Sometimes indentifying an object you have observed as an UnID can be quite a challenge. Sometimes it's really quite easy. This note explains in detail how to use QuickSat to identify members of one class of objects that are very easy to identify. A large percentage of all the bright LEO satellites are in orbits of similar inclination. There are many objects in sun-synchronous orbits of 82 or 98 degrees inclination. Even a casual stroll thru Ted Molczan's file of elsets will demonstrate this. Thus, it is very common, while observing one of these objects, to detect another object moving on a directly opposing course, i.e., in the opposite direction. Typically these objects are at heights of 600 to 1000 km, so that these objects move at roughly similar speeds. This means that you may be able to identify the UnID very readily, just by looking at the times of culmination of other bright objects. If you see the UnID appulse the known object 1 minute after the known object culminates, then it is a very good guess that the UnID will itself culminate 1 further minute later. (Conversely, if you see the UnID appulse the known object 1 minute before the known object culminates, then it is a very good guess that the UnID itself culminated 1 minute prior to the appulse). Let's see how this works in practice. At 960810 023350.61 I was observing MOS 1 just as it was appulsed by an UnID (which was also flashing) moving on an opposite course. I wasn't able to get much info on the UnID, just that it was a little ways to the right of MOS 1. But according to a QuickSat run I had made earlier, MOS 1 culminated at 023312, or 38.61 s prior to the appulse with the UnID. Thus, as a first approximation, I would predict that the UnID didn't culminate until 38.61 s after that, or 023429.22. (I think Mike McCants could tell us that there is a slight offset of 1 or 2 seconds in QS between objects headed North and objects headed South, so he might be able to compute an even closer estimate of the culmination time of the UnID). But I had already calculated the culmination times of all(?) the bright objects around that time, in the same list from which I plucked the info for MOS 1. If I hadn't done that already, I would have had to cobble together a QUICKSAT.CTL file that would look something like this: 1996 8 Year, month number 09 09 Start date, end date .8 -6.3 Start time, end time 41.3735 81.8637 840. Nissen, OH 0 UT correction and time zone name for UT to CDT F True means generate Radio predictions 1950 Epoch of predicted RA, Dec 11.0 Magnitude limit 5 Altitude cut-off value 0.1 The search/step parameter value T True means accept only the most recent elements for each object F True means ignore shadow test F 0 True means generate multiple prediction points, how many each way F True means output distance values in miles F True means generate a blank line before each object's prediction. QUICKSAT.MAG Intrinsic magnitudes input file UNID.TK Output file MOLCZAN.TLE Elements input file EOF The only tricky part of this is the time specification. If you get truly desperate trying to subtract in sexagesimal, "-1.0 1.0" should cover all possibilities. However I obtained it, I ended up looking at this list of objects: 41.374 81.864 840. Nissen, OH 1950 11.0 5 F F F F F *** 1996 Aug 10 *** Times are UT *** 127 936 H M S TIM AL AZI C U MAG SHD RNG R A DEC 12389 2 26 27 66 97 C 41 3.3 432 979 2011 34.3 C* 1263 r 22196 2 27 24 16 239 114 3.9 21 908 1426 -11.2 Lageos-II r 13992 2 27 50 56 108 C 41 3.6 253 926 2036 24.8 C* 1452 r 21734 2 28 4 82 79 C 138 4.81027 1443 1855 42.2 C* 2157 r 17974 2 29 41 49 249 C 138 3.5 554 1062 1534 19.2 C* 1844 r 11080 2 29 53 69 284 C 137 20.8 669 1012 1624 43.1 Nimbus 7 20433 2 30 16 48 107 C 41 3.7 163 991 21 7 20.2 C* 2056 r 20465 2 31 0 83 100 C 41 3.0 215 629 1854 39.6 C* 2058 6323 2 31 2 49 296 C 45 21.1 579 1004 1427 46.0 C* 540 22219 2 32 44 85 296 C 44 3.3 488 865 1756 43.1 C* 2219 22220 2 33 3 25 308 C 51 5.2 783 1627 12 3 45.0 C* 2219 r 17527 2 33 12 86 77 C 41 3.3 499 913 1841 41.9 MOS 1 21153 2 34 26 87 80 C 138 3.9 550 967 1834 41.5 Nadezhda 3 r 21656 2 34 39 40 91 C 40 21.5 417 1679 22 8 24.1 Meteor 3-5 R 12457 2 36 26 70 284 C 42 20.5 500 881 1637 43.0 M* 2-7 r 11286 2 38 18 54 295 C 45 4.2 442 865 15 5 46.5 IntCos 19 r 22286 2 38 19 20 67 45 5.4 32 1499 020 29.9 C* 2228 11155 2 38 23 58 76 C 137 2.9 35 615 2117 40.7 C* 1063 21305 2 39 36 80 262 C 138 21.51079 1486 1736 39.1 C* 2143 R 23751 2 42 23 36 71 C 44 21.1 212 1271 23 9 36.0 IRS-1C Now I have to find an object that culminates at 023429.22, or thereabouts. Hmmm, not too hard. Nadezhda 3 r culminated at 023426. Pretty close. I guess that's it. Actually, we may be done. We'll go on and confirm the identification. The UnID should culminate at about the same altitude and azimuth as the known object. Nadezhda 3 r fits beautifully. It should be going the opposite direction (U should be totally different, or more precisely should be the supplement of the U for the known object, 180 - U). Nadezhda 3 r fits beautifully. Computing the locations of the two objects at the observed time of the appulse (this can be done with a tiny step in QS using just 1 or 2 input elsets, or in most any tracking program) confirms that Nadezhda 3 r was just to the right of MOS 1. Checking Flash, we confirm that Nadezhda 3 r is a known flasher. Pretty solid. The truly obsessive-compulsive (like the typical SeeSat-Ler) will obtain updated elsets from OIG and bracket both positions by using one elset from immediately before the pass and one from immediately after. That is a successful identification. The other major possibility is failure. At 960816 021458.09 I was observing C* 1077 when a much fainter object, maybe mag 7, appulsed it very closely (10' or 15'?) going the opposite direction. The QS output looks like this: 41.374 81.864 840. Nissen, OH 1950 11.0 30 F F F F F *** 1996 Aug 16 *** Times are UT *** 118 943 H M S TIM AL AZI C U MAG SHD RNG R A DEC 20443 2 6 37 72 77 C 42 3.5 429 827 1952 42.6 Spot 2 r 18585 2 7 4 59 295 C 44 20.8 608 916 1528 46.9 C* 1898 192 2 7 27 86 97 C 138 8.33189 3554 1836 40.6 Midas 4 18121 2 7 29 59 105 C 40 5.71056 1882 2034 27.2 C* 1851 r 15427 2 9 26 38 71 C 44 7.0 349 1266 2251 37.0 NOAA 9 13553 2 9 56 70 262 C 138 5.4 369 690 1641 35.7 C* 1408 r 11309 2 11 16 35 288 C 43 8.5 906 1524 1337 35.3 C* 1089 r 21305 2 11 20 70 263 C 138 21.71217 1534 1643 36.3 C* 2143 R 8688 2 12 53 33 310 C 50 8.1 393 916 1240 50.0 C* 803 5105 2 14 27 53 311 C 51 21.5 856 1235 1453 55.3 C* 402 11268 2 14 31 80 78 C 138 3.5 113 496 1916 42.5 C* 1077 19038 2 15 7 12.7 44 298 C 46 21.5 633 1087 14 4 45.1 C* 1937 7727 2 15 22 41 116 C 42 20.8 168 1270 2118 10.5 C* 724 9482 2 16 21 38 289 C 43 22.0 721 1278 1350 36.9 M* 1-26 r 11458 2 17 51 66 283 C 42 3.5 193 550 1618 42.4 C* 1116 r 17535 2 19 28 83 293 C 43 21.51158 1503 1754 43.6 C* 1823 3129 2 21 20 79 293 C 43 21.1 873 1223 1733 44.7 C* 203 5729 2 21 54 80 251 C 137 22.01541 1918 1745 37.3 Aureole 1 8343 2 22 22 41 62 C 133 20.8 272 1120 23 7 44.1 C* 773 20528 2 23 26 43 92 C 40 4.5 280 1390 2210 24.7 C* 2061 r 23324 2 23 47 43 72 C 43 20.8 257 1149 2242 37.8 IRS-P2 r 10142 2 24 20 67 282 C 42 6.0 705 1082 1631 42.1 C* 928 r 9443 2 25 13 82 292 C 43 20.2 419 812 1752 43.9 C* 858 22207 2 25 14 .4 52 94 C 40 20.7 323 1198 2134 28.5 C* 2218 C* 1077 culminated at 021431. So the UnID culminated about 021525.18. But C* 724 didn't go high enough, nor did C* 1937. It couldn't have been as late as C* 1116 r. It appears that my file of 1000 bright objects doesn't contain an elset for the UnID. Perhaps someone with a larger file will step in and satisfy my curiosity about the identity of this UnID. Cheers. Walter Nissen dk058@cleveland.freenet.edu