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