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

From: satrack@libero.it
Date: Tue Nov 15 2011 - 07:46:58 UTC

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    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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