In article , Alan Anderson
says...

(Henry Spencer) wrote:

John Halpenny wrote:
There is also a big black sky full of stars, so a set of automatic star
trackers could provide a good navigation system.

That gives you attitude fixes, but it doesn't determine location on the
Moon unless you either have some closer reference (like Earth) as well,
or can measure the direction of the local vertical accurately.

Local vertical is easy: it's *down*.

Well-calibrated accelerometers are one option, but even a reasonably
simple pendulum will tell you which way gravity is pulling. A pendulum
with a lit point on it can even use the star tracker to read its
orientation.


Measuring "down", to three significant figures, from a moving vehicle
(or even an only-temporarily-not-moving vehicle), is actually not that
easy to do. And if you can only get two significant figures, your
position fix on the lunar surface will likely be in error by farther
than you can walk before the oxygen runs out.


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