More Analysis: Phobos-Grunt & 2nd stage Zenit contrasting delta apsides http://twitpic.com/7ea8iv/full http://twitpic.com/7ea8ne/full The graphs show the difference for apogee, perigee, mean from the most recent measures. Looking at the mean (semi-major axis): The second stage is decaying smoothly, as expected, especially if rotation is sufficient to present a nice average over an orbit (I saw myself very early on significant light fluctuation to indicate a decent rotation rate). The spacecraft itself has a mean anomaly :-) It appears to fluctuate from around an expected ~0.3 * second stage decay rate, including actually gain height. A reduced decay rate in line with orientation might be expected, but not an increase. Note, I am not looking at the TLE decay value, but the actual osculating perigee/apogee values. When the decay rate returns to the expected value, it does it from that point, so it is not a correction to the TLE. Note, the first of these commenced 2011-11-10 20:00UT and appeared to stop 2011-11-12 20:00UT. It now appears the same thing happening again commencing ~ 2011-11-14 02:00UT. I believe it fits with the space craft being under autonomous active attitude control (with thrusters). This also fits with the recent (and very slim) information that is being reported by ROSCOSMOS which is : 'Everything is operating, except we can't talk to it, yet...' Also, if the spacecraft is under autonomous control, and without knowing the details of how it operates, and for how long it can operate, it would be hard to make decay predictions. For example, the changes over 5 days resulted in a delay of 1 day in decay (also a slight lifting of the perigee which will reduce drag further). Using a Numerical Orbital Program, and matching the As*Cd values to the observed "base" decay rates: (The values that match that I'm using are : Zenit (len)10.4x(diam)3.9m cd=0.560, Ph-G (len)4.5x(diam)4.5m cd=0.400) The (expected) decay of Zenit 2nd stage (4km/day mean base rate) appears to be roughly in the range 24-Nov-2011 to 27-Nov-2011 The (unwanted) decay of Phobos-Grunt spacecraft (1km/day mean base rate) without any forces acting on it (no active attitude control) appears to be roughly in the range 29-Dec-2011 to 8-Jan-2012. Add 2 weeks with "attitude control" (or whatever) at its current rate/influence. And for the rubberiest figures of all: I'm putting the current odds of gaining communication at about 4 to 1 (against), and mission salvage at about 8 to 1 (against). That is, I'm hopeful. For observations, here is a world visibility guide to see who is close to a visible pass http://twitpic.com/7eavsk/full Paul Salanitri -------------- next part -------------- An HTML attachment was scrubbed... URL: http://mailman.satobs.org/mailman/private/seesat-l/attachments/20111115/49bae40b/attachment.html _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-l
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