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    Re: It's Moon-landing Monday
    From: Brad Morris
    Date: 2009 Jul 24, 11:59 -0400

    I suspect that method would work, albeit a bit clumsy.  There will be a nasty 
    transformation for the vector described by the telescope to the direction 
    vector. This will be nasty simply because the window probably won't be 
    orthogonal AND the craft will probably be tumbling in all three angular 
    directions of roll, pitch and yaw simultaneously.  That would be the job of a 
    computer program and not hand driven reductions (Space Bygrave anyone?).  And 
    since it would be computer driven, there would be a corresponding hard mount 
    location for the telescope, certainly not the ubiquitous duct tape!
    
    
    
    -----Original Message-----
    From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of frankreed{at}HistoricalAtlas.com
    Sent: Friday, July 24, 2009 2:22 AM
    To: NavList@fer3.com
    Subject: [NavList 9206] Re: It's Moon-landing Monday
    
    
    Brad you wrote:
    "That would be an interesting exercise.  The sextant must therefore be aligned
    to the thrust axis of the vehicle.  In other words, holding your sextant in
    your hand and pointing it out the window (with the previously agreed exercise
    on distance, RA and declination of the center of your vehicle) does not
    really tell you how your vehicle is pointed!  Assuming that the roll of the
    vehicle doesn't matter, then the vehicular pitch and yaw will not be known
    UNLESS the sextant is referenced to the vehicle.  I am not sure how we do
    that with our high end marine sextant!"
    
    How about this: take the telescope off the sextant and tape it to a window 
    (with duct tape, always assumed to be available) so that the end of the 
    telescope is flush against the glass. Now put the spacecraft in a slow roll 
    about the axis of thrust for the main engine. We can assume that this can be 
    done. Now you fire up your star chart software on your laptop and plot the 
    stars that you see while you look through the telescope during one roll. 
    Those stars will lie along a circle (probably not a great circle) on the 
    celestial sphere, and the center of that circle is the direction in which 
    you're oriented. When you fire your rocket, you will need to maintain that 
    orientation, so you have to fire the thrusters occasionally while you look 
    through the telescope maintaining whatever stars you see centered in the 
    field of view.
    
    On the Apollo missions, there was a sextant built into the spacecraft but it 
    was rarely used as a sextant is intended to be used --to measure angles 
    between objects. Instead it was used to get spacecraft orientation (since it 
    was built in, it was aligned to the spacecraft axes in a known way), and it 
    was used as a telescope to observe the lunar surface.
    
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