R: Phobos-Grunt: ... manoeuvring, venting, active attitude control

From: satrack@libero.it
Date: Tue Nov 15 2011 - 14:10:23 UTC

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    The new TLE (11319.45294171) seems to confirm the trend. Update figures:
    
    http://digilander.libero.it/SATrack/Phobos.html?q=phobos
    
    Regards,
    Simone
    
    >----Messaggio originale----
    >Da: satrack@libero.it
    >Data: 15-nov-2011 8.46
    >A: <paul.salanitri@gmail.com>, "Ted Molczan"<ssl3molcz@rogers.com>
    >Cc: <seesat-l@satobs.org>
    >Ogg: R: Phobos-Grunt: ... manoeuvring, venting, active attitude control
    >
    >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
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