[alexsanchez (OP)]

I'm wondering, on Apollo, how the lunar ascent to rendezvous was accomplished on the moon, such as how did they do an IMU alignment.  Ideally, I think they would have done an IMU alignment to moon-centered coordinates in order to launch and rendezvous.  They needed an elevation and azimuth, at least that is what's done on earth for a launch.  Getting moon-centered coordinates would be impossible without a survey marker.  I suppose they could use the optics to get a bearing from the stars (star finder,) but they said they could not see stars with the naked eye.   If they used the optics for a star reading, how could they see a star through the optics?  Was there some kind of light enhancement?  It seems like using radar alone would make it difficult to do a rendezvous with the CM orbiting the moon if launching without an IMU alignment.  I know the Delta rocket always used to do a precision IMU alignment using a survey marker and a theodolite before launch and am just wondering if they did something similar on the moon.

[Phractality]

About that same time, I was trained to repair astrotrackers for USAF. Using a best known attitude from various other instruments, like magnetic compass and gyroscopic stable platform, the astrotracker would find a guide star in its telescope. A spinning radial raster would generate a signal indicating which direction the telescope needed to look to center on the guide star. Once it locked onto the guide star, it became the new best known attitude reference.

Back then, they still used mechanical gyroscopes. Nowadays, the gyros are electronic with no moving parts. The astrotrackers I worked on were heavy and bulky. NASA must have had a less massive version.

Also, I think NASA must have dropped some navigation aids on the lunar surface before they attempted any maned landings.