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 From the web page it's not clear to me how much the devices resemble
the astro-inertial navigation systems I've seen.
http://aa.usno.navy.mil/otherprojects/

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the shortwave receiver has been replaced by a GPS time standard.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.

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