NavList:

Meg,

Thanks for your questions regarding Celestial Navigation(CN) and Polynesian Navigation (PN).  I believe that you have the majority of information needed to correctly answer your questions.  The folks on this list know more about the older navigation techniques than any other group of people I know.

As you have found, they are the best place to ask these questions.

Would like to add something.  CN is also used in space navigation.  Yes, it is a backup form of navigation to things such as inertial navigation systems and RADAR.  It serves as a check and balance mechanism with respect to the more modern techniques.

As far as the proposed Mars missions, they have been practicing with CN trying to determine its applicability and practically.  In this case, systems such as GPS serve no purpose for long range navigation.

I worked in the space program from the early 1970’s to the mid 1980’s.  Some of what I worked on were the computer-based systems developed for vehicles that would be launched from high orbit, that would “wake up” and start searching for stars on known magnitude.  After finding a possible candidate, the craft would rotate and start looking for another star.  This would continue until multiple stars had been located and the position could be determined.  Then the required orientation, flight path and acceleration to the target planet could be calculated and executed.  The space craft could also have the flight path and other elements uploaded from the earth-based control systems and not rely on the onboard computers.

The question regarding how accurate the space craft determined position was supposed to be, the target was a sphere a couple of miles in diameter.  This would get the payload to the general area of the target planet, where the other systems could then take the payload in for a more exact landing or fly by.

Was this ever used?  To my knowledge, no.  I worked on the systems needed to do this, in theory it worked.  But was not really practical.  It took a lot of computing power (for that time) to accomplish the tasks.  More than what was practical for the level of expected results.

Hope that provides some additional information.

derrick