ERS-1 and Spot 4 Encounter

by Ted Molczan

Notes:

This analysis provides details of the circumstances of an encounter during which Spot 4 imaged ERS-1.

Vang is the angular velocity of the target from the vantage point of the observer.

PhA is the phase angle of the target, defined as the angle between the target, observer and the sun. The target is fully illuminated when phase angle is zero deg; and fully in shadow when phase angle is 180 deg.

ILL is the percent illumination of a sphere located at the position of the target.

mv is the target's estimated visual magnitude, the measure of brightness used in astronomy.

AZ and EL are the target's azimuth and elevation. Azimuth is measured clockwise from north. Elevation is relative the observer's local horizontal; negative values indicate that the target is below local horizontal.

The latitude reported for both objects is the geodetic latitude.

The altitude reported for both objects is relative to Earth's oblate shape.

Orbital elements are as issued by NASA/OIG. The meaning and format of the 2-line orbital elements is explained here.

Results:

Target object:
ERS-1            3.5  2.0  2.0  5.0 v 25.7
1 21574U 91050A   98126.17263383  .00000070  00000-0  42286-4 0  6689
2 21574  98.5426 201.3026 0001235  83.1087 277.0239 14.32247747355922

Observer object:
Spot 4           5.0  3.0  0.0  5.5 d 13.6
1 25260U 98017A   98126.17055851  .00000456  00000-0  23474-3 0  1561
2 25260  98.7362 201.2859 0000952  82.4523 277.6761 14.20029398  6122

Encounter date: 1998 May 6 UTC
                                                       Target               Observer
                                                --------------------  --------------------
  Time    Range  Vang   PhA ILL        AZ  EL    Lat     Lon    Alt    Lat     Lon    Alt
  UTC      km    deg/s  deg  %    mv   deg deg   deg     deg    km     deg     deg    km
-------- ------ ------  --- ---  ----  --- ---  ------ ------- -----  ------ ------- -----
09:55:00     42   0.04   11  99  -3.1  312 -79  20.0 N  11.8 E   787  19.9 N  11.9 E   828
09:55:01     42   0.04   11  99  -3.1  312 -79  19.9 N  11.8 E   787  19.9 N  11.9 E   828
09:55:02     42   0.04   11  99  -3.1  311 -79  19.9 N  11.8 E   787  19.8 N  11.9 E   828
09:55:03     42   0.04   11  99  -3.1  311 -79  19.8 N  11.8 E   787  19.8 N  11.9 E   828
09:55:04     42   0.04   11  99  -3.1  311 -79  19.7 N  11.8 E   787  19.7 N  11.8 E   828
09:55:05     42   0.04   11  99  -3.1  310 -79  19.7 N  11.8 E   787  19.6 N  11.8 E   828
09:55:06     42   0.04   11  99  -3.1  310 -80  19.6 N  11.8 E   787  19.6 N  11.8 E   828
09:55:07     42   0.04   11  99  -3.1  310 -80  19.6 N  11.7 E   787  19.5 N  11.8 E   828
09:55:08     42   0.04   11  99  -3.1  309 -80  19.5 N  11.7 E   787  19.5 N  11.8 E   828
09:55:09     42   0.04   11  99  -3.1  309 -80  19.4 N  11.7 E   787  19.4 N  11.8 E   828
09:55:10     42   0.04   11  99  -3.1  309 -80  19.4 N  11.7 E   787  19.4 N  11.8 E   828
09:55:11     42   0.04   11  99  -3.1  308 -80  19.3 N  11.7 E   787  19.3 N  11.7 E   828
09:55:12     42   0.04   11  99  -3.1  308 -80  19.3 N  11.7 E   787  19.2 N  11.7 E   828
09:55:13     42   0.04   11  99  -3.1  308 -80  19.2 N  11.7 E   787  19.2 N  11.7 E   828
09:55:14     42   0.04   11  99  -3.1  307 -80  19.2 N  11.6 E   787  19.1 N  11.7 E   828
09:55:15     42   0.04   11  99  -3.1  307 -80  19.1 N  11.6 E   786  19.1 N  11.7 E   828
09:55:16     42   0.04   11  99  -3.1  307 -80  19.0 N  11.6 E   786  19.0 N  11.7 E   828
09:55:17     42   0.04   11  99  -3.1  306 -80  19.0 N  11.6 E   786  18.9 N  11.7 E   828
09:55:18     42   0.04   11  99  -3.1  306 -80  18.9 N  11.6 E   786  18.9 N  11.6 E   828
09:55:19     42   0.04   11  99  -3.1  305 -80  18.9 N  11.6 E   786  18.8 N  11.6 E   828
09:55:20     42   0.04   11  99  -3.1  305 -80  18.8 N  11.6 E   786  18.8 N  11.6 E   828
09:55:21     42   0.04   11  99  -3.1  305 -81  18.7 N  11.5 E   786  18.7 N  11.6 E   828
09:55:22     42   0.04   11  99  -3.1  304 -81  18.7 N  11.5 E   786  18.6 N  11.6 E   828
09:55:23     42   0.04   11  99  -3.1  304 -81  18.6 N  11.5 E   786  18.6 N  11.6 E   828
09:55:24     42   0.04   11  99  -3.1  303 -81  18.6 N  11.5 E   786  18.5 N  11.6 E   828
09:55:25     42   0.04   11  99  -3.1  303 -81  18.5 N  11.5 E   786  18.5 N  11.5 E   828
09:55:26     42   0.04   11  99  -3.1  303 -81  18.4 N  11.5 E   786  18.4 N  11.5 E   828
09:55:27     42   0.04   12  99  -3.1  302 -81  18.4 N  11.5 E   786  18.4 N  11.5 E   828
09:55:28     42   0.04   12  99  -3.1  302 -81  18.3 N  11.5 E   786  18.3 N  11.5 E   828
09:55:29     42   0.04   12  99  -3.1  301 -81  18.3 N  11.4 E   786  18.2 N  11.5 E   828
09:55:30     42   0.04   12  99  -3.1  301 -81  18.2 N  11.4 E   786  18.2 N  11.5 E   827
09:55:31     42   0.04   12  99  -3.1  300 -81  18.1 N  11.4 E   786  18.1 N  11.5 E   827
09:55:32     42   0.04   12  99  -3.1  300 -81  18.1 N  11.4 E   786  18.1 N  11.4 E   827
09:55:33     42   0.04   12  99  -3.1  299 -81  18.0 N  11.4 E   786  18.0 N  11.4 E   827
09:55:34     42   0.04   12  99  -3.1  299 -81  18.0 N  11.4 E   786  17.9 N  11.4 E   827
09:55:35     42   0.04   12  99  -3.1  298 -81  17.9 N  11.4 E   786  17.9 N  11.4 E   827
09:55:36     42   0.04   12  99  -3.1  298 -82  17.8 N  11.3 E   786  17.8 N  11.4 E   827
09:55:37     42   0.04   12  99  -3.1  297 -82  17.8 N  11.3 E   786  17.8 N  11.4 E   827
09:55:38     41   0.04   12  99  -3.1  297 -82  17.7 N  11.3 E   786  17.7 N  11.4 E   827
09:55:39     41   0.04   12  99  -3.1  296 -82  17.7 N  11.3 E   786  17.6 N  11.3 E   827
09:55:40     41   0.04   12  99  -3.1  296 -82  17.6 N  11.3 E   786  17.6 N  11.3 E   827
09:55:41     41   0.04   12  99  -3.1  295 -82  17.6 N  11.3 E   786  17.5 N  11.3 E   827
09:55:42     41   0.04   12  99  -3.1  295 -82  17.5 N  11.3 E   786  17.5 N  11.3 E   827
09:55:43     41   0.04   12  99  -3.1  294 -82  17.4 N  11.2 E   786  17.4 N  11.3 E   827
09:55:44     41   0.04   12  99  -3.1  294 -82  17.4 N  11.2 E   786  17.4 N  11.3 E   827
09:55:45     41   0.04   12  99  -3.1  293 -82  17.3 N  11.2 E   786  17.3 N  11.3 E   827
09:55:46     41   0.04   12  99  -3.1  293 -82  17.3 N  11.2 E   786  17.2 N  11.2 E   827
09:55:47     41   0.04   12  99  -3.1  292 -82  17.2 N  11.2 E   786  17.2 N  11.2 E   827
09:55:48     41   0.04   12  99  -3.1  291 -82  17.1 N  11.2 E   786  17.1 N  11.2 E   827
09:55:49     41   0.04   12  99  -3.1  291 -82  17.1 N  11.2 E   786  17.1 N  11.2 E   827
09:55:50     41   0.04   12  99  -3.1  290 -82  17.0 N  11.1 E   786  17.0 N  11.2 E   827
09:55:51     41   0.04   12  99  -3.1  290 -82  17.0 N  11.1 E   786  16.9 N  11.2 E   827
09:55:52     41   0.04   12  99  -3.1  289 -82  16.9 N  11.1 E   786  16.9 N  11.2 E   827
09:55:53     41   0.04   12  99  -3.1  288 -82  16.8 N  11.1 E   786  16.8 N  11.1 E   827
09:55:54     41   0.04   12  99  -3.1  288 -82  16.8 N  11.1 E   786  16.8 N  11.1 E   827
09:55:55     41   0.04   12  99  -3.1  287 -83  16.7 N  11.1 E   786  16.7 N  11.1 E   827
09:55:56     41   0.04   12  99  -3.1  287 -83  16.7 N  11.1 E   786  16.7 N  11.1 E   827
09:55:57     41   0.04   12  99  -3.1  286 -83  16.6 N  11.0 E   786  16.6 N  11.1 E   827
09:55:58     41   0.04   12  99  -3.1  285 -83  16.5 N  11.0 E   786  16.5 N  11.1 E   827
09:55:59     41   0.04   12  99  -3.1  285 -83  16.5 N  11.0 E   786  16.5 N  11.1 E   827
09:56:00     41   0.04   12  99  -3.1  284 -83  16.4 N  11.0 E   786  16.4 N  11.0 E   827
09:56:01     41   0.04   12  99  -3.1  283 -83  16.4 N  11.0 E   786  16.4 N  11.0 E   827
09:56:02     41   0.04   12  99  -3.1  283 -83  16.3 N  11.0 E   786  16.3 N  11.0 E   827
09:56:03     41   0.04   12  99  -3.1  282 -83  16.2 N  11.0 E   786  16.2 N  11.0 E   827
09:56:04     41   0.04   12  99  -3.1  281 -83  16.2 N  11.0 E   786  16.2 N  11.0 E   827
09:56:05     41   0.04   12  99  -3.1  280 -83  16.1 N  10.9 E   786  16.1 N  11.0 E   827
09:56:06     41   0.04   12  99  -3.1  280 -83  16.1 N  10.9 E   786  16.1 N  11.0 E   827
09:56:07     41   0.04   12  99  -3.1  279 -83  16.0 N  10.9 E   786  16.0 N  11.0 E   827
09:56:08     41   0.04   12  99  -3.1  278 -83  16.0 N  10.9 E   786  15.9 N  10.9 E   827
09:56:09     41   0.05   12  99  -3.1  278 -83  15.9 N  10.9 E   786  15.9 N  10.9 E   827
09:56:10     41   0.05   12  99  -3.1  277 -83  15.8 N  10.9 E   786  15.8 N  10.9 E   827
09:56:11     41   0.05   12  99  -3.1  276 -83  15.8 N  10.9 E   786  15.8 N  10.9 E   827
09:56:12     41   0.05   12  99  -3.1  275 -83  15.7 N  10.8 E   786  15.7 N  10.9 E   827
09:56:13     41   0.05   12  99  -3.1  275 -83  15.7 N  10.8 E   786  15.7 N  10.9 E   827
09:56:14     41   0.05   12  99  -3.1  274 -83  15.6 N  10.8 E   786  15.6 N  10.9 E   827
09:56:15     41   0.05   12  99  -3.1  273 -83  15.5 N  10.8 E   786  15.5 N  10.8 E   827
09:56:16     41   0.05   12  99  -3.1  272 -83  15.5 N  10.8 E   786  15.5 N  10.8 E   827
09:56:17     41   0.05   12  99  -3.1  271 -83  15.4 N  10.8 E   786  15.4 N  10.8 E   827
09:56:18     41   0.05   12  99  -3.1  271 -83  15.4 N  10.8 E   786  15.4 N  10.8 E   827
09:56:19     41   0.05   12  99  -3.1  270 -83  15.3 N  10.7 E   786  15.3 N  10.8 E   827
09:56:20     41   0.05   12  99  -3.1  269 -83  15.2 N  10.7 E   786  15.2 N  10.8 E   827
09:56:21     41   0.05   13  99  -3.1  268 -83  15.2 N  10.7 E   786  15.2 N  10.8 E   827
09:56:22     41   0.05   13  99  -3.1  267 -83  15.1 N  10.7 E   786  15.1 N  10.7 E   827
09:56:23     41   0.05   13  99  -3.1  267 -83  15.1 N  10.7 E   786  15.1 N  10.7 E   827
09:56:24     41   0.05   13  99  -3.1  266 -83  15.0 N  10.7 E   786  15.0 N  10.7 E   827
09:56:25     41   0.05   13  99  -3.1  265 -83  14.9 N  10.7 E   786  14.9 N  10.7 E   827
09:56:26     41   0.05   13  99  -3.1  264 -83  14.9 N  10.6 E   786  14.9 N  10.7 E   827
09:56:27     41   0.05   13  99  -3.1  263 -83  14.8 N  10.6 E   786  14.8 N  10.7 E   827
09:56:28     41   0.05   13  99  -3.1  263 -83  14.8 N  10.6 E   786  14.8 N  10.7 E   827
09:56:29     41   0.05   13  99  -3.1  262 -83  14.7 N  10.6 E   786  14.7 N  10.6 E   827
09:56:30     41   0.05   13  99  -3.1  261 -83  14.6 N  10.6 E   786  14.7 N  10.6 E   827
09:56:31     41   0.05   13  99  -3.1  260 -83  14.6 N  10.6 E   786  14.6 N  10.6 E   827
09:56:32     41   0.05   13  99  -3.1  259 -83  14.5 N  10.6 E   786  14.5 N  10.6 E   827
09:56:33     41   0.05   13  99  -3.1  258 -83  14.5 N  10.6 E   786  14.5 N  10.6 E   827
09:56:34     41   0.05   13  99  -3.1  258 -83  14.4 N  10.5 E   786  14.4 N  10.6 E   827
09:56:35     41   0.05   13  99  -3.1  257 -83  14.4 N  10.5 E   786  14.4 N  10.6 E   827
09:56:36     41   0.05   13  99  -3.1  256 -83  14.3 N  10.5 E   786  14.3 N  10.6 E   827
09:56:37     41   0.05   13  99  -3.1  255 -83  14.2 N  10.5 E   786  14.2 N  10.5 E   827
09:56:38     41   0.05   13  99  -3.1  254 -83  14.2 N  10.5 E   786  14.2 N  10.5 E   827
09:56:39     41   0.05   13  99  -3.1  253 -83  14.1 N  10.5 E   786  14.1 N  10.5 E   827
09:56:40     41   0.05   13  99  -3.1  253 -83  14.1 N  10.5 E   786  14.1 N  10.5 E   827
09:56:41     41   0.05   13  99  -3.1  252 -83  14.0 N  10.4 E   786  14.0 N  10.5 E   827
09:56:42     41   0.05   13  99  -3.1  251 -83  13.9 N  10.4 E   786  13.9 N  10.5 E   827
09:56:43     41   0.05   13  99  -3.1  250 -83  13.9 N  10.4 E   786  13.9 N  10.5 E   827
09:56:44     41   0.05   13  99  -3.1  249 -83  13.8 N  10.4 E   786  13.8 N  10.4 E   827
09:56:45     41   0.05   13  99  -3.1  248 -83  13.8 N  10.4 E   786  13.8 N  10.4 E   827
09:56:46     41   0.05   13  99  -3.1  248 -83  13.7 N  10.4 E   786  13.7 N  10.4 E   827
09:56:47     41   0.05   13  99  -3.1  247 -83  13.6 N  10.4 E   786  13.7 N  10.4 E   827
09:56:48     41   0.05   13  99  -3.1  246 -83  13.6 N  10.3 E   786  13.6 N  10.4 E   827
09:56:49     41   0.05   13  99  -3.1  245 -83  13.5 N  10.3 E   786  13.5 N  10.4 E   827
09:56:50     41   0.05   13  99  -3.1  244 -83  13.5 N  10.3 E   786  13.5 N  10.4 E   827
09:56:51     41   0.05   13  99  -3.1  244 -83  13.4 N  10.3 E   786  13.4 N  10.3 E   827
09:56:52     41   0.05   13  99  -3.1  243 -83  13.3 N  10.3 E   786  13.4 N  10.3 E   827
09:56:53     41   0.05   13  99  -3.1  242 -83  13.3 N  10.3 E   786  13.3 N  10.3 E   827
09:56:54     41   0.05   13  99  -3.1  241 -83  13.2 N  10.3 E   786  13.2 N  10.3 E   827
09:56:55     41   0.05   13  99  -3.1  240 -83  13.2 N  10.3 E   786  13.2 N  10.3 E   827
09:56:56     41   0.05   13  99  -3.1  240 -83  13.1 N  10.2 E   786  13.1 N  10.3 E   827
09:56:57     41   0.05   13  99  -3.1  239 -83  13.0 N  10.2 E   786  13.1 N  10.3 E   827
09:56:58     41   0.05   13  99  -3.1  238 -83  13.0 N  10.2 E   786  13.0 N  10.2 E   827
09:56:59     41   0.05   13  99  -3.1  237 -83  12.9 N  10.2 E   786  12.9 N  10.2 E   827
09:57:00     41   0.05   13  99  -3.1  237 -83  12.9 N  10.2 E   786  12.9 N  10.2 E   827