between we get the same, so this is really a regular interval.
21.3 +- 0.2 (or 0.1) / 22 = 0.97 seconds
97- 34 C 98-06-16  2:52:16.8 WN   21.3  .1  22    0.97 irr afterwards

Just taking out another part :
> 2 54 35.51    2 54 36.00      .99 0
> 2 54 36.45    2 54 36.94      .94 1
> 2 54 37.42    2 54 37.91      .97 2
> 2 54 38.26    2 54 38.75      .84 
> 2 54 39.24    2 54 39.73      .98 
> 2 54 40.25    2 54 40.74     1.01 
> 2 54 41.25    2 54 41.74     1.00 
> 2 54 42.27    2 54 42.76     1.02 
> 2 54 43.25    2 54 43.74      .98 
> 2 54 44.25    2 54 44.74     1.00 
> 2 54 45.36    2 54 45.85     1.11 10
> 2 54 46.18    2 54 46.67      .82 11
> 2 54 47.03    2 54 47.52      .85 12
> 2 54 48.00    2 54 48.49      .97 13
Taking 10 consecutive flashes (0-10, 1-11,...) we get :
9.9, 9.7, 9.6, 9.7 mean : 9.7 / 10 = 0.97 seconds
97- 34 C 98-06-16  2:54:47.5 WN   9.7  .1  10    0.97 

Other comments welcome.

Greetings,

Kurt J

-------------------------------------------------------------------------
    Kurt Jonckheere (kjonckheere@unicall.be)  51.2 N  2.9 E  4m ASL 
      Accelerations : http://uc2.unicall.be/kjonckheere/index.htm
    Observations collector for the Belgian Working Group Satellites: 
Send your observations of flashing satellites, preferrably in the correct
             PPAS format to ppas@lists.satellite.eu.org
 "Join as at Eurosom 3 in Edinburgh, Scotland on October 24/25, 1998"
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