According to the last two TLEs (11318.89142147 and 11319.07858799) the perigee height increased of almost 1 km. Apparently, from Nov 11 this increment is continuous, however further TLEs should be analyzed. I reported the updated figures along with a proposed interpolation in my web page: http://digilander.libero.it/SATrack/Phobos.html?q=phobos Regards, Simone >----Messaggio originale---- >Da: paul.salanitri@gmail.com >Data: 15-nov-2011 0.33 >A: "Ted Molczan"<ssl3molcz@rogers.com> >Cc: <seesat-l@satobs.org> >Ogg: Phobos-Grunt: ... manoeuvring, venting, active attitude control > >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 > _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-l
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