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    Re: automatic celestial navigation
    From: Fred Hebard
    Date: 2008 Jan 9, 17:09 -0500

    I would tend to doubt it.  Heh Iran, need a guidance system for your  
    missiles?
    
    On Jan 9, 2008, at 3:10 PM, Greg R. wrote:
    
    >
    > Wonder if those ANS units have been declassified and are now available
    > on the surplus market? Although I think the inertial part of it might
    > be a little pragmatic on a sailboat... ;-) (Though maybe it actually
    > *could* actually track the various pitching/rolling/etc. movements?).
    >
    > --
    > GregR
    >
    >
    >
    > --- Dan Allen  wrote:
    >
    >>
    >>
    >> On Nov 28, 2007, at 11:25 PM, Paul Hirose wrote:
    >>
    >>> Interestingly, that paper says the SR-71 astro-inertial unit had a
    >>> catalog of 57 stars. I wonder if those were the same 57 stars
    >> listed
    >>> in
    >>> the nautical almanac.
    >>
    >> I was reading today in Richard H. Graham's excellent "SR-71 Revealed:
    >>
    >> The Inside Story" (Motorbooks, 1996) and came across this info where
    >>
    >> he -- an SR-71 pilot and squadron commander, and retired head of all
    >>
    >> SR-71s, so he is an authority -- states there were 61 stars in the
    >> SR-71 catalog.  Here is an extract from pages 65 and 66 of his book:
    >>
    >> ---
    >>
    >> Navigational Systems
    >>
    >> The SR-71�s high speed and sensitive missions demanded a navigational
    >>
    >> system that was highly accurate, reliable, and didn�t depend on
    >> inputs
    >> from other sources subject to electronic jamming. Patterned after
    >> navigational systems used on ICBMs, the SR-71�s Astro-inertial
    >> Navigation System (ANS) filled those requirements. Simplistically,
    >> the
    >> ANS was a star tracking navigation system. At least two different
    >> stars had to be tracked for optimum navigation performance. With a
    >> highly accurate chronometer (to the 100th of a second) supplying
    >> Greenwich Mean Time (GMT) and the Julian date, along with a 61-star
    >> catalog stored inside the ANS computer, it was possible to know
    >> precisely where SR-71 was over the ground.
    >>
    >> Selection of which star to track was made by the ANS computer a
    >> function of latitude, longitude, day of year, time of day, aircraft
    >> pitch and roll, and location of the sun. The computer selected a star
    >>
    >> by going through its star catalog, which was arranged in decreasing
    >> star brightness until it found a star. A telescope-like star tracker
    >>
    >> looked for the stars in an expanding rectangular spiral search
    >> pattern. The ANS window was located on top of the fuselage, just
    >> forward of the air refueling door and consisted of a round piece of
    >> distortion-free quartz glass (about 9 inch diameter) that allowed the
    >>
    >> star tracker to see through.
    >>
    >> On the cockpit ANS panel a star �ON� light indicated that a minimum
    >> of
    >> two different stars had been tracked within the last five minutes.
    >> Star tracking was automatic. However, the RSO could assist the system
    >>
    >> in overcoming conditions such as overcasts, changes of sky background
    >>
    >> brightness, long periods of ground time, and air refueling when the
    >> boom obscures the tracking window. Former RSO, Col. Phil Loignon
    >> (Ret), recalls a sortie he flew over North Vietnam that changed
    >> future
    >> ANS procedures.
    >>
    >> Jim Watkins and I launched on a operational sortie. We had solid
    >> cloud
    >> cover to 60,000 feet and no star lock on at coast in. A viewsight fix
    >>
    >> revealed a position error, so I updated the ANS. After exiting North
    >>
    >> Vietnam, the �STAR� light came on, and our track showed a 10 nautical
    >>
    >> mile error. The inquisition hy the 15th Air Force following that was
    >>
    >> something to hehold. We had flown over Hanoi instead of 10 miles
    >> away.
    >> Our error had allowed intelligence to determine that a new device on
    >>
    >> the North Vietnam radar sites was actually an optical device for
    >> tracking low level fighters. Although I was thought to have �screwed
    >>
    >> up,� Lockheed came through with the determinations that the ANS
    >> tracked a light bulb in the hangar and had induced a heading error.
    >> We
    >> changed our ANS turn-on procedures as of that date.
    >>
    >> By comparing the position of the stars to their known location, and
    >> with the exact time of day, the ANS could then compute the aircraft�s
    >>
    >> precise position. A normal gyro compass alignment of the ANS required
    >>
    >> 36 minutes of warm-up time and provided the SR-71 with great-circle
    >> navigational accuracy of 1,885 feet (0.3 nautical mile) for up to ten
    >>
    >> hours of flying time. It still amazes me even today that astronomers
    >>
    >> have charted our solar system so accurately that it allows the ANS to
    >>
    >> calculate the SR-71�s position so precisely. Things may change here
    >> on
    >> Earth from century to century, but the same stars guided both
    >> Christopher Columbus and Habus.
    >>
    >> The heart of the ANS was a large, self-contained unit�about half the
    >>
    >> size of a large refrigerator�called the Guidance Group. A computer
    >> inside the Guidance Group computed auto-navigation, guidance and
    >> avionics control, and maintained a continuously updated account of
    >> navigational status and coordinate values. The computer also stored
    >> instrument and mathematical coefficients, predetermined data
    >> references that defined the stars, and the mission flight plan. For
    >> continuous accuracy. the computer initiated and evaluated self-tests
    >>
    >> periodically throughout the flight. Software corrections to the star
    >>
    >> data were provided for the supersonic shock wave over the star
    >> tracker
    >> window that refracts the star light and for pressure and temperature
    >>
    >> gradients acting on the window causing optical lens effects.
    >>
    >> The aircraft�s flight plan and sensor operation for the entire
    >> mission
    >> were contained on a wide tape punched with holes and loaded inside
    >> the
    >> Guidance Group computer memory. The tape was made by the 9th SRW�s
    >> Mission Planning Branch, a group of highly experienced Air Force
    >> officers who knew how to plan SR-71 missions down to the finest
    >> detail. Many former SR-71 RSOs worked as mission planners to provide
    >>
    >> expertise. As the tape ran inside the Guidance Group, the pattern of
    >>
    >> holes �told� the aircraft where to navigate, what bank angle for
    >> turns, when various sensors were to turn ON/OFF, and where to have
    >> the
    >> sensors �look� for intelligence gathering.
    >>
    >> Prior to every flight, ANS maintenance personnel loaded the tape and
    >>
    >> ran the Guidance Group in their shop to insure the programming was
    >> correct. The Guidance Group was delivered to the aircraft several
    >> hours before flight. It was hoisted up by a crane assembly and slowly
    >>
    >> lowered into its air conditioned bay located directly in front of the
    >>
    >> air refueling door. Once inside its bay, numerous electrical, air
    >> conditioning, and computer connections were completed, mating the
    >> Guidance Group to the aircraft. An exterior aircraft panel containing
    >>
    >> the star tracker window bolted over the Guidance Group.
    >>
    >> The RSO had all the ANS controls in his cockpit. On the ANS panel,
    >> the
    >> RSO had a constant digital readout of longitude and latitude, wind
    >> direction and velocity, time to turn, and distance to the next turn
    >> point. By use of his keyboard a variety of other information was
    >> available from the ANS display panel, such as ground speed and true
    >> air speed. As long as everything was working satisfactorily, the RSO
    >>
    >> monitored the readouts to insure their accuracy. At any time, the RSO
    >>
    >> could manually override the ANS�s preprogrammed flight path and
    >> sensor
    >> action points, if required. It was an automatic abort if the ANS
    >> wasn�t working correctlv, and since Don had first-hand knowledge of
    >> that, he had total responsibility in making abort decisions
    >> concerning
    >> our navigational accuracy. If we were in clouds or couldn�t achieve a
    >>
    >> satisfactory star lock-on, the SR71 navigated by an inertial-only
    >> guidance system. The inertial system had to be aligned and was
    >> updated
    >> automatically by the ANS when it was navigating normally. By using
    >> fix
    >> points every hour, the inertial-only system maintained a navigational
    >>
    >> accuracy of two nautical miles per hour.
    >>
    >> ---
    >>
    >> Exciting!  I wish I had a pocket star tracker.
    >>
    >> Dan
    >>
    >>
    >>
    >>>
    >>
    >
    >
    > >
    
    
    
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