RE: any search orbits for this upcoming dmsp launch

From: Ted Molczan (molczan@rogers.com)
Date: Mon Sep 29 2003 - 01:47:44 EDT

  • Next message: Kevin Fetter: "re:gorizont 17 and mars"

    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
    
    
    
    
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