MESSENGER tank pressurization

From: Richard Clark (rclark@lpl.arizona.edu)
Date: Sat Nov 19 2005 - 03:43:35 EST

  • Next message: Leo Barhorst: "Lb Superbird A obs 2005 Nov 19"

    Well, on topic if something goes wrong...
    
    I'm posting this for a friend at the MESSENGER operations and control
    center at JHU who informs me of an upcomming critical event. In the event
    of something going wrong there could possibly be something visible to
    observers on Earth within a limited geographical area. She has set up an
    email contact for questions or reports (should that come to pass) and I
    will also forward any discussion from the list.
    
    ------
    
    On 21 November, day of year 325, shortly after 14:30 UT, MESSENGER is
    going to pressurize the oxygen tank in the delta-V thruster system.
    
    If all goes well, there'll be nothing to see. However, this is a critical
    event and there have been cases of spacecraft being lost during these
    activities. Some of the failure modes could be observable to well equiped
    properly situated observers on Earth.
    
    This is a 'real time' activity (1-way light time is 3.5 minutes)-- there
    are pauses to wait for confirmation of successful completion at a couple
    of steps leading up to and during the pressurization so we can't be too
    certain about the timing. The current timeline calls for:
    
     14:30 begin preparatory commanding from ground
     15:06 poll system engineers for readiness to execute pressurization macro
     15:13 begin ox tank pressurization
     15:25 verify pressurization macro completed
    
    Actual events could be delayed, but should not occur earlier than this.
    
    Visibility:
    
    A serious failure of the O2 tank or pressurization system could also
    result in rupture of an adjacent hydrazine tank. We have very crudely
    estimated that such a failure could be as bright as mag 21. Quite
    challenging, though there should be a number of groundbased observers who
    can reach that deep.
    
    Also quite limiting is the geographical window for visibility, given the
    spacecraft proximity to the sun for Earthbound observers.
    
    MESSENGER is near the ecliptic at 30 deg western elongation from the sun,
    .42 au from Earth and .66 from the sun. Extreme western Canada, Alaska,
    and the eastern Pacific will have the best chance for visibility.
    
    Hawaii is ideally placed, based on the nominal timeline. Using Honolulu as
    a proxy for both the Big Island and Maui...
    
    Honolulu:
     Date__(UT)__HR:MN     R.A.__(a-apparent)__DEC Azi_(a-appr)_Elev
    ****************************************************************
     2005-Nov-21 14:30  m  13 43 42.80 -14 03 07.6 104.6721  -1.0834
     2005-Nov-21 14:45  r  13 43 43.99 -14 03 07.3 106.0467   2.2903
     2005-Nov-21 15:00  m  13 43 45.18 -14 03 07.0 107.4816   5.6403
     2005-Nov-21 15:15  m  13 43 46.36 -14 03 06.7 108.9867   8.9633
     2005-Nov-21 15:30 Am  13 43 47.54 -14 03 06.4 110.5734  12.2557
     2005-Nov-21 15:45 Am  13 43 48.71 -14 03 06.1 112.2542  15.5130
     2005-Nov-21 16:00 Nm  13 43 49.88 -14 03 05.8 114.0428  18.7302
    ****************************************************************
    ('m' is moon up, 'r' is target rise, 'A' is astronomical twilight)
    
    
    Here are the geocentric coordinates from Horizons:
    
    Geocentric RA/DEC
     Date__(UT)__HR:MN     R.A.__(a-apparent)__DEC             r         delta
    **************************************************************************
     2005-Nov-20 12:00     13 41 37.85 -14 04 34.3  0.6627197982  0.4121169908
     2005-Nov-21 00:00     13 42 32.94 -14 03 44.3  0.6606331586  0.4174553376
     2005-Nov-21 12:00     13 43 29.50 -14 03 06.4  0.6585710703  0.4228467929
     2005-Nov-22 00:00     13 44 27.54 -14 02 40.6  0.6565342985  0.4282909228
     2005-Nov-22 12:00     13 45 27.05 -14 02 26.6  0.6545236118  0.4337872680
    
    The JPL Horizons site (http://ssd.jpl.nasa.gov) recognizes 'MESSENGER' as
    the spacecraft name and can provide detailed topocentric ephemerides for
    specific locations.
    
    Of course the goal here is to see nothing since the operation will go
    smoothly and MESSENGER will continue on to Mercury and return a wealth of
    new science! But in the event of loss of contact with the spacecraft this
    next monday...
    
    If anyone out in the eastern Pacific feels up to an observing challenge,
    questions or reports can be sent to msgr_helen@yahoo.com.
    
    Helen Hart, Mission Analyst
    Space Science Mission Operations
    Johns Hopkins University, Applied Physics Laboratory
    msgr_helen@yahoo.com
    
    --
    Richard Clark
    rclark@lpl.arizona.edu
    
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