Re: Noss 3-3 passing by vega

From: C. Bassa (
Date: Sat Mar 09 2013 - 11:59:13 UTC

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    Hi Kevin,
    Thanks for posting this video.
    I've determined the following positions from it:
    28537 05 004A   1775 G 20130309085150221 17 25 1828698+374966 37 S
    28537 05 004A   1775 G 20130309085159635 17 25 1841140+390367 37 S
    28537 05 004A   1775 G 20130309085206453 17 25 1850163+395237 37 S
    28541 05 004C   1775 G 20130309085154321 17 25 1825904+365984 37 S
    28541 05 004C   1775 G 20130309085159635 17 25 1832830+374398 37 S
    28541 05 004C   1775 G 20130309085209636 17 25 1845867+390010 37 S
    The NOSS 3-3 pair has not been seen for 22 days, yet they are only 40s early.
    This is interesting because the whole NOSS 3-X constellation has been
    reorganized after the launch of NOSS 3-6 on 13 September 2012. NOSS
    3-5 went into a higher orbit at the end of October and returned to a
    mean motion of 13.4062 around the end of January 2013. NOSS 3-3 went
    into a higher orbit around the 20th of October 2012.
    The higher orbit of NOSS 3-3 could mean two things. It could have been
    decomissioned. This is what happened to the NOSS 3-1 pair, which was
    were into lower orbits, with the reorganization after the arrival of
    NOSS 3-5. However, since the NOSS 3-3 pair is still intact, the
    observations seem to suggest that it is still in the higher orbit and
    has not arrived at the required spacing relative to the other
    operational NOSS 3-X pairs.
    It is interesting to predict what the required spacing would be. I
    haven't had a chance to do this in much detail, but a quick look
    suggests the following. The RA of the ascending nodes of the first
    four pairs (3-1 to 3-4) are approximately offset by succesive offsets
    of 90 degrees. NOSS 3-5 was launched in a plane with an RA of about 25
    degrees lower than NOSS 3-1 and NOSS 3-6 with an RA about 25 degrees
    lower than NOSS 3-2. Prior to the arrival of NOSS 3-6, NOSS 3-2 and
    3-3 were at about the same relative place in their orbits (with
    respect to their own ascending nodes); at a node passage of NOSS 3-2,
    NOSS 3-4 had about 20 degrees to travel in its orbit to reach its
    ascending node. At the same time NOSS 3-3 and 3-5 were about half an
    orbit offset, with NOSS 3-5 being about 40 degrees from its node when
    NOSS 3-3 went through the ascending node of its orbit.
    This table shows the RA of the ascending nodes (ASCN) as well as the
    orbital longitudes (with respect to the ascending node) before (PRE)
    and after (POST) the arrival of NOSS 3-6. All angles are in degrees.
    3-1     90
    3-2    195  340  340
    3-3     65  160   ??
    3-4    320  320  320
    3-5    250  120   70
    3-6    170       180
    Now where will NOSS 3-3 end up? Since both NOSS 3-3 and NOSS 3-5
    repositioned after the arrival of NOSS 3-6, I can only assume that
    some sort of symmetry needs to be reached. My guess is that NOSS 3-3
    will stay in its orbit until it reaches a point where it will be
    offset from NOSS 3-5 by about 20 degrees, i.e. at an orbital longitude
    of 50 degrees. In its present orbit it would reach that near the end
    of May.
    If I can find the time I'll try to back this up with a simulation of
    how often and how regular NOSS pairs pass certain latitudes at a given
    longitude. However, I wouldn't be surprised if all of these guesses
    are wrong.
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