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 ----------------------------------------------------------------- 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 Dec 15 2003 - 09:35:29 EST