re: Anticipating STS viewing conditions

Walter Nissen (dk058@cleveland.Freenet.Edu)
Thu, 11 Jul 1996 07:39:52 -0400

Assuming one made a pretty strong effort to gather elsets preparatory to 
attempting an observation of Columbia on July 6th, one might have come up 
with the first 23 elsets which appear in the appendix (the 24th is the one 
I obtained which is closest to the time of passage, and together with the 
one preceding it (the 23rd), they are the two closest I obtained to bracket 
the time of passage).  As Murphy's Law would have it, the orbiter was 
maneuvered at about 960706 0800.  However, it was a small manuever and 
occurred such a short time earlier (than the latest elset) that there was 
no time for its effects to accumulate into any very noticable error (the 
sharp-eyed will see some minor evidence of it).  So, I ignore the maneuver 
completely. 
 
This is QuickSat output for the 24 elsets.  As before, one can match the 
output lines (the would-be "predictions") with the elsets by noting that 
the REVS value is higher for elsets with earlier epochs.  The single case 
of identical epochs, which arises because I inserted my own guesstimate 
with an identical epoch, is also distinguishable, because I used a larger 
ndot2, which results in an earlier pass (predicted) time, 7 51 59. 
 
  39.000  77.000    0.    DC <----------------- 1950  7.5  4 F F F F F 
23931 STS78                             .1 
 
***  1996 July  6  *** Times are UT ***   133  850 
 H  M  S  TIM AL AZI C   U  MAG   REVS  HGT SHD  RNG  EW PHS  R A   DEC 
 7 49  7   .2 17 105    72  1.2   41.1  265  17  767  .9 105  2 7   -.7 
 7 49 48   .0 18 106    72  1.0   -1.8  270  17  741  .9 103  2 1   -.8 / real 
 7 49 53   .0 18 106    72  1.1   11.1  267  17  748  .9 104  2 4   -.7 \ 
 7 49 57   .0 18 106    72  1.1   12.1  267  17  746  .9 104  2 3   -.7 
 7 50  8   .0 18 106    72  1.0   17.1  268  17  740  .9 104  2 2   -.8 
 7 50 12   .0 18 106    72  1.0   23.1  268  18  740  .9 104  2 2   -.7 
 7 50 15   .1 18 106    72  1.0   43.1  268  18  740  .9 104  2 2   -.7 
 7 50 16   .0 18 106    72  1.0   28.1  268  17  738  .9 103  2 1   -.8 
 7 50 29   .0 19 106    72  1.0   44.1  268  17  732 1.0 103  2 0   -.8 
 7 50 36   .0 19 106    72  1.0   50.1  268  18  732 1.0 103  2 0   -.7 
 7 51 40   .1 19 107    72   .9   66.1  269  18  708 1.0 102  156   -.8 
 7 51 59  1.0 19 107    72   .9  110.1  267  17  706 1.0 103  157   -.8  mine 
 7 53 15   .8 21 109    72   .7  110.1  269  17  678 1.1 101  151   -.9 
 7 53 25   .1 21 109    72   .7   82.1  270  17  671 1.1 101  149   -.9 
 7 54  1  1.1 21 109    72   .6  122.1  268  18  665 1.1 101  150   -.8 
 7 56 23   .1 24 112    72   .3  103.1  271  17  614 1.3  98  137  -1.0 
 7 59 25   .1 27 116    72   .0  125.1  273  18  557 1.6  94  120  -1.1 
 8  2  3   .1 30 120    72  -.3  141.1  273  17  511 1.9  90  1 3  -1.2 
 8  3 30   .1 32 122    72  -.5  151.1  274  18  489 2.0  88  054  -1.3 
 8  4 52   .2 34 125    72  -.6  167.1  274  18  468 2.2  85  043  -1.3 
 8  6 37   .2 37 129    72  -.8  189.1  274  18  442 2.5  82  028  -1.4 
 8  8 32   .2 40 134    72 -1.0  199.1  275  18  419 2.7  78  010  -1.5 
 8 16 12   .3 49 165 C  72 -1.6  237.1  276  22  360 3.6  58 2244  -1.3 
 8 17 53   .3 50 165 C  72 -1.7  242.1  276  31  355 3.7  59 2245   -.2 
 
The two elsets closest to the pass time (i.e., those with the smallest 
REVS values) agree on the pass time to within 5 seconds, 07 49 48 and 
07 49 53, so I assume that the correct value is very close to both. 
 
I would divide these results into the crappy and the acceptable and the 
good.  For comparison, for typical payloads and rockets more than a few 
weeks from reentry, the successive elsets from OIG usually would rank as 
excellent, or at least, very good. 
 
All the elsets more than 50 REVS (3 days) prior to the pass were crappy, 
wrong by about 2 minutes or even as much as half an hour, and every 
#$%^#%$^ one of them is LATE.  (If you think half an hour isn't half bad, 
consider that it is impossible to be wrong by more than 45 minutes, and 
that a random guess will probably be off by less than 23 minutes.  Then 
hold your head in the same position for half an hour.  For variety, check 
out the E-W value and slew your head accordingly).  Even mine, because I 
projected the implied ndot2 of .00119 from the first week of the mission 
into the second week.  The actual implied ndot2 for the second week was a 
substantially larger .00161.  (Mine was lots better than any contemporary 
elset from a NASA source, and remained so for days.  This comes as no 
surprise; I've typically done this for each mission over the past couple 
of years).  Could mine have been better?  Oh, yes.  In the 2 and a half 
days prior to the epoch of my elset, the implied ndot2 was .00173, so I 
could have chosen that and gotten a reasonable accurate estimate for the 
general character of the pass and the time of the pass.  'Course the 
implied ndot2 for the day prior was .00199.  Had I rolled those dice, I 
would have been very early.  Better than very late, I suppose. 
 
The only good elsets were the 2 or maybe 3 elsets prior to the pass, ones 
that were available only after newspaper and even TV deadlines had already 
passed.  Had I been forced to guess 3 days in advance (in fact, I just 
didn't bother), I would have looked at the implied ndot2 of .00199 from 
96180.583 to 96184.25 and probably gone with this elset from Spacelink: 
STS-78 
1 23931U 96036A   96184.50054051  .00222049  20506-6  32670-3 0   417 
2 23931  39.0153 290.2605 0006024 356.0348 266.9815 16.03912849  1917 
which would have given the not very good (but at least early): 
 7 48 20   .4 16 104    72  1.3   62.1  264  17  785  .8 105  210   -.7 
 
These last couple of elsets had bad ndot2's, but that doesn't matter. 
ndot2 is important only at a distance from the pass time.  When you come 
right up on the time, any old ndot2 will do just fine.  Which, I suppose, 
is the main reason very fresh elsets are so much better. 
 
(QuickSat assumes that the ndot2 is plausible in generating its TIM 
value (yes, Mike?).  When you have values of ndot2 that are wrong by 
orders of magnitude, you can get the paradoxical situation, as here, that 
results with larger TIM values are more accurate.) 
 
I welcome any comments, information or sources of information. 
 
Cheers. 
 
Walter Nissen                   dk058@cleveland.freenet.edu 
 
--- 
 
Except as noted all these elsets are from sts78.tle at OIG.  I deleted a 
few from that file which were preliminary, incomplete, or at very close 
intervals.  I added some from other sources to fill in gaps or provide 
alternative guesstimates (guesstimate is a somewhat derisive or cynical 
combo of guess and estimate).  The intermediate values at the right are 
ndot2s as implied by the values of MM in successive elsets. 
 
STS78 
1 23931U 96036A   96173.25000000  .00000778  54141-5  44766-5 0    57 
2 23931  39.0156   5.7513 0007759 278.5891 160.5994 16.00552170   116 
STS78                                                                 .00178 
1 23931U 96036A   96173.58333333  .00000786  54136-5  44616-5 0    70 
2 23931  39.0132   3.5128 0007725 282.2939 280.5779 16.00670877   159 
STS78                                                                 .00132 
1 23931U 96036A   96175.95833333  .00000935  54243-5  45634-5 0   142 
2 23931  39.0141 347.6118 0007167 297.2025 294.5643 16.01302571   533 
STS78                                                                 .00139 
1 23931U 96036A   96176.58333333  .00000935  54274-5  45183-5 0   173 
2 23931  39.0152 343.4150 0007303 298.7583 301.6552 16.01477005   637 
STS78                                                                 .00064 
1 23931U 96036A   96177.91666667  .00001001  54296-5  45856-5 0   211 
2 23931  39.0136 334.4807 0007000 309.0038  70.6884 16.01650295   852 
STS78                                                                 .00078 
1 23931U 96036A   96178.91666667  .00001019  54315-5  45745-5 0   243 
2 23931  39.0125 327.7739 0007079 317.0835  77.5024 16.01807412  1015 
STS78                                                                 .00132 
1 23931U 96036A   96179.58333333  .00001083  54364-5  46366-5 0   265 
2 23931  39.0149 323.2952 0006902 319.0054 325.9736 16.01983738  1115 
STS78                                                                 .00177 
1 23931U 96036A   96180.58333333  .00001017  54423-5  44356-5 0   289 
2 23931  39.0156 316.5857 0006804 325.1376 336.4631 16.02338754  1279 
STS-78  www.shuttle.gov (jsc)                                         .00251 
1 23931U 96036A   96180.71807878  .00096478  00000-0  16223-3 0  9117 
2 23931  39.0150 315.6828 0006893 328.8907  31.1662 16.02406423  1316 
STS-78  spacelink                                                     .00190 
1 23931U 96036A   96181.50325579  .00089828  33585-7  14206-3 0   301 
2 23931  39.0143 310.4050 0006652 331.3657 245.5070 16.02705157  1435 
STS-78  mine                                                            - 
1 23931U 96036A   96181.50325579  .00120000  33585-7  17000-3 0    0x 
2 23931  39.0143 310.4050 0006652 331.3657 245.5070 16.02705157  1435 
Element set number = 4     OIG                                        .00123 
1 23931U 96036A   96181.91666667 +.00001085 +54473-5 +44230-5 0 00322 
2 23931 039.0123 307.6345 0006817 338.7460 107.0967 16.02807430001494 
STS78                                                                 .00211 
1 23931U 96036A   96183.25000000  .00001334  54571-5  46601-5 0   380 
2 23931  39.0139 298.6751 0006585 342.4241 250.0840 16.03372654  1701 
STS78                                                                 .00212 
1 23931U 96036A   96184.25000000  .00001404  54639-5  46505-5 0   422 
2 23931  39.0138 291.9477 0006401 350.6143 263.6309 16.03797918  1861 
STS78                                                                 .00160 
1 23931U 96036A   96185.25000000  .00001438  54680-5  46131-5 0   454 
2 23931  39.0124 285.2187 0005944 358.9496 278.5269 16.04119382  2026 
STS78                                                                 .00061 
1 23931U 96036A   96185.58333333  .00001399  54709-5  45474-5 0   466 
2 23931  39.0142 282.9755 0005540   4.8751  40.4887 16.04160593  2082 
STS-78  www.shuttle.gov (jsc)                                         .00184 
1 23931U 96036A   96185.69999331  .00023442  00000-0  34581-4 0  9169 
2 23931  39.0134 282.1909 0005801   7.7238 352.3830 16.04203539  2113 
STS-78  spacelink                                                    -.00019 
1 23931U 96036A   96185.79263657  .00221036  20316-6  31959-3 0   450 
2 23931  39.0119 281.5668 0005956   9.0094 166.9158 16.04199967  2129 
Element set number = 5    OIG                                         .00041 
1 23931U 96036A   96186.58333333 +.00001469 +54735-5 +46212-5 0 00498 
2 23931 039.0138 276.2450 0005410 015.4251 053.9004 16.04266331002249 
STS78                                                                 .00065 
1 23931U 96036A   96186.91666667  .00001467  54739-5  46051-5 0   509 
2 23931  39.0133 274.0011 0005695  17.0346 180.3556 16.04309937  2293 
STS78                                                                 .00074 
1 23931U 96036A   96187.27083333  .00001563  54732-5  47285-5 0   513 
2 23931  39.0111 271.6131 0005407  20.8685  65.1675 16.04363041  2359 
STS78                                                                 .00368 
1 23931U 96036A   96187.58333333  .00001645  54791-5  47812-5 0   528 
2 23931  39.0138 269.5118 0005380  23.1268  70.7032 16.04593546  2402 
STS-78  www.shuttle.gov (jsc)  &  spacelink                           .00221 
1 23931U 96036A   96187.69158781  .00088752  00000-0  12713-3 0  9197 
2 23931  39.0136 268.7820 0005581  26.2942 333.8320 16.04641595  2431 
STS-78  spacelink                                                    -.00243 
1 23931U 96036A   96188.50142940  .00225495  21143-6  32535-3 0   546 
2 23931  39.0135 263.3278 0004924   7.7275 357.7822 16.04246835  2565 
 
 
Using only elsets with epochs at roughly 1 day intervals to provide a 
somewhat more stable numerical environment, I obtain these implied 
ndot2's: 
 
epoch            ndot2 (pretend this column is displayed 1/2 line lower) 
96173.58333333   .00132 
96175.95833333   .00139 
96176.58333333   .00064 
96177.91666667   .00078 
96178.91666667   .00132 
96179.58333333   .00177 
96180.58333333   .00175 
96181.91666667   .00211 
96183.25000000   .00212
96184.25000000   .00136
96185.58333333   .00052
96186.58333333   .00163
96187.58333333