Re: Superbird A for Thursday night, Nov. 1st

From: Bjoern Gimle (bjorn.gimle@tietotech.se)
Date: Fri Nov 02 2001 - 03:39:41 EST

  • Next message: Bjoern Gimle: "Re: What did I see"

    The geoflashers are not like tumbling rockets; to be visible at large
    distances they are only seen by mirror-like ("specular") reflections - more
    like Iridiums.
    
    But they are tumbling, uncontrolled. Ideally they are spinning like a slow
    gyro, and the "mirror" surfaces trace cones around the spin axis. The
    reflections trace cones of twice the size.
    
    This means that they are "fixed" in space and the same for all observers -
    except for the different position of the Sun, and the precession of the spin
    axis. You can only see a flash when the satellite passes near a reflection
    cone.
    
    SO, first an analyst must get a large number of flash observations and
    determine the axis position and precession, and surface cone angles.
    
    At the moment, you also depend on an analyst (or using an Excel spreadsheet
    I posted a year ago) to compute the flash positions.
    
    Then, you can plot your predictions on a star map and determine if the
    tracks cross the flash paths.
    
    I will convert my algorithm into a program that allows SkyMap to show the
    possible flash locations along with predictions.
    
    In the case of Superbird A, the mirror cone is almost a pole-to-pole great
    circle, and since all geosats move more or less on a constant declination,
    the flash location moves about one degree in Right Ascension per day.
    
    At the moment, Superbird A flash location RA DECREASES by 3.8 minutes/day.
    
    
    > Hi Rob
    > Sorry if these appear naive but could you tell me. What is a flash window?
    > Dont the geoflash sats flash all the time? How do I compute flash window
    and
    > flash location for my site?
    
    
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