DRA update

Bart De Pontieu (BDP@MPEPL)
Tue, 18 Jun 1996 18:26:25 +0100 (CET)

Hi everyone,

The Determination of Rotation Axis project (DRA) of the Belgian Working Group
Satellites continues thanks to the efforts of the hard-core flash period
observers (you know who you are). Recently several people have reported making
DRA observations. I would like to receive reports of them as quickly as possible
after the observation so I can warn other observers of what objects they should
concentrate on. 

The way DRA is running now, many of the observational efforts are rendered
useless, because of the lack of quasi-simultaneous observations. We need more
observers contributing if we want to get significant results. So, this is a call
to all would-be satellite observers out there to join us.

Q: What is DRA?
A: DRA is a project aimed at determining the direction of the rotation axis of
   tumbling satellites. Tumbling satellites (usually third stages of rockets)
   usually give off regular flashes. By recording the times of a long series of
   these flashes, it is possible to determine the direction of the rotation 
   axis.

Q: Why bother trying to determine the rotation axis of a satellite ?
A: The (change of) direction of the rotation axis gives information about the
   torques acting on the satellite. These torques provide insight into what
   makes the rotation period of tumbling satellites change. It can be used to
   check the theoretical models (for rotation periods going up with time) or
   it can help development of such models (for so-called accelerating rockets).
   Why certain rockets show an accelerating flash period is, as of yet, a 
   mystery. 

Q: How can I help ?
A: The goal is to accurately measure the absolute time of all (primary) 
   flashes during the pass of one of the satellites in the DRA list 
   (see below). 

Q: How do I measure flashes?
A: There are basically two techniques for this. 
   The first involves using a stopwatch that can store 50 or more split 
   timings. Each time you see a flash, you push the button. At the end you 
   stop your stopwatch on a known time signal (radio, GPS receiver, etc...) 
   so that the time measurements are absolute. Afterwards you write down the 
   absolute time of the first flash and the time (elapsed since that start 
   time) for all flashes you've seen. 
   The second method involves using a tape-recorder, on which you record a 
   radio time signal (beep-beep-beep,yeah). Each time you see a flash, you 
   shout or make some (preferrably short) noise. Afterwards you analyze the
   tape to write down the times of all flashes. 
   The first method is used by most observers I know (though there are
   notable exceptions), presumably because it is less technical (no need for
   tape-recorder, time signal, etc...).

Q: Is it as simple as this?
A: Yes and no. Yes, you just need to predict the satellite's pass, find it
   in your binoculars and start timing, and afterwards write out the times.
   No, because all of the above may not be straightforward for beginning
   observers. Practice is the only advice I can give :-)
   And beginning observers should be aware that even experienced observers
   have nights where everything seems to go wrong.

Q: Is there anything I should be careful about when timing?
A: Yes. First off, you should try to keep track of which flashes are primary 
   and stick to timing the same type of flash. Some rockets show different
   types of flashes all during one rotation period. You are allowed to time
   and report all the flashes, but you should indicate which ones are of
   the same type. Some rockets change flashing behaviour during the pass.
   This is guaranteed to confuse you, but it can also be very interesting as
   far as the rotation axis is concerned. The most accurate measurements of
   the rotation axis have been made using such observations!

Q: Should I report secundary flashes as well?
A: If it's not a burden, yes please! Times of secundary flashes can give
   insight in the rotational geometry, which is important for the analysis.

Q: What (timing) accuracy should I be aiming for ?
A: As best as you can. This will largely depend on the type of maximum in the
   light curve, i.e. whether the maximum is roundish, flat or very sharp. If
   the satellite is showing very diffuse maxima, you should report that, since
   it is important for the analysis. You should also try to estimate how 
   accurate your times are. 

Q: How should I report my observations ?
A: Preferrably in the DRA format, so that your observations can be fed into my
   software directly. The format is simple:

-------------------------------------------------------------------------
   94    4  Year and month (2I5)
   38.9911  -77.0342      273.  lat, long, hgt (3F10.0)
   14    8   21 25.9   11  Start day,hr,mn,sec  nbr timings
  0.00  0
 18.91  1
 37.35  2
 56.34  3
 74.44  4
 89.01  5
 99.00  6
117.15  7
136.50  8
155.31  10
175.19  12
1 21231U 91029  B 94104.48615656  .00000071  00000-0  57773-4 0  6852
2 21231  82.9474 253.5211 0037446  99.0698 261.4696 13.74759322150327
-----------------------------------------------------------------------
   The first 3 lines show year, month (line 1); latitude, longitude (west is
   negative) and height of observing place (line 2); day, hour, minutes, seconds
   of first flash (all in UTC) and number of timings (line 3). The above example
   is Walter Nissen's famous observation of 91- 29 B on April 14, 1994 at
   8h21m25.9s with 11 timings.
   The following lines give the time (in seconds) of all flashes timed, with
   respect to the time of the initial flash. Each line contains the time, and
   the 'index' of the flash. It's not necessary to time all flashes. Sometimes
   you get distracted and have to skip one flash. That's allowed, but you should
   make that clear with the 'index number', if at all possible. In the example
   flashes 9 and 11 were not timed.
   The orbital elements are optional, but if you don't provide them, please make
   sure to indicate the *name* of the satellite somewhere :-)

Q: What satellites should I observe ?
A: In the first place 95- 32 B (23604). Next, the satellites of which DRA
   observations have recently appeared on SeeSat-L or which have been mentioned
   in my DRA-update messages. Also, the satellites in the 
   BWGS-program of flashing satellites that are marked with the priority code 
   'x' (orbital elements of some of these objects are appended at the end).
   But, in general all flashing satellites with clear-cut flash behaviour and
   with a flash period that is generally between 5 and 20 s, of which the
   flash can be accurately timed (0.5 to 1 seconds accuracy). Top-priority
   objects of the BWGS are always good candidates. 

Q: How many timings does BDP need for his analysis?
A: As many as possible. Timing only 5 flashes is a *lot less* useful than timing
   50 flashes! Also, unless something 'peculiar' happened during your pass, I
   will need measurements of a pass shortly before or after yours. My analysis
   works best if information of two or more passes (on about the same day) is
   included. I call these 'quasi-simultaneous observations'.

Q: So should I just observe two consecutive passes?
A: If you can, yes! And if at all possible, try to choose passes that have 
   different observer-sun geometry. This means that you should try to see as 
   many different passes as possible, e.g. don't always observe the south-to-
   east pass, but try to observe the west-to-north pass as well. Another 
   example : try to observe not just the zenithal pass, but also the pass that 
   is only 40 degrees above the horizon. This approach will maximize the
   accuracy obtained during analysis. 

Q: Who should I report my observations to?
A: Me. Send me a message with your obs, as soon as you can. I'm at
   bdp@mpe-garching.mpg.de
   You may also report to SeeSat-L as well, but if you do, I much prefer to 
   receive a DRA format report at my address as well.

Q: What is going to happen to my observations?
A: I will analyze them at regular intervals using the software I developed
   last year. Usually I combine your observations with those of other 
   observers (at about the same time). At this phase of the DRA project, we
   are still trying to validate the usefulness of the method. 

Q: Where can I read about the results?
A: I am working on a publication for a refereed scientific journal using the
   results obtained so far. Regular updates have and will appear in Flash, the
   newsletter of the BWGS (see http://www.rzg.mpg.de/~bdp/flash/flash.html).
   Check out http://www.rzg.mpg.de/~bdp/flash/101/node31.html 
   for recent results of 95- 32 B.
   In any case, you will get regular feedback through SeeSat-L as well. And 
   your observations will be used for scientific purposes. All observers will
   be acknowledged in the scientific paper(s) that may come out of the DRA
   project.

Q: Can't you use video observations to get more accurate results?
A: Yes, and I invite everyone who has video-capacity to send his video-obser-
   vations to me. I am working on a project to digitize video-tapes, and use
   the light-curves deduced from the video-passes to make more accurate
   determinations of the rotation axis. You will hear more about this soon.
   Contact me for details.

Q: What about high-resolution observations?
A: Those are even more promising for determination of the rotation axis. 
   I hope to set up some sort of collaboration with high-res observers :-)
   But timings derived with binoculars and just two human eyes remain very much
   useful until these new techniques have become more productive.

Contact me if you have even more questions :-)

Cheers,
   Bart
-------------------------------------------------------------------------------
Bart De Pontieu --  Max-Planck-Institute for extraterrestrial Physics, Garching
bdp@mpe-garching.mpg.de  --      http://www.rzg.mpg.de/~bdp/satintro.html
Join us at Eurosom 2, Oct 19/20 1996 -- http://www.rzg.mpg.de/~bdp/eurosom.html
BWGS-coordinator -- Flash editor -- SeeSat-L administrator -- would-be-observer
         "I love Americans, but not when they try to talk French"
    "What a blessing it is that they never try to talk English" -- Saki 
-------------------------------------------------------------------------------
4794
1 04794U 70106B   96169.42149410 -.00000027  00000-0  10000-3 0  4881
2 04794 101.4723 132.7974 0037130 219.8339 140.0006 12.53090500559337
13168
1 13168U 82040J   96169.37361609 -.00000003 +00000-0 +10000-3 0 02141
2 13168 074.0461 122.7842 0135492 084.3189 277.3278 12.22840477630200
14179
1 14179U 83069J   96169.21603193 -.00000004 +00000-0 +10000-3 0 01865
2 14179 074.0233 048.8271 0130893 325.2077 034.0454 12.25970761579600
15360
1 15360U 84109B   96169.44531021 +.00000046 +00000-0 +32286-4 0 04455
2 15360 082.9389 345.4832 0040121 259.9391 099.7241 13.75876547586544
15752
1 15752U 85041B   96169.08594357 +.00000046 +00000-0 +33622-4 0 06038
2 15752 082.9487 202.2633 0022732 209.9396 150.0458 13.72474544553481
16144
1 16144U 85094G   96169.18651624 +.00000027 +00000-0 +10000-3 0 01009
2 16144 082.6109 081.9402 0036132 116.1227 244.3586 12.54994435489631
16728
1 16728U 86037B   96169.30110039 +.00000010 +00000-0 -56237-5 0 04186
2 16728 082.9526 261.8665 0032674 056.0099 304.4154 13.75819063505513
18340
1 18340U 87074G   96169.46545819 +.00000027 +00000-0 +10000-3 0 08959
2 18340 082.5660 148.9173 0039105 235.1978 124.5413 12.55488114402242
20528
1 20528U 90023B   96169.44155855 +.00000041 +00000-0 +28096-4 0 00192
2 20528 082.9320 327.2045 0033522 086.1445 274.3541 13.72104744312947
20578
1 20578U 90036B   96169.37282238 +.00000058 +00000-0 +44682-4 0 00309
2 20578 082.9397 290.0912 0012618 161.2446 198.9178 13.75449268309203
21876
1 21876U 92008B   96169.21207525 +.00000041 +00000-0 +26980-4 0 07558
2 21876 082.9260 053.8282 0034148 185.9874 174.0878 13.74480470217196
21903
1 21903U 92012B   96169.30832537 -.00000028 +00000-0 -45706-4 0 07483
2 21903 082.9366 100.7005 0039932 211.7129 148.1621 13.73642363214258
22161
1 22161U 92064A   96169.46669731 -.00000175 +00000-0 -19592-4 0 06259
2 22161 062.9821 240.3362 0840907 017.9656 344.9243 13.21900948178466
22208
1 22208U 92073B   96169.42707044 -.00000006 +00000-0 -22857-4 0 05426
2 22208 082.9157 321.1118 0033344 165.4695 194.7415 13.74209054182263
22803
1 22803U 93059B   96169.33282797 +.00000299 +00000-0 +17632-3 0 05380
2 22803 070.9828 201.5388 0018401 185.1794 174.9138 14.15836978142256
23093
1 23093U 94024B   96169.18781324 -.00000041 +00000-0 -57322-4 0 02581
2 23093 082.9479 054.4395 0022839 261.5034 098.3533 13.76471556575657
23180
1 23180U 94041B   96169.23065375 -.00000009 +00000-0 -25010-4 0 01902
2 23180 082.9443 235.1574 0030531 111.2250 249.2173 13.77151927096902
23190
1 23190U 94045B   96169.16113465 +.00000062 +00000-0 +90587-4 0 02568
2 23190 074.0225 206.7199 0022198 054.5313 305.7867 13.73334930093952
23279
1 23279U 94061B   96169.41671135 +.00000674 +00000-0 +63647-4 0 02909
2 23279 082.9931 171.3229 1020883 284.5798 064.4404 13.25589041083277
23343
1 23343U 94074B   96169.09073908 -.00000001 +00000-0 +77586-5 0 01655
2 23343 097.9708 227.1011 0006806 207.1620 152.9259 14.70624863086805
23405
1 23405U 94077B   96169.40482649 -.00000029 +00000-0 +10000-4 0 02544
2 23405 070.9844 130.1455 0001067 087.4495 272.6750 14.14208829080734
23466
1 23466U 95002D   96169.16540281 +.00000222 +00000-0 +22175-3 0 01539
2 23466 082.9251 191.9906 0029746 307.8110 052.0351 13.73489135070000
23604
1 23604U 95032B   96169.30236658 +.00000015 +00000-0 +00000-0 0 01183
2 23604 082.9040 099.2669 0027849 019.5357 340.6858 13.73608150047796
23705
1 23705U 95058B   96169.37607814 -.00000047 +00000-0 +00000-0 0 00921
2 23705 071.0211 270.2417 0011006 106.5785 253.6555 14.14159369032452
----------------------