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    Re: Sight Reduction Tables (HO 249 Vol 1 and HO 229 Vol4) - AProblem
    From: Gary LaPook
    Date: 2015 Nov 23, 07:24 +0000
    I should add that the planets in addition to the moon might be used for in flight navigation for daylight fixes from high flying aircraft. My in flight celestial observations were from relatively low altitudes and I was never able to see a planet during the day. But from high altitude, where the sky is darker providing greater contrast, it is possible to take daylight observations of planets for a fix crossed with a sun  line. HO 249 volumes 2 and 3 provide only for declinations that encompass all the solar system objects, sun, moon and planets. Of course some of the 57 navigation stars fall in this declination range but the objective of HO 249 was for all stars to be computed with volume 1. Remember, at the time HO 249 was developed, planes had started flying lying at high altitudes, above the clouds, so the selected stars should be available, no reason to provide for other stars. 

    Celestial navigation was the primary method of navigation for oceanic flights until the development of INS systems about 50 years ago. Even then, INS was very expensive and only available in some models of the Boeing 747 so all the DC-8s and Boeing 707s still continued to use celestial navigation through the 1980's. Our Air Force used it until about 15 years ago since they figured that the Ruskies would shut off their navaids in the event of a war, 

    The Air force contemplated polar operations. Near the pole half of each year is in night allowing normal night time celestial fixes but during the other half it is daytime all the time. During these periods  a sunline is always available and using the moon and planets would allow for daytime fixes. More than half the time the moon would not be available, 1/2 the time it's declination was south and not observable from near the north pole, and even if it was in northerly declinations, part of each month it did not provide a good enough "cut" for accurate fixes so, if a planet were available, it would be used. If none of these objects were available then all they had available was running fixes, crossing advanced sunlines, and then the landfall procedure, positioning the plane on a sunline that passed through the target.

    gl

    From: Gary LaPook <NoReply_LaPook@fer3.com> 
    To: garylapook---.net
    Sent: Sunday, November 22, 2015 10:40 PM
    Subject: [NavList] Re: Sight Reduction Tables (HO 249 Vol 1 and HO 229 Vol4) - AProblem

    Remember, HO 249 was developed for use by flight navigators where speed of obtaining a fix is of utmost importance. Flight navigators precompute all of their sights so refer to HO 249 volume 1 first to select which stars they will plan to shoot. Since flight navigators use metods that allow the use of just one AP for all the shots of stars and allow for movement of the plane and of the stars during the shooting period he can put the fix on his chart within 5 minutes of the finsh of the last shot. If he is shooting the sun or the moon (which is what the other two volumes are really for. If shooting at night there is no reason to use the moon or planets, just use the stars in Volume 1) for a daylight LOP or daylight fix he does the same kind of computation that you do with HO 229 but he does all the computations prior to picking up his sextant. 
    See:
    gl




       
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