RE: NOSS 3-2 Payloads Maneuver Analysis

From: Ted Molczan (molczan@rogers.com)
Date: Mon Dec 15 2003 - 09:27:14 EST

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    The NOSS 3-2 duo appear to be manoeuvring more rapidly and deliberately to their
    planned orbits than the NOSS 3-1 did.
    
    During their first 8 days in orbit, both have made two easily detectable
    manoeuvres. NOSS 3-1 (C) manoeuvred for the first time about 9 days after
    launch; NOSS 3-1 (A), about 16 d after launch.
    
    Historically, new NOSS have adopted very nearly the same mean motion as
    previously launched NOSS still in their fully intact formations. These are the
    current examples:
    
    1 16623U 86014D   03341.19250594  .00000100  00000-0  86668-4 0    05
    2 16623  63.3942 349.8846 0502000   7.8985 352.1015 13.40412824    09
    
    1 20691U 90050C   03343.82972441  .00000030  00000-0  37357-4 0    07
    2 20691  63.4190 271.5431 0360000   1.0791 358.9209 13.40449209    05
    
    1 21799U 91076C   03341.69604567  .00000030  00000-0  40883-4 0    08
    2 21799  63.4200 163.5863 0314500   1.1019 358.8981 13.40449618    04
    
    1 23908U 96029C   03342.25833408  .00000020  00000-0  33500-4 0    03
    2 23908  63.4190  74.6642 0169000 357.4459   2.5541 13.40447217    09
    
    1 26907U 01040C   03342.24159773  .00000030  00000-0  53975-4 0    08
    2 26907  63.4360  11.5452 0065000 176.8885 183.1115 13.40434516    01
    
    Since the NOSS 3-2 mean motion now is about 13.4058 rev/d, their next manoeuvres
    may be to raise their altitude slightly, to move toward a mean motion near
    13.4044 rev/d.
    
    Still to be seen is whether or not they will manoeuvre to separate their planes.
    A couple of months after launch, the NOSS 3-1 manoeuvred to cause their planes
    to drift apart. One increased its inclination slightly; the other decreased it
    inclination. A few months later, their planar separation reached 0.2 deg, about
    the same as 2nd generation NOSS, at which point both manoeuvred to match
    inclination, thus halting the planar drift.
    
    Our initial orbits appear to show a small difference in inclination almost from
    the outset, but I am not yet confident that is real because the arcs between
    manoeuvres have been short.
    
    That the operational NOSS tend to maintain similar mean motions may mean that
    the constellation is synchronized to some degree. It might be interesting to
    evaluate the long-term evolution of the relative time of ascending node passage
    of the intact and partially intact NOSS formations.
    
    Another question to be answered is their method of station-keeping. A
    significant clue may be that they do not maintain a fixed mean motion - they
    gradually decay, but still nearly match mean motion across all active
    triads/duos, and maintain their individual stable formations.
    
    Once in their operational orbits, NOSS seem never to make detectable manoeuvres
    (possibly I am forgetting a few, so a retrospective of their orbits would be
    worthwhile). 
    
    The 84012 and 86014 triads made several manoeuvres in recent years to maintain
    their formations and keep their mean motions close to those of other intact
    formations. In their cases, the perturbing effect of Earth's odd zonal harmonics
    had pushed their perigee heights low enough to create considerable drag, perhaps
    forcing the use of conventional thrusters.
    
    Perhaps when in their usual low-drag regimes, they rely on other means to remain
    together. Tethers can be safely ruled out - for at least the reason that we
    should have seen them. Ion engines and solar sails have been mentioned. 
    
    Could they alter their ballistic coefficient to even out small differences in
    their rate of decay?
    
    Perhaps their orbits possess some inherent stability, akin to the "frozen orbit"
    concept, used by Topex/Poseidon (92052A / (22076), and apparently the Lacrosses.
    
    Ted Molczan
    
    
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