Miss Distances inquiry

From: Difflimited@aol.com
Date: Thu Apr 30 2009 - 19:40:59 UTC

  • Next message: Marco Langbroek: "re: heavensat and lacrosse2"

    Hi All:  thanks for the responses to my "Miss Distances"  inquiry.  All 
    your feedback and comments are appreciated.
     
    Peter Wakelin wrote:  "In a recent message I recall your saying you  used 
    several pairs of
    binoculars.  With differing fields of view this  must make estimating
    star separation very difficult.  I strongly  recommend you stick to one
    pair."  
     
    For SatObs I use the 15x70 except for Noss sats that I use 11x56 for a  
    wider FOV and I've not counted appulses for Nosses.  The 11x56 are  sometimes 
    set-up on a second, usually higher elevation of a satellite pass  (greater 
    than 60d) since the tripod they are on allows for more confortable  viewing at 
    that angle.  The 10x50's are for scanning to pick up the area of  my "Field 
    of Acquistion"  The 7x 50 are for following (hand-held) the pass  of the 
    occassional bright satellite that catches my eye--no serious positional  data 
    taken.  Still, I haven't used appulses with the  11x56's since they don't 
    show dim stars.  I don't really use any  appulse that is further than about 2 
    "Jupiter diameters" ~ 90 arc seconds or  0.025 degree.  Most are a fraction 
    of a Jupiter diameter...so a few to 45  arc seconds. 
    
    Brad wrote:  "IMO splits are a lot more accurate than appulses for  visual 
    positions, and ratios a lot easier to estimate than miss distance. And,  you 
    don't have to remember direction."
    
    I'd like to collect enough data to test the accuracy and precision of using 
     splits and appulses.  My feeling now is that splits-method depends on how  
    perpendicular the reference stars are-- using reference stars that are  
    skewed rapidly loses accuracy, except when really close.  But I need to  
    collect more data.  Also, splits are really good when I concentrate on one  field, 
    but if I try to track a sat -- the fields have to be judged quickly and I  
    think counting appulses may be better.  Again I need more data.  I've  rid 
    myself of most need to remember (long-term) by using a voice recorder.
     
    Ted wrote:  "A good strategy is to use a second or third near-by star  to 
    judge the
    miss-distance, as described in Section D.9.1.3 of the  manual"  
     
    Thanks Ted, I've actually used that at least once, it's a helpful  hint.
     
    Ted wrote:  "My fussiness depends somewhat on the circumstances. If  the 
    existing elements are
    very accurate, and the orbit seems stable, then I  tend to reject all but 
    the
    very best reference stars. If the elements are  significantly inaccurate, 
    as is
    the case for a new launch, or after recovery  of a lost object, then I 
    might be
    sufficiently desperate for data to observe  in bright twilight, or very 
    near the
    horizon - conditions unlikely to offer  very good reference stars. In such
    circumstances, it is better to obtain a  poor or mediocre observation than 
    none
    at all."
     
    Good point.  For most sats, I've been satified to concentrate on one  field 
    that will give me the best reference stars and only 1 or 2 data  points.  
    Visually tracking a sat to get more points per pass is sort of a  current 
    experiment of mine to get a "feel" for it.  I am still essentially  making a 
    survey of different satellites and methods.  But I want to analyze  
    objectively the accuracy of my methods.  My main focus now is refining my  methods, 
    not using much discretion regarding the utility of them.  That  judgment will 
    come in time as I gain experience I hope.
     
    Again, thanks 
    Peter Gertson
     
     
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