Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: automatic celestial navigation
    From: Paul Hirose
    Date: 2007 Nov 28, 22:25 -0800

     From the web page it's not clear to me how much the devices resemble
    the astro-inertial navigation systems I've seen.
    However, judging from this USNO paper, "Celestial Augmentation of
    Inertial Navigation Systems", the main idea is to eliminate the
    mechanical complication and expense of a gimballed star tracker. In
    its place will be a fixed, wide angle tracker similar to those currently
    used to sense spacecraft orientation.
    www.dtic.mil/dticasd/sbir/sbir021/n104.pdf (about 30 k)
    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.
    Note the tiny field of view: 6 minutes of arc.
    The B-2 AINS (astro-inertial navigation system) uses 61 stars. It
    operates day and night. Accuracy is classified, but the statement in the
    paper that it renders GPS "virtually superfluous" is food for thought.
    Time comes from a battery powered time transfer unit. The ground crew
    synchronizes this to a time code generator (regulated by a rubidium
    oscillator) and installs it in the plane shortly before flight.
    Back in my day (1990s) the time code generator itself was periodically
    checked against WWV time ticks from a receiver in the same rack. A
    digital readout showed the amount of error. You had to input distance in
    miles via a row of thumbwheels to account for propagation delay from the
    transmitter. Reception was frequently lousy, however. Nowadays I suspect
    the shortwave receiver has been replaced by a GPS time standard.
    The AINS is interesting to play with -- for a short while. After you try
    all the functions and look at all the screens, there isn't much more to
    do. No expert eye or skilled touch is needed. Just push the right
    buttons and the machine does the rest with fantastic accuracy. That's
    exactly what you want if the objective is to get the job done. But if
    you're looking for fun and a feeling of accomplishment, a bubble sextant
    beats the B-2 AINS.
    I block messages that contain attachments or HTML.
    To post to this group, send email to NavList@fer3.com
    To unsubscribe, send email to NavList-unsubscribe@fer3.com

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site