NROL-39 search elements

From: Ted Molczan (
Date: Thu Dec 05 2013 - 16:19:33 UTC

  • Next message: Ted Molczan: "RE: NROL-39 search elements"

    NROL-39 remains scheduled to launch FIA Radar 3 (aka Topaz 3) on an Atlas V-501, from Vandenberg AFB, on 2013 Dec 06, at
    07:13 UTC. The duration of the launch window has not been made public.
    The weather forecast is unfavourable for launch, but preparations continue in case conditions improve.
    If the launch is delayed to another day, and if the launch window is planar, as seems likely, then the launch window
    will move later at the rate of 8.5 min per day of delay.
    Per my earlier message, launch at 07:13 UTC would result in the following orbit:
    Primary payload 07:13 UTC launch                      1067 X 1080 UTC
    1 78802U          13340.34639405  .00000000  00000-0  00000-0 0    03
    2 78802 122.9957 219.8171 0008930  69.2445 290.9476 13.49595610    01
    I estimated the 78802 search TLE based on the initial orbit of NROL-41 (FIA Radar 1), since it employed the same launch
    vehicle as NROL-39 (Atlas V-501). The initial orbit of NROL-25 (FIA Radar 2) was a bit higher, which I assume was due to
    the use of the Delta IVM+(5,2). In the event that the orbit proves similar to that of FIA Radar 2, then the object will
    trail the above elements by about 2 min on the first pass over North America, and fall farther behind by about 20 s per
    As of yesterday's update, the Broadcast Warnings still do not show evidence that the Centaur will be de-orbited.
    I have found what appears to be a fairly recent source for the approximate planned orbit of one of the secondary
    payloads. The penultimate page of the following document states "Incl.: 123; Alt.: 465 x 972 km". I suspect that the
    Centaur will be in about the same orbit.
    I derived the following very approximate search TLE for the Centaur, based on the assumption that its manoeuvres will be
    roughly similar in timing and effect to those of NROL-36, which targeted a primary payload altitude of similar mean
    altitude, but 63.4 deg inclination.
    Centaur after 09:54 UTC                                  465 X 972 km
    1 78803U          13340.41255787  .00000000  00000-0  00000-0 0    09
    2 78803 122.9957 220.0284 0357216 140.0536 184.0000 14.52130000    03
    I assumed that the first manoeuvre would occur at 09:00 UTC, resulting in a 972 x 1067 km orbit, followed by a manoeuvre
    at 09:54 UTC to 465 x 972 km.
    I did not attempt to include any out-of-plane or in-plane components, which were evident on NROL-36. I would not be
    surprised to find that the actual orbit is ~1 deg higher in inclination and ~1 deg lower in RAAN (or vice versa), and it
    could differ by many tens of degrees in argument of perigee.
    Since the 78803 TLE is derived from 78802, the above-noted potential prediction time error applies. 78803 has an
    additional time uncertainty of a few minutes, and potentially significant topocentric track errors. A wide field of view
    is recommended.
    I would not be surprised if a better estimate materializes closer to launch; perhaps one already is somewhere on the
    web. If you have information that you are at liberty to share, please do.
    For guidance regarding visibility windows, North American visibility of the first rev, and a discussion of the payload,
    please see my earlier message:
    Ted Molczan
    Seesat-l mailing list

    This archive was generated by hypermail 2b29 : Thu Dec 05 2013 - 16:21:34 UTC