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Henry Spencer wrote: In article , Alan Anderson wrote: 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*. It's easy only if your sensor is absolutely motionless during the measurement period. This is not that easy to achieve aboard vehicles, which are one of the major applications of such navigation devices. Also, when you start wanting to get seriously accurate, you need a gravity model of the Moon to determine the relationship between (so to speak) local gravity vertical and local geometric vertical. I think for lunar vehicles, a combination of inertial gyros, distance measurement, and terrain contour mapping will be fine and cheap. The Terrain Contour Mapping will be easy for a powerful enough computer and some good optics. An alternative is you shine a light to L1, and the L1 station tells you where you are. |
#22
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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. -- *John Schilling * "Anything worth doing, * *Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" * *Chief Scientist & General Partner * -13th Rule of Acquisition * *White Elephant Research, LLC * "There is no substitute * * for success" * *661-951-9107 or 661-275-6795 * -58th Rule of Acquisition * |
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