Kevin Fetter asked: > Anyone going to generate a search orbit for the planned Oct > 15 launch of dmsp F16 craft. > > I don't even want to try, as I have no idea how to do it. I do it by rotating an elset generated soon after a previous similar launch. Here they are for the past 5 DMSP launches: 1 21798U 91 82 A 91333.24036573 .00010071 00000-0 53978-2 0 00046 2 21798 98.9227 322.6846 0011990 253.4815 106.5013 14.13110286 97 1 23233U 94057A 94241.85103091 -.00000026 00000-0 10000-4 0 13 2 23233 98.9229 296.9607 0011569 236.1370 123.8962 14.12539782 33 1 23533U 95015A 95084.34059369 -.00000025 00000-0 10000-4 0 41 2 23533 98.8300 87.8939 0005392 261.5937 98.4412 14.12672879 119 1 24753U 97012A 97095.87799397 .00000141 00000-0 10000-3 0 80 2 24753 98.9423 140.3021 0007807 257.5582 102.4693 14.12966013 171 1 25991U 99067A 99347.55843551 .00000147 00000-0 10000-3 0 71 2 25991 98.8968 40.6463 0009849 330.2544 29.8080 14.14456903 116 There appears to be little reason to prefer one over the other. 99067A's mean motion was a bit greater than that of the others. Was it an aberration, or the start of a trend? I don't know, but I see no reason not to use it as the basis for DMSP F16. 99067A was launched on 1999 Dec 12 at 17:38 UTC, or day 99346.73472222 in 2-line elements format. The epoch of the above elset was 99347.55843551 - 99346.73472222 = 0.82371329 d later. The start of DMSP F16's 10 min launch window is 2003 Oct 15 at 16:17 UTC, or day 03288.67847222 in 2-line elements format. Since the epoch of the 99067A elset was 0.82371329 d after launch, I add this difference to DMSP F16's launch time of 03288.67847222, yielding day 03289.50218552 as the epoch of the search elements. Now, I compute the amount of Earth's rotation between the epoch of 99067A's elements and DMSP F16's search elements. First, I compute the number of days between the epochs: 1999 17.44156449 (i.e. 365 - 347.55843551) 2000 366 2001 365 2002 365 2003 289.50218552 ------------------ Total 1402.94375001 d Earth's rotation = 1402.94375001 d * 24 h/d * 15.0410686401 deg/h = 506442.55781 deg Adding this to the RAAN of 99067A's elset, 40.6463 deg, yields the RAAN of DMSP F16's search elements: 506483.2041 mod 360 = 323.2041 deg. Finally, I insert the computed epoch and rotated RAAN into 99067A's elset: DMSP F16 0.0 0.0 0.0 6.5 v 1 70001U 03289.50218552 .00000147 00000-0 10000-3 0 07 2 70001 98.8968 323.2041 0009849 330.2544 29.8080 14.14456903 110 To reduce the chance of the search elements being mistaken for actual elements, I always use dummy catalogue numbers and omit the International Designator, even if they are known. The above process is simple, but it is easy to make a error, so I always check my work by comparing predictions made with the source elset and the derived search elset. For example, my ephemeris generator yields the following passes relative the launch site, VAFB, nearest both satellite's launch times: 12/12/99 17:00 - 24:00 UTC J2000.0 EL > 15 Vandenberg AFB DMSP F15 99067A 25991 Bull = 7 SGP4 Age = -0.8 d Unc = 0 s ( 25%) Src = 0 TIME %I Mvv AZ EL R.A. DEC FE VANG RANGE ALT -------- -- ---- --- -- -------- --------- ---- ---- ----- ----- 17:38:07 74 7.2 13 15 00:41:51 67:03:07 6.2 0.10 2141 859 17:39:19 70 6.8 13 24 23:36:07 74:17:47 6.2 0.15 1691 858 17:40:09 65 6.5 13 33 21:22:18 78:42:46 6.1 0.20 1400 857 17:40:46 60 6.3 13 42 18:32:25 77:21:34 6.1 0.27 1204 857 17:41:14 54 6.2 13 50 16:56:45 71:48:19 6.1 0.33 1075 857 17:41:37 49 6.2 13 58 16:09:17 64:48:47 6.1 0.38 985 857 17:41:57 44 6.2 13 66 15:41:58 57:16:03 6.1 0.43 923 856 17:42:14 39 6.4 13 74 15:25:02 49:57:38 6.1 0.47 885 856 17:42:30 34 6.5 11 82 15:12:35 42:31:18 6.0 0.49 863 856 17:42:45 30 6.7 342 89 15:03:05 35:15:34 5.0 0.50 856 856 17:43:00 26 6.9 198 83 14:55:08 27:56:34 12.2 0.49 861 856 17:43:15 23 7.2 196 76 14:48:22 20:47:24 12.2 0.47 880 856 17:43:31 20 7.5 195 68 14:42:09 13:32:49 12.2 0.44 913 855 17:43:48 18 7.9 195 61 14:36:26 06:27:06 12.1 0.40 961 855 17:44:07 16 8.2 195 54 14:30:51 -00:38:52 12.2 0.35 1029 855 15/10/ 3 16:00 - 24:00 UTC J2000.0 EL > 15 Vandenberg AFB DMSP F16 70000A 70000 Bull = 0 SGP4 Age = -0.8 d Unc = 0 s ( 25%) Src = 3 TIME %I Mvv AZ EL R.A. DEC FE VANG RANGE ALT -------- -- ---- --- -- -------- --------- ---- ---- ----- ----- 16:17:07 58 7.9 13 15 19:32:04 67:02:36 6.2 0.10 2141 859 16:18:19 54 7.5 13 24 18:26:27 74:17:37 6.2 0.15 1691 858 16:19:09 50 7.2 13 33 16:12:43 78:43:20 6.1 0.20 1400 857 16:19:46 47 7.0 13 42 13:22:35 77:22:45 6.1 0.27 1204 857 16:20:14 43 6.9 13 50 11:46:46 71:49:36 6.1 0.33 1075 857 16:20:37 40 6.9 13 58 10:59:16 64:50:02 6.1 0.38 985 857 16:20:57 37 6.8 13 66 10:31:58 57:17:15 6.1 0.43 923 856 16:21:14 34 6.9 13 74 10:15:02 49:58:48 6.1 0.47 885 856 16:21:30 32 6.9 11 82 10:02:34 42:32:27 6.0 0.49 863 856 16:21:45 30 7.0 342 89 09:53:05 35:16:41 5.0 0.50 856 856 16:22:00 28 7.1 198 83 09:45:08 27:57:39 12.2 0.49 861 856 16:22:15 27 7.3 196 76 09:38:23 20:48:28 12.2 0.47 880 856 16:22:31 26 7.4 195 68 09:32:10 13:33:52 12.2 0.44 913 855 16:22:48 26 7.5 195 61 09:26:27 06:28:08 12.1 0.40 961 855 16:23:07 26 7.7 195 54 09:20:53 -00:37:52 12.2 0.35 1029 855 Compare the corresponding entries of both ephemerides, reveals that their Times differ from the launch time by the same interval, and their Azimuth, Elevation, angular velocity (VANG), Range and ALTitude, are identical, which confirms the accuracy of the elset rotation used to estimate the search elset. The search elset reveals that DMSP F16 will be well placed for evening observation by most northern and southern hemisphere observers. Ted Molczan ----------------------------------------------------------------- To unsubscribe from SeeSat-L, send a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@satobs.org List archived at http://www.satobs.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Mon Sep 29 2003 - 01:56:21 EDT