See the New Tether! and re: Orientation Format

Walter Nissen (dk058@cleveland.Freenet.Edu)
Fri, 16 Aug 1996 07:49:25 -0400

The new tether is entering a window of morning observability from 
mid-Northern latitudes.  It is a fine binocular object, to say the least. 
Detailed observations of its orientation are desired. 
 
TiPS             3.5  0.0  0.0  5.7 
1 96290U 96029  ? 96203.14225450  .00000250  00000-0  31455-3 0    06 
2 96290  63.4290  89.9941 0003001 264.4275  95.5725 13.63763114    04 
 
>From any one location, TiPS displays extremely regular passage behavior. 
E.g., here is a small (slightly munged) excerpt of QuickSat output for my 
location for the rest of the month: 
 D  H  M  S  TIM AL AZI C   U  MAG   REVS  HGT SHD  RNG  EW PHS  R A   DEC 
16  9 37 45   .5 29 115 C  40  6.7  358.4 10321019 1785  .7 114  518   2.4 
18  9  8 39   .6 29 115 C  40  6.6  385.4 1032 943 1790  .7 107  457   2.3 
20  8 39 33   .6 29 115 C  40  6.5  412.4 1032 801 1796  .7 100  437   2.2 
22  8 10 27   .7 29 115 C  40  6.4  439.4 1032 593 1801  .7  93  416   2.1 
24  7 41 20   .7 28 115 C  40  6.3  466.4 1032 317 1807  .6  86  355   2.0 
26  7 13 52   .8 26  91    45  6.6  493.4 1033 341 1896  .5  98  440  16.3 
28  6 44 45   .9 26  91    45  6.5  520.4 1033  42 1901  .5  91  419  16.1 
30  6 17 16   .9 20  72    51  7.2  547.4 1033 147 2184  .5 101  5 4  25.9 
 
TiPS repeatedly reappears 29m6s earlier, and 2 days later, at virtually 
the same altitude and azimuth, the strings of such appearances being 
limited at one end by twilight and at the other end by the shadow of the 
Earth. 
 
By the 30th, I will have three visible passages per night: 
30  6 17 16   .9 20  72    51  7.2  547.4 1033 147 2184  .5 101  5 4  25.9 
30  8  2 55   .9 59 312 C  51  4.9  548.4 1033 149 1178 1.1  64 2218  55.2 
30  9 53 25   .9 17 333 C  67  7.2  549.5 1033 891 2323  .6  82 1829  56.8 
All of these display the same pattern of precision repetition, some coming 
29m7s earlier, but at the same altitude and azimuth. 
 
 
> From: BDP@MPEPL.PLASMA.MPE-GARCHING.MPG.DE (Bart De Pontieu) 
> Subject: TiPS format 
 
> Some quick comments on your observing format for the TiPS satellite: 
 
> >azimuth could be given 
 
> Either that, or ask for accurate timing with which the position in the sky 
> can be reconstructed. Of course, since elements are classified, it might be 
> better to ask for accurate position *and* timing. 
> This is also provides redundancy. 
 
Uncertainty is the paralysis of action.  I don't have (at least in my 
mind) a clear answer to Jay's question about just which part of the tether 
would be measured for position.  So I didn't know exactly how to propose 
that. 
 
Also, doesn't the RGO or COSPAR or somebody already have a format for 
reporting positions?  Do I want to invite us to infringe on that? 
 
What I have done is focus on collecting reports of orientation. 
 
I don't know if alt/az adequately substitutes for ra/decl. 
 
> >left->right could be given 
 
> Don't think this is necessary unless you want to know in what orientation 
> the observer observed. 
 
Redundancy, easy to record, possibly indepndently useful? 
 
> >sp could be count of sparkles 
 
> Yes, I think that would be better. 
 
Anybody else with an opinion? 
 
> >length could be given in minutes of arc 
 
> Also a good idea, and another redundancy thing that can indicate how good 
> the obs was. 
 
In 3D a clue to orientation.  But much harder to measure and I wouldn't 
want someone with limited skills (like me) to hold back a report because 
it wasn't measured (like me). 
 
> >vvv.vv format could be used for vertex angle (i.e., fractional degrees of 
> >angle) 
 
> Well, if you do that, you'd have to do it for the other angles as well 
> notably 'al' and 'az', since the vertex angle will change 0.01 degree at 
> least if 'al' changes 1 degree. 
> Generally, I think 1 degree should be enough, even with CCD you can't do much 
> better, I'd guess (very wild guess). But it all depends on what you want to do 
> with the data, of course. Do you intend to look for oscillations, etc... ? 
 
This is why I am asking for comments.  To establish these kinds of 
considerations. 
 
> >The dashes(-) in the date and the colons(:) in the time are an unnecessary 
> >affectation. 
 
> They are, and so are the spaces everywhere. You have to choose a compromise 
> between being terse and being understandable. 
 
Exactly. 
 
 
> From: jvarney@mail2.quiknet.com (Jim Varney) 
> Subject: Re: Orientation format 
 
> My personal opinion is that the "20 degrees Lower Mass Leading" convention 
> is preferred.  It abbreviates to a short, elegant "20 deg LML." 
 
A good point, though " deg " may not fit, especially if Bart's 
suggestions are adopted. 
 
>  I also 
> like the "LML" or "LMF" format because it translates very naturally from 
> what we actually observe -- deviation from apparent vertical. 
 
> Vertex angle is usually not measured from the apparent vertical. 
 
I don't know this.  Do you have a reference? 
 
> To create a 
> new definition of vertex angle with a different coordinate reference might 
> introduce confusion. 
 
It is precisely for this reason that I suggested conformance with the 
existing practice explained by David Dunham in the appendix to my first 
message: 
 
David Dunham writes: 
... vertex angle in occultation predictions ... is measured like 
position angle, but 0 is the local vertical direction, rather than north. 
Hence, 0 deg. is up, 90 is to the left, 180 is down, and 270 is to the 
right. 
 
I suggest using his definition. 
 
> In the engineering world the term for deviation from vertical is "slope." 
 
The engineers I know about have been taught that slope is the "m" 
coefficient in y = mx + b.  Which is not measured in degrees. 
 
> A vertical slope is a 90 degree slope; so 20 deg LML would be reported as 
> 70 deg, while 20 LMF would be noted as 110 degrees.  This would work, 
> but it seems awkward in comparison to the "LML" convention. 
 
I agree that it is more awkward, and (based on the info I have) there is a 
tradeoff there with conformance to the existing definition of vertex 
angle. 
 
Is there some (desirable) way the observer could be given a choice?  I'm 
trying to make it easy for the observer to get it right. 
 
 
Thanks to both of you for your responses. 
 
I do not pretend to have all the answers to the questions Bart, Jim and I 
have raised, and welcome insights and opinions. 
 
Cheers. 
 
Walter Nissen                   dk058@cleveland.freenet.edu

---

Have you seen the evening star?